Tight junction protein cingulin is expressed by maternal and embryonic genomes during early mouse development

The expression of the tight junction peripheral membrane protein, cingulin (140 x 10(3) M(r), was investigated in mouse eggs and staged preimplantation embryos by immunoblotting and immunoprecipitation. Polyclonal antibody to chicken brush cingulin detected a single 140 x 10(3) M(r) protein in immunoblots of unfertilised eggs and all preimplantation stages. Relative protein levels were high in eggs and early cleavage stages, declined during later cleavage and increased again in expanding blastocysts. Quantitative immunoprecipitation of metabolically labelled eggs and staged embryos also revealed a biphasic pattern for cingulin synthesis with relative net levels being high in unfertilised eggs, minimal during early cleavage, rising 2.3-fold specifically at the onset of compaction (8-cell stage, when tight junction formation begins), and increasing further at a linear rate during morula and blastocyst stages. Cingulin synthesis in eggs is not influenced by fertilisation (or aging, if unfertilised), but this level declines sharply after first cleavage. These results indicate that cingulin is expressed by both maternal and embryonic genomes. The turnover of maternal cingulin (unfertilised eggs) and embryonic cingulin at a stage before tight junction formation begins (4-cell stage) is higher (t1/2 approximately 4 hours) than cingulin synthesised after tight junction formation (blastocysts; t1/2 approximately 10 hours). This increase in cingulin stability is reversed in the absence of extracellular calcium. Cingulin synthesis is also tissue-specific in blastocysts, being up-regulated in trophectoderm and down-regulated in the inner cell mass. Taken together, the results suggest that (i) cingulin may have a role during oogenesis and (ii) cell-cell contact patterns regulate cingulin biosynthesis during early morphogenesis, contributing to lineage-specific epithelial maturation.