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Laboratory for Early Embryogenesis

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 interactions) 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 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.