A critical step in the early development of the vertebrate embryo is the establishment of the three principle germ layers. While work from many laboratories has demonstrated that Nodal intercellular signals are essential for specifying where in the embryo the mesoderm and endoderm will form, a critical question remains: what determines where Nodal signaling occurs? This laboratory has shown that in zebrafish, the Yolk Syncytial Layer (YSL) is a source of an unknown signal that activates the expression of the two gastrula-stage nodals, squint (sqt) and cyclops, in the so-called marginal region of the embryo where the mesoderm and endoderm forms. The aim of this proposal is to understand how the YSL induces the marginal expression of sqt.
Two general directions will be pursued. A fragment of genomic DNA that directs the marginal expression of sqt has been isolated, and deletion analysis has defined a 300 bp region that is necessary for this expression. In the first two aims, the essential transcription factor that regulates this element will be determined. The third aim will initially determine which intercellular signaling pathway regulates sqt expression, and then will define the specific factor secreted by the YSL.
The studies proposed here will provide a basic mechanistic understanding of the process that regulates germ layer formation in the vertebrate embryo. While several studies have elucidated how nodal expression is regulated by a localized transcription factor in the frog Xenopus laevis, other vertebrates such as zebrafish instead use intercellular signaling to regulate the nodals. Thus these studies will provide novel insight into the mechanism of germ layer patterning.
Two graduate students will be trained during the course of this project, as will several undergraduates. Particular emphasis will be placed on training underrepresented minority undergraduates who are recruited to the lab through Dr. Kimelman's participation in the STAR and BRIDGES4 programs at the U.W. Dr. Kimelman will provide services to the larger scientific community through serving on the editorial boards of Cell, Developmental Cell, Developmental Biology, as a reviewer for many journals, as a frequent review of NSF proposals, as a member of the Faculty of 1000, and through the writing of reviewer articles. Dr. Kimelman also serves as the director of a large training grant at the U.W., which provides additional training (through monthly meetings and an annual retreat) for 33 graduate students each year.
