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J. Embryol. exp. Morph. 90, 335-361 (1985) 335 Printed in Great Britain © The Company of Biologists Limited 1985 Saccharide structures of the mouse embryo during the first eight days of development Inferences from immunocytochemical studies using monoclonal antibodies in conjunction with glycosidases J. E. PENNINGTON, Applied Immunochemistry Research Group, Clinical Research Centre, Watford Road, Harrow, Middlesex, HA1 3UJ, U.K. S. RASTAN, Comparative Medicine Division, Clinical Research Centre, Watford Road, Harrow, Middlesex, HA1 3UJ, U.K. D.ROELCKE Institute for Immunology and Serology, University of Heidelberg, Heidelberg 1, Federal Republic of Germany ANDT. FEIZI Applied Immunochemistry Research Group, Clinical Research Centre, Watford Road, Harrow, Middlesex, HA1 3UJ, U.K. SUMMARY Monoclonal anti-carbohydrate antibodies have been used in conjunction with glycosidases in immunofluorescence studies to derive information about the structures and in situ distribution of saccharides of the mouse embryo during the first 8 days of development. The salient findings are as follows: (a) Branched poly-N-acetyllactosamine sequences of L-antigen type are detectable from the first day onwards and are widely distributed in cells of the endoderm, ectoderm and mesoderm. (b) Linear poly-N-acetyllactosamine sequences of i-antigen type are detectable from the fifth day onwards in cells of all three lineages, but have a more restricted distribution than the sequences of I-type. (c) Poly-N-acetyllactosamine sequences that are susceptible to digestion with endo-/3galactosidase are the main carriers of the SSEA-1, C14 and the blood group B-like antigens, which have the following structures Galj81-4GlcNAc, I 1,3 Fucor Gal/31-4GlcNAc and Galarl-3Gal, I 1,2 I 1,3 Fucor Fuca respectively and are found in endoderm and ectoderm but not in mesoderm cells. In the trophoblast however, these antigens are borne on saccharides that are resistant to endo-j8-galactosidase. Key words: carbohydrate structures, carbohydrate antigens, embryonic antigens, differentiation antigens, mouse embryo, saccharides, immunocytochemistry, monoclonal antibodies, glycosidases. 336 J. E . P E N N I N G T O N , S. R A S T A N , D . R O E L C K E AND T. FEIZI (d) A proportion of the poly-N-acetyllactosamine structures in the endoderm and the ectoderm of the 5- and 6-day embryos may contain the following novel structures: Galarl-Gal/31-4GlcNAc and Galorl-Galj81-4GlcNAc I 1,3 | 1,2 | 1,3 Fucar Fuca Fucar in which antigenicities of SSEA-1 and C14 determinants are masked. (e) There are several types of sialyl-oligosaccharides: (1) those reactive with anti-Gd, which has a specificity for NeuAccv2-3Galj31-4GlcNAc sequence in the extraembryonic mesoderm and the heart; (2) those reactive with anti-Pr2 but not with anti-Gd, which may correspond to other N-acetylneuraminic acid containing sequences such as NeuAcar2-3Gal/31-3GalNAc or NeuAca2-6Gal in preimplantation embryos and in the yolk sac, neural ectoderm and mesenchyme of the 8-day embryo; (3) those with other sialic acid forms or linkages that do not react with anti-Gd and Pr2; among these are sialosyl-i sequences in the extraembryonic ectoderm, and sialosyl-I sequences in most cell types during the first 8 days. The latter are the main poly-N-acetyllactosamine structures in the neural ectoderm of the 8-day embryo. (f) The sequence Galj31-3GlcNAc/31-3GaljSl-4Glc/GlcNAc, or cross-reactive structures, which bind FC10.2 antibody occur in the extraembryonic endoderm and yolk sac. The roles of specific carbohydrate structures as receptors during embryonic development and cell growth are important topics of current research. The cytochemical approach with monoclonal antibodies in conjunction with glycosidases, as in the present study, provides a unique opportunity to visualize the in situ disposition of specific carbohydrate sequences in individual cells of the whole organism, and should facilitate systematic investigations of their functions. INTRODUCTION Early mouse embryos and embryonal carcinoma cells are rich in glycans with poly-N-acetyllactosamine (Gal/31-4GlcNAc/31-3)n sequences (Muramatsu et al. 1978). Immunocytochemical studies with the natural monoclonal antibodies, anti-I and anti-i have shown that in the developing mouse embryo and in embryonal carcinoma cells which are induced to differentiate in vitro, stage-specific changes occur in the branching patterns of these saccharides (Kapadia, Feizi & Evans, 1981; Feizi, Kapadia, Gooi & Evans, 1982). Branched type 2 backbone structures (I-antigen type) are detectable at the zygote stage and throughout the first 6 days of gestation, while linear structures of i-antigen type are first detectable at the onset of differentiation of primary endoderm cells. The hybridoma-defined stagespecific embryonic antigen, SSEA-1 (Solter & Knowles, 1978) consists of 3fucosyl-N-acetyllactosamine (Gooi et al. 1981; Hounsell, Gooi & Feizi, 1981). All three antigens (I, i and SSEA-1) are masked in the presence of the blood group Hassociated arl-2 linked fucose (Feizi et al. 1971; Gooi et al. 1981; Gooi et al. 1983b) or in the presence of sialic acid (Gooi et al. 1983b). Thus some of the sequential changes in antigenicity that occur during embryogenesis may result from changes in glycosylation of glycoproteins and. glycolipids (Feizi, 1981a), analogous to the developmentally regulated changes that occur on human erythrocytes (Feizi, 1981b; Hakomori, 1981). Several other hybridoma-defined saccharide antigens of the blood group series change during the development of mouse embryos (Blaineau et al. 1983) or the differentiation of human embryonal carcinoma cells (Gooi et al. 1983d), as do the major blood group antigens A, B and H in various Saccharide structures of the mouse embryo 2>2>1 organs of the human foetus (Szulman, 1980), and the B-like structures reactive with B. simplicifolia lectin in the mouse embryo (Wu, Wan & Damjanov, 1983). However, such developmental changes are not confined to the blood group family. Studies with monoclonal antibodies have shown that during mouse embryonic development, changes also occur on carbohydrate chains of glycolipids of the globo series which express the Forssman (Stern et al. 1978; Willison et al. 1982), SSEA-3 and SSEA-4 (Kannagi et al. 1983a,b) antigens. Thus, monoclonal antibodies have been invaluable in providing structural information on the surface carbohydrates of embryonic cells which cannot be readily characterized structurally on account of their limited amounts and marked heterogeneity. In view of the association of several of the carbohydrate differentiation antigens with receptor systems (reviewed by Feizi & Childs, 1985), it is of considerable interest to visualize their in situ disposition in individual cells and tissues during embryogenesis. In the present studies several hybridoma antibodies against blood group related oligosaccharides have been used in conjunction with monoclonal human autoantibodies anti-I, i and glycosidases to derive new information on the backbone and peripheral regions of saccharides of the cells of pre- and postimplantation mouse embryos up to the eighth day of development. In addition, two human monoclonal autoantibodies recognizing N-acetylneuraminic-acid-containing structures have provided information on changes in sialylation during development. MATERIALS AND METHODS Antibodies Four monoclonal antibodies with anti-I or I-like specificities were used (Table 1). Anti-I Ma, anti-I Step and anti-i Den are human antibodies (Feizi, 198LZ?) and the anti-I-like antibodies M39 and M18 (Gooi et al. 1983c) are mouse hybridoma antibodies [Foster, Edwards, Dinsdale & Neville (1982) gifts of Dr P. A. W. Edwards, Ludwig Institute for Cancer Research, Sutton, U.K.]. IgM w o ° (gift of Dr E. Osserman, Columbia Medical Center, New York), is a Waldenstrom macroglobulin with specificity for the type 1 (Gal/81-3GlcNAc)-based backbone sequence (Kabat, Liao, Shyong & Osserman, 1982). Anti-Pr2 (designated LTh) and anti-Gd (designated Kn) are human monoclonal antibodies which recognize the NeuAc-Gal sequence (Table 1). The former reacts with both the <*2-3 and ar2-6 linked sequence whereas the latter reacts only with the a2-3 linked sequence (Uemura, Roelcke, Nagai & Feizi, 1984). The specificities of the mouse hybridoma antibodies anti-SSEA-l (Gooi et al. 1981; Hounsell et al. 1981, gift of Dr D. Solter, The Wistar Institute, Pennsylvannia, U.S.A.), Hll (Knowles, Bai, Daniels & Watkins, 1982, gift of Dr W. M. Watkins, Clinical Research Centre, Harrow, U.K.), TL5 (Gooi et al. 1983a, gift of Dr J. Schlessinger, Weizmann Institute, Rehovot, Israel), C14 (Brown et al. 1983, gift of Professor R. W. Baldwin, Nottingham University, U.K.) and FC10.2 (Gooi et al. 1983d, gift of Dr R. A. J. Mcllhinney, Ludwig Institute, Sutton, U.K.) for the respective structures, 3,fucoslyl-N-acetyllactosamine (Lex antigen), the blood group H structure, the blood group A structure, 2'3-difucosyl-N-ac:etyllactosamine (Ley antigen) and the type 1 based backbone sequence are shown in Table 1. The monoclonal anti-B antibody (NB10/3B4, gift of Dr E. Lennox, Laboratory of Molecular Biology, Cambridge, U.K.) has been cited by Voak et al. 1983. This antibody reacts (H. C. Gooi, unpublished observations) equally well with untreated and defucosylated group B ovarian cyst substances [mild acidtreated under conditions which remove fucose residues (Gooi etal. 1983b)]. Thus we deduce that the specificity involves the B-like sequence shown in Table 1. The isolectin BS I-B4 from Bandeiraea simplicifolia, conjugated with fluorescein isothiocyanate was purchased frdm Sigma 338 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. F E I Z I Table 1. Carbohydrate sequences known to react with the antibodies and lectin used in the present studies Carbohydrate structures known to react Antibodies/Lectin Anti-I Gal/51-4GlcNAc)8K. s JjGal/Sl-4GlcNAc/SlMa M18 M39 Step Ma M18 M39 Gal)81-4GlcNAc/Sls 6 Gal/fr-4GlcNAc/Sl N A ~ N v,Gal/31-4GlcNAc/31" " - ^ N ^Gal/n-4GlcN Ac/ft ^ Gal/31-4GlcNAc/Sl 6Gal/Man (GalNAc) Anti-i Den Gal)81-4GlcNAcj81-3Gal/Sl-4GlcNAc/Sl-3Gal/31-4GlcNAc/3l- Anti-SSEA-1 (anti-'LeX)) Gal/Sl-4GlcNAcj8Fucar H l l (anti-H) Gal)81-4GlcNAcj8- 11,2 Fucar C14 (anti-'Ley>) Gal/31-4GlcNAc/JFucar Fucar wo IgM ° FC10.2 Gal)81-3GlcNAc/31-3Gal/51-4Glc/GlcNAc)8l- Anti-Pr2 NeuAca2-3/6Gal... including brain gangliosides such as: NeuAco2-3Gal/31-4Glc-Cer Gal/31-3GalNAc/31-4Galj81-4Glc-Cer |2,3 NeuAcar (GM1) NeuAca2-3Gal/Sl-3GalNAcj81-4Gal/Sl-4Glc-Cer |2,3 NeuAco" (G Dla ) Anti-Gd NeuAca2-3Gal/31-4GlcNAc/31-(3Gal/Sl-4GlcNAc/Sl-)n TL5 (anti-A) GalNAcarl-3Galj81-3 /4GlcNAc/31 | | | / ± Fucar ± Fucar NB10/3B4 (anti-B) Galal-3Gal/3|1,2 (± Fuca) BS I-B4 lectin Galarl-3Gal/S- The determinants on the branched poly-N-acetyllactosamine sequences recognized by anti-I Ma, M18 and M39 antibodies are indicated by dotted underlining and those recognized by anti-I Step, solid underlining. Anti-I Ma and Step and anti-i Den can react, whereas M18 and M39 cannot react, with their antigenic determinants in the presence of peripheral galactose residues joined by arl-3 linkage to the terminal /Sl-4 linked galactoses. Reactivities with the anti-I, anti-i, M18 and M39 antibodies are masked in the presence of terminal sialic acid residues. Anti-Pr2 shows a preferential reaction with the short chain glycolipid G M3 although it can also react with the poly-N-acetyllactosamine based structures; in addition this antibody reacts with sialoglycolipids of the ganglio series which do not react with anti-Gd; this latter antibody has a preferential reaction with a2-3 sialylated poly-N-acetyllactosamine sequences. Anti-Pr2 and anti-Gd do not react with N-glycolylneuramic acid-containing sequences. Saccharide structures of the mouse embryo 339 Chemical Company (Poole, Dorset, U.K.). This lectin also recognizes the blood group B-like sequence (Wood, Kabat, Murphy & Goldstein, 1979). The human antibodies were used as plasma dilutions: anti-I Ma (1:100) anti-I Step (1:700) anti-i Den (1:700) anti-Pr2 (1:50), anti-Gd (1:10). Mouse hybridoma ascites containing antiSSEA-1, H l l , M18 and M39 antibodies were used at 1:100 dilution. Antibody TL5 was used as an IgG preparation at 6 fig ml"1. Antibodies C14, NB10/3B4 and FC10.2 were used as undiluted culture supernatants. The isolectin BS I-B4 was used for immunofluorescence at 200jugml~1; lectin in the presence of 0-lM-D-galactose was used as a negative control. Normal human serum, supplemented with human IgM (Feizi, Kapadia & Yount, 1980), mouse ascites containing an irrelevant monoclonal antibody (anti-house dust-mite) and Dulbeccos MEM medium with 10 % foetal calf serum were also used as appropriate negative controls. Embryos 6- to 8-week-old (C57Bl/10xCBA)F! female mice were superovulated with 5i.u. pregnant mare serum gonadotrophin (Intervet, Science Park, Middleton, Cambridge, U.K.), followed 44h later by 5i.u. human chorionic gonadotrophin (HCG, Intervet). They were caged with (C57Bl/l0xCBA)F1 male mice and checked the following morning for the presence of copulation plugs to confirm mating. Ovulation was assumed to occur 12 h post HCG. The day of copulation plug was designated day 1 of pregnancy. Preimplantation embryos were flushed from the oviducts 24 and 48 h post HCG at the zygote and 2- to 4-cell stages respectively, using a Hepes-buffered medium M2 (Quinn, Barros & Whittingham, 1982) containing 4 mg bovine serum albumin (BSA) ml"1. Embryos were cultured at 37°C until the morula stage in microdrops of medium M16 (Whittingham, 1971) containing 4mg BSA ml"1 and overlaid with paraffin oil in Falcon tissue culture dishes in a humidified atmosphere of 5 % CO2 in air. Manipulations of embryos were carried out in Hepes-buffered M2 under a Wild dissecting microscope. Zygotes were freed from cumulus cells by 1-2 min incubation with a lOOmgrnl"1 solution of hyaluronidase (Sigma Chemical Company, Poole, U.K.) in 001 M-phosphate-buffered saline pH7-4. The zonae pellucidae were removed by treating embryos for 5 min at 37°C with a 5 ing ml"1 solution of Pronase (Calbiochem-Behring Corp., La Jolla, California, U.S.A.) in 0-01 M-phosphate-buffered saline pH7-4 containing 10mg polyvinyl pyrrolidinemP1 (Calbiochem-Behring Corp.), for 5min at 37°C, followed by three washes in M2 medium. Previous time-course experiments (Rastan et al. 1985) show that the expression of the I and SSEA-1 antigens is unaffected by treatment of the embryos with Pronase for 5-15 min. In exploratory experiments we observed a similar antigenicity of the embryos whether they were tested in suspension or as sections after fixation; moreover the antigenicity of cultured 1-cell to 16-cell embryos was the same as that of embryos tested directly after flushing from the oviducts. Postimplantation embryos in their decidua were dissected from the oviduct at 5 to 8 days gestation, fixed in 10% v/v neutral formalin, embedded in paraffin and serially sectioned at 4^m thickness. Sections were dewaxed in xylene and hydrated through absolute to 70% v/v alcohol and washed in phosphate-buffered saline before enzyme treatment and immunofluorescence staining. Glycosidases Endo-/S-galactosidase (gift of Dr P. Scudder) was isolated from culture filtrates of Bacteroides fragilis (Scudder et al. 1983; Scudder, Hanfland, Uemura & Feizi, 1984). Knowledge on the specificity of this enzyme, namely its ability to cleave internal /3-galactosyl linkages in unbranched domains of poly-N-acetyllactosamine sequences but not those adjacent to branch points has been summarized by Rastan et al. (1985). Treatment of preimplantation embryos with this enzyme, and the effects on antigenicity have been described elsewhere (Rastan et al. 1985) and the results are cited in this report for completeness. Sections of postimplantation embryos were incubated with this enzyme (2i.u. ml"1) dissolved in 50mM-sodium acetate pH5-8 containing O^mgml" 1 BSA (incubation conditions are given below). For removal of terminal sialialic acid residues, sialidase from Vibrio cholerae (Behringwerke, AG, Marburg, W. Germany) dissolved in 50mM-sodium acetate pH5-5, at li.u.ml" 1 was used for postimplantation embryos and from Clostridium perfringens (Sigma) reconstituted in M2 medium at 340 J. E . P E N N I N G T O N , S. R A S T A N , D . R O E L C K E AND T. FEIZI 2i.u. ml" 1 for preimplantation embryos. Coffee bean a-galactosidase (Sigma) suspended in ammonium sulphate lOi.u. ml"1 was diluted in 50mM-phosphate buffer pH6-5, and used at 1 i.u. ml"1 on postimplantation embryos. The preimplantation embryos were incubated with this enzyme (2i.u. ml"1) which had been dialysed against M2 medium for 5 h at 4°C; the activity of this enzyme was determined before use according to the method of Li & Li (1972) using p-nitrophenyl ar-D-galactoside as substrate. Preimplantation embryos were incubated with enzymes for l h at 37°C in an atmosphere of 5 % CO2 in air, fixed with 4 % formaldehyde (w/v) in phosphate-buffered saline containing 0-lM-CalCl2 for l h at room temperature, and washed three times in M2 medium before immunofluorescence. Sections of postimplantation embryos (dewaxed) were incubated for 16 h with enzymes or control buffers at 37 °C and washed for 20min in phosphate-buffered saline at 4°C. Immunofluorescence of pre- and postimplantation embryos was performed as described by Rastan et al. (1985) and Kapadia et al. (1981) respectively. Individual experiments were repeated on at least two occasions. RESULTS Reactivities with anti-I Ma, anti-I Step and with antibody M39 and M18 Embryos from the zygote stage onwards showed intense immunofluorescence with the anti-I antibodies Ma and Step throughout the first 7 days of embryogenesis (Figs 1A, 6). However, reactivities with M39 and M18 antibodies were restricted to the trophoblast and the luminal aspects of cells lining the proamniotic cavity until the 6-day stage (Figs IB, 3,5) when the visceral endoderm reacted weakly. On the 7th day both the embryonic and extraembryonic endoderm, the cells lining the exocoelom, and, to a lesser extent, the embryonic ectoderm were immunostained by these two antibodies (Figs IB, 7). On the 8th day the immunofluorescence with M39 and M18 was similar to that seen with the anti-I antibodies (Figs IB, 7) being predominantly in cells lining various lumens, including the yolk sac endoderm, the amnion, dorsal aorta, coelom, neural groove and gut. The lack of reactivity of all or part of the embryo with M39 and M18 antibodies during the first 6 days suggested that certain peripheral glycosylations might be hindering reactivities of the branched I-type oligosaccharides with these antibodies. This was confirmed by immunofluorescence after treatment of the embryos with ar-galactosidase or sialidase. With the exception of the zygote stage, which was unaffected by ar-galactosidase treatment (Fig. 3), the preimplantation and the 5- to 7-day embryos showed moderate or strong immunofluorescence after treatment with either ar-galactosidase or sialidase (Figs 3, 5, 7), and the distribution of immunofluorescence was similar to that observed with anti-I antibodies using untreated embryos (Fig. 1A,B). At 8 days, sialidase, but not argalactosidase, revealed new immunofluorescence with M18 antibody as with anti-I Ma and Step (see below). The giant cells of the trophoblast stained by anti-I Ma and Step (Fig. 7) were rendered reactive with M18 antibody after sialidase treatment (Fig. IB). Neither enzyme treatment affected the immunofluorescence with anti-I Ma and Step during the first 7 days of embryogenesis (immunofluorescence of the untreated cells was already so intense that an increase of immunoreactivity might Saccharide structures of the mouse embryo 341 not be detectable). However, treatment in the 8-day embryo with sialidase revealed a strong immunofluorescence of the mesenchyme, mesoderm cells of the yolk sac, epimyocardium and of cells of the neural ectoderm at the posterior end of the neural tube (Fig. 7); treatment with ar-galactosidase was without effect. The relative intensities of immunofluorescence with M18 revealed by the two glycosidases and the increased reactivities with anti-I antibodies after sialidase treatment of the 8-day embryo are consistent with the presence of a higher proportion of sialylated branched poly-N-acetyllactosamine structures during the 1st and 2nd days and the 7th and 8th days of development. This contrasts with a higher proportion of a'-galactosyl termini during the 3rd to the 6th days of development. Reactivities with anti-i antibody Den Immunofluorescence with this antibody was first detectable in the parietal and visceral endoderm of the 5-day embryo (Fig. 1A) and was not affected by pretreatment with <*-galactosidase or sialidase. However at 6 days, the reactivity of the extraembryonic ectoderm with anti-i Den was substantially enhanced by sialidase treatment (Fig. 5), consistent with the presence of sialosyl-i sequences. In the 7-day embryo, both layers of the amnion and the cells lining the amniotic cavity and the exocoelom (Fig. 6) and cells in the mesoderm layer of the chorion were strongly stained, whereas those lining the ectoplacental cavity were not. Primary giant cells of the trophectoderm also reacted with this antibody at this stage. This immunofluorescence was not affected by pretreatment with either agalactosidase or sialidase. On the 8th day, reactivities with anti-i Den were similar to those with the anti-I antibodies except that secondary giant cells did not react with this antibody, and no additional reactivities were revealed either after sialidase or ar-galactosidase treatment (Fig. 1A). Reactivities with anti-SSEA-1 and C14 antibodies In contrast to the extensive immunofluorescence with anti-SSEA-1, only two out of a dozen 8-cell embryos and only small areas of the 5-day embryo showed immunofluorescence with C14 antibody (Figs 2A,B, 4). However at the 6-day stage, the distribution of immunofluorescence with C14 antibody resembled that seen with anti-SSEA-1. On days 7 and 8, reactivity with C14 antibody was again more restricted (Fig. 6). For example, cells of the embryonic ectoderm on day 7 (Fig. 6 insets) or neural ectoderm (on day 8) reacted only with anti-SSEA-1 (Fig. 2A,B). Pretreatment of the embryo sections with sialidase did not affect immunofluorescence with these two antibodies (results not shown). However, pretreatment with ar-galactosidase resulted in a substantial increase in immunofluorescence of the 8-cell embryo (Fig. 3) and the embryonic ectoderm of the 5- and 6-day embryos with anti-SSEA-1 and the endoderm of the 5- and 6-day Ii Ii Ii Embryonic endoderm Gut Ii Parietal Neural ectoderm Embryonic ectoderm J Embryonic ectoderm Primitive ectoderm I [I] s Mesenchyme Embryonic mesoderm (D s Heart Ii Somatopleura Ii I Yolk sac Ii Chorion Extraembryonic mesoderm Amnion-ect Amnion-mes ^Allantois Ii Ectoplacental cavity j Extraembryonic ectoderm Secondary giant ceils Ectoplacental cone | Primary giant cells | Primary giant cells | Mural Trophectoderm DAY 1 2 3 (4) Fig 1 The distribution of carbohydrate antigens recognized by monoclonal antibodies during the first 8 days of development of the mouse embryo (blastocyst stage, day 4, not tested). Observations with anti-I Ma, Step and anti-i Den are shown in panel A; M39 and/or M18 in panel B; anti-Pr2 and anti-Gd in panel C. Abbreviations: I, denotes reactivity with anti-I Ma and anti-IStep; i, with anti-i Den- M, with M39 and/or M18; P, with anti-Pr2; G, with anti-Gd; m, immunofluorescence detected with M18 or M39 antibodies only after treatment of embryos with siaUdase or *-galactosidase (i.e. cryptic determinants); [I], immunofluorescence detected with anti-I antibodies only after treatment of embryos with siaUdase (i.e. cryptic I determinants). When immunoreactivity was revealed or enhanced after treatment of embryos with siaUdase and ar-galactosidase, the superscripts s and g are used respectively; curved brackets indicate weak immunofluorescence. Yolk sac Ii Embryonic visceral endoderm Parietal Ii Visceral Ii Extraembryonic visceral endoderm Parietal I i Visceral Ii Primitive 'endoderm' • Inner cell mass- -Blastocyst— 8 cells I 2-4 cells I Zygote I C/5 W 4 to M Yolk sac M Extraembryonic Embryonic IM visceral visceral • endoderm endoderm B M Embryonic endoderm Gut Parietal l\/f(s)g • Inner cell mass Neural ectoderm m s Embryonic ectoderm ms Mesenchyme m M Somatopleura ms Yolk sac Extraembryonic mesoderm Amnion-ect ^ / \ Amnion-mes^Allantois Chorion (s)g M Blastocyst Fig. IB Ms Heart ,s(g) s(g) 8 cells m 2-4 cells Zygote III M Ectoplacental cavity Extraembryonic ectoderm M ms Secondary giant cells M Ectoplacental cone M Ectoplacental M Primary giant y cells cells M Primary giant 6 cells M Mural •Trophectoderm 2 3 (4) DAY 1 1 I P Yolk sac Embryonic visceral endoderm Embryonic endoderm Gut Parietal Parietal Visceral Extraembryonic visceral endoderm Parietal Visceral Primitive 'endoderm' • Inner cell mass Neural ectoderm P Mesenchyme GP Heart Fig. 1C Somatopleura P Yolk sac \ Chorion Extraembryonic mesoderm Ectoplacental cavity Extraembryonic ectoderm Secondary giant cells Ectoplacental cone Ectoplacental cone Primary giant cells Primary giant cells Mural •Trophectoderm 2 3 (4) > z o H GO z H O z z o DAY w 1 z W Saccharide structures of the mouse embryo 345 embryos with both antibodies (Fig. 4). There was no immunofluorescence of mesoderm-derived cells with either antibody. These observations indicate that there are terminal ar-galactosyl residues in close proximity to the Lex antigen sequence in the 8-cell embryo and to both the Lex and Ley antigen sequences in the 5- and 6-day embryos. Reactivity with monoclonal anti-B antibody and Bandeiraea simplicifolia lectin There was no immunofluorescence of preimplantation embryos with the anti-B monoclonal antibody, NB10/3B4 (preimplantation stages were not tested with the lectin). In postimplantation embryos there was a similar distribution of immunofluorescence with the anti-B antibody and lectin (Fig. 2C), but the reactions with the lectin were always weaker. The visceral endoderm was strongly stained at the 5- and 6-day stages, and there was also weak staining of the parietal endoderm and trophoblast at the 6-day stage (Fig. 4). On day 7, immunofluorescence was restricted to the extraembryonic endoderm and primary giant cells of the trophoblast (Fig. 6). At the 8-day stage, reactivity with the anti-B antibody was restricted to the primitive gut and primary giant cells of the trophoblast (Fig. 2C). The immunofluorescence data, summarized in Figs IB and 2C, indicate that only a proportion of ar-galactosyl termini are available for reaction with the anti-B antibody and lectin. Effect of endo-f$-galactosidase Additional evidence for the presence of linear poly-N-acetyllactosamine sequences was sought by comparing the immunofluorescence with anti-I, anti-i, M18, M39, anti-SSEA-1, C14 and anti-B antibodies before and after treatment with endo-/3-galactosidase. In accordance with the known susceptibility of linear poly-N-acetyllactosamine domains to digestion by endo-/3-galactosidase (Scudder et al. 1984), immunofluorescence with anti-i Den at the 6- and 8-day stages tested was abolished after treatment with this enzyme (results not shown). Immunofluorescence of preimplantation embryos with both anti-I antibodies Ma and Step, was reduced but not abolished by treatment with this enzyme [these observations are described elsewhere (Rastan etal. 1985)]. With the postimplantation embryos, immunofluorescence with anti-I Step was slightly reduced but with anti-I Ma there was no effect. These observations suggest that in preimplantation embryos, there is a higher proportion of linear segments on the branched, I-active, poly-Nacetyllactosamine chains than in postimplantation embryos. Immunofluorescence with M39 and M18 antibodies was enhanced after treatment of the 6-day embryo with endo-jS-galactosidase (Fig. 5 inset), suggesting that digestion of long-chain oligosaccharides of poly-N-acetyllactosamine type resulted in the exposure of short unsubstituted Gal/31-4GlcNAc sequences which were formerly inaccessible. Pretreatment of both the preimplantation (Rastan et al 1985) and postimplantation embryos (Fig. 4) with endo-/J-galactosidase abolished reaction with 3 Neural ectoderm Embryonic endoderm Gut s s Mesenchyme Heart 8 cells S Somatopleura Yolk sac Chorion Extraembryonic mesoderm Amnion-ect ^^AllQntm Allantois Amnion-mes s -Blastocyst g Ectoplacental cavity Extraembryonic ectoderm Secondary giant cells Ectoplacental cone Ectoplacental Primary giant « cells Primary giant cells S Mural •Trophectoderm DAY 1 2 3 (4) Fig. 2. The distribution of carbohydrate antigens recognized by monoclonal antibodies during the first 8 days of development of the mouse embryo (blastocyst stage, day 4, not tested). Observations with anti-SSEA-1 and C14 are shown in panels A and B, respectively and those with the anti-B antibody NB10/3B4 and Bandeiraea simplidfolia lectin in panel C. Abbreviations: S, denotes reactivity with anti-SSEA-1; C, with C14 antibody, B a with the B antibody (NB10/3B4) and B L with the Bandeiraea simplidfolia lectin. s Yolk sac Cg Primitive ectoderm a Embryonic o ectoderm Parietal ^ Parietal Parietal Extraembryonic Embryonic o visceral visceral § endoderm endoderm S g Visceral S g Visceral Primitive ''endoderm' . Inner cell mass- 2-4 cells Zygote w H D 5S w w c Yolk sac c Embryonic endoderm Gut Parietal QS Parietal Visceral \ Extraembryonic Embryonic p visceral visceral | endoderm endoderm Parietal Primitive 'endoderm' Primitive £ ectoderm . Inner cell mass- Qfi Visceral B Mesenchyme Fig. 2B Heart Somatopleura -Blastocyst- 8 cells 2-4 cells Zygote Yolk sac Chorion Extraembrvonic Ectoplacental cavity Extraembryonic ectoderm Secondary giant cells Ectoplacental cone Primary giant cells Primary giant cells Q Mural •Trophectoderm £r* (4) i 3 DAY o, Visceral B Yolk sac Extraembryonic visceral endoderm Embryonic visceral endoderm B a B L Visceral BaBL Mesenchyme Somatopleura Fig. 2C Heart Yolk sac Chorion \ Extraembryonic mesoderm cavity Ectoplacental Extraembryonic ectoderm Primary giant D cells BaBL cells Primary giant £>n£>i D Secondary giant cells Ectoplacental Ectoplacental cone Mural •Trophectoderm 6 5 DAY 1 2 3 (4) -p>- N w H CO z o H o w Z m 00 Saccharide structures of the mouse embryo 349 G+ GS- S+ B M18 SSEA-1 *'•*-., K Fig. 3. lmmunofluorescence of zygote (A-C), 2-cell stage (D-F) and 8- to 16-cell stage (G-L) embryos with M18 antibody or with anti-SSEA-1. Results with untreated embryos are shown under G S - , those with ar-galactosidase or sialidase-treated embryos are under columns G+ or S+ respectively. Inset in panel E shows an additional 2-cell-stage embryo with an accentuation of immunofluorescence at sites of contact between blastomeres. Magnification A-C x530, D-F x490, G-L x460. Inset EX240. 350 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. FEIZI anti-SSEA-1, with the exception of the trophoblast cells whose reactions were unaffected. These observations suggest that the 3-fucosyl-N-acetyllactosamine sequence is carried on two types of carbohydrate backbones: those with linear 03 •o 10 • C14 o '« , >'• ) SS •o E- E+ i Fig. 4. Immunofluorescence of 5- and 6-day embryos with anti-SSEA-1 (SS), C14 antibody, or anti-B antibody, NB10/3B4 (Ba). Transverse sections were tested untreated ( E - or G - ) or after treatment with endo-j8-galactosidase (E+) or agalactosidase (G+). Abbreviations: ee, embryonic ectoderm; pc, proamniotic cavity; pe, parietal endoderm; t, trophoblast; ve, visceral endoderm. Magnification of 5-day embryos X320 and 6-day embryos x270. Saccharide structures of the mouse embryo M18 Den Fig. 5. Immunofluorescence of 6-day embryos with M18 antibody or anti-i Den. Longitudinal sections were tested before treatment with ar-galactosidase or endo-/3galactosidase ( G / E - ) or sialidase (S-) and after treatment with ar-galactosidase (G+) or sialidase (S+). Small inset E+, shows a part of the embryo stained with M18 antibody after treatment with endo-j8-galactosidase. Abbreviations: xe, extraembryonic ectoderm, other abbreviations are as in Fig. 4. x270. 351 352 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. FEIZI poly-N-acetyllactosamine domains in the embryo proper and those with other, endo-/3-galactosidase-resistant, sequences in the trophectoderm. Similarly, the partial staining of the 5-day embryo seen with C14 antibody (Fig. 4),,and the anti-B reactivity of 6-day (Fig. 4) and 7-day embryos (results not shown) were markedly diminished after endo-/J-galactosidase treatment. However, immunofluorescence of primary giant cells of the trophoblast with anti-B (tested at 7 days), was unaffected by endo-/3-galactosidase: this suggests that as xv e Fig. 6. Immunofluorescence of 7-day embryos. The four large panels on the left show immunofluorescence of almost complete sections of embryos with anti-i Den (De); anti-I Ma (Ma); anti-SSEA-1 (SS); and C14. The six panels on the right show parts of embryo sections; the two uppermost show immunofluorescence of the extraembryonic visceral endoderm with FC10.2 (Fc) and the anti-B antibody (Ba); the four lower panels show the amnion reacting with anti-i Den (De), anti-SSEA-1 (SS), anti-Gd (Gl), and the allantois with anti-Gd (G2). Insets to panels SS and C14, show immunofluorescence of embryonic ectoderm (ee) with anti-SSEA-1, contrasting with the lack of immunofluorescence with C14 antibody. Abbreviations: oc, amniotic cavity; cd, allantois; am, amnion; ame, ectoderm layer of the amnion; amm, mesoderm layer of the amnion; ch, chorion; ec, ectoplacental cavity; exo, exocoleom; pg, primary giant cells of the trophoblast; xve, extraembryonic visceral endoderm; other abbreviations are as in previous figures. Magnification x70 except for insets xl20 and the four small panels lower right X130. Saccharide structures of the mouse embryo 7 day 353 8 day S+ Sm ne ye_ Fig. 7. Immunofluorescence of parts of 7 and 8 day embryos. Sections of embryos were stained with M18 antibody or with anti-I Ma before (S-) or after (S+) treatment with sialidase. With anti-I Ma, two areas of the 8 day embryo, cephalic (left panels) and caudal (right panels) are shown. Immunofluorescence with anti-Pr2, anti-Gd and FC10.2 (FC) was performed on untreated (S-) sections. Abbreviations: g, gut; h, heart; m, mesenchyme; ne, neural ectoderm; nf, neural fold; ng, neural groove; sg, secondary giant cells; sm, somatopleura; y, yolk sac; ye, yolk sac endoderm; ym, yolk sac mesoderm. Other abbreviations are as in previous figures. Magnification of 7-day embryo xl60; 8-day embryo stained with M18 x60; anti-I Ma xlOO; FC10.2 x290; anti-Gd x!50 and anti-Pr2 xlOO. 354 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. FEIZI with SSEA-1, the blood group B-like antigen is carried on more than one type of carbohydrate chain in the developing embryo. Reactivities with anti-Pr2 and Gd antibodies There was patchy immunofluorescence of the preimplantation embryos with anti-Pr2. This antibody did not react with the 5- to 7-day postimplantation embryos, but in the 8-day embryo it reacted with the neural ectoderm, the heart and the mesoderm cells of the yolk sac (Figs 1C, 7). The staining was abolished after sialidase treatment (results not shown). The reaction pattern with anti-Gd was different from that observed with antiPr 2 . Reactivity with anti-Gd was absent in the preimplantation embryos and was first observed at the 7-day stage, on cells of mesodennal origin lining the exocoelom and including the mesoderm-derived cells of the amnion and the allantois (Fig. 6). At 8 days, the Gd determinant was expressed in the neural groove and the mesoderm-derived cells of the epimyocardium (Fig. 7). These observations suggest that there are at least two types of N-acetylneuraminic acidcontaining sequences in the mouse embryos: (a) those reactive with anti-Pr2 but not with anti-Gd, occurring in preimplantation embryos and in several cell types in the 8-day embryo, and (b) those preferentially reactive with anti-Gd occurring in mesodermal cells of the 7- and 8-day embryos. Reaction with FC10.2 antibody and lack of reaction with IgMw0°, anti-Hand anti-A antibodies Contrasting with the abundance of type 2 (Gal/?l-4GlcNAc)-based structures reactive with the anti-I, anti-i, M18 and M39 antibodies, and with anti-SSEA-1, C14 and anti-Gd, there was evidence for only a limited amount of type 1 (Gal/3l-3GlcNAc) chain. Immunofluorescence with FC10.2 was restricted to the extraembryonic visceral endoderm of the 7-day embryo (Fig. 6) and in the yolk sac endoderm of the 8-day embryo (Fig. 7). No additional immunofluorescence was revealed after treatment of 6- and 8-day embryos with ar-galactosidase and sialidase. No immunofluorescence was observed with I g M w o ° , the anti-H and the anti-A antibodies during the first 8 days of development. DISCUSSION These studies provide considerable insight to the in situ distribution of specific carbohydrate structures in embryonic tissues and the changes that take place during the first 8 days of development. The following inferences can now be made: Poly-N-acetyllactosamine structures persist during thefirst8 days of development Immunofluorescence with anti-I Ma and Step and anti-i Den has shown that poly-N-acetyllactosamine sequences are widely distributed in cells of the mouse Saccharide structures of the mouse embryo 355 embryo throughout the first 8 days of development. As summarized in Fig. 1A, branched poly-N-acetyllactosamine (I-type) structures occur throughout the first 8 days of development and the linear structures (i-type) are detectable from the 5th day onward in endoderm and mesoderm-derived cells and the extraembryonic ectoderm, but hardly at all in the embryonic ectoderm. Poly-N-acetyllactosamine sequences are capped to varying degrees with sialic acid or alinked galactose residues during the first 8 days of development Studies with two antibodies (anti-I and M18) before and after treatments with ocgalactosidase or sialidase, indicate that considerable changes occur in the capping of the poly-N-acetyllactosamine sequences with sialic acid and ar-linked galactose, during the first 8 days of development (Fig. 1A,B). The majority of these carbohydrate backbones are capped with these residues during the first 6 days of development, whereas, an abundance of uncapped sequences, accessible to M18 and M39 antibodies, is evident at 7 and 8 days. Furthermore, the relative proportions of chains capped with sialic acid and. ar-galactosyl residues change during development [deduced from the observations with M18 and M39 antibodies (Fig. IB), anti-SSEA-1, C14 and the anti-B antibody (Figs 1C, 2B,C)]; there is a higher proportion of sialylated chains at the first 2 days and the 7th and 8th days of development, contrasting with a higher proportion of ar-galactosyl substitutions during the 3rd to the 6th days. The observations of Fenderson, Hahnel & Eddy (1983), who used two monoclonal antibodies reactive with N-acetyllactosamine, are also consistent with the presence of sialylated N-acetyllactosamine sequences in pre- and postimplantation embryos. Poly-N-acetyllactosamine sequences are carriers of the SSEA-1, C14 (Lex) (Ley) and B-like antigens The loss of immunofluorescence with anti-SSEA-1, C14 and NB10/3B4 antibodies after treatment of embryos with endo-/3-galactosidase indicates that the antigenic determinants they recognize are borne predominantly on backbone structures of poly-N-acetyllactosamine type, containing linear domains susceptible to digestion with this enzyme (Scudder et al 1984). Only in the trophoblast were the SSEA-1 and B-like activities resistant to digestion with this enzyme, suggesting that they are borne on highly branched poly-N-acetyllactosamine or other types of carbohydrate backbone structures. Evidence for three types of chains with terminal oc-linked galactose residues There are at least three types of carbohydrate structure terminating with agalactosyl residues. Firstly, there is evidence for the presence of branched poly-Nacetyllactosamine structures reactive with the anti-i antibodies but unreactive with M18 antibody unless the embryos are pretreated with ar-galactosidase. Secondly, there is evidence suggestive of the presence of terminal ar-galactosyl residues 356 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. FEIZI which mask the reactivities of SSEA-1 and C14 determinants. Thus, novel structures such as the following: Galarl-Galj31-4GlctfAc I 1,3 Fucar Galarl-Gal)31-4GlcNAc | 1,2 | 1,3 Fucar Fucar may be present during the 5th and 6th days of embryogenesis, and distributed as indicated in Fig. 2B,C. Thirdly, in preimplantation embryos and the ectoderm of 5- and 6-day embryos there is evidence for the presence of short GalarlGalj81-4GlcNAc sequences which do not react with NB10/3B4 antibody, and on which reactivities with M18 antibody are revealed after treatment of the embryos with ar-galactosidase. Evidence for several types of sialyloligosaccharide sequences This study provides evidence for the presence of several types of sialyloligosaccharide sequences in the developing mouse embryo. The reaction patterns of anti-Pr2 and anti-Gd (Fig. 1C) suggest that the mesodermal tissues of the 7-day embryo, including the mesoderm layer of the amnion, the allantois and chorion contain the NeuAcar2-3(Gal/31-4GlcNAc/31-3)n sequence in quantities that are only detectable with anti-Gd. The Pr2 reactivities of the preimplantation embryos and of the neural ectoderm, mesenchyme and yolk sac of the 8-day embryo may reflect their content of sialoglycolipids of the ganglio series which have been detected in embryonal carcinoma cells of the mouse (Coulon-Morelec & BucCaron, 1981; K. Uemura, J.P., D.R. & T.F., unpublished observations). It is possible that the sialosyl-i sequence detected in the extraembryonic ectoderm on day 6 (Fig. 1A) and the sialosyl-I sequences inferred to be in the endoderm and ectodermal tissues of the embryo during days 5 and 6 (Fig. 1A), contain N-glycolyl or other forms of sialic acid, or they may contain N-acetylneuraminic acid with other types of linkage to the backbone structures that are not reactive with anti-Pr2 and anti-Gd. A lack of expression of the H and A antigens during the first 8 days of development The reactions with C14 antibody indicates that 2'3-difucosyl type 2 chains are present in the embryo during days 5 to 8 of development. However, no immunofluorescence with the anti-H monoclonal and polyclonal antibodies was observed suggesting that the majority of chains with Fucad-2Gal/31-4GlcNAc sequence also contain fucose arl-3 linked to N-acetylglucosamine which hinders reactivities with the anti-H antibody. There was also a lack of immunofluorescence with the monoclonal anti-A antibody, (TL5), which can react with mono- and difucosyl blood group A antigens, as well as non-fucosylated 'A-like' structures (Table 1). Saccharide structures of the mouse embryo 357 TL5 antibody also reacts (Gooi et al. 1983a) with the terminal disaccharide sequence of the Forssman antigen, GalNAcad-3GalNAc-, which was previously detected, using monoclonal antibody Ml/22.25, on the surface of pre- and postimplantation embryos (Stinnakre, Evans, Willison & Stern, 1981). The lack of reactivity of the paraffin-embedded sections used in the present study, with antibody TL5 may be due, in part, to the extraction of glycolipids by solvents used in the dewaxing procedures (Limas & Lange, 1982; Thorpe & Feizi, 1983). Thus, it will be necessary to test the reactivities of cryostat sections and suspensions of unfixed cells, with this and other antibodies for the reliable assessment of glycolipid-associated carbohydrate antigens. Possible occurrence of type 1 backbone sequences The immunofluorescence of FC10.2 antibody raises the possibility that some type 1 backbone structures may be present in the extraembryonic visceral endoderm and yolk sac. However, there was no reactivity with I g M w o ° which has a specificity similar to that of FC10.2. These observations require biochemical proof for we are unaware of previous reports of the presence of type 1 chains in mouse tissues. An alternative possibility is that there exist other structures which can cross react with this antibody but not with I g M w o ° . The value and limitations of monoclonal antibodies in analysis of the glycoconjugates of cells The structural inferences are dependent on information available on the reactions of each antibody with structurally characterized glycans. Thus, the precision with which structural assignments can be made depend, on the one hand, on the availability of the relevant oUgosaccharide or glycolipid haptens for testing with each antibody, and, on the other, they reflect the degree of cross reactions of different carbohydrate structures with a given monoclonal antibody. Whereas the anti-I, anti-i and anti-SSEA-1 antibodies seem highly specific for the type 2 based backbone structures (Feizi, 1981a,b\ Gooi et al. 1984) and their arl-3 fucosylated derivatives (Hounsell et al. 1981), respectively, anti-Pr2 has a broader specificity (as discussed above). The special virtue of the immunocytochemical approach is the ability to clearly visualize the differences in the saccharides of single cells and of various cell types within a single tissue. For example, there are considerable differences in the saccharide antigens of the two cell layers of the amnion and those of the chorion. As summarized in Figs 1, 2 and 6, both layers of the amnion have branched and linear poly-N-acetyllactosamine antigens, whereas the fucose containing antigens are found only on the ectoderm layer, and poly-N-acetyllactosamine chains with N-acetylneuraminic acid were detected only in the mesoderm layer of the amnion. In the chorion, both layers have poly-N-acetyllactosamine sequences with Nacetylneuraminic acid termini, and there is evidence that both layers contain branched poly-N-acetyllactosamine structures; however, linear poly-N-acetyllactosamine structures were detected predominantly in the mesoderm layer. 358 J. E. PENNINGTON, S. RASTAN, D. ROELCKE AND T. F E I Z I These differences in distribution should be taken into account when studying the functions of the various carbohydrate antigens in embryonic development. However the immunocytochemical approach does not distinguish carbohydrate structures synthesized by the cells with which they are associated from those on glycoproteins and glycolipids that are absorbed or endocytosed. Biosynthetic experiments will be required to distinguish these possibilities. Biological roles of carbohydrate structures Knowledge of the functions of these saccharides is still in its infancy. However, recent observations suggest that carbohydrate structures of the poly-N-acetyllactosamine series may have roles in cell interactions during early embryogenesis (reviewed by Rastan et al. 1985). The major carriers of these sequences in embryonal carcinoma cells are proteins of high relative molecular mass (Childs et al. 1983). This family of carbohydrate structures has also been detected on the receptor for epidermal growth factor, and an antibody against one of these saccharides has been reported to act as a growth factor agonist and another as an antagonist (reviewed by Childs et al. 1984; Feizi & Childs, 1985). On the other hand, the major carriers of the Pr2 determinants on embryonal carcinoma cells are gangliosides (Uemura, J.P., D.R. & T.F., unpublished observations). There is evidence that the gangliosides G M3 and G M1 may modulate the phosphorylation and hence the function of the receptor for platelet-derived growth factor of a 3T3 cell line (Bremer etal. 1984). Both of these gangliosides are among those that react with anti-Pr2, and the former also reacts weakly with anti-Gd (Uemura et al. 1984, Table 1) and their levels are known to change in embryonal carcinoma cells which have been induced to differentiate in vitro (Coulon-Morelec & Buc-Caron, 1981; Uemura et al, unpublished observations). Thus the roles of specific saccharide sequences during embryonic development and cell growth, and as determinants of the tropisms of infective agents, are important topics of current research (Feizi, 1982, 1985; Feizi et al. 1984) and monoclonal antibodies should greatly facilitate future studies in this field. J.P. was supported by the Cancer Research Campaign. The authors are grateful to colleagues who have provided monoclonal antibodies, to Drs E. F. Hounsell, H. C. Gooi and P. Scudder for their constructive criticisms and to Sheila Brown for technical assistance. REFERENCES C , LE PENDU, J., ARNAUD, D., CONNAN, F. & AVNER, P. (1983). The glycosidic antigen recognized by a novel monoclonal antibody, 75. 12, is developmentally regulated on mouse embryonal carcinoma cells. EMBOJ. 2, 2217-2222. BREMER, E. G., HAKOMORI, S., BOWEN-POPE, D. F., RAINES, E. & Ross, R. (1984). Gangliosidemediated modulation of cell growth, growth factor binding and receptor phosphorylation. /. biol. 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