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Description
The formation of sensory organs, structures, and cells that make up the peripheral nervous system (PNS) relies on the activity of transcription factors encoded by proneural genes. Integrating spatial and temporal cues, proneural genes interact with each other to form a complex gene regulatory network that controls the development of the PNS. Although extensive studies have identified proneural genes in both invertebrates and vertebrates and have shown a high degree of conservation among diverse species, the contextual complexity of their interactions, especially in vertebrates, has complicated efforts to understand their functions. To gain insight into the regulatory network of proneural gene activity in chordates, we investigated the roles of proneural homologs in regulating PNS development of the invertebrate chordate Ciona intestinalis. The relatively simple tail PNS of C. intestinalis larvae consists of ciliated epidermal sensory neurons (ESNs) that extend from epidermal midline cells into the outer tunic covering the larva. We found that the proneural homologs of MyTF, POU-IV, Amos, and NeuroD are expressed in a sequential cascade in ESNs during development and act downstream of Notch signaling, which negatively regulates the number of ESNs that develop in C. intestinalis. Overexpression of the proneural genes in the epidermis drove the development of ectopic neurons that formed at the expense of epidermis along the midlines. POU-IV, and MyTF to a lesser extent, also induced the neural conversion of nearly all epidermis cells outside the midlines when misexpressed. These results suggest that in C. intestinalis, MyTF, POU-IV, Amos, and NeuroD have a role in regulating the development of ESNs in the midlines that is mediated by Notch signaling.
