Transcriptional regulation of pluripotency in the early vertebrate embryo

Weinstein, Daniel

Abstract

The emergence of the primary germ layers (ectoderm, mesoderm, endoderm) is an early and critical event in vertebrate embryogenesis; elucidation of the mechanisms underlying this process is a fundamental goal of developmental biology. Much of our understanding of germ layer formation comes from studies in the amphibian embryo, in particular those of the frog, Xenopus laevis?a well-supported model has emerged that emphasizes inductive interactions in the formation of both mesoderm and endoderm. While a prominent role for induction remains unchallenged, work from our group and others have identified an additional requirement for germ layer inhibition in establishing the vertebrate body plan. Recently, we have found that Tbx2, a T-box transcriptional repressor, plays a central role in this process: Tbx2, expressed in the presumptive ectoderm, is both necessary and sufficient for the suppression of ectopic mesoderm and endoderm. Studies described in this application are designed to elucidate the mechanisms underlying Tbx2-mediated germ layer suppression in Xenopus laevis. Experiments proposed here will identify the transcriptional mechanisms by which Tbx2 suppresses mesoderm and endoderm (Aim 1), will establish the timing of Tbx2 activity during the progressive loss of embryonic pluripotency (Aim 2), and will define the role of Tbx2-mediated BMP/Smad signal inhibition during early embryonic development (Aim 3). Undergraduate and Master?s students will perform the majority of these studies, providing them in many cases with their first exposure to research; this project will thus strengthen significantly the research environment at Queens College, which currently has limited extramural funding for the biomedical sciences. The experiments outlined in this proposal will extend considerably our understanding of germ layer suppression, and should be of particular interest to those in the fields of oncology and regenerative medicine. Tbx2 and the closely related Tbx3 are frequently overexpressed in melanoma and breast cancers; loss-of- function mutations in the T-domain have been implicated in oncogenesis. Our research, which will provide key insights into the mechanisms of T-box protein function, may serve as the basis for anticancer therapeutics. Our studies further suggest that pluripotent cell fate can be regulated through the combinatorial effects of activator and repressor T-box proteins; the studies proposed in this application may thus inform efforts by researchers seeking to generate pancreatic, hematopoietic, neural, and other lineages, in vitro. Our research, which both addresses fundamental questions of developmental biology and has clear potential for translational application, aligns well with the dual mission of the National Institutes of Health (www.nih.gov/about-nih/what-we- do/mission-goals): ??to seek fundamental knowledge about the nature and behavior of living systems and the application of that knowledge to enhance health, lengthen life, and reduce illness and disability.?

Public Health Relevance

We have found that the T-box transcription factor Tbx2 suppresses ectopic differentiation of both mesoderm and endoderm during early vertebrate development. Experiments proposed in this application are designed to establish the mechanisms by which Tbx2 regulates embryonic cell fate.