CEH-28 and ZAG-1 Function in Regulating Differentiation of the C. elegans M4 Pharyngeal Neuron

M4 is a multifunctional neuron in the C. elegans pharynx that can both stimulate peristaltic contractions of the muscles in the pharyngeal isthmus and function systemically to regulate an enhanced sensory response under hypoxic conditions. In this work, we extend our understanding of M4 function by investigating the roles of two transcription factors, CEH-28 and ZAG-1. We find that CEH-28 regulates a neuroendocrine signaling function of the M4 neuron by activating expression of the family gene dbl-1 gene, which encodes a TGF-β ligand, egl-17 gene, which encodes the FGF family ligand and the FMRF family gene, flp-5. DBL-1 secreted from M4 functions in an R-Smad independent TGF-β signaling pathway to affect g1 gland cell morphology. ZAG-1 functions in M4 and activates isthmus muscle contractions required for normal feeding. zag-1(hd16) null mutants completely lack isthmus peristalsis and are defective in serotonin signaling. Furthermore, ZAG-1 acts as an upstream regulator of ceh-28 and its downstream targets in M4, and regulates additional aspects of M4 differentiation by activating expression of M4 markers ser-7b and flp-2. Taken together, my work identifies a new hierarchical gene regulatory network in the M4 neuron, which regulates signaling and differentiation, and also provides insights regarding how multifunctionality of motor neurons is regulated.