Heart Malformations in Transgenic Mice Exhibiting Dominant Negative Inhibition of Gap Junctional Communication in Neural Crest Cells

Transgenic mice were generated expressing an alpha1 connexin/beta-galactosidase fusion protein previously shown to exert dominant negative effects on gap junctional communication. RNase protection analysis and assays for beta-galactosidase enzymatic activity showed that the transgene RNA and protein are expressed in the embryo and adult tissues. In situ hybridization analysis revealed that in the embryo, expression was predominantly restricted to neural crest cells and their progenitors in the dorsal neural tube, regions where the endogenous alpha1 connexin gene is also expressed. Dye-coupling analysis indicated that gap junctional communication was inhibited in the cardiac neural crest cells. All of the transgenic lines were homozygote inviable, dying neonatally and exhibiting heart malformations involving the right ventricular outflow tract-the same region affected in the alpha1 connexin knockout mice. As in the knockout mice, the conotruncal heart malformations were accompanied by outflow tract obstruction. Histological analysis showed that this was associated with abnormalities in the differentiation of the conotruncal myocardium. These results suggest that the precise level of gap junctional communication in cardiac neural crest cells is of critical importance in right ventricular outflow tract morphogenesis. Consistent with this possibility is the fact that cardiac crest cells from the alpha1 connexin knockout mice also exhibited a greatly reduced level of gap junctional communication. These studies show the efficacy of a dominant negative approach for manipulating gap junctional communication in the mouse embryo and demonstrate that targeted expression of this fusion protein can be a powerful tool for examining the role of gap junctions in mammalian development.