A Dominant Loss-of-Function Gja1 (Connexin43) Mutation Alters Decidual Angiogenesis and Placental Orientation in Mice.

Abstract

The gap junction protein connexin43 (CX43) is expressed in the uterine stroma and in mice is required for appropriate angiogenesis during decidualization. Previous work had shown that loss of CX43 from the uterine stroma causes growth of the implanting embryo to arrest in conjunction with reduced production of angiogenic factors and restricted growth of new decidual blood vessels. The objective of the present study was to characterize placental development in mice carrying the dominant loss-of-function Gja1Jrt allele which, rather than eliminating CX43 function, alters it by substituting serine for glycine at residue 60 (CX43G60S) in the first extracellular loop. This mutation restricts but does not eliminate CX43-based gap junctional intercellular coupling and mutant females exhibit > 50% reduction in litter size. Matings were designed so that placental development could be analyzed in mutant vs. wildtype females into which embryos of both genotypes were implanting, with the genotype of each embryo being determined by PCR. Expression of genes involved in angiogenesis was analyzed by qRT-PCR. Histological and immunohistochemical analysis revealed abundant and enlarged sinusoids combined with an ectoplacental cone with disturbed orientation in the invasion route. This phenomenon leads to placentas with broadened invasion fronts or with laterally shifted orientation into the maternal compartment. This phenotype is independent of the implanting embryo's genotype and thus is hypothesized to be due to the changes in maternal decidual vessel development. The morphological changes are correlated with significantly (P < 0.05) increased levels of transcripts encoding HOXA10 and VEGF, both of which are known to play essential roles in decidualization. In contrast, previous work had revealed HOXA10 and VEGF to be down-regulated in implantation sites lacking CX43. The present findings confirm the important role played by CX43 in stromal angiogenesis and placental development but indicate that a mutant form of CX43 can have adverse effects that would not have been predicted from analysis of mice lacking this protein. Supported by the Deutsche Forschungsgemeinschaft and Canadian Institutes of Health Research.