Together these transcription factors function in a positive feedback loop that strengthens the ICM to TE cellular allocation. Initial polarization of blastomeres occurs at the 8-16 cell stage. An apical-basolateral polarity is visible through the visualization of apical markers such as Par3, Par6, and aPKC as well as the basal marker E-Cadherin. The establishment of such a polarity during compaction is thought to generate an environmental identity for inside and outside cells of the embryo. Consequently, stochastic expression of the above transcription factors is amplified into a feedback loop that specifies outside cells to a TE fate and inside cells to an ICM fate. In the model, an apical environment turns on "Cdx2", which upregulates its own expression through a downstream transcription factor, Elf5. In concert with a third transcription factor, Eomes, these genes act to suppress pluripotency genes like "Oct4" and "Nanog" in the outside cells. Thus, TE becomes specified and differentiates. Inside cells, however, do not turn on the "Cdx2" gene, and express high levels of "Oct4", "Nanog", and "Sox2". These genes suppress "Cdx2" and the inside cells maintain pluripotency generate the ICM and eventually the rest of the embryo proper.