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Guojun SHENG, Ph. D. 
We
study the molecular and cellular mechanisms of gastrulation, an early
developmental process conserved throughout the animal kingdom. During
gastrulation, three germ layers (ectoderm, mesoderm and endoderm) are
formed from a uniform layer of epiblast cells. Each of these germ layers
undergoes further regional specification to form the functional tissues
and organs of a developing embryo. Using chick as our main model, we are
interested in developing a more complete understanding of how signaling
molecules affect cellular behavior (morphology, migration and cell-cell
interaction) during initial germ layer patterning, and how they act together
with local molecular cues in specifying cell fates. Our research focuses
on two aspects of gastrulation: the initial patterning of the neural ectoderm
and mesoderm by signals from the organizer and the primitive streak, and
the differentiation of posterior mesodermal precursors into hematopoietic
and angiogenic cell lineages.
In the chicken embryo, signals from the organizer (Hensen's node) and the primitive streak induce molecular markers specific to either neural ectoderm or mesoderm cells, and control their distinct cell migratory behaviors. This induction is a multistep process involving gradual commitment, ultimately leading to the assignment of a terminal fate. We are studying the signaling processes involved in the induction of cell fate-specific gene expression and behavioral changes in these systems.
The
extraembryonic mesoderm gives rise to the earliest functioning cell types
in the developing embryo, and serves as a simple model for the study of
how subdivisions occur immediately after initial germ layer induction.
Our team is investigating how two types of extraembryonic mesoderm cells
(blood cells and endothelial cells) are specified by focusing on signaling
inputs from adjacent tissues as well as these cells' autonomous differentiative
properties.
In a third area of interest, we are beginning to study FGF molecules, which are involved in the initial induction and later cellular differentiation of both mesoderm and neural ectoderm. We are currently investigating the biochemical nature of this pathway's diverse roles by focusing on the properties of different ligand/receptor combinations as well as intracellular mediators of FGFR signaling.
