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Immunocytochemical detection of integrins [[alpha].sub.3] and [[beta].sub.1] in allografts of the marine sponge, Microciona prolifera.

Integrins are a widely expressed family of cell surface adhesion receptors whose existence in sponges, the oldest extant Metazoan phylum, has been clearly established. In sponges, cell adhesion is mainly achieved through species-specific interactions of a type of proteoglycan molecule termed aggregation factor (AF). The deglycosylated AF protein in the marine sponge Microciona prolifera was cloned in our prior work and found to contain the integrin-binding motif RGD. In subsequent grafting experiments, we observed that antibodies raised against this protein detected a type of sponge stem cell, the archeocyte, that accumulated in the contact zone of allografts (between tissue from different individuals), but not of isografts (between genetically identical tissues). A similar distribution was observed for another type of sponge cell, the gray cell, which is specifically recognized by antibodies raised against the hyaluronan receptor CD44, also implicated in cellular adhesion. We also showed that immunoblots of M. prolifera cell membrane proteins revealed the presence of specific bands decorated by antibodies raised against mouse integrins [[alpha].sub.3] and [[beta].sub.1]. The purpose of the present work was to determine the distribution of [[alpha].sub.3] and [[beta].sub.1] integrins in sponge grafts by means of immunocytochemical experiments. Double-staining experiments of allografts show colocalization of integrin and CD44 in the same cells concentrated at the zone of contact. Furthermore, epithelial pinacocytes do not express either integrin, but the internal core of the sponge (mesohyl) is abundant in cells that stain very strongly for [[alpha].sub.3]. The [[beta].sub.1] staining was much weaker but reached levels similar to those of [[alpha].sub.3] if the tissue was desulfated prior to immunodetection. Since deglycosylated AF (archeocyte marker) will be more likely to have the RGD sequence exposed, we hypothesize that AF proteins expressed in archeocytes might interact with integrins expressed in gray cells in the initial stages of allogeneic recognition.

Funding was provided for Clarissa Sabella by HHMI (#71100-505003)

Clarissa A. Sabella (1), Ellen E. Faszewski (2), Jane C. Kaltenbach (1), William J. Kuhns (3), Max M. Burger (4), and Xavier Fernandez-Busquets (5)

(1) Mount Holyoke College, South Hadley, Massachusetts

(2) Wheelock College, Boston, Massachusetts

(3) Hospital for Sick Children, Toronto, Canada

(4) Friedrich Miescher Institute, Basel, Switzerland

(5) University of Barcelona, Barcelona, Spain

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Author:Sabella, Clarissa A.; Faszewski, Ellen E.; Kaltenbach, Jane C.; Kuhns, William J.; Burger, Max M.; F
Publication:The Biological Bulletin
Geographic Code:1USA
Date:Oct 1, 2004
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