| During mammalian development, the first two lineages to be specified are trophectoderm (TE) and inner cell mass (ICM). Proper segregation of these two cell types requires precise spatial control of the Hippo signaling pathway and its downstream transcriptional activator, Yap. In outside, future TE cells of the embryo, Yap is nuclear-localized and can influence the expression of TE-specifying transcription factors such as Cdx2. In contrast, in inside cells, the Hippo pathway kinases Lats1/2 and the adaptor protein Amot induce phosphorylation and cytoplasmic retention of Yap, preventing this transcriptional influence. The factors acting upstream of Lats1/2, Amot and Yap in this context are not well understood. In this thesis, I have investigated the role of the upstream Hippo pathway member Nf2 in TE/ICM segregation. First, using a dominant negative approach, I show that Nf2 is required in a cell-autonomous manner for the proper localization of Yap in inside cells of the embryo. Second, by generating both zygotic and maternal/zygotic Nf2 mutant embryos, I confirm that Nf2 is required for Hippo signaling and demonstrate that this signaling is broadly required for the segregation of ICM from TE. Finally, using maternal/zygotic mutant embryos as a tool, I provide evidence that Nf2 regulates levels of Amot at the plasma membrane of inside cells during active Hippo signaling. Together, these studies demonstrate that Nf2 is essential for both Hippo signaling and lineage specification in the early embryo and provide molecular insights into how these functions are achieved. |
