Heart malformations in transgenic mice exhibiting dominant negative inhibition of gap junctional communication in neural crest cells

Transgenic mice were generated expressing an alpha 1 connexin/beta-galactos idase fusion protein previously shown to exert dominant negative effects on gap junctional communication. RNase protection analysis and assays for bet a-galactosidase enzymatic activity showed that the transgene RNA and protei n are expressed in the embryo and adult tissues. In situ hybridization anal ysis revealed that in the embryo, expression was predominantly restricted t o neural crest cells and their progenitors in the dorsal neural tube, regio ns where the endogenous al connexin gene is also expressed. Dye-coupling an alysis indicated that gap junctional communication was inhibited in the car diac neural crest cells. All of the transgenic lines were homozygote inviab le, dying neonatally and exhibiting heart malformations involving the right ventricular outflow tract-the same region affected in the alpha 1 connexin knockout mice. As in the knockout mice, the conotruncal heart malformation s were accompanied by outflow tract obstruction. Histological analysis show ed that this was associated with abnormalities in the differentiation of th e conotruncal myocardium. These results suggest that the precise level of g ap junctional communication in cardiac neural crest cells is of critical im portance in right ventricular outflow tract morphogenesis. Consistent with this possibility is the fact that cardiac crest cells from the alpha 1 conn exin knockout mice also exhibited a greatly reduced level of gap junctional communication. These studies show the efficacy of a dominant negative appr oach for manipulating gap junctional communication in the mouse embryo and demonstrate that targeted expression of this fusion protein can be a powerf ul tool for examining the role of gap junctions in mammalian development. ( C) 1998 Academic Press.