HEART AND NEURAL-TUBE DEFECTS IN TRANSGENIC MICE OVEREXPRESSING THE CX43 GAP JUNCTION GENE

Transgenic mice were generated containing a cytomegaloviral promoter d riven construct (CMV43) expressing the gap junction polylpeptide conne xin 43. RNA and protein analysis confirmed that the transgene was bein g expressed. In situ hybridization analysis of embryo sections reveale d that transgene expression was targeted to the dorsal neural tube and in subpopulations of neural crest cells. This expression pattern was identical to that seen in transgenic mice harboring other constructs d riven by the cytomegaloviral promoter (Kothary, R., Barton, S. C., Fra nz, T., Norris, M. L., Hettle, S. and Surani, M. A. H. (1991) Mech. De velop. 35, 25-31; Koedood, M., Fitchel, A., Meier, P. and Mitchell, P. (1995) J. Virol. 69, 2194-2207), and corresponded to a subset of the endogenous Cx43 expression domains. Significantly, dye injection studi es showed that transgene expression resulted in an increase in gap jun ctional communication. Though viable and fertile, these transgenic mic e exhibited reduced postnatal viability. Examination of embryos at var ious stages of development revealed developmental perturbations consis ting of cranial neural tube defects (NTD) and heart malformations. Int erestingly, breeding of the CMV43 transgene into the Cx43 knockout mic e extended postnatal viability of mice homozygote for the Cx43 knockou t allele, indicating that the CMV43 trangsene may partially complement the Cx43 deletion. Both the Cx43 knockout and the CMV43 transgenic mi ce exhibit heart defects associated with malformations in the conotrun cus, a region of the heart in which neural crest derivatives are known to have important roles during development. Together with our results indicating neural-crest-specific expression of the transgene in our C MV-based constructs, these observations strongly suggest a role for Cx 43-mediated gap junctional communication in neural crest development. Furthermore, these observations indicate that the precise level of Cx4 3 function may be of critical importance in downstream events involvin g these migratory cell populations. As such, the CMV43 mouse may repre sent a powerful new model system for examining the role of extracardia c cell populations in cardiac morphogenesis and other developmental pr ocesses.