Question

Compare and contrast the role of Notch/Delta signaling in Drosophila neural stem cell (NSC) and C. elegans germline stem cell (GSC) fate specification

Answer 1

Cell-cell interactions mediated by the Notch signaling pathway occur throughout C. elegans embryogenesis. These interactions have major roles in specifying cell fates and in tissue morphogenesis. The network of Notch interactions is linked in part through the Notch-regulated expression of components of the pathway, allowing one interaction to pattern subsequent ones. The Notch signal transduction pathway is highly conserved in animal embryogenesis. The REF-1 family of bHLH transcription factors are major targets of Notch signaling in the C. elegans embryo, and are distantly related to HES proteins that are targets of Notch signaling in Drosophila and vertebrates.

Germline stem cells are key to genome transmission to future generations. In most organisms, PGCs are set aside early during embryogenesis. Two distinct mechanisms have been identified in model organisms that specify germ cells. In flies, worms, fish, and frogs, maternally synthesized germ plasm is deposited into the egg during oogenesis. This specialized cytoplasm harbors germline-specific, electron-dense RNA-protein particles required for multiple aspects of germ cell fate. Embryonic nuclei inheriting germ plasm are destined to become PGCs. In contrast, in mammals and many other species traversing all animal phyla, germ cells are specified among the cells of the embryo independent of preexisting maternal information. Specification occurs in some species early during development, when germ cell fate is induced in a subset of otherwise pluripotent progenitors cells such as epiblast cells of the early mouse embryo, and in other species at later embryonic and postembryonic stages, when germ cells can originate from multipotent progenitors within the mesoderm.