Gap junction-mediated cell-cell communication modulates mouse neural crestmigration

Previous studies showed that conotruncal heart malformations can arise with the increase or decrease in alpha(1) connexin function in neural crest cel ls. To elucidate the possible basis for the quantitative requirement for al pha(1) connexin gap junctions in cardiac development, a neural crest outgro wth culture system was used to examine migration of neural crest cells deri ved from CMV43 transgenic embryos overexpressing alpha(1) connexins, and fr om alpha(1) connexin knockout (KO) mice and FC transgenic mice expressing a dominant-negative alpha(1) connexin fusion protein. These studies showed t hat the migration rate of cardiac neural crest was increased in the CMV43 e mbryos, but decreased in the FC transgenic and alpha(1) connexin KO embryos . Migration changes occurred in step with connexin gene or transgene dosage in the homozygous vs. hemizygous alpha(1) connexin KO and CMV43 embryos, r espectively. Dye coupling analysis in neural crest cells in the outgrowth c ultures and also in the living embryos showed an elevation of gap junction communication in the CMV43 transgenic mice, while a reduction was observed in the FC transgenic and al connexin KO mice. Further analysis using oleami de to downregulate gap junction communication in nontransgenic outgrowth cu ltures showed that this independent method of reducing gap junction communi cation in cardiac crest cells also resulted in a reduction in the rate of c rest migration. To determine the possible relevance of these findings to ne ural crest migration in vivo, a lacZ transgene was used to visualize the di stribution of cardiac neural crest cells in the outflow tract. These studie s showed more lacZ-positive cells in the outflow septum in the CMV43 transg enic mice, while a reduction was observed in the alpha(1) connexin KO mice. Surprisingly, this was accompanied by cell proliferation changes, not in t he cardiac neural crest cells, but in the myocardium-an elevation in the CM V43 mice vs. a reduction in the alpha(1) connexin KO mice, The latter obser vation suggests that cardiac neural crest cells may have a role in modulati ng growth and development of non-neural crest-derived tissues. Overall, the se findings suggest that gap junction communication mediated by alpha(1) co nnexins plays an important role in cardiac neural crest migration. Furtherm ore, they indicate that cardiac neural crest perturbation is the likely und erlying cause for heart defects in mice with the gain or loss of alpha(1) c onnexin function.