DEVELOPMENTAL EXPRESSION OF CONNEXINS IN THE CHICK-EMBRYO MYOCARDIUM AND OTHER TISSUES

Background: Connexins are cell surface proteins that form specialized regions of cell-cell communication called gap junctions. These allow i mpulse conduction in involuntary muscle tissue such as the heart, but also allow the formation of communities of like cells during developme nt of organs. Methods: We used an antipeptide antibody to connexin 43 in immunolocalization studies and an anti-peptide antibody to an exter nal loop domain common to most connexins in Western blotting of total heart protein to measure the accumulation of connexins in the heart as it develops from 33 hours to 21 days (hatching), and in the adult. Re sults: Immunolocalization revealed that connexin 43 is widely distribu ted in the earliest organ rudiments. It is especially prominent in the neural tube and its derivatives, in the lens and nasal placodes, in t he foregut and its derivatives, in the somites, in the mesonephric tub ules, and in the heart and major arteries. Heart tissue staining grew more intense with development through day 8. However, at day 11 and da y 15, and in the adult, heart staining diminished. Endocardium and val ve tissue did not stain. Western blotting of heart homogenates with th e antibody directed against the external loop domain peptide showed 26 , 32, 43, 45, and 56 kilodalton connexins, which changed in relative a bundance, displaying unique patterns during development. Conclusions: Our results show patterns of connexin immunolocalization in early germ layers and organ rudiments that are similar to those known in the mou se, but with certain differences. Our results show a distinctive patte rn of multiple connexin gene expression in the developing heart from d ays 2-21. (C) Wiley-Liss, Inc.