Gerald B. Grunwald

The structural and functional analysis of cadherin calcium-dependent cell adhesion molecules

During the past year considerable progress has been made in our understanding of cadherin structure and function. Recent research has concentrated on several aspects of the cell and molecular biology of cadherins, including genomic organization, cytoskeletal interactions, regulation of expression and function by post-translational modifications, differential expression during embryonic development, and the emerging role of cadherin misexpression and malfunction in pathogenesis.

Cadherin Function Is Required for Axon Outgrowth in Retinal Ganglion Cells In Vivo

The cell-cell adhesion molecule N-cadherin strongly promotes neurite outgrowth in cultured retinal neurons. To test whether cadherins regulate process outgrowth in retinal neurons in vivo, we have blocked cadherin function in single cells by expression of a dominant negative N-cadherin mutant. We report that when cadherin function is inhibited, axon and dendrite outgrowth are severely impaired, particularly in retinal ganglion cells. Laminar migration and cell type specification, by contrast, appear unaffected. Further, expression of the catenin-binding domain of N-cadherin, which blocks cadherin-mediated adhesion in early embryos, does not affect axon outgrowth, suggesting that outgrowth and adhesion are mediated by distinct regions of the cytoplasmic domain. These findings indicate that cadherins play an essential role in the initiation and extension of axons from retinal ganglion cells in vivo.

Expression of calcium-dependent cell adhesion during ocular development: A biochemical, histochemical and functional analysis☆

Previous studies of the adhesive properties of embryonic chick neural retina cells indicate a gradual decrease in the expression of calcium-dependent adhesions during retinal histogenesis, a function which has been attributed in part to gp130/4.8, a retinal calcium-dependent adhesion-associated cell surface membrane glycoprotein with a molecular weight of approximately 130 kDa and an isoelectric point of 4.8 (G. B. Grunwald, R. Pratt, and J. Lilien, 1982, J. Cell Sci. 55, 69-83). The experiments described here were done to define the relationship of gp130/4.8 to N-cadherin, another calcium-dependent adhesion molecule found in chick retina, which has a reported molecular weight of 127 kDa and which is recognized by monoclonal antibody NCD-2 (K. Hatta and M. Takeichi, 1986, Nature (London) 320, 447-449). Using two-dimensional gel electrophoresis followed by Western blotting as well as quantitative solid-phase immunoassays, polyspecific antisera recognizing gp130/4.8 were compared with monoclonal antibody NCD-2 for reactivity with proteins of retina and other tissues. The data lead us to conclude that retinal calcium-dependent adhesion proteins gp130/4.8 and N-cadherin are likely to be the same molecule. In order to obtain evidence for a direct correlation of changes in expression of these adhesion proteins with changes in retinal cell adhesivity and related morphogenetic events, parallel studies were carried out with cells from various ocular tissues to examine the functional, biochemical, and immunohistochemical expression of N-cadherin during ocular development. Immunohistochemical mapping of N-cadherin in the developing chick eye reveals three modes of N-cadherin expression which occur simultaneously in different ocular tissues: (1) down-regulation, (2) up-regulation, and (3) steady-state expression. These patterns of expression correlate with changes in the adhesive behavior of cells as well as with discrete stages in the morphogenesis of several ocular tissues. The results suggest that N-cadherin is a versatile cell adhesion protein with a role in both the development of several ocular tissues and the maintenance of specialized structures in the mature eye.

Microphthalmia-associated Transcription Factor (MITF) Promotes Differentiation of Human Retinal Pigment Epithelium (RPE) by Regulating microRNAs-204/211 Expression

Background: microRNAs 204/211 regulate retinal pigment epithelial cell phenotype. Results: In RPE, MITF regulates miR-204/211 expression and down-regulation of MITF results in loss of RPE phenotype, which can be prevented by overexpressing miR-204/211. Conclusion: MITF-mediated expression of miR-204/211 directs RPE differentiation. Significance: miR-204/211-based therapeutics may be effective treatments for diseases that involve loss of RPE phenotype. The retinal pigment epithelium (RPE) plays a fundamental role in maintaining visual function and dedifferentiation of RPE contributes to the pathophysiology of several ocular diseases. To identify microRNAs (miRNAs) that may be involved in RPE differentiation, we compared the miRNA expression profiles of differentiated primary human fetal RPE (hfRPE) cells to dedifferentiated hfRPE cells. We found that miR-204/211, the two most highly expressed miRNAs in the RPE, were significantly down-regulated in dedifferentiated hfRPE cells. Importantly, transfection of pre-miR-204/211 into hfRPE cells promoted differentiation whereas adding miR-204/211 inhibitors led to their dedifferentiation. Microphthalmia-associated transcription factor (MITF) is a key regulator of RPE differentiation that was also down-regulated in dedifferentiated hfRPE cells. MITF knockdown decreased miR-204/211 expression and caused hfRPE dedifferentiation. Significantly, co-transfection of MITF siRNA with pre-miR-204/211 rescued RPE phenotype. Collectively, our data show that miR-204/211 promote RPE differentiation, suggesting that miR-204/211-based therapeutics may be effective treatments for diseases that involve RPE dedifferentiation such as proliferative vitreoretinopathy.

Modulation of MCT3 Expression during Wound Healing of the Retinal Pigment Epithelium

PURPOSE MCT3 is a proton-coupled monocarboxylate transporter preferentially expressed in the basolateral membrane of the retinal pigment epithelium (RPE) and has been shown to play an important role in regulating pH and lactate concentrations in the outer retina. Decreased expression of MCT3 in response to trauma or disease could contribute to pathologic changes in the retina. The present study followed the expression of MCT3 after wounding and re-epithelialization of chick RPE explant and human fetal (hf) RPE cultures. METHODS Immunofluorescence microscopy and immunoblotting were performed to determine changes in MCT expression after scratch wounding and re-epithelialization of chick RPE/choroid explant cultures and hfRPE cell monolayers. RESULTS MCT3 expression and basolateral polarity were maintained in chick RPE/choroid explant cultures and hfRPE monolayers. Wounding resulted in loss of MCT3 and the upregulation of MCT4 expression in migrating cells at the edge of the wound. On re-epithelialization, MCT3 was detected in chick and hfRPE cells when cells became hexagonally packed and pigmented. However, in hfRPE cells, MCT4 was consistently expressed throughout the epithelial monolayer. RPE cells at the edges of chick explants and hfRPE cultures with a free edge expressed MCT4 but not MCT3. CONCLUSIONS Wounding of RPE monolayers resulted in dedifferentiation of the cells at the edge of the wound, as evidenced by a loss of MCT3 and increased MCT4 expression. Collectively, these findings suggest that both cell-cell and cell-substrate interactions are essential in directing and maintaining differentiation of the RPE and expression of MCT3.

EVIDENCE THAT TYROSINE PHOSPHORYLATION REGULATES N-CADHERIN TURNOVER DURING RETINAL DEVELOPMENT

N-cadherin, a member of the cadherin family of calcium-dependent cell adhesion molecules, mediates adhesive and signaling interactions between cells during development. N-Cadherin undergoes dynamic spatiotemporal changes in expression which correlate with morphogenetic movements of cells during organogenesis and histogenesis. We have previously shown that N-cadherin expression during development is regulated by several mechanisms, including mRNA expression, cytokine modulation, and proteolytically mediated turnover, yielding the NCAD90 protein. The present study was directed at determining the extent to which N-cadherin in primary embryonic cells is the target of endogenous kinases and phosphatases, as well as the effects of modulation of these enzymes on NCAD90 expression. The results of phosphoamino acid analyses, peptide mapping, and measurements of N-cadherin and NCAD90 expression in embryonic tissues indicate that N-cadherin is indeed the target of endogenous kinase and phosphatase action, and that modulation of different classes of these enzymes can result in either stimulation or inhibition of NCAD90 production. These results provide a mechanistic explanation for observations that cadherin function is downregulated following expression of exogenously introduced viral tyrosine kinases and provide a function for the tyrosine phosphatases recently found in association with cadherins. The results indicate that N-cadherin expression during retinal development is possibly regulated in part by modulation of its phosphorylation state, the balance of which may determine whether N-cadherin remains stably expressed or is targeted for proteolytically mediated turnover to produce NCAD90.

The Conceptual and Experimental Foundations of Vertebrate Embryonic Cell Adhesion Research

As embryology underwent its transformation from a descriptive to an experimental science, new research programs began to seek a causal understanding of the striking morphogenetic changes that had been observed to occur during embryogenesis. Whether these underlying morphogenetic forces were intrinsic properties of individual cells or whether they were some holistic property of the embryo in toto was a question fueled by several sources. On the one hand, His (1) hypothesized that morphogenetic movements occurred as a result of unequal growth among different populations of cells which led to bending and stretching of tissues, much as pushing and pulling on a sheet of some deformable material could lead to the production of complicated shapes. Roux (2), on the other hand, claimed to have observed specific positive and negative cytotropisms among populations of individual cells isolated from early amphibian embryos. The issue of developmental regulation as a cell-autonomous property, as opposed to a holistic expression of special attributes of embryos, was further exacerbated by the disparate interpretations of Roux (3) and Driesch (4) regarding their experiments on the developmental fate of isolated amphibian and sea urchin embryo blastomeres. While Roux’s interpretation of independent cellular development in these specific cases were not supported by later investigation, his methods nevertheless served as a potent stimulus for further investigation on the individual cellular behaviors that contributed to the overall program of morpho-genesis.

Identification of mammalian and invertebrate analogues of the avian calcium-dependent cell adhesion protein N-cadherin with synthetic-peptide directed antibodies against a conserved cytoplasmic domain

N-cadherin, a 130kD transmembrane adhesive glycoprotein, is a mediator of specific cellular interactions during development. Analysis of N-cadherin at the protein level, to date, has been largely dependent upon monoclonal antibody NCD-2 which recognizes only avian N-cadherin. We produced a monospecific polyclonal antiserum, C-NCAD(838-856), to a synthetic peptide corresponding to a portion of the highly conserved c-terminal cytoplasmic domain of chick N-cadherin. Using polyacrylamide gel electrophoresis and immunoblotting to map tissue distribution we show that the antiserum detects chick N-cadherin with a similar tissue distribution as NCD-2. Unlike NCD-2, however, anti-C-NCAD(838-856) recognizes N-cadherin analogues in a wide variety of species, including mouse, human, fish and drosophila. The results of comparative immunoblot studies demonstrate similar tissue-specific patterns and apparent molecular weight variation in the chick, mouse and human. This indicates that N-cadherin structure and expression, and most likely function as well, have been highly conserved in evolution. The antiserum recognizes an epitope unique to N-cadherin which is conserved among N-cadherins from a variety of species but is absent from other members of the cadherin gene family, as no immunoreactivity was detected with tissues bearing these other cadherins. The antiserum is thus a useful tool for the phylogenetic and biochemical investigation of N-cadherin from a variety of tissue sources.

Discovery and Analysis of the Classical Cadherins

Publisher Summary This chapter focuses on the classical cadherins, those members of the cadherin gene superfamily that include the first described and most structurally conserved of these proteins and that have been found only in vertebrate animals. The classical cadherins are part of a growing cadherin gene superfamily comprising a phylogenetically ancient, large and diverse group of molecules with a rich variety of structural motifs, spatiotemporal expression patterns and functional roles in the development and mature function of vertebrate and invertebrate organisms alike. The cadherins are cell surface integral membrane glycoproteins found in the wide variety of organisms that mediate calcium dependent adhesive interactions critical for the stable associations of cells in solid tissues. Cadherins have important functions in the maintenance of mature tissues throughout the life of an individual, and their malfunction or misexpression may contribute to unfortunate pathogenetic changes that may herald disease and premature demise. Computer analysis of sequence homologies has led to the construction of a cadherin family tree. This analysis sorts the cadherins into three groups, consisting of (1) N- and R-cadherins; (2) P-, E-, EP-, and B-cadherins; and (3) the distinct M- and T-cadherins.

A Century of Cell Adhesion: From the Blastomere to the Clinic Part 1: Conceptual and Experimental Foundations and the Pre-Molecular Era

Abstract The historical roots of cell adhesion research stretch back over a hundred years, commencing with fundamental questions from the advent of experimental embryology in the late nineteenth century. The transition of embryology from a descriptive to an experimentally driven and mechanistic branch of the biological sciences included investigations focused on the interactions of the first cells of the newly developing embryo, the blastomeres, and followed the movement, interactions and fate of these cells as the tissues and organs of the growing embryo took form. Of special interest to early investigators were cell-cell contacts, which were obviously dynamic but of an obscure nature. This historical review, the first of a series, explores the early years of the cell adhesion field, including the work of Roux, Wilson, Galtsoff, Just and Holtfreter, and discusses the classical experiments, observations and conceptual developments that formed the cornerstone of cell adhesion research during its premolecular era.