UC San Diego

This dissertation explores the roles of the Tribbles pseudokinase NIPI-3 and its downstream signaling in regulating C. elegans development. It was previously reported that in the absence of NIPI-3, expression of the stress-response transcription factor CEBP-1 increases significantly, leading to upregulation of the PMK-1/p38 MAP kinase pathway and developmental arrest. Moreover, the developmental arrest of nipi-3(0) animals is rescued by loss of function in cebp-1. This genetic interaction formed the basis for a forward genetic screen where, through random mutagenesis, genes that are necessary for the signaling downstream of NIPI-3 can be identified, as they will rescue animal development. The genes identified from this forward genetic screen and their signaling pathways are the subject of my dissertation. First, I isolated many alleles in two genes, CEBP-1 and MAK-2, which allowed for deeper analysis of the residues required for protein function. With further interrogation using genome-editing, I identified a novel domain that is critical for the in vivo function of CEBP-1. This domain is not only required for CEBP-1 function in development, but also axon regeneration. By protein structural prediction, I found that the region containing this unique domain has a predicted propensity to form alpha helices. Second, using a transcriptional reporter of sek-1 transcription as a readout of p38 MAPK activation by CEBP-1, I found novel positive regulation from pmk-1/MAPK and mak-2/MAPKAPK to sek-1/MAPKK transcription. It also appears that SEK-1 activity may activate its own gene transcription, suggesting another positive possible feedback loop in this pathway. Finally, I describe a collaborative study revealing that histone deacetylation and N-terminal acetylation are involved in the regulation of development in C. elegans. We found that a gain of function mutation within the histone deacetylase hda-4 prevents developmental arrest of nipi-3(0) animals via transcriptional regulation of sek-1/MAPKK. We also found that loss of function of any of the components of the N-acetyltransferase C (NatC) complex (natc-1, natc-2, or natc-3) prevents developmental arrest of nipi-3(0) animals, partially via regulation of the PMK-1 pathway, and partially via a parallel pathway. Altogether, my thesis work has contributed to the understanding of the intricate regulation of p38 MAPK pathway activity during C. elegans development.