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

滋养外胚层（TE）和内细胞团（ICM）的建立是小鼠发育过程中的第一个细胞谱系分离。TE细胞谱系的确定被认为是由Caudal型转录因子Cdx 2基因的表达触发的。为了研究Cdx 2的详细表达模式和植入前发育过程中的细胞行为，我们建立了Cdx 2-EGFP报告小鼠，通过其Cdx 2的内源性表达可以可视化为EGFP荧光。我们通过活体成像观察了Cdx 2-GFP报告小鼠植入前胚胎，发现在molura期内化的细胞在定位于外部位置时，一旦开始表达Cdx 2，内化后参与ICM并下调Cdx 2。这些数据表明，这些内化的细胞可以重新抑制TE-特化途径一旦激活，并表现为多能细胞群的一部分。

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.