Abstract
The mechanism underlying mammalian preimplantation embryogenesis has been a subject of long-standing controversy. The central question has been if any "determinants" play a critical role in a manner comparable to the non-mammalian model of development. During the last decade, the issue has been revitalized by claims that the axes of the mouse blastocyst can be anticipated at the egg ("prepatterned model"), similar to the non-mammalian development model. However, several recent studies by other laboratories do not support these claims ("regulative model"). The debate over these developmental models has led many researchers to search for markers of cell lineage that may provide further evidence. I have focused my efforts on Cdx2 and Oct4 because these two transcription factors are excellent markers of the first morphologically evident embryonic differentiation into inner cell mass, ICM, (0ct4) and trophectoderm, TE, (Cdx2) during blastulation. My goal was to establish whether or not it is possible to predict the lineage (IE or JCM) of a single blastomere prior to blastulation, based on the differential gene expression of Cdx2 and Oct4. Specifically, if a particular cell in the early embryo exhibits elevated Oct4 and repressed Cdx2, this cell may be postulated as a lineage founder of the ICM. Conversely, a cell with high Cdx2 and low Oct4 could postulated as a lineage founder of the TE. This paper describes the utility of RT•LATE-PCR and the PurAmp method for quantitative analysis of Oct4 and Cdx2 RNA expression in whole embryos and their single cells. My findings indicate that the consistent up-regulation of Cdx2 expression begins in the late morula stage of mouse embryonic development. Single cell expression profiles in late morulas was suggestive of reciprocal expression in some cases, however the difficulty of isolating cells at this stage (due to cell-to-cell adhesion), prevented the collection of a more complete expression profile.