Download Insulin-like growth factor II may play a local role in the

Development 107, 123-130(1989)
Printed in Great Britain © The Company of Biologists Limited 1989
123
Insulin-like growth factor II may play a local role in the regulation of ocular
size
R. A. CUTHBERTSON1*, F. BECK2, P. V. SENIOR2, J. HARALAMBIDIS1, J. D. PENSCHOW1
and J. P. COGHLAN1
toward Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, 3052, Victoria, Australia
Department of Anatomy, University of Leicester, Leicester, UK
2
* Author for correspondence
Summary
The ultimate size and shape of the eye has a profound
influence on its refraction and function. However, the
role of growth factors in normal ocular development is
poorly understood. Insulin-like growth factors IGF-I
and -II have major effects on cell growth and differentiation in tissue culture. Recently their importance for in
vivo development has been studied; IGF-II is predominant prenatally, with a probable local role in the
differentiation of some mesodermally derived tissues.
Ocular development and size is partially dictated by the
condensation of the outer collagenous scleral coat (the
'white') of the eye from orbital mesoderm. We investigated IGF-II expression and IGF-II receptor distribution during normal ocular development in the mouse
fetus using in situ hybridization and immunohistochemistry.
IGF-II mRNA was expressed by the loose mesenchymal orbital tissue as it differentiated to form the sclera,
but not in the compact mature sclera or cornea, or in the
ectodermally derived retina or skin. IGF-II gene expression was seen in the orbit at E14, reached a peak just
before parturition and then declined to background
levels after birth. Similarly, type 2 IGF receptors were
shown with immunohistochemistry to be present on
developing scleral cells and to be modulated in parallel
with IGF-II mRNA expression.
We suggest the IGF-II expression by differentiating
cells that compact to form the collagenous ocular coat
plays a local role in determining the ultimate shape and
size of the developing eye.
Introduction
ocular growth and therefore ultimate ocular size may
well depend on a locally acting growth factor or growth
factors.
The insulin-like growth factors IGF-I and -II are
peptides homologous to insulin which have major
effects on cell growth and differentiation in cell culture
(Zapf et al. 1979; Baxter, 1986); and recently their
importance for in vivo development has been studied
(Brown et al. 1986; Lund et al. 1986). IGF-II is
important prenatally, with a probable local role (autocrine and/or paracrine) in the differentiation of some
mesodermally derived tissues (Hall and Sara, 1983;
Hyldahl et al. 1986; Beck et al. 1987). Insulin and IGF-I
have receptors that are homologous (Ullrich et al.
1986). Both the insulin and the type 1 IGF receptors
have cytoplasmic tyrosine kinase domains and share a
heterotetrameric structure. The type 2 IGF receptor is a
glycoprotein with quite a different structure (Kasuga et
al. 1981), and is identical with the cation-dependent
mannqse-6-phosphate (M6P) receptor, which has a
probable role in the cellular transport of lysosomal
Successful ocular function depends on a fine balance
between refractive power and ocular size. If the eye is
too long or the refractive power too high, myopia
results. Conversely, hypermetropia results from an eye
that has a short axial length compared with its refractive
power. As the ultimate size and shape of the eye has a
profound influence on its function, these parameters
must be tightly regulated during ocular development.
One possible level of regulation is by growth factors,
peptide hormones that influence cell division and differentiation (Jost, 1960; Adamson, 1983; Heath and
Roberts, 1985). Although the role of growth factors in
systems such as haematopoiesis (Metcalf, 1984), the
development of tissues derived from mesenchyme
(Beck etal. 1987) and neuronal development (Crutcher,
1986) is now known in some detail, the function of
growth factors in ocular development is poorly understood. While the notion that a single growth factor can
dictate all aspects of eye development is simplistic,
Key words: growth factors; eye growth; IGF-II; myopia.
124
R. A. Cuthbertson and others
enzymes (Lobel et al. 1987). This receptor preferentially binds IGF-II (Kd = 1 nM) with higher affinity than
IGF-I, but has no affinity for insulin.
The physiological role of the type 2 IGF receptor is
unclear (Gammeltoft, 1989). IGF-II has been shown to
stimulate cell division and metabolism in vitro by
interaction with the type 1 IGF receptor (Yu and
Czech, 1984) and it has been suggested that the type 2
IGF receptor molecule might not propagate a signal
after IGF-II binding (Roth, 1988) but might act as a
local sump in an analogous way to the described IGF-II
binding proteins (Zapf et al. 1979; Froesch et al. 1985).
Very recently, however, it has been shown that M6P
increases the affinity of the type 2 IGF receptor for
IGF-II (Roth et al. 1987; MacDonald et al. 1988) and
several in vitro responses have been reported following
IGF-II binding to the type 2 IGF receptor. Production
of anti-type 2 IGF receptor antibodies (Scott and
Baxter, 1987; Hartshorn etal. 1989) has made it possible
to map the distribution of these receptors in tissues
using immunohistochemistry. Higher levels of both
type 2 IGF receptor and circulating IGF-II peptide are
found in developing animals compared with adults
(Moses et al. 1980) suggesting that the receptor-ligand
system may play an important role in the regulation of
fetal development.
Ocular size is physically defined by the sclera, the
rigid, collagenous outermost coat of the eye. The sclera
grows and differentiates as a condensation of the orbital
mesoderm surrounding the optic cup during intrauterine life (Ozanics etal. 1976; Sellheyer and Spitznas,
1988). There has been debate as to whether the refractive state during eye development is under the direct
control of environmental influences and, if so, what
these influences might be (Sorsby et al. 1961; Banks,
1980; Wallman and Adams, 1987). Coulombre (1956)
demonstrated that scleral growth is in some ways
directed by the intraocular pressure. It has been shown
in a variety of species that neonatal deprivation of visual
form may induce myopia (Wiesel and Raviola, 1977;
Sherman etal. 1977; Wallman etal. 1978). So, while the
growth of the eye is physically defined by the sclera,
there may be transduction of a signal produced by light
falling on the developing neural retina, which regulates
the growing outer ocular coats.
We were interested in testing whether IGF-II might
play a local role in the control of ocular growth by
mapping both the site of expression of the IGF-II gene
and the presence of type 2 IGF receptors, during
murine ocular development.
Materials and methods
Hybridization histochemistry
Swiss mouse embryos were collected at E14, E16 and E18 by
counting from the day of appearance of vaginal plugs. The
morning on which the vaginal plug was observed was taken as
day zero of pregnancy. Specimens were also taken on the day
of birth (E18/19) and from adult mice. Embryos were
oriented in OCT compound (Lab Tek, Naperville, IL) and
quickly frozen in a mixture of hexane and dry ice. 7/<m-thick
frozen coronal sections through the developing eye were then
thawed onto gelatine-coated slides and transferred to dry ice
for 30 min to adhere the sections to the slides and inhibit
ribonuclease activity. The sections were then fixed at 4°C for
5 min in 4 % glutaraldehyde and 20 % ethelyne glycol in ()• 1 Mphosphate buffer at pH7-3. Sections were prehybridized and
stored for hybridization as previously described (Penschow et
al. 1986).
Synthesis of oligodeoxyribonudeotide probes
To locate IGF-II mRNA, we used a 30-mer probe complementary to a part of the mRNA to rat IGF-11 (Whitfield et
al. 1984), the details of which have previously been described
(Beck et al. 1987). IGF-I was studied using a 30-mer probe
complementary to a part of the mouse IGF-I mRNA (Bell et
al. 1986; Beck et al. 1987). Both probes were synthesized using
the solid-phase phosphosamidite procedure (Beaucage and
Caruthers, 1981) on an Applied Biosystems Inc. 380A Automated DNA Synthesizer and purified on polyacrylamide gels.
The sequences were selected for these probes specifically to
eliminate cross hybridization.
A 26-mer probe complementary to the predicted sequence
of mouse rhodopsin mRNA (5'-AGC GTG AGG AAG TTG
ATG GGG AAG CC-3') was synthesized from the published
bovine and human sequences, using mouse preferred codons,
for use as a control.
100 ng samples of each probe were 5'-end labelled with
20 pmol of gamma- [32P] ATP (Amersham) using 20 units of T4
polynucleotide kinase for 1 h. The labelled probe was purified
on a Sephadex G-25 column, precipitated in ethanol with
tRNA carrier, dried under vacuum and diluted to 400ngml~'
in hybridization buffer. The specific activity obtained was in
the order of 6-9xlO 8 counts min~' f.ig~l (2-3xlO 6 counts
min"1 pmol"1).
Hybridization
Self-complementary interactions were minimized by heat
denaturation of the probes at 90 °C immediately before
application to coverslips over which the sections were then
inverted. Hybridization was performed for 48 h in humidified
chambers at 40°C. Slides were subsequently immersed in 2x
standard saline citrate (0-3M-sodium chloride and 0-03 Msodium citrate) to dislodge the coverslips and then washed at
40°C in single-strength saline citrate for 30 min, rinsed in
absolute ethanol and allowed to dry.
At each stage of embryological development, additional
sections were hybridized with IGF-1 and rhodopsin-specific
control probes.
Auto radiography
Slides were taped to a backing sheet and exposed to Kodak
X-Omat AR5 film (Eastman Kodak Co., Rochester, NY) for
18 h in an X-ray cassette from which the intensification sheet
had been removed. The signal obtained by this method served
as a guide for subsequent autoradiography. The slides were
then dipped using Ilford K5 emulsion (Ilford, Essex, England) diluted to 1/3 strength, exposed on average for one
week, developed, fixed and stained with haematoxylin and
eosin. Dark-field photography was performed with matching
bright-field exposures for orientation.
Immunohistochemistry
5 /tm-thick sections were taken from the same specimens and
air-dried for 2h at room temperature onto gelatine-coated
slides. Sections were then fixed in 100% acetone at 4°C for
lOmin, washed in 0-lM-phosphate-buffered saline (PBS)
(pH7-4) and stained using the immunoperoxidase technique.
IGF-II and ocular size
The primary antibody used was a purified rabbit anti-type 2
IGF receptor antibody prepared and characterized by Scott &
Baxter (1987). A rabbit anti-human factor viii-related protein
control primary antibody was also used (A082, Dakopatts,
Denmark), as was a normal rabbit serum control.
Sections were blocked by incubating with normal serum for
30min at room temperature. Rabbit anti-rat type 2 IGF
receptor antiserum C-l was diluted 1:2000 in PBS with 0-5 %
Triton X-100 and 200 jd incubated with the section for 1 h at
room temperature in a humidified chamber. The samples
were then washed in PBS and incubated with biotinylated
second antibody (Vector Laboratories, Burlingame, CA) for
30 min and then nonspecific peroxidase activity was blocked
by exposing sections to 0-2% hydrogen peroxide in 100%
methanol for 30 min at room temperature. After rehydrating
with PBS the sections were incubated with complex (Vector),
washed in PBS and then exposed to 04 % 3-3' diaminobenzidine tetrahydrochloride (DAB) in 0-1 M-Tris buffer, pH7-2
for 4imin. Sections were washed in tap water and then
staining was enhanced by incubation in 1 % copper sulphate
solution, counterstained with haematoxylin, dehydrated
through graded ethanols and mounted.
Results
Hybridization histochemistry
As may be seen in Fig. 1 (A-E), the corneo-scleral unit
formed by head mesodermal cells condensing and
differentiating into keratinocytes and scleracytes.
These cells then secreted collagen, elastin and other
proteins to create the characteristic extracellular
matrix. The formation of the extraocular muscles may
also be seen (Fig. I D, E).
Figure 2 (A-C) shows that by E14 the cells of the
primitive sclera, in common with the rest of the orbital
mesoderm, were expressing the gene for IGF-II. The
expression seemed to intensify as the periocular mesoderm condensed and differentiated to form the future
ocular outer coat (Fig. 2 A, B). The dense cellularity of
the ectodermally derived neural retina provided an
excellent negative control tissue. Hybridization with the
IGF-1 and rhodopsin control probes was negative at this
stage (Fig. 2 C).
The cornea differentiated earlier than the posterior
sclera. IGF-II expression, although present in the
cornea at E14, was less intense than that of the
posterior pole of the eye (Fig. 2 A, B). The apparent
anteroposterior progression in the maturation of the
ocular outer coat can be seen by comparing corneal to
scleral signal in this figure, with the signal in Figures 3
and 4. In each case, the signal from the rest of the head
mesenchyme provided a useful comparison.
The intensity of IGF-II expression increased by E16
and appeared to peak at E18 (Figs 3, 4). Again, the
developing retina was negative, but the developing
sclera, the extraocular muscles and the retinal and
hyaloid blood vessels traversing the optic nerve and
entering the vitreous cavity, all showed high levels of
IGF-II expression. As it had been at E14, hybridization
with an IGF-I probe was negative (Fig. 3). By E18, the
cornea did not express IGF-II at nearly the same level
as the sclera.
125
IGF-II expression declined just after birth and was
virtually undetectable in sclera in the neonatal mouse
eye (Fig. 5 A, B), as opposed to rhodopsin mRNA,
which could be demonstrated in the photoreceptor
layer of the neonatal retina (Fig. 5C).
Immunohistochemistry
The type 2 IGF receptor was detectable on developing
scleral cells at E14, but not on the cells of the developing neural retina. Using an antiserum to Factor viiirelated peptide, and using normal serum in place of first
antibody, we showed that the scleral staining with the
anti-type 2 IGF receptor antibody was specific. In a
pattern similar to scleral IGF-II gene expression, type 2
IGF receptor staining increased to peak just before
birth (Fig. 6), and then declined to very low levels in the
adult sclera.
Discussion
We have shown that IGF-II expression by head mesoderm intensifies in the periocular mesoderm as it
condenses and differentiates to form the outer collagenous coat of the developing eye. This expression rises
from E14, to a peak before birth, and declines after
parturition to undetectable levels in the neonate. The
clear anterior cornea and the 'white' sclera are developmentally and anatomically the same layer, with their
different optical properties determined by their ultrastructural arrangements. IGF-II expression appears to
follow an anteroposterior wave, declining in the cornea
and increasing posteriorly in the eye with advancing
developmental age. We were not able to demonstrate a
developmental time at which corneal expression of
IGF-II exceeded expression by the sclera, but it is
possible that this might occur prior to E14. This
anteroposterior wave of IGF-II expression parallels the
reported pattern of morphological scleral differentiation in humans (Sellheyer and Spitznas, 1988), which
begins in the cornea and lags some days behind in the
posterior sclera. Our observations also confirm those of
Hyldahl et al. (1986) who showed, using Northern
analysis, that IGF-II was expressed in the posterior part
of the eye, but not in the cornea, at the end of the first
trimester in the human foetus.
We have also shown that the developing scleral cells
contain significant levels of the type 2 IGF receptor
protein during development which seems to follow the
developmental progression of IGF-II mRNA production. The close anatomical proximity of cells
expressing the IGF-II gene and IGF-II responsive cells
during the phase of ocular growth leads us to propose
an important local regulatory role for IGF-II in ocular
development, an idea first proposed by Hyldahl et al. in
1986. Within this paracrine or autocrine system, the
type 2 IGF receptor could function either as a biological
transducer or as a sump to control local IGF-II levels
(MacDonald et al. 1988).
The regulation of eye growth, and its perturbation to
produce disorders such as myopia, have excited signifi-
126
R. A. Cuthbertson and others
V;'> :,Y/.
V ia. UH^t
//7S
Fig. 1. The primitive sclera (s) and the extraocular muscles
(eom) may be seen condensing and differentiating from the
head mesoderm (meso) at E14 in the mouse (Fig. 1A).
Bar= 120 f.im. By A7 the cornea (Fig. IB) and sclera
(Fig. 1C) are well differentiated. Bar = 70//m. The
condensation and alignment of mesodermal cells to form the
primitive sclera (s) and the insertion of the extraocular
muscles (eom) is more obvious at higher power (D and E).
In D, the differentiating neuroblastic layer of the retina is
seen (r) and around this the mesodermal cells (meso)
condense to form the primitive sclera (s). E shows the
differentiation of cells forming one of the extraocular muscles
(eom), as the muscle inserts into the developing sclera (s).
Bar = 30fim.
cant research interest. In his classic series of experiments, Coulombre (1956) showed that a decrease in
intraocular pressure in the developing chick eye caused
the scleral outer coat, but not the retina, to stop
growing. More recently Wallman etal. (1978) and other
workers have shown that visual deprivation leads to
myopia in the chick. That is, by occluding the whole
retina or even half the retina from formed visual input
with a white translucent shield during eye development,
the deprived eye or eye segment continued to grow and
became myopic. Thus both retinal function and intraocular pressure seem to dictate scleral growth. Coulombre pointed out that eye size was, as a first approximation, a balance between intraocular pressure
(favouring expansion) and the resistance to expansion
favoured by the sclera. Scleral resistance to expansion
IGF-II and ocular size
•
•
•
"
•
"
•
127
• • • *
^
^v-;
^
Fig. 2. Hybridization histochemistry: the light-field picture
(Fig. 2A) provides orientation, while the dark-field pictures
reveal the distribution of silver grains over a section of
mouse eye and orbit on the 14th day of embryological
development probed with an oligonucleotide
complementary to IGF-II (Fig. 2B) and IGF-I mRNAs
(Fig. 2C). IGF-Il-positive cells may be seen in the orbital
mesoderm and condensing sclera (Fig. 2B), while no
positive hybridization with the IGF-I probe is detected
(Fig. 2C). Bar= 130^m.
'
•
^
^
Fig. 3. By the eighteenth day of embryological
development (Fig. 3A), the higher density of silver grains
over the sclera compared with the cornea, when probed for
IGF-II mRNA, is obvious (Fig. 3B). The extraocular
muscles and the inner vascularizing part of the retina are
also positive for IGF-II. As a further negative control, the
section shown in (Fig. 3C) was treated with RNase A prior
to hybridization with the IGF-II probe. This pretreatment
abolished the positive hybridization. Bar = 200Jum.
128
R. A. Cuthbertson and others
-.'•
•!*£*'%
Fig. 4. At higher power the positive
IGF-II hybridization may be seen over
the compacting sclera (s) and
extraocular muscles (eom). Again, the
developing neural retina (nr) provides a
highly cellular negative control tissue.
The marked hybridization along the
optic nerve (on) and onto the inner
surface of the retina (ir, arrows) follows
the course of the central retinal artery
and vein, and the developing retinal
circulation. The outer retina, which
shows no positive hybridization, is
avascular. Bar = 70,u.m.
depends primarily on the cessation of scleral cell
division and the differentiation of scleral cells to produce extracellular proteins like collagen and elastin.
Wallman and Adams (1987) have proposed that an
active mechanism regulates eye growth in a manner
dependent on refractive error. Therefore, at least in the
chick, there appears to be a link between retinal
function and the control of scleral growth.
Our experiments suggest that part of this transduction mechanism may be local IGF-II acting in a permissive manner. By 'permissive' we mean that scleral cell
growth may require the local action of IGF-II and that
cessation of IGF-II and type 2 IGF receptor expression
may coincide with terminal scleral cell differentiation.
Even though mouse eyes do not open until 14 days after
birth, light transmitted through the lids after parturition
may provide the retinal signal responsible for terminating IGF-II and type 2 IGF receptor gene expression in
the developing sclera.
It is well known from morphological studies that the
anterior cornea differentiates earlier than the posterior
sclera (Ozanics et al. 1976). In a detailed electron
microscopic study of human embryonic scleral development, Sellheyer and Spitznas (1988) showed that there
was an anteroposterior pattern of scleral development
in the human which could morphologically be defined.
It has been suggested that a relative lack of posterior
scleral differentiation, as measured by the delay in
laying down extracellular components such as collagen
and elastin, combined with intraocular pressure, may
account for the continued eye elongation in myopia
(Weale, 1982). We have demonstrated an anteroposterior pattern of IGF-II expression and type 2 IGF
receptor expression, which spatially and temporally
follows the sequence of tissue growth and differentiation. This is strikingly shown at EL8, when the
corneal stromal cells, being highly differentiated, express little IGF-II compared with the relatively imma-
" S
eom
Fig. 6. Immunoperoxidase staining of a developing eye at E17 using an
antiserum to the type 2 IGF receptor. The cellular distribution of the receptor
has the same pattern, being positive in the sclera (s) and the extraocular
muscles (eom), as the expression of IGF-II mRNA. Bar = 70/«n.
Fig. 5. By the eighth day after birth the sclera forms a well-defined
differentiated layer (Fig. 5A). and the expression of IGF-II is markedly
decreased (Fig. 5B). In contrast, probing this section for rhodopsin mRNA
reveals expression of this gene in the developing outer segments of the
photoreceptors (small arrows) inside the maturing sclera (larger arrows).
00
IGF-II and ocular size
ture sclera and extraocular muscles, which express this
gene at high levels.
It seems that different epigenetic events may regulate
IGF-II expression in a tissue-specific manner. It has
previously been documented that most fully matured
tissues of mesodermal origin (e.g. mature chondrocytes
as opposed to the chondroblasts of the perichondrium)
lose much of their ability to produce IGF-II mRNA
(Beck et al. 1987; 1988a). IGF-II expression is diminished between 18 and 20 days postnatally in the rat liver,
perhaps in response to a physiological surge in serum
glucocorticoid levels (Beck et al. 19886), while other
tissues such as the choroid plexus continue to express
IGF-II and type 2 IGF receptors into adult life (Valentino et al. 1988). Light falling on the retina may
constitute the tissue-specific stimulus for the developing
sclera.
Recently Morgan et al. (1987) have shown that a
single receptor binds to both IGF-II and mannose-6phosphate. This latter receptor is thought to be involved in transport of lysozymal enzymes and is probably present to some degree in most living cells (MacDonald et al. 1988). However, the striking expression of
the type 2 IGF receptor on developing scleral cells that
we have shown immunohistochemically would seem to
indicate some special role for this hormone receptor in
eye development, apart from its ubiquitous metabolic
function. Recent evidence suggests that IGF-II can
promote cell proliferation via the specific type 2 IGF
receptor (Tally et al. 1987), and a relationship between
the number of type 2 cell surface receptors and cell
division has been demonstrated (Scott and Baxter,
1987; Scott et al. 1988).
Our results suggest the possibility of a light-dependent growth-regulating mechanism in the mouse that
has the effect of controlling eyeball size during development. In view of the results of others showing that
occluding retinal input may cause continued ocular
growth (Wiesel and Raviolla, 1977; Sherman et al. 1977;
Wallman and Adams, 1987), we speculate that light
falling on local retinal regions after birth may control
adjacent eye growth via a transduction mechanism,
which includes the continued permissive effect of an
IGF-Il/type 2 IGF receptor interaction in the developing sclera.
We would like to thank Dr Carolyn Scott, University of
Sydney, for the kind donation of her anti-type 2 IGF receptor
antiserum. These studies were supported in part by grants-inaid from the National Health and Medical Research Council
of Australia, the Myer Family Trusts, and the Ian Potter
Foundation. R.A.C. was further supported by the British
Council and the Anatomical Society of Great Britain and
Ireland. R.A.C. is an NH & MRC Post-Doctoral Fellow of
the Australian National Health and Medical Research Council.
References
ADAMSON, E. D. (1983). Growth factors in development. In
Biological Basis of Reproductive & Developmental Medicine, (ed.
J.B. Warshaw), pp. 307-336. London: Edward Arnold.
BANKS, M. S. (1980). Infant refraction and accomodation. In
129
Electrophysiology and Psychophysics: Their Use in Ophthalmic
Diagnosis, (ed. S. Sokol). Int. Ophthalmol. Clin. 20, 205.
BAXTER, R. C. (1986). The somatomedins: insulin-like growth
factors. Adv. Clin. Chem. 25, 49-115.
BEAUCAGE, S. L. & CARUTHERS, M. H. (1981). Deoxynucleoside
phosphoramidites - a new class of key intermediates of
deoxypolynucleotide synthesis. Tetrahedron Lett. 22, 1859-1862.
BECK, F., SAMANI, N. J., BYRNE, S., MORGAN, K., GEBHARD, R. &
BRAMMAR, W. J. (1988<J). Histochemical localization of IGF-I and
IGF-II mRNA in the rat between birth and adulthood.
Development 104, 29-39.
BECK, F., SAMANI, N. J., PENSCHOW, J. D . , THORLEY, B . , TREGEAR,
G. W. & COGHLAN, J. P. (1987). Histochemical localization of
IGF-I and -II mRNA in the developing rat embryo. Development
101, 175-184.
BECK, F., SAMANI, N. J., SENIOR, P., BYRNE, S., MORGAN, K.,
GEBHARD, R. & BRAMMAR, W. J. (19886). Control of IGF-II
mRNA levels by glucocorticoids in the neonatal rat. J. molec.
Endocr. 1, R5-R8.
BELL, G. I., STAMPIEN, M. M., FONG, N. M. & RALL, L. B. (1986).
The sequences of cDNAs encoding two different mouse insulinlike growth factor/precursors. Nucleic Acids Research 14,
7873-7882.
BROWN, A. L., GRAHAM, D. E., NISSLEY, S. P., HILL, D. J.,
STRAIN, A. J. & RECHLER, M. M. (1986). Developmental
regulation of insulin like growth factor II mRNA in different rat
tissues. J. biol. Chem. 261, 13144-13150.
COULOMBRE, A. J. (1956). The role of intraocular pressure in the
development of the chick eye. I. Control of eye size. J. exp.
Zool. 133, 211-225.
CRUTCHER, K. A. (1986). The role of growth factors in neuronal
development and plasticity. CRC Critical Reviews in Clinical
Neurobiology 2, 297-333.
FROESCH, E. R., SCHMID, C. H., SCHWANDER, J. & ZAPF, J. (1985).
Actions of insulin-like growth factors. A. Rev. Physiol. 47,
443-467.
GAMMELTOFT, S. (1989). Insulin-like growth factors and insulin:
gene expression, receptors and biological actions. In
Prohormones, Hormones and their Fragments: Processing,
Biological Activity and Pharmacology, (ed. J. Martinez), pp.
176-210. England: Ellis Horwood.
HALL, K. & SARA, V. R. (1983). Growth and somatomedins. In
Vitamins and Hormones, vol. 40, pp.175-233. New York:
Academic Press.
HARTSHORN, M. A., SCOTT, C. D. & BAXTER, R. C. (1989).
Immunofluorescent localization of type II insulin-like growth
factor receptor in rat liver and hepatoma cells. J. Endocrinol.
121, 221-227.
HEATH, J. K. & ROBERTS, A. R. (1985). Growth factors in
mammalian embryogenesis. In Growth Factors in Biology and
Medicine, Ciba Foundation Symposium, vol. 116, pp.3-14.
London: Pitman.
HYLDAHL, L., ENGSTROM, W. & SCHOFIELD, P. N. (1986).
Stimulatory effects of insulin-like growth factors on DNA
synthesis in the human embryonic cornea. J. Embryol. exp.
Morph. 98, 71-83.
JOST, A. (1960). The role of fetal hormones in prenatal
development. Harvey Lectures 55, 201-226.
KASUGA, M., VAN OBBERGHEN, E., NISSLEY, S. P. & RECHLER, M.
M. (1981). Demonstration of two sub-types of insulin-like growth
factor receptors by affinity cross-linking. J. biol. Chem. 256,
5306-5308.
LOBEL, P., DAHMS, N. M., BREITMEYER, J., CHIRGWIN, J. M. &
KORNFELD, S. (1987). Cloning the bovine 215-kDa cationindependent mannose 6-phosphate receptor. Proc. natn. Acad.
Sci. U.S.A. 84, 2233-2237.
LUND, P. K., MOATS-STAATS, M., HYNES, M. A., SIMMONS, J. G.,
JANSEN, M., D'ERCOLE, A. J. & VAN WYK, J. J. (1986).
Somatomedin C/insulin like growth factor I and insulin like
growth factor II mRNAs in rat fetal and adult tissues. J. biol.
Chem. 261, 14539-14 544.
MACDONALD, R. G., PFEFFER, S. R., COUSSENS, L., TEPPER, M.
A., BROCKLEBANK, C. M., MOLE, J. E., ANDERSON, J. K.. CHEN.
E., CZECH, M. P. & ULLRICH, A. (1988). A single receptor binds
130
R. A. Cuthbertson and others
both insulin-like growth factor II and mannose-6-phosphate.
Science 239, 1134-1137.
METCALF, D. (1984). The Hemopoietic Colony Stimulating Factors.
Amsterdam: Elsevier.
MORGAN, D. O., EDMAN, J. C , STANDRING, D. N., FRIED, V. A.,
SMITH, M. C , ROTH, R. A. & RUTTER, W. J. (1987). Insulin-like
growth factor II receptor as a multifunctional binding protein.
Nature, Lond. 329, 301-307.
MOSES, A. C , NISSLEY, S. P., SHORT, P. S., RECHLER, M. M.,
WHITE, R. M., KNIGHT, A. B. & HIGA, O. Z. (1980). Increased
levels of multiplication stimulating activity, or insulin-like growth
factor, in fetal rat serum. Proc. natn. Acad. Sci. U.S.A. 77,
3649-3653.
OZANICS, V., RAYBORN, M. & SAGUN, D. (1976). Some aspects of
corneal and scleral differentiation in the primate. Expl Eye Res.
22, 305-327.
PENSCHOW, J. D . , HARALAMBIDIS, J., ALDRED, P., TREGEAR, G. W.
& COGHLAN, J. P. (1986). Location of gene expression in the
CNS using hybridization histochemistry. Methods in Enzymology
124, 534-548.
ROTH, R. A. (1988). Structure of the receptor for insulin-like
growth factor II: the puzzle amplified. Science 239, 1269-1271.
ROTH, R. A., STOVER, C , HARI, J., MORGAN, D . O., SMITH, M. C ,
SARA, V. & FRIED, V. A. (1987). Interactions of the receptor for
insulin-like growth factor II with mannose-6-phosphate and
antibodies to the mannose-6-phosphate precursor. Biochem.
biophys. Res. Commun. 149, 600-606.
SCOTT, C. D. & BAXTER, R. C. (1987). Purification and
immunological characterization of the rat liver insulin-like growth
factor-II receptor. Endocrinology 120, 1-9.
SCOTT, C. D . , TAYLOR, J. E. & BAXTER, R. C. (1988). Differential
regulation of insulin-like growth factor II receptors in rat
hepatocytes and hepatoma cells. Biochem. biophys. Res.
Commun. 151, 815-821.
SELLHEYER, K. & SPITZNAS, M. (1988). Development of the human
sclera: a morphological study. Graefe's Archive for Clinical and
Experimental Ophthalmology 226, 89-100.
SORSBY, A., BENJAMIN, B. & SHERADIN, M. (1961). Refraction and
its Components During the Growth of the Eye from the Age of
Three. Medical Research Council, London.
TALLY, M., L I , C. H. & HALL, K. (1987). IGF-II stimulated growth
mediated by the somatomedin type II receptor. Biochem.
biophys. Res. Commun. 148, 811-816.
ULLRICH, A., GRAY, A., TAM, A. W., YANG-FENG, T., TSUBOKAWA,
M., COLLINS, C , HENZEL, W., LEBON, T., KATHURIA, S., CHEN,
E., JACOBS, S., FRANKE, U., RAMACHANDRAN, J. & FUJITA-
YAMAGUCHI, Y. (1986). Insulin-like growth factor I receptor
primary structure: comparison with insulin receptor suggests
structural determinants that define functional specificity. EMBO
J. 5, 2503-2512.
VALENTINO, K. L., PHAM, H., OCRANT, I. & ROSENFELD, R. G.
(1988). Distribution of Insulin-like growth factor II receptor
immunoreactivity in rat tissue. Endocrinology 122, 2753-2763.
WALLMAN, J. & ADAMS, J. I. (1987). Developmental aspects of
experimental myopia in chicks: susceptibility, recovery and
relation to emmetropization. Vision Research 27, 1139-1163.
WALLMAN, J., TURKEL, J. & TRACHTMAN, J. (1978). Extreme
myopia produced by modest changes in early visual experience.
Science, N.Y. 201, 1249-1251.
WEALE, R. A. (1982). A Biography of the Eye. London: Lewis.
WHITFIELD, H. J., BRUNI, C. B., FRUNZIO, R., TERRELL, J. E.,
NISSLEY, S. P. & RECHLER, M. M. (1984). Isolation of a cDNA
clone encoding rat insulin-like growth factor-II precursor.
Nature, Lond. 312, 277-280.
WIESEL, T. N. & RAVIOLA, E. (1977). Myopia and eye enlargement
after neonatal lid fusion in monkeys. Nature, Lond. 266, 66-68.
Yu, K. T. & CZECH, M. P. (1984). The type I insulin-like growth
factor receptor mediates the rapid effects of multiplicationstimulating activity on membrane transport systems in rat soleus
muscle. J. biol. Chem. 259, 3090-3095.
ZAPF, J., SCHOENLE, E., JAGARS, G., SAND, I., GRUNWALD, J. &
FROESCH, E. R. (1979). Inhibition of the action of nonsuppressible insulin-like activity on isolated rat fat cells by
binding to its carrier protein. J. Clin. Invest. 63, 1077-1084.
SHERMAN, S. M., NORTON, T. T. & CASAGRANDE, V. A. (1977).
Myopia in the lid-sutured tree shrew (Tupaia glis). Brain Res.
124, 154-157.
{Accepted 20 June 1989)