EXPRESSION PATTERNS OF CONNEXIN43 PROTEIN DURING FACIAL DEVELOPMENT IN THE CHICK-EMBRYO - ASSOCIATIONS WITH OUTGROWTH, ATTACHMENT, AND CLOSURE OF THE MIDFACIAL PRIMORDIA

Background: In a prior report, evidence was presented for the presence of gap junction proteins [connexin32 and connexin43 (Cx43)] in embryo nic facial primordia. The purpose of the present study was, first, to examine in detail the patterns of distribution of Cx43 protein in embr yonic chick facial primordia and, second, to consider the possible rol es played by this protein during midfacial development. Methods: Chick embryo heads were serially sectioned and processed for immunofluoresc ent localization of Cx43. The developmental stages examined encompasse d the period of formation, enlargement, and union of the facial primor dia. Western blot analysis of the facial primordia was also performed. Results: Analysis of serial sections revealed the presence of signal in both epithelium and mesenchyme at sites of attachment in each of th e midfacial primordia (i.e., the medial nasal, lateral nasal, and maxi llary processes). Furthermore, although signal was concentrated in mes enchyme in the distal tips of the primordia at sites of attachment, im munoreactivity was absent, sparse, or less intense outside the areas o f attachment. In some cases (i.e., the maxillary process), immunoreact ive signal in mesenchyme did not appear in the distal tip until the pr imordia approximated each other or contact of the primordia was initia ted. Most significantly, signal was also found between the facial prim ordia in nonprimordial epithelium and mesenchyme at sites where the pr imordia were joined. Conclusions: These data suggest that the expressi on of Cx43 protein is spatially and temporally regulated in the facial primordia and that the patterns of expression that were observed are significant to the cascade of events that ultimately lead to the attac hment and union of the primordia that form the midface. (C) 1997 Wiley -Liss, Inc.