Respective roles of protein tyrosine kinases and protein kinases C in the upregulation of β-catenin distribution, and compaction in mouse preimplantation embryos: a pharmacological approach

Abstract

The cellular distribution of β-catenin was determined by western blotting and laser confocal scanning microscopy in both control and pharmacologically-manipulated mouse preimplantation embryos. Most of the stored maternal β-catenin is Triton X–100-extractable and distributed throughout the cytoplasm. In 2-cell stage embryos, the remaining molecules are concentrated in regions of cell contact and, to a lesser extent, at non apposed surfaces. Association of β-catenin with the cortex of non apposed membranes decreases as cleavage proceeds, and is lost at compaction. In contrast to the rapid cross-linking of cell surfaces induced by wheat germ agglutinin, the diacylglyceride-induced compaction-like adhesion of 2- and 4-cell embryos correlates with complete restriction of β-catenin to the apposing membranes. On the contrary, tyrphostin B46, a specific protein tyrosine kinase inhibitor, fails to induce both premature β-catenin relocalisation and compaction. In addition, we show that orthovanadate induces a dramatic increase in the level of phosphotyrosine labelling of cell-cell junctions in compacted 8-cell stage embryos without inducing their decompaction. However, most of these orthovanadate tyrosine-phosphorylated proteins are detergent-soluble, while β-catenin restricted to the apposing membranes is not. In conclusion, our results confirm that diacylglycerol-dependent kinases upregulate both β-catenin redistribution and compaction, and indicate that neither tyrosine kinases, nor tyrosine phosphatases are critical for the proper onset of compaction which seems, in addition, not causally linked to tyrosine dephosphorylation of β-catenin.