MULTIPLE MEMBERS OF THE CONNEXIN GENE FAMILY PARTICIPATE IN PREIMPLANTATION DEVELOPMENT OF THE MOUSE

The connexin gene family, of which there are at least 12 members in ro dents, encodes the protein subunits of intercellular membrane channels (gap junction channels). Because of the diverse structural and biophy sical properties exhibited by the different connexins, it has been pro posed that each may play a unique role in development or homeostasis. We have begun to test this hypothesis in the preimplantation mouse emb ryo, in which de novo gap junction assembly is a developmentally regul ated event. As a first step, we have used reverse transcription-polyme rase chain reaction (RT-PCR) to determine the connexin mRNA phenotype of mouse blastocysts, and have identified transcripts of connexins 30. 3, 31, 31.1, 40, 43, and 45. Quantitative measurements indicated that all six of these connexin genes are transcribed after fertilization. T hey can be divided into two groups with respect to the timing of mRNA accumulation: Cx31, Cx43, and Cx45 mRNAs accumulate continuously from the two- or four-cell stage, whereas Cx30.3, Cx31.1, and Cx40 mRNAs ac cumulate beginning in the eight-cell stage. All six mRNAs were found t o co-sediment with polyribosomes from their time of first appearance, indicating that all six are translated. The expression of Cx31.1 and C x40 was examined by confocal immunofluorescence microscopy; whereas bo th could be detected in compacting embryos, only Cx31.1 could be seen in punctate membrane foci indicative of gap junctions. Taken together with other results (published or submitted), our findings indicate tha t at least four connexins (Cx31, 31.1, 43, and 45) contribute to gap j unctions in preimplantation development. The expression of multiple co nnexin genes during this early period of embryogenesis (when there are only two distinct cell types) raises questions about the functional s ignificance of connexin diversity in this context. (C) 1996 Wiley-Liss , Inc.