Molecular mechanisms controlling Xenopus neurogenesis
Xenopus has proven itself as a valuable model system to elucidate the cascade of events that controls early vertebrate neurogenesis owing to simplicity and accessibility of primary neurogenesis. In Xenopus, the first primary neurons are born within the induced neuroectoderm shortly after gastrulation in three bilateral longitudinal domains. The neurons can be visualized by whole mount in situ hybridization by the expression of neural-specific beta-Tubulin (N-Tubulin) (see figure). The differentiation of the primary neurons is driven by the bHLH transcription factor neurogenin-related 1 (X-ngnr-1), which induces later acting genes required for withdrawal of the progenitor cells from the cell cycle and terminal differentiation. In addition, X-ngnr-1 induces the expression of the ligand Delta, which in turn activates Notch signaling in the neighboring cell. Activation of the Notch pathway gives rise to the expression of the enhancer of split related repressor bHLH proteins that inhibit both the expression and function of X-ngnr-1. Thus, neuronal differentiation does occur in this cell at this time. Our research is focused on the identification and characterization of the intrinsic factors and signaling pathways that promote and restrict primary neuron formation.