Asymmetric distribution of CRUMBS polarity complex proteins from compacted 8-cell to blastocyst stage during mouse preimplantation development

During mouse preimplantation development, blastomeres are equipotent until polarity establishment at compacted 8-cell stage. The intrinsic nature of polarity is the asymmetric distribution of polarity proteins between inside and outside blastomeres along the direction of apical-basal axis. This study investigated the early developmental temporal and spatial expression of the main CRUMBS polarity complex proteins in the mouse preimplantation embryo. We observed that Crb3, Pals1, Patj and Mpdz are transcribed in the mouse preimplantation embryo. However, the asymmetric distribution of these polarity proteins is not established until the compacted 8-cell stage. From compaction and thereafter, CRB3 and PALS1 are progressively enriched in the apical membrane, while PATJ and MPDZ are discretely localized at both tight junctions and the apical membrane adjacent to tight junctions. These temporal and spatial distribution patterns suggest that CRUMBS polarity complex might be involved in the cell polarity establishment in the early mouse embryo and reinforce the viewpoint that developmentally spatial asymmetries are first set up at the compaction stage. The present study provides a foundation for further investigation on the functions of CRUMBS polarity complex in trophectoderm specification and blastocyst morphogenesis.