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The Inhibitory Effects of Integrin Antibodies and the RGD Tripeptide on Early Eye Development

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The Inhibitory Effects of Integrin Antibodies and the RGD Tripeptide on Early Eye Development The Inhibitory Effects of Integrin Antibodies and the RGD Tripeptide on Early Eye Development E. Svennevik and P. J. Linser Purpose. The authors investigated the effects of probes that disrupt integrin-extracellular matrix interactions on early eye development. Methods. Antibodies and peptides that have been shown in other studies to block the interac- tion of cell surface integrins with various ligands were microinjected into the preoptic regions of chick embryos. Eye morphogenesis and biochemical differentiation of ocular tissue layers were assessed by histologic and immunohistochemical analyses. Results. Antibodies that bind to the jS, subunit of integrin and block its function prevented normal eye morphogenesis but did not block expression of certain cell differentiation markers. The RGD tripeptide showed the same inhibitory capacity as did the anti-integrin antibodies. Conclusions. Integrin-based cell-cell and/or cell-extracellular matrix interactions are impor- tant in early eye morphogenesis. By contrast, certain aspects of tissue and cell differentiation, such as the expression of carbonic anhydrase II, are controlled independent of morphogene- sis. Invest Ophthalmol Vis Sci. 1993; 34:1774-1784. JL he complexity of the vertebrate eye presumably re- studies have attempted to define the mechanisms in- flects complicated developmental strategies for regula- volved. Evidence has been presented that indicates tion of morphogenesis and biochemical differentia- that both soluble and insoluble signal molecules are tion. As a model for studying "embryonic induction" involved in eye induction.1"4 Several studies have the eye has been a favored system for several de- shown that a prominent extracellular matrix (ECM) is cades.1"3 The early events of eye development, such as laid down between NE and SE as an early event in eye the thickening and folding of neural (NE) and skin morphogenesis.5"8 Furthermore, deposition of this ectoderm (SE) and the appearance of tissue-specific ECM and attachment of the apposing epithelial sheets gene products, are regulated in part by specific inter- to it seems to influence eye maturation.7 actions between the different tissue layers in the eye Numerous studies during the last several years primordium.2i3 The molecular bases of the inductive have shown that a family of surface receptor molecules tissue interactions remain obscure, although many called integrins can mediate cell-ECM interactions.9"20 To examine the role of integrin in early eye develop- ment, we have chosen to investigate the effects of in- hibiting integrin-ECM binding. The paradigm was to From the Whitney Uibondory and the. Department of Anatomy and Cell Biology, University of Florida, St. Augustine, Florida. microinject inhibitory antibodies or a synthetic tripep- Supported by grant 1-1030 from the March of Dimes Birth Defects Foundation, tide RGD,1518"20 which mimics an amino acid se- grant BNS-8819743 from the National Science Foundation (PJL), grant BBS-8804980 from the Research Experience for Undergraduates program of the quence common to several ligands of integrin, into the National Science Foundation (ES), and a grant from the Grass Foundation. region of the eye primordium. Then embryos were Submitted for publication: September 25, 1991; accepted August 25, 1992. Proprietary interest category: C7. allowed to continue development for several days. Fi- Reprint requests: P. J. Linser, The Whitney Laboratory and the Department of nally, they were analyzed for structural development Anatomy and Cell Biology, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32086. of the eye and biochemical differentiation. Two spe- Investigative Ophthalmology & Visual Science, April 1993, Vol. 34, No. 5 1774 Copyright © Association for Research in Vision and Ophthalmology Downloaded from iovs.arvojournals.org on 09/30/2021 Integrins Affect Eye Morphogenesis 1775 cine biochemical markers of ocular differentiation in phosphate-buffered saline (PBS) at a concentration were analyzed. One of the earliest gene products to be of 10 mg/ml. Phenol red was added to the solution to synthesized in apparent response to eye induction is ensure proper placement of the micropipette. the lens-specific protein delta crystallin.21 Thus, we used immunocytochemical analysis for delta crystallin Microinjection to evaluate successful lens induction. In addition, we Micropipettes were prepared with a tip diameter of show here that the enzyme carbonic anhydrase II (CA- approximately 20 jum. With the aid of a Nikon SMZ-10 II) is also expressed very early during eye develop- (Nikon Inc., Garden City, NJ) dissecting microscope, ment. Unlike delta crystallin, CA-II shows limited ex- the embryos were injected with approximately 4 nl of pression in both the SE (prelens) and the NE (preret- antibody solution, control hybridoma supernatant, ina) of the early eye rudiment and, thus, serves as one peptide solution, or PBS sham solution. This resulted of the earliest known markers of retina and lens bio- in the delivery of approximately 40 ng of RGD or chemical differentiation. Comparison of these two bio- RGES tripeptide or 2 ng monoclonal antibody to each chemical markers of eye induction with the morpho- embryo that was injected. The solutions were injected logic analyses allowed us to follow lens and retina dif- into the cephalic region of the embryo in the space ferentiation even in the context of disrupted between the SE and the diencephalon of the four to morphology. Our results indicate that the morpho- five somite pair chick embryo (26-29 hr of develop- logic development of the eye is strongly dependent on ment). After injection, the embryos were incubated an integrin-mediated interactions. By contrast, early bio- additional 48 hr before harvest for analysis. chemical differentiation of both lens and retina seem to occur, even when morphogenesis is severely Fixation disrupted. Thus, it appears that aspects of biochemical The embryos were harvested from the surrounding differentiation and morphogenesis are regulated by yolk and embryonic membranes and fixed in Zenker's separate mechanisms. fixative for 2 hr followed by 2 hr of a water wash. The embryos were dehydrated through an alcohol series 25 MATERIALS AND METHODS and xylene and then embedded in paraffin as before. Embryos Immunohistochemical and Histologic Analysis All the investigations presented here were conducted The embryos were sectioned at 6 fim. In most cases, in adherence to the ARVO Statement for the Use of the entire head region was serially sectioned, and all Animals in Ophthalmic and Vision Research. None of sections were analyzed. For analysis of CA-II and delta these experiments involved human subjects in any crystallin distribution, the 7C6 monoclonal antibody way. Fertilized eggs of white leghorn chickens were to CA-II was used with rabbit anti-delta crystallin in a obtained from the University of Florida Division of double-label analysis as previously described.25 In Poultry Sciences. The eggs were incubated at 38°C in a some cases, the sections were immunostained with humidified chamber. For microinjection experiments, monoclonal antibodies to fibronectin (kindly provided the egg shells were removed, and the contents were by D. Fambrough, Johns Hopkins University, Balti- 2223 placed in culture dishes, essentially as described. more, MD) again by standard techniques. After immu- The embryo cultures were maintained in a humidified nohistochemical analysis, the sections were stained sec- chamber at 38°C with an atmosphere of 1% CO2 in air. ondarily with hematoxylin and eosin, and an image of each of the serial sections was recorded on video tape Monoclonal Antibodies to Integrin for later reconstruction. For serial reconstruction, the Monoclonal antibodies to the (5X subunit of integrin images of sections were traced, and the tracings were were the JG22 antibody (generously provided by Da- digitized and reconstructed with the DANCAD3D pro- vid Gottlieb13) and the CSAT and 1-G antibodies (pro- gram of Daniel Higgins (San Francisco, CA) using an vided by Clayton Buck9). Hybridomas were grown International Business Machines AT-compatible com- under standard conditions.24 For microinjection ex- puter (CompuAdd Corp., Austin, TX). periments, hybridoma supernatants were concen- trated 20-fold with an Amicon (Danvers, MA) pressure concentrator and Ultrafilter XM50 membranes. Con- RESULTS centrates were passed through a 0.2-jtm filter before Biochemical differentiation of optic tissues can be de- injection. tected as early as the 20 somite pair stage. It was shown that CA-II is immunodetectable in both the lens and Synthetic Peptide retina portions of the embryonic chick eye as early as The RGD and RGES peptides were purchased from day 3.5 of development.26 Others reported detecting Peninsula Laboratories. (Belmont, CA) and dissolved CA-II messenger RNA in the chick eye at approxi- Downloaded from iovs.arvojournals.org on 09/30/2021 1776 Investigative Ophthalmology & Visual Science, April 1993, Vol. 34, No. 5 mately 48 hr of development.27 In Figure 1, we show pair stage.28 The use of monoclonal antibodies to CA- that CA-II antigen first begins to accumulate in ocular II has increased the sensitivity of the immunohisto- tissues at 20 somite pairs of development (48 hr). Fig- chemical technique, making it possible, for the first ure 1 also shows that no CA-II is detectable in the time, to pinpoint the earliest period of CA-II accumu- ectodermal structures of the eye rudiment (prelens lation. At this time, CA-II can be detected in a few and preretina) at the 18-somite-pair stage of develop- mesenchymal cells throughout the embryo, particu- ment, which is only a few hours before the 20-somite- larly at the borders of epithelial organs, such as the brain (Fig. 1). These may represent cells destined to give rise to choroid and blood vessels. Erythrocytes also show CA-II immunoreactivity at this early develop- mental stage. Most other cells and tissues of the em- bryo do not contain CA-II at this time. Hence, it is likely that CA-II expression in the very early eye rudi- ment indicates a specific role for this enzyme in eye development.
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