* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download regional mapping of the gene coding
Ridge (biology) wikipedia , lookup
Gene therapy of the human retina wikipedia , lookup
Quantitative trait locus wikipedia , lookup
History of genetic engineering wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genomic imprinting wikipedia , lookup
Microevolution wikipedia , lookup
Minimal genome wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene expression profiling wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Mir-92 microRNA precursor family wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Designer baby wikipedia , lookup
Y chromosome wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Human–animal hybrid wikipedia , lookup
Neocentromere wikipedia , lookup
J. Cell Set. 53, S45-254 (198a) Printed in Great Britain © Company of Biologists Limited 1982 245 REGIONAL MAPPING OF THE GENE CODING FOR ENOLASE-2 ON HUMAN CHROMOSOME 12 MARTHA LIAO LAW AND FA-TEN KAO Eleanor Roosevelt Institute for Cancer Research and The Department of Biochemistry, Biophysics and Genetics, University of Colorado Health Sciences Center, Denver, Col. 80262, U.S.A. SUMMARY Enolase-2 (ENO2), previously termed 14-3-2 protein, is an isozyme of enolase that is enriched in neuronal tissue. The gene coding for ENO2 was previously assigned to human chromosome 12. The present study presents data for a regional mapping of gene ENO2 using cell hybrids containing various deletions of human chromosome 12. These deletions were produced by treatment with chromosome-breaking agents. Cytogenetic analysis has allowed assignment of ENO2 to the short arm of chromosome 12, in the region of pter-pi2O5. This assignment is consistent with the segregation pattern of the 93 hybrid clones analysed. The segregation pattern has also established the linear order of 6 genes on chromosome 12: pter - TPI- GAPD - LDHB - ENO2 - centromere - SHMT - PEPB - qter. Estimation of the relative distances between the 6 genes on chromosome 12 has been made by a statistical mapping analysis of the segregation data of the hybrid clones. A set of deletion hybrids containing various combinations of these 6 markers has been established for a rapid regional mapping of genes in one of these regions on chromosome 12. INTRODUCTION Previously we reported a regional assignment of 5 genes on human chromosome 12 (Law & Kao, 1979). These genes code for the following enzymes: triose phosphate isomerase-i (TPIi), glyceraldehyde-3-phosphate dehydrogenase (GAPD), lactate dehydrogenase B (LDHB), serine hydroxymethyltransferase (SHMT), and peptidase B (PEPB). The linear order and the map positions of these genes have been determined by both cytogenetic and statistical mapping analyses. In this paper, we present data for a-regional assignment of another gene on human chromosome 12, coding for enolase-2 (ENO2; EC 4.2.1.11), an enzyme previously termed neuronal-specific 14-3-2 protein. The chromosomal assignment of the ENO2 gene was made by Grzeschik (1975) and Herbschleb-Voogt et al. (1978). An abstract reporting preliminary studies of this regional assignment has been presented (Law & Kao, 1980). MATERIALS AND METHODS Cells and cell culture The various hybrid cells used in this study were derived from fusions between human cells and the glycine-requiring mutant gly'A of the Chinese hamster ovary (CHO-K1) cells. The chromosomal deletions induced in human chromosome 12 were achieved by treatment of the cells with either X-rays or 5-bromodeoxyuridine +near-visible light, as described in detail 246 M. L. Law and F.-T. Kao previously (Law & Kao, 1978, 1979). The hybrid clone 12A containing theglyh genome and a single human chromosome, 12, was grown in glycine-free medium F12D supplemented with 10% of the macromolecular fraction of foetal calf serum. The CHO-K1 cells and the gly'A mutant were grown in complete F12 medium supplemented with 8% foetal calf serum. The following cells were used to assay for enolase-2 activities: IMR-32, a human neuroblastoma cell line obtained from the American Type Culture Collection; P2, a mouse neuroblastoma cell line obtained from K. Spuhler; FS10, a diploid human fibroblastic culture established from a foreskin biopsy. These cells were grown in complete Fi2 medium supplemented with 8 % foetal calf serurn. In addition, the enolase-2 activity has been assayed in various tissue cells obtained from human biopsy, human brain grey and white matter, and Chinese hamster brain tissue biopsy. These tissue cells were used directly for enzyme assays without in vitro culture. Cellogel assay for enolase-z The crude cell extracts were prepared from the cultured cells and cell hybrids using the procedures previously described (Law & Kao, 1978). Similar methods were used for cells from tissue biopsies. Horizontal Cellogel electrophoresis (Meera Khan, 1971) was carried out at room temperature using c o i M-phosphate buffer (pH 6-2), for detecting enolase activity. The staining solution of Chen & Giblett (1976) was used, which contained c i M-Tris-HCl buffer (pH 7-8), 8 mM-MgSO4, o-i M-KCI, I mM-2-phosphoglycerate, 2 mM-ADP, 1 mM-NADH, 10 units per ml of pyruvate kinase, 30 units per ml of lactate dehydrogenase. After staining, the dark enolase bands can be seen against a fluorescent background, by long-wave ultraviolet illumination. Since ENO2 is generally less active than enolase-i (ENOi), it is necessary to stain longer for detecting ENO2 activity. In order to avoid over-staining of ENOi in some gels, the reaction was carried out first for 30 min; the gel was then cut and ENOi bands were removed. The gel was stained for another 90 min to reveal ENO2 bands. Cytogenetic analysis The trypsin-banding techniques described previously for karyotypic analysis were used (Kao, Jones & Puck, 1976). RESULTS Enolase-z activities in various tissues and cultured cells Fig. i A shows the enolase patterns of the various neuronal cells. Enolase is a dimer consisting of a and /? subunits. In Cellogel assays, 3 bands are formed: the cathodal band aa, the anodal band /?/?, and the middle band aft. The human homodimer a ^ is termed human enolase-1; the human homodimer Pxft\ is termed human enolase-2; the middle band is a heterodimer ct1fiv Chen & Giblett (1976) have shown that ENO2 is abundant in human brain tissue cells, but this isozyme is also present in lower concentrations in other tissues and in cultured skin fibroblasts. In Fig. 1 A, lane 1 shows a mouse neuroblastoma cell line P2, which contains 2 bands, presumably a homodimer oioux type (lower band) and a heterodimer ay? (upper band). Lanes 2, 4 and 5 show tissue cells obtained from, respectively, human brain, human grey matter, and human white matter. Each of these cell types has 3 bands corresponding to (from the bottom): a ^ , cLxfSx and fixP\- Lane 3 shows a human neuroblastoma cell line IMR-32. The homodimer fix^ is weak, but shows a definite band after 2 h of staining. Regional mapping of human enolase-z 247 Enolase-z assay in hybrid cells In Fig. IB, lane 1 shows the enolase assay in the hybrid clone 12A, which contains a single human chromosome 12. The cathodal band in lane 1 is the homodimer a^tz in which the a 2 subunit is coded for by a CHO gene. The band migrated to the same position as the cathodal band of CHO-Kl (lane 2). After 2 h of staining, a second band appeared above the a^xt band in 12A (lane 1), but not in CHO-Kl (lane 2). This bard is interpreted to be a heterodimer composed of subunits at^1 in which the fix subunit Fig. 1. Cellogel electrophoretic patterns stained for enolases. Lanes in A: I, mouse neuroblastoma cell line P2; 2, human brain tissue cells; 3, human neuroblastoma cell line IMR-32; 4, human brain grey matter; 5, human brain white matter. Lanes in B: 1, 12A; 2, CHO-Kl; 3, Chinese hamster brain tissue cells; 4, human brain tissue cells; 5, cultured human fibroblasts FS10. The human enolase subunits are designated as a t and filt and the Chinese hamster enolase subunits are designated as otj and j3t. The band a-ifii in B, lane 1, was very faint after staining for 45 min, but became darker after longer staining. The gels in A and B were stained for 2 h. The subunit composition of each enolase band is indicated by arrows. is coded for by a gene on human chromosome 12. The band a ^ migrated slightly faster than the Chinese hamster heterodimer ai^l (second band from top in lane 3), and considerably faster than the human heterodimer a2y32 (lanes 4, 5). The presence of the band a ^ in the 93 hybrid clones assayed has been used as indication of the presence of the ^ subunit of the ENO2 marker. In each individual assay for ENO2 activity in the hybrid clones, cell extracts from CHO-Kl and 12A were always included as controls and, in every case, the band a2/?! was absent in CHO-KI and present in 12A. Grzeschik (1975) showed the formation of interspecies heteropolymers between human and mouse enolase subunits. We demonstrated here that similar heteropolymers can also be formed between human and Chinese hamster subunits. 248 M. L. Law and F.-T. Kao The ENO2 activity and the activities of the 4 other isozymes were assayed in 93 hybrid clones and the results are presented in Table 1. Of these 93 clones, 44 were isolated by method B (Law & Kao, 1978), in which human cells were treated with chromosome-breaking agents followed by fusion with the gly~A mutant. SHMT+ hybrids were selected in F12D for the retention of human chromosome 12, either intact or partial. The other 49 hybrids were isolated either by method A (Law & Kao, 1978), or by a modified method A (Law & Kao, 1979), in which the 12A cells were treated with chromosome-breaking agents and the survivors were isolated. Table 1. Isozyme analysis of 93 hybrid clones each possessing at least one human marker on chromosome 12 Human isozyme marker — TPI GAPD + + + — + - + + + + + + + + + + — — — — — — — + — — + + + + + — + — Method B + — + — — — — - Method A + — LDHB - - - + — ENO2 - + — PEPB Number of hybrids + + 18 + + + + + 4 3 4 + + + + + + + + — + — — + - 1 2 i 1 1 1 8 + + + + 44 2 SHMT The 93 hybrid clones can be grouped into various phenotypic classes and arranged in order according to the map position of the genes on the chromosome. From the segregation patterns shown in Table 1, it is logical to place ENO2 between LDHB and SHMT. Moreover, ENO2 was assayed and shown to be positive in the 2 previously described independent clones MAi and MA2, which had large deletions in the long arm of chromosome 12 with the breakpoint at qi2 (Law & Kao, 1979). Thus, based on the karyotype and the phenotype (TPI+GAPD+LDHB+EN^+SHMT-PEPB-) of these 2 clones, ENO2 can be placed in the region pter-qi2, or between LDHB and qi2. Cytogenetic analysis The hybrid clone A9 was derived from 12A after treatment with bromodeoxyuridine + near-visible light (Law & Kao, 1979). The phenotype of A9 is TPI-GAPD"LDHB-ENO2-SHMT+PEPB+. This clone has a terminal deletion in the short arm with the breakpoint at pi205 (Fig. 2). Thus, like TPI, GAPD and LDHB, ENO2 can also be assigned to the region pter-pi2O5. This regional assignment is consistent with the location of ENO2 being pter-qi2 as derived from clones MAi and MA2. Regional mapping of human enolase-2 249 Statistical mapping analysis Regional mapping by statistical analysis of the segregation data (Table 1) was performed following closely the procedures described in our previous paper (Law & Kao, 1979). We used the methods of Goss & Harris (1975, 1977a, b) to derive the linear order of the 6 genes on chromosome 12 and to estimate the relative distances of these genes in relation to the selected locus SHMT. B D I Fig. 2. Trypsin-banded metaphase chromosomes in the 12A cell (A) containing a single human chromosome 12 (Hui2, arrow), and the A9 cell (B) containing a partial human chromosome 12 with a terminal deletion pter-pi2os (arrow). In the lower section are presented the enlarged human chromosome 12 (c) and the partial chromosome 12 (D). The segregation data of the 44 deletion hybrids (Table 1, method B) show that TPI is lost in 21 hybrids (48 ±7%); GAPD is lost in 16 hybrids (36 ±7%); LDHB is lost in 14 hybrids (32 ±7%); ENO2 is lost in 9 hybrids (20 ±6%); and PEPB is lost in 15 hybrids (34 ± 7%). The numbers in brackets refer to the frequency ± standard error. These segregation frequencies reflect the relative distances between SHMT and any one of these markers. Thus the following order of relative distances can be arranged, beginning with the smallest distance: ENO2, LDHB, PEPB, GAPD, TPI. This order of relative distances is consistent with our previous results (Law & Kao, 1979), and also adds the ENO2 marker, which is closest to the locus of selection. Our previous data based on statistical calculation and cytogenetic analysis have also shown that TPI, GAPD and LDHB are on the short arm of chromosome 12, 9 CEL53 M. L. LawandF.-T. Kao 250 while SHMT and PEPB are on the long arm. It is evident from the segregation patterns that, when ENO2 is lost, TPI, GAPD and LDHB are also lost. However, the reverse is not true; that is, when TPI, GAPD or LDHB is lost, there is on average a 50% chance that ENO2 is still retained in the hybrid. Therefore, we conclude that ENO2 is closer to SHMT than the other markers. PEPB appears to segregate independently of ENO2, indicating that they are on opposite sides of the selected locus SHMT. Indeed, our cytogenetic data support this conclusion. Table 2. Estimation of target size {i.e. distance between 2 loci) using co-transfer frequency (F) of unselected markers with SHMT Unselected marker TPI No. of clones exhibiting unselected markers and SHMT 23 F -log F -logF' GAPD LDHB ENO2 PEPB 28 3° 35 29 066 0-18 0-52 0-28 0-64 0-19 068 080 0-17 I'OO o-68 061 o-io 0-36 0-64 Total number of clones = 44 •SHMT s L90 SHMT •TPI -GAPD •LDHB •ENO2 CO 0-6 TPI GAPD LDHB EN02 6 - CO •PEPB 6 PEPB Fig. 3. Diagrams showing cytogenetic map (left) and statistical gene map (right) of human chromosome 12. Finally, the relative distance between 2 loci can be estimated using a simple target theory (Goss & Harris, 1975, 1977a, b), which to a first approximation equates the relative distance between 2 markers to — log of the frequency of hybrids possessing both markers. Table 2 presents the calculations based on these analyses. The last row represents the relative distance between SHMT and each of the syntenic markers, normalized to a distance of i-oo between TPI and SHMT. Corrections for interstitial deletions and other complex chromosomal rearrangements as described by Goss and Harris were not attempted here because of the small sample size of our deletion hybrids. Thus, the relative distance presented here is only an estimate. Regional mapping of human enolase-2 251 Comparison of cytogenetic and statistical maps of human chromosome 12 Fig. 3 presents the gene maps of human chromosome 12 constructed by both cytogenetic and statistical analyses. In general, the order of the 6 markers on chromosome 12 is consistent in the 2 maps. A significant difference in the 2 maps exists in the relative positions of the 4 genes on the distal part of the short arm. The cytogenetic map assigns the 4 genes to the region pter-pi2O5, but the statistical map shows that the 4 genes occupy a larger section, with ENO2 extended to the band pi 1. DISCUSSION Enolase, or 2-phospho-D-glycerate hydrolase, reversibly converts 2-phosphoglycerate to phosphoenol pyruvate in the glycolytic pathway. Three enolase isozymes have been identified: a non-neuronal enolase (ENOi), a neuronal enolase (ENO2), and a hybrid form of ENOi and ENO2 (Schmechel et al. 1978). ENOi is present in all tissues and consists of 2 identical subunits ct^x.lt each of about 39000 molecular weight. ENO2 is enriched in neuronal tissue but is also present in smaller quantities in other tissues. This enzyme consists of 2 identical subunits filfi1 each of about 43 500 molecular weight. The third form of enolase is a heterodimer consisting of cc^i subunits. The locus for human a subunit ( a j has been mapped to chromosome 1 both by family study (Giblett, Chen, Anderson & Lewis, 1974) and by cell hybrid analysis (Meera Khan, Deppert, Hagemeijer & Westveld, 1974). The locus for human fi subunit (/fj) has been mapped to chromosome 12 using cell hybrids (Grzeschik, 1975; Herbschleb-Voogt et al. 1978). Here we present data to assign regionally the fix locus for the enolase-2 phenotype to the short arm of chromosome 12, in the distal region pter-pi2O5. This regional assignment is consistent with the segregation data of 6 syntenic genes on human chromosome 12 (Table 1). The cytogenetic and segregation data also place ENOz between LDHB and the breakpoint pi205. Previously, TPI and GAPD were regionally assigned to pi3 by Serville et al. (1978), and LDHB to I2-I-I2-2 by Rethore et al. (1975). In their nomenclature, the band pi2 is divided into 3 equal parts designated 12-1, pi2-2 and 12-3, with 12-1 being contiguous with pi 1. Thus, the region pi2-i-pi2-2 is roughly equivalent to the region 1201-1207 in the system recommended by the Paris Conference Supplement (1976). Based on this regional mapping of LDHB and our assignment of ENOz between LDHB and pi205, we can further localize both LDHB and ENO2 to P1207-P1205, with the order of the 2 genes being LDHB distal and ENO2 proximal to the centromere. In the IV International Workshop on Human Gene Mapping, Bruns & Regina reported a possible second TPI locus (TPI2) on human chromosome 12 coding for a heat-labile subunit of the TPI isozyme. In our assays for this heat-labile TPI2 isozyme, we found no segregation between TPIi and TPI2 in the 93 hybrids analysed, as we reported previously for a smaller number of these hybrids (Law & Kao, 1980). In the present paper, we used the term TPI to represent both of these isozymes; the 9-2 252 M. L. Law and F.-T. Kao precise nature and the identity of TPI2 require further biochemical and genetic studies. The set of hybrids carrying various marker deletions can divide chromosome 12 into the following 8 regions: pter -1- - TPI -2- - GAPD -3- - LDHB -4- - ENO2 -8- centromere -6- - SHMT -7- - PEPB -8- - qter. Thus a set of a minimum of 5 clones exhibiting unique combinations of these markers can be selected from Table 1 and used for rapid regional mapping of other genes assigned to chromosome 12. However, the assignment to regions 5 and 6 will also require karyotypic analysis. A similar set of deletion hybrids has been established for the X chromosome by Becker et al. (1979). We previously used the statistical mapping analysis of Goss & Harris (1975, 1977 a,b) to estimate distances for the 5 genes on human chromosome 12 (Law & Kao, 1979). The statistical map in general agrees with the cytogenetic map. However, Serville et al. (1978) assigned TPI and GAPD to pi3 by cytogenetic analysis, while our statistical map places GAPD in pi2. Moreover, the statistical map position for ENO2 is more proximal to the centromere than its position in the cytogenetic map (Fig. 3). By comparing the 2 maps for the 4 genes on the short arm, it appears that the genes on the statistical map are extended to a greater distance. The significance of this disparity requires further study. It is worthwhile to point out that in the statistical mapping of the human chromosome 1, Goss & Harris (19776) found a similar non-coincidence, one interpretation of which was that radiation-induced rearrangements occurred preferentially in Giemsa-stained light material. It should also be pointed out that the cytogenetic map is constructed on the basis of the location of genes in the highly condensed metaphase chromosomes, whereas the statistical map is based on the location of genes in the extended state of the interphase chromosome in which radiation-induced breaks occur. Thus, while the statistical map measures the distance between genes in the extended DNA sequences, the cytogenetic map measures the distance between genes in the condensed metaphase chromosomes. Since meiotic crossing-over takes place during close-pairing of homologous chromosomes in an extended state, the statistical map should resemble more closely the genetic map based on recombination events observed in higher organisms. The regional assignment of ENO2 to the short arm of chromosome 12 is particularly interesting. It is the fourth enzyme of the glycolytic pathway for which the gene has been assigned not only to the same chromosome, but also to the same arm. Since these 4 genes are all separated by some distances as shown in the map, they are clearly not contiguous in the DNA sequences. However, the assignment of 4 genes related in a common pathway to a specific region of the chromosome may have some significance in evolution and possibly in gene regulation. The possible relationship between the coordinate regulation of functionally related genes and the physical linkage of these genes on a segment of the chromosome certainly requires further investigation. Mapping of these 4 genes in other species may provide additional insight into the significance of this linkage relationship. Regional mapping of human enolase-2 253 This investigation is a contribution from the Eleanor Roosevelt Institute for Cancer Research and the Florence R. Sabin Laboratories for Development Medicine (Contribution no. 350), and the Department of Biochemistry, Biophysics and Genetics, University of Colorado Health Sciences Center, Denver, Colorado. This work was supported by grants from the American Cancer Society (CD105) and the National Institutes of Health (GM26631, HD02080). We thank Drs T . T . Puck and D. Patterson for critical reading of the manuscript. This paper is no. 34 in the series entitled 'Genetics of Somatic Mammalian Cells'. The preceding paper is by Meisler, Wanner, Kao & Jones (1981). REFERENCES BECKER, M. A., YEN, R. C. K., ITKIN, P., Goss, S. J., SEEGMILLER, J. E. & BAKAY, B. (1979). Regional localization of the gene for human phosphoribosylpyrophosphate synthetase on the X chromosome. Science, N. Y. 203, 1016-1019. CHEN, S. H . & GIBLETT, E. R. (1976). Enolase: Human tissue distribution and evidence for three different loci. Arm. hum. Genet. 39, 277-280. ^ GIBLETT, E. R., CHEN, S. H., ANDERSON, J. E. & LEWIS, M. (1974). A family study suggesting genetic linkage of phosphopyruvate hydratase (enolase) to the Rh blood group system. Cytogenet. Cell Genet. 13, 91-92. Goss, S. & HARRIS, H. (1975). New method for mapping genes in human chromosomes. Nature, Lond. 255, 680-684. Goss, S. & HARRIS, H. (1977 a). Gene transfer by means of cell fusion. I. Statistical mapping of the human X-chromosome by analysis of radiation-induced gene segregation.,7. Cell Set. 25, 17-37Goss, S. & HARRIS, H. (19776). Gene transfer by means of cell fusion. II. The mapping of 8 loci on human chromosome 1 by statistical analysis of gene assortment in somatic cell hybrids. J.CellSci. 25, 39-58. GRZESCHIK, K. H. (1975). Assignment of human genes: /?-glucuronidase to chromosome 7, adenylate kinase-i to 9, a second enzyme with enolase activity to 12, and mitochondrial I D H to 15. Cytogenet. Cell Genet. 16, 142-148. HERBSCHLEB-VOOGT, E., MONTEBA-VAN HEUVEL, M., WIJNEN, L. M. M., WESTERVELD, A., PEARSON, P. L. & MEERA KHAN, P. (1978). Chromosomal assignment and regional localization of CS, E N O , , GAPDH, LDH B , PEPB, and T P I in man-rodent cell hybrids. Cytogenet. Cell Genet. 22, 482-486. KAO, F. T., JONES, C. & PUCK, T . T . (1976). Genetics of somatic mammalian cells: Genetic, immunologic, and biochemical analysis with Chinese hamster cell hybrids containing selected human chromosomes. Proc. natn. Acad. Sci. U.S.A. 73, 193-197. LAW, M. L. & KAO, F. T . (1978). Induced segregation of human syntenic genes by 5-bromodeoxyurdine + near visible light. Somat. Cell Genet. 4, 465-476. LAW, M. L. & KAO, F. T . (1979). Regional assignment of human genes T P I t , GAPDH, LDH B , S H M T , and PEPB on chromosome 12. Cytogenet. Cell Genet. 24, 102-114. LAW, M. L. & KAO, F. T . (1980). Regional assignment of human chromosome 12 of seven genes TPI 1 ( T P I . , GAPDH, LDHB, ENO,, S H M T and PEPB. Cytogenet. Cell Genet. 25, 179-180. MEERA KHAN, P. (1971). Enzyme electrophoresis on cellulose acetate gel: Zymogram patterns in man-mouse and man-Chinese hamster somatic cell hybrids. Archs Biochem. Biophys. I4S. 47°-483MEERA KHAN, P., DOOPERT, B. A., HACMEIJER, A. & WESTERVELD, A. (1974). T h e human loci for phosphopyruvate hydratase and guanylate kinase are syntenic with the P G D - P G M ! linkage group in man-Chinese hamster somatic cell hybrids. Cytogenet. Cell Genet. 13, 130-131. MEISLER, M. H., WANNER, L., KAO, F. T . & JONES, C. (1981). Localization of the uroporphy- rinogen I synthase locus to human chromosome region n q i 3 - q t e r and interconversion of enzyme isomers. Cytogenet. Cell Genet. (In Press.) RETHORE, M . O., KAPLAN, J. C , JUNIEN, C , CRUVEILLER, J., DUTRILLAUX, B., AURIAS, A., CARPENTIER, S., LAFOURCADE, J. & LEJEUNE, J. (1975). Augmentation de l'activite de la LDH-B chez un garcon trisomique I2p par malsegrcgation d'une translocation maternelle t ( i 2 : i 4 ) ( q i 2 : p n ) . Annls Genet. 18, 81-87. 254 M. L. Law and F.-T. Kao D., MARANCOS, P. J., Zis, A. P., BRIGHTMAN, M. & GOODMAN, F. K. (1978). Brain enolases as specific markers of neuronal and glial cells. Science, N.Y. 199, 313-315. SERVILLE, F., JUNIEN, C , KAPLAN, J. C, GACHET, M., GADOUX, J. & BROUSTET, A. (1978). Gene dosage effect for human triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase in partial trisomy 12P13 and trisomy i8p. Httm. Genet. 45, 63-69. SCHMECHEL, {Received 2 June 1981)