Background: In a prior report, evidence was presented for the presence of gap junction proteins [connexin32 and connexin43 (Cx43)] in embryonic facial primordia. The purpose of the present study was, first, to examine in detail the patterns of distribution of Cx43 protein in embryonic chick facial primordia and, second, to consider the possible roles played by this protein during midfacial development.
Methods: Chick embryo heads were serially sectioned and processed for immunofluorescent localization of Cx43. The developmental stages examined encompassed the period of formation, enlargement, and union of the facial primordia. 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 the midfacial primordia (i.e., the medial nasal, lateral nasal, and maxillary processes). Furthermore, although signal was concentrated in mesenchyme in the distal tips of the primordia at sites of attachment, immunoreactivity was absent, sparse, or less intense outside the areas of attachment. In some cases (i.e., the maxillary process), immunoreactive signal in mesenchyme did not appear in the distal tip until the primordia approximated each other or contact of the primordia was initiated. Most significantly, signal was also found between the facial primordia in nonprimordial epithelium and mesenchyme at sites where the primordia were joined.
Conclusions: These data suggest that the expression 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 attachment and union of the primordia that form the midface.