An eye-derived growth factor regulates epithelial cell proliferation in the cultured lens

The control of lens growth: relationship to secondary cataract

A lens growth factor was identified that is present in the anterior chamber of the embryonic chicken eye. The mitogen is similar to an embryo-specific activity found in embryo serum. Several purified growth factors, applied singly or in combination, did not stimulate cell division in embryonic lens cells. The serum mitogen is a protein which does not bind to heparin-Sepharose. The possibility is presented that the lens epithelium contains two distinct cell types, the proliferating cells of the germinative zone and the mitotically quiescent central epithelial cells. It is proposed that only cells in the germinative zone are capable of responding to normal lens growth factors. It is likely, therefore, that these cells present the greatest risk for secondary cataract formation.

Insulin and IGF-I affect the protein composition of the lens fibre cell with possible consequences for cataract

Explanted newborn rat lens epithelial cells were cultured with various concentrations of FGF-2 and/or insulin or IGF-I for 8-20 days. The accumulation of alphaA-, alphaB-, betaA3/1-, betaB2- and gammaA-F-crystallin was measured. During culture with insulin only, i.e. in the absence of fibre cell differentiation, alphaA- and alphaB-crystallin accumulated to the same level as found in differentiating cells. Culture of epithelial cells with IGF-I led to an increase in alphaB-crystallin, but not in alphaA-crystallin. The addition of insulin under differentiation conditions (in the presence of 25 ng ml(-1)FGF-2) augmented the accumulation of alphaA-crystallin 1.5-fold, the accumulation of betaB2-crystallin two-fold and the accumulation of gammaA-F-crystallin five-fold over that found with FGF-2 only. The accumulation of alphaB- and betaA3/1-crystallin was not affected by insulin in the presence of FGF-2. Adding IGF-I to fibre cells differentiating in the presence of 25 ng ml(-1)FGF-2 resulted in a 1.5-fold increase (of questionable statistical significance) in both alphaA- and alphaB-crystallin and a two to three-fold increase in gammaA-F-crystallin compared to cells cultured with FGF-2 only, no significant effect of IGF-I on the accumulation of betaA3/1- or betaB2-crystallin was found. Comparison of the levels of mRNA and protein suggests that insulin acts to increase the level of transcription. Our results show that the response of fibre cells to insulin or IGF-I differs. Hence, even though half the maximum dosage required for the insulin effect was rather high (between 0.1 and >5 micro g), the effect of insulin cannot be merely transmitted by the IGF-I receptor. Our data further predict that insulin or IGF-I increases the overall ratio of beta- and gamma-crystallin to alpha-crystallin in the fibre cell, which could predispose the lens to cataract.

Modulation of basic fibroblast growth factor effect by retinoic acid in cultured retinal pigment epithelium

PURPOSE

We investigated the effect of retinoic acid (RA) on basic fibroblast growth factor (bFGF)-stimulated proliferation of cultured human retinal pigment epithelial (hRPE) cells and of 125I-bFGF-binding to the bFGF plasma membrane receptors of hRPE.

METHODS

Proliferation of hRPE cells in the presence of increasing concentrations of bFGF and bFGF + RA was measured by 3H-thymidine incorporation into hRPE cells. To characterize bFGF receptors, hRPE cells were incubated at 4 degrees C with 125I-bFGF in the presence or absence of heparin.

RESULTS

Basic-FGF stimulated 3H-thymidine incorporation into hRPE cells in a dose-dependent manner. RA inhibited bFGF-stimulated 3H-thymidine incorporation in the presence or absence of heparin. Increasing concentrations of unlabeled bFGF decreased the binding of 125I-bFGF to hRPE cells. Scatchared analysis indicated the presence of high and low affinity binding sites for bFGF with an apparent affinity Kd of 50 pM and 330 pM, respectively, and a binding capacity (Bmax) of 1.25 X 10(5) and 3.38 X 10(5) binding sites per cell. Inhibition of 125I-bFGF binding was also possible by the carboxyl-terminal region peptide fragment bFGF-(106-120)-NH2, but not amino-terminal region peptide fragment bFGF-(1-24)-NH2. The addition of heparin to the medium during binding studies did not prevent RA from inhibiting binding of 125I-bFGF to hRPE cells. Scatchard analysis demonstrated that, in the presence of heparin, there is a decrease in the number of high affinity binding sites (from 1.12 +/- 0.11 x 10(5) to 0.7 +/- 0.03 x 10(5) binding sites per cell, a reduction of 36.7 +/- 0.04%, n = 3, p < 0.05). There was no significant change in affinity constants.

CONCLUSIONS

These results suggest that RA inhibits bFGF cell proliferation in hRPE cells by decreasing the bFGF receptor number.

Calcium mobilisation modulates growth of lens cells

The modulating effect of calcium cell signalling agonists on tissue growth was studied in a rabbit lens cell line (NN1003A). Calcium mobilisation was measured after Fura-2 incorporation and growth assayed either by direct Coulter counting or [3H]-thymidine incorporation. Transient increases in cytoplasmic calcium were elicited by rabbit serum, histamine, ATP and PDGF. Thapsigargin induced a prolonged increase and all of the above agonists failed to elicit a response after thapsigargin. Rabbit serum and PDGF both increased cell growth in a concentration-dependent manner. While histamine and ATP had little effect in serum-free medium, they reduced serum-stimulated growth. Acetylcholine and FGF did not produce a marked rise in cytoplasmic calcium and neither did they modulate growth. Both thapsigargin and caffeine greatly inhibited growth. These findings indicate that, in lens cells, agonists that mobilise calcium, whether by acting through G-protein or tyrosine kinase receptors, also modulate lens cell growth. Agents such as thapsigargin and caffeine that inactivate the same calcium store also inhibit growth.

Up-regulation of aFGF expression in quiescent cells is related to cell survival

Exogenously administrated acidic FGF modulates the proliferation of several cell types, controls cell differentiation, and promotes cell survival. Most cells that are sensitive to exogenous aFGF are also capable of expressing it at very low levels. Thus in order to establish the role of endogenous aFGF as a mitogenic, differentiation, or survival factor, we studied the regulation of aFGF expression by evaluating the level of mRNA by PCR amplification and the concentration of protein by Enzyme Immuno Assay (EIA). In the lens, the amount of aFGF transcripts in nondividing cells of the central epithelium and in the differentiated fiber cells located at the periphery of the lens is similar, suggesting that endogenous aFGF is not involved with lens differentiation. In cultures, depending on the growth conditions, the endogenous aFGF expressed by Bovine Epithelial Lens (BEL) cells is subject to modulation. Cells arrested either by contact inhibition or by serum deprivation express more aFGF transcripts and protein than in exponentially growing cells, implying that endogenous aFGF has no mitogenic role under these conditions. In serum-deprived cells, the addition of specific aFGF antisense primers inhibits endogenous aFGF expression and leads to the death of these cells. These results associated with the higher expression of aFGF in nondividing BEL cells, suggesting that, contrary to exogenous aFGF, endogenous aFGF is not a mitogenic factor but a survival factor.

Regulation of lens cell growth and polarity by an embryo-specific growth factor and by inhibitors of lens cell proliferation and differentiation

We used a double-label method, which monitors the rate at which cells enter S-phase of the cell cycle, to identify factors that control the growth of chicken embryo lens epithelial cells in vivo. With this assay, we identified a mitogen for lens epithelial cells in the anterior segment of the embryonic eye. When the anterior chamber was opened briefly, by tearing the cornea or displacing the lens, the growth-promoting activity was lost. None of the purified growth factors tested replaced this growth activity, including EGF, bFGF, PDGF, IGF-1, IGF-2, TGF beta and mixtures of these factors. However, chicken embryo serum or plasma did cause chicken embryo lens epithelial cells to progress through the cell cycle. The activity in serum was destroyed by heat and protease treatment. It was most active in serum from 10-day embryos, decreased with subsequent development and was undetectable from 2 days after hatching through adulthood. When embryo serum or plasma was mixed with vitreous humor or IGF-1, agents that induce lens fiber cell formation, cell elongation was prevented. In contrast to the mitogenic activity in serum, this inhibitor of differentiation was insensitive to trypsin treatment. We also identified an activity in vitreous humor that inhibited the growth-promoting agent in embryo serum. Plasma proteins readily enter the anterior chamber of the eye of chicken embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Lens fiber cell differentiation and expression of crystallins in co-cultures of human fetal lens epithelial cells and fibroblasts

Growth of the ocular lens is directed by the division and differentiation of a single layer of epithelial cells located at the equatorial region. It is conceivable that this region of the lens capsule presents a special microenvironment modulated by molecular cues emanating from the surrounding tissues. In an effort to investigate the source and nature of these molecular cues, we co-cultured human fetal lens epithelial cells and fibroblasts derived from the ciliary body. We observed morphological differentiation as evidenced by the appearance of differentiating lentoid structures associated with fibroblasts. Characterization of the expression of lens-specific proteins revealed that in addition to alpha B-crystallin, these lentoid structures contain the lens fiber cell-specific proteins, alpha A-crystallin, beta B2-crystallin and gamma S-crystallin. None of these crystallins could be found in the surrounding undifferentiated lens epithelial cells. Interestingly, alpha B-crystallin usually present in lens epithelial cells when cultured alone, was found to be markedly decreased, both in synthesis and content in the cells surrounding the differentiated structures, suggesting that the process of differentiation in vitro may concomitantly produce a factor(s) which modulates alpha B-crystallin expression in these cells.

Polarized distribution of coated pits and coated vesicles in the rat lens: an electron microscopy and WGA-HRP tracer study

The presence and distribution of coated pits (CPs) and coated vesicles (CVs) in the rat lens were studied by thin-section electron microscopy (TEM) and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer. TEM revealed that CPs and CVs were approximately 150 nm in diameter, of which the characteristic clathrin coat was approximately 20 nm thick. CPs and CVs were found in both epithelium and superficial fiber cells of the entire lens, and were distributed preferentially along the basal membrane facing the lens capsule. It was estimated that more than 80% of CPs and CVs in the entire epithelium were seen along the basal membrane. The number of CPs and CVs along the basal membrane in the equatorial epithelium (4.4 per 10 microns membrane) was similar to that at the central zone (3.8 per 10 microns membrane), but there was a significant increase along the apical and lateral surfaces of the equatorial epithelium compared to that of the central epithelium, although the overall number was considerably smaller. In the lens fibers, CPs and CVs were usually found within 2-3 superficial layers of fiber cells. The number of CPs and CVs along the basal membrane of young fibers at the post-equatorial region (3.1 per 10 microns membrane) was 3-fold greater than that of the mature fibers at the posterior polar area (1 per 10 microns membrane). Thus, CPs and CVs along the entire basal membrane showed a gradual decrease in number from the anterior (and equatorial) regions to the posterior polar surface of the lens. WGA-HRP experiments showed that approximately 80% of tracer-carrying pits and vesicles were also found along the basal surface of the equatorial epithelium. This study suggests that a polarized distribution of CPs and CVs along the basal surface of epithelium and superficial fiber cells may facilitate receptor-mediated endocytosis of important macromolecules directly from the aqueous humor and vitreous body into metabolically active lens cells.

Ontogeny of basic fibroblast growth factor binding sites in mouse ocular tissues

Basic fibroblast growth factor (bFGF) binding to ocular tissues has been studied by autoradiographical and biochemical approaches directly performed on sections during mouse embryonic and postnatal development. Frozen sections of embryos (9 to 18 days), newborns, and adults (1 day to 6 months) were incubated with iodinated bFGF. One specific FGF binding site (KD = 2.5 nM) is colocalized with heparan sulfate proteoglycans of the basement membranes and is heparitinase sensitive. It first appears at Day 9 around the neural tube, the optic vesicles, and below the head ectoderm and by Day 14 of embryonic development is found in all basement membranes of the eye. At Day 16, very intensely labeled patches appear, corresponding to mast cells which have been characterized by metachromatic staining of their heparin-rich granulations with toluidine blue. In addition to the latter binding, we have also observed a general diffuse distribution of silver grains on all tissues and preferentially in the ecto- and neuroectodermic tissues. From Days 17-18, there is heterogeneous labeling inside the retina, localized in the pigmented epithelium and in three different layers colocalized with the inner and outer plexiform layers and with the inner segments of the photoreceptors. This binding is heparitinase resistant but N-glycanase sensitive and may represent a second specific binding site corresponding to cellular FGF receptors (KD = 280 pM). Both types of binding patterns observed suggest a significant role for bFGF in eye development and physiology.

Age-related changes in the response of chick lens cells during long-term culture to insulin, cyclic AMP, retinoic acid and a bovine retinal extract

We have reported that 1-day-old post-hatch chick lens epithelial cells lose the capacity for lentoid body formation and delta-crystallin expression during long-term serial subculture, although they continue to synthesize, but not to accumulate, alpha- and beta-crystallins, even in cells with a transformed phenotype. Here we present evidence that dedifferentiation may reflect an age-related change in the capacity for response to regulatory signals. We have tested the capacity of these cells in serial subcultures to respond to agencies which affect lens cell growth and differentiation in primary culture: retinoic acid (RA), insulin, cAMP and bovine retinal extract (BRE). Secondary cultures responded only to RA and BRE, by an increase in lentoid formation and by alpha- and beta-accumulation, while RA also restored delta-crystallin expression. Later cultures showed no such responses. The results suggest that the process of lens cell dedifferentiation may, at first, be reversible but later becomes irreversible, despite the continuing persistence of low levels of crystallin expression.

Phosphorylation and lipocortin-like activity of a 34-kD surface protein in lens epithelial cells: relation to mitogenesis induced by basic fibroblast growth factor

In order to elucidate the molecular mechanism whereby basic fibroblast growth factor (bFGF) exerts its action on cell proliferation, we investigated the possible relationship between the mitogenic response to bFGF of bovine lens epithelial cells and the phosphorylation and phospholipase A2 (PLA2) activity of a 34-kD protein (p34) present in the basal plasma membrane of these cells. When p34 was obtained from the peripheral epithelial cells which were not capable of being stimulated with bFGF, pretreatment with bFGF led to decreased phosphorylation and PLA2 activity of p34. In contrast, both an increased phosphorylation of p34 and a strong activation of PLA2 occurred when p34 was derived from the central epithelium which was induced to proliferate in the presence of bFGF. It is hypothesized that p34 might play a key role as part of signal transduction of bFGF in controlling DNA synthesis of bovine lens epithelial cells.

Cultured human retinal pigment epithelial cells express basic fibroblast growth factor and its receptor

Basic fibroblast growth factor (bFGF) has been implicated in the maintenance of neuronal differentiation, the induction of neovascularization and intravitreal proliferative diseases. We have found that human retinal pigment epithelial (RPE) cells grown in vitro transcribe the bFGF gene and synthesize a peptide that crossreacts with anti-bFGF antibodies. In culture, these cells appear to release activity with biological and biochemical properties similar to bFGF. RPE cells have specific bFGF receptors and proliferate in response to bFGF. Thus, it is possible that the RPE cell is an important source of retinal bFGF and may respond to bFGF in an autocrine manner.

Identification and isolation from bovine epithelial lens cells of two basic fibroblast growth factor receptors that possess bFGF-enhanced phosphorylation activities

Cross-linking of bound 125I-basic fibroblast growth factor (bFGF) to bovine epithelial lens cells identified two labelled species whose apparent molecular weights were identical with those of two phosphorylated proteins. The bFGF-stimulated phosphorylation of these proteins was shown to be rapid, suggesting an autophosphorylation process. To demonstrate that the phosphorylated proteins were indeed the bFGF-binding molecules, the two components were purified to homogeneity and their bFGF-binding activity was examined. We conclude that bFGF stimulates the phosphorylation of two receptors of 130 and 160 kDa in bovine epithelial lens cells.

Purification of an autocrine growth factor in conditioned medium obtained from primary cultures of scleral fibroblasts of the chick embryo

Scleral fibroblasts of the chick embryo were found to secrete autocrine growth factors. One of the factors was purified from conditioned medium collected from growing-phase cultures of these cells by DEAE-Sepharose column chromatography and following non-denaturing polyacrylamide gel electrophoresis. The specific activity was increased 1100-fold by this purification. The chromatographically purified growth factor was still active after incubation at 95 degrees C, at pH 10 or pH 3, or with glycosidase H, but inactive after incubation with dithiothreitol or trypsin. An active protein having a molecular weight of 32 kDa was found to be the major component of the final preparation.

The effect of eye-derived-growth-factor (EDGFs) on methionine incorporation in the different cell populations of bovine adult lens in organ culture

When adult bovine lenses were cultured in vitro, the purified retina-derived growth factors EDGF I or EDGF II, as well as the soluble fraction of the retina RE, increased the rate of incorporation of [35S]methionine into protein in cells belonging to different populations in the anterior epithelium as well as in fibers from the most superficial region of the cortex. These fiber cells were the most sensitive to stimulation by the retinal factors as they exhibit a significant increase of total protein synthesis 24 hr after addition of the factors to the culture medium. The epithelial cells studied--central epithelial cells and germinative cells--appeared stimulated only 1 day later. The stimulation of incorporation was not directed towards a particular subset of proteins but to all major polypeptides constituting the electrophoretic pattern of each cell population. It is suggested that this type of ocular signal, which stimulates the expression of a definite program, may act as a permissive signal.

Differential assemblage of the basal membrane-cytoskeleton complex in bovine epithelial lens cells

We have investigated the membrane-cytoskeleton complex involved in interactions between the epithelial cells and the capsule of the bovine eye lens. The organization of the molecular complex was determined from cell extraction, immunoprecipitation and immunoblotting experiments and from ultrastructural studies by scanning electron microscopy. We show that marked differences exist in the organization of this basal complex between the central epithelium (mitotic quiescent) and the peripheral epithelium which initiates lenticular differentiation into fibres. Our results support the view that: (a) the organization of several major membrane components in the peripheral epithelium differs from that of the central epithelium; (b) microfilaments and vimentin filaments are independent of each other in the peripheral epithelium, whereas microfilaments are involved in an inter-relationship with vimentin filaments in the central epithelium; (c) two surface proteins of 24 and 27 kD and two surface glycoproteins of 46 and 220 kD appear to be bound to vimentin filaments in the peripheral region, whereas the intermediate filaments appear to be solely in close association with the 46 and 220 kD glycoproteins in the central zone.

In vivo binding of topically applied human bFGF on rabbit corneal epithelial wound

We present the results of the first evaluation of human placenta extracted basic fibroblast growth factor (bFGF) in a rabbit corneal epithelium wound-healing model. Healing dose-response experiments after selective epithelial wounding with iodine vapors demonstrated that bFGF accelerated the repair process in a saturable manner. Corneal binding of topically applied 125I-labeled bFGF was investigated using radioassay and autoradiographic techniques. Basic FGF was shown to bind specifically to denuded epithelial basement membrane in a very stable fashion and not to the intact epithelium. No transfer of the topical bFGF to the aqueous humor or any intraocular structure could be observed. The stability of this interaction was further demonstrated by reextracting and characterizing the labeled factor from treated corneas. The specificity of the fixation was documented by in vivo topical competition with unlabeled bFGF or heparin. We propose that bFGF-basement membrane interactions play a role in corneal wound healing.

Human retinal extract stimulates the proliferation of human lens epithelial cells

The proliferation of lens epithelial cells remaining attached to the capsule after extracapsular cataract extraction represents a potential cause of posterior capsule opacification. In view of the reported mitogenic effects of eye derived growth factors on lens epithelial cells in animal studies, we determined to establish whether the human retina produces a factor capable of inducing a similar response in human lens epithelial (HLE) cells. We report that an extract of the human neural retina is capable of increasing the proliferative capacity of HLE cells in culture by 50%. The possible mechanisms are discussed. The presence of such a growth factor in the human eye would have important consequences for the epithelial cells remaining after cataract surgery.

Potential and limitations of cultivated fibroblasts in the study of senescence in animals. A review on the murine skin fibroblasts system

Senescence is the last period of the life span, leading to death. It happens in all animals, with the exception of a few didermic species (Hydras) having a stock of embryonic cells and being immortal. The causes of animal senescence are badly known. They depend both on genetic characters (maximum life span of a species) and on medium factors (mean expectation of life of the animals of a species). Animal senescence could depend on cell aging: (1) by senescence and death of the differentiated cells, (2) by modified proliferation of the stem cells of differentiated tissues, (3) by alterations in the extracellular matrices, (4) by interactions between factors (1) (2) and (3) in each tissue, and (5) by interactions between the several tissues of an organism. This complexity badly impedes the experimental study of animal senescence. Normal mammal cells are aging when they are cultivated (in vitro aging). Present literature upon in vitro aging of cultivated human fibroblasts consists essentially of papers devoted to proliferation and differentiation characteristics and not to cell senescence. Murine skin fibroblasts have been studied in our laboratory, using different systems: (1) primary cultures isolated from peeled skins of mouse embryos, (2) mouse derms analysed in the animals, (3) cultivated explants of skins, (4) serial sub-cultures of fibroblasts isolated from these explants, (5) cells cultivated comparably on plane substrates (glass, plastic, collagen films) and on three-dimensional matrices (collagen fibres). In primary cultures (system 1) all the cell generations have been analysed, including the last one until death of the culture. We have shown that many characters are varying with cell generation. All the observed variations were: progressive, non-linear and correlated (intracellular feedbacks). We come to the conclusion that the main effects of cell mitotic age are (1) to depress the plasticity of the chromatin, (2) to change the organization of the cytoplasmic filaments, (3) to change the organization of the extracellular matrix. The collagen fibres are also acting upon nucleus and filaments either in the animals or in the cultures. The phenotype of a fibroblastic cell is thus both age- and environment-dependent. Overall data on in vitro cell aging point to the hypothesis that senescent cells are phenotypic variants and not mutant cells. Aging cell cultures are remarkably useful to the studies on cell proliferation decrease and cell cycle lengthening shown by the stem cells in animal tissues. We propose the hypothesis that the fibroblasts of the vertebrates would be homologous to the pluripotent mesenchyme cells of their embryos.

Influence of fibroblast growth factor on phosphorylation and activity of a 34 kDa lipocortin-like protein in bovine epithelial lens cells

We examined the effect of basic fibroblast growth factor (FGF) on phosphorylation and lipocortin-like activity of the 34 kDa protein present in the basal membrane of epithelial peripheral cells which initiate growth and differentiation in the bovine lens. We found that: (i) the 34 kDa protein possesses anti-phospholipase A2 (PLA2) activity of lipocortin; (ii) in response to FGF, the anti-PLA2 activity of this protein is enhanced whereas its phosphorylation is markedly decreased. It is suggested that the 34 kDa protein might represent an important biological activity in controlling FGF induction of growth and differentiation in the adult eye lens.

Characterization of acidic and basic fibroblast growth factors in brain, retina and vitreous chick embryo

We have purified acidic and basic fibroblast growth factors (c-aFGF, c-bFGF) from 11 day-old chick embryo brain, retina and vitreous by heparin-Sepharose chromatography and reverse phase HPLC. The analysis of their biological activity as well as their molecular weight indicates that they were analogous to basic or acidic human and bovine FGF. The ratio of c-aFGF to c-bFGF activity depended of the tissue. In brain c-aFGF represented 66% of the total mitogenic activity retained on the heparin-sepharose column and c-bFGF 34% while retina contained 16% of c-aFGF and 84% of c-bFGF; vitreous 78% of c-aFGF and 22% of c-bFGF. Like human aFGF, Heparin stimulated purified c-aFGF mitogenic activity in the absence of serum but inhibited the activity of the retina acid soluble extract, in the presence of foetal calf serum (FCS). Thus, chick embryo and adult human acidic and basic FGF respectively share the same biochemical properties. Since there are no blood vessels in chick retina or vitreous, their presence in these tissues suggests that angiogenesis is not the only role of these growth factors.

Specific fixation of bovine brain and retinal acidic and basic fibroblast growth factors to mouse embryonic eye basement membranes

The labeling pattern of mouse embryonic eye frozen sections incubated with radioiodinated brain acidic and basic fibroblasts growth factors (aFGF and bFGF) was investigated by autoradiography. Both growth factors bind to basement membranes in a dose-dependent way, with a higher affinity for bFGF. Similar data were obtained with eye-derived growth factors (EDGF), the retinal forms of FGF. There was a heterogeneity in the affinity of the various basement membranes toward these growth factors. The inner limiting membrane of the retina and the posterior part of the lens capsule have a higher binding capacity than the posterior part of the Bruch's membrane. The specificity of the growth factor-basement membrane interaction was demonstrated by the following experiments: (i) an excess of unlabeled growth factor displaced the labeling; (ii) unrelated proteins with different isoelectric points--gelatin, serum albumin, histones--did not modify the labeling; and (iii) iodinated EGF or PDGF did not label basement membrane. In order to get a better understanding of the nature of this binding, we performed the incubation of the frozen sections with iodinated FGFs preincubated with various compounds: (i) heparin which is known to have a strong affinity for aFGF and bFGF partially decreases the labeling, and (ii) chondroitin sulfate B and dextran sulfate at high concentrations were also partially effective. In addition, enzymatic treatment of the sections reveals that only heparitinase, not collagenase or chondroitinase ABC, completely prevents the labeling without destroying the overall structure of the basement membrane. An antibody against the proteic part of EHS mouse proteoheparan sulfate does not affect the signal. Esterification of the acidic groups cancelled the binding. These results demonstrate that FGFs bind specifically to basement membranes, probably on the polysaccharidic part of the proteoheparan sulfate, and suggest that this type of interaction may be a general feature of the mechanism of action of these growth factors.

Lens regeneration from cultured newt irises stimulated by retina-derived growth factors (EDGFs)

It has been shown that lens regeneration from the iris of the newt Notophthalmus viridescens is dependent on the presence of neural retinal tissue in organ culture and in vivo. The recent discovery of various eye-derived growth factors (EDGFs) in the bovine retina [14] prompted us to investigate whether one of these factors may be involved in the stimulation of lens regeneration. Dorsal irises were cultured for 20 days in serum-supplemented diluted Eagle's medium. Growth factors from bovine retina of various degrees of purification were added. Lens regeneration was assessed on the basis of morphological lens-regeneration stages and by immunofluorescent detection of a lens-specific marker protein, alpha-crystallin. Crude isotonic retinal extract at 80-800 micrograms/ml significantly augmented lens regeneration. Very similar results were obtained when EDGF III, the nonretained retinal factor after heparin-affinity chromatography, was present at 2-20 micrograms/ml. Lens regeneration was also significantly increased when EDGF II, the retinal form of acidic fibroblast growth factor (aFGF) at 50-500 ng/ml was added to the cultures. On the other hand, EDGF I at 4-40 ng/ml and brain basic FGF at 5-50 ng/ml did not seem to significantly stimulate lens regeneration under the conditions used. Our results suggest that at least two retina-derived growth factors (EDGF II and III) can stimulate lens regeneration. These growth factors may be the putative signal that is naturally produced by the retina during lens regeneration in the newt.

Isolation of heparin-binding growth factors from dogfish (Mustela canis) brain and retina

We have purified two growth factors from dogfish brain and retina by using their binding affinity for heparin-Sepharose. These growth factors were eluted at 1 and 2 M NaCl similarly to those purified from bovine brain or retina. Their mitogenic activity was assayed in vitro on the same mammalian cells: bovine lens epithelial cells or human fibroblasts. All these data seem to indicate that these growth factors belong to the families of other well defined mammalian growth factors: EDGF I, brain basic FGF, AGF II, on the one hand and EDGF II, brain acidic FGF, AGF I, ECGF, on the other. Thus, these growth factors have been widely distributed during evolution and retain at least a conservative sequence to stimulate cell proliferation, in mammalian cells.