Analysis of Cdx2 gene expression patterns and cell movement in mouse preimplantation embryos by live-cell imaging

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Establishment of Trophectoderm (TE) and inner cell mass (ICM) is the first cell lineage segregation in mouse development. Determination of the TE cell lineage is thought to be triggered by expression of Caudal-type transcriptional factor Cdx2 gene. To examine detailed expression patterns of Cdx2 and cell behavior during preimplantation development, we established Cdx2-EGFP reporter mice by which endogenous expression of Cdx2 can be visualized as EGFP fluorescence. We observed preimplantation embryos from Cdx2-GFP reporter mice by live-imaging, and found that cells internalized during molura stage once started to express Cdx2 when they were localized in outer position, then after internalization they participated in ICM and down-regulated Cdx2. These data suggest that these internalized cells can re-repress TE-specification pathway once activated, and behave as a part of pluripotent cell population.