Person:

Rosains, Jacqueline

FoxA transcription factors are central regulators of gut development in all species. In C. elegans, pha-4/FoxA is necessary to generate cells of the foregut, or pharynx. FoxA factors need to be precisely regulated for proper development, yet we know very little about FoxA regulation. To look for potential genes that act as pha-4 regulators, the Mango lab previously conducted two screens for suppressors of the lethality associated with a partial loss of pha-4 activity. Both screens uncovered smg-8, a novel gene that is highly conserved amongst metazoans. Interestingly, the human homolog of smg-8 is amplified in some breast cancers, which also depend on FoxA1. This observation makes smg-8 a very exciting gene to investigate. The goal of my thesis is to analyze smg-8 to better understand its function and potential role as a candidate regulator of pha-4/FoxA, using C. elegans as a model system. In this thesis, I show that C. elegans smg-8 does not have a role in the Nonsense Mediated Decay pathway. I find that smg-8 modulates pha-4 protein levels during embryonic development. This work is the first direct evidence that smg-8 is a modulator of pha-4. I used biochemical and bioinformatic approaches to uncover possible partners of smg-8. These approaches identified several interesting candidates that will help place C. elegans smg-8 in a functional pathway. This work has expanded our understanding of smg-8 function and lays the foundation for further investigation of the role of this novel gene as a regulator of pha-4/FoxA in C. elegans.

BACKGROUND: The cleavage-stage mouse embryo is composed of superficially equivalent blastomeres that will generate both the embryonic inner cell mass (ICM) and the supportive trophectoderm (TE). However, it remains unsettled whether the contribution of each blastomere to these two lineages can be accounted for by chance. Addressing the question of blastomere cell fate may be of practical importance, because preimplantation genetic diagnosis requires removal of blastomeres from the early human embryo. To determine whether blastomere allocation to the two earliest lineages is random, we developed and utilized a recombination-mediated, noninvasive combinatorial fluorescent labeling method for embryonic lineage tracing. RESULTS: When we induced recombination at cleavage stages, we observed a statistically significant bias in the contribution of the resulting labeled clones to the trophectoderm or the inner cell mass in a subset of embryos. Surprisingly, we did not find a correlation between localization of clones in the embryonic and abembryonic hemispheres of the late blastocyst and their allocation to the TE and ICM, suggesting that TE-ICM bias arises separately from embryonic-abembryonic bias. Rainbow lineage tracing also allowed us to demonstrate that the bias observed in the blastocyst persists into postimplantation stages and therefore has relevance for subsequent development. CONCLUSIONS: The Rainbow transgenic mice that we describe here have allowed us to detect lineage-dependent bias in early development. They should also enable assessment of the developmental equivalence of mammalian progenitor cells in a variety of tissues.