Interactions of Multiple Signaling Pathways Generate Tail Patterning During the Development of Caenorhabditis elegans

Author: Jiang, Li (Lily)

Year: 1999

Degree: Dissertation (Ph.D.)

Advisor: Sternberg, Paul W.

Committee Members: Sternberg, Paul W.; Meyerowitz, Elliot M.; Fraser, Scott E.; Zinn, Kai George; Simon, Melvin I.

Option: Biology

DOI: 10.7907/qn4g-ce71

Abstract

The specification of a certain cell fate and cell function involves three fundamental questions. First, what genes control the specification of a certain cell fate? Second, how do multiple extrinsic and intrinsic factors interact to coordinate this developmental decision? Third, what genes regulate cellular behaviors and the exertion of cell functions? I addressed these developmental issues by studying the patterning of C. elegans tail.

In hermaphrodite tail, the specification of the P12 neuroectoblast fate involves three classes of genes. The conserved EGF signaling pathway is utilized for P12 fate specification, and the LIN-3 epidermal growth factor is an inductive signal to promote the P12 fate. Hox gene egl-5 is a downstream target of the lin-3/let-23 pathway in specifying P12 fate. Wnt pathway components lin-44 and lin-17 act synergistically with the EGF pathway in the specification of the P12 fate. The Wnt pathway may function early in development to regulate the competence of the cells to respond to the LIN-3 inductive signal.

A SPD neuron specific marker is used to study the terminal cell fate specification during C. elegans male spicule development. The specification of glial vs. neuronal cell fate in a canonical neurogenic lineage is rather dependent on Wnt signaling. Inactivation of the lin-17-mediated Wnt signaling pathway transforms the SPD sheath cell into its sister, the SPD neuron. A genetic screen identified a new mutant, son-1, which displays the same cell fate transformation. son-1 genetically interacts with lin-17 in several developmental processes. Cloning of son-1 revealed that it encodes an HMG1/2-like DNA binding protein. This result provides evidence for the specific in vivo functions of the HMG1/2-like proteins. SON-1 acts in the Wnt responding cells to facilitate gene transcription.

During spicule morphogenesis, the spicule neurons and sheath cells are dispensable while the socket cells are essential for spicule morphology. The two functional aspects of socket cells, spicule elongation and secretion of spicule cuticle, are genetically separable and are controlled by the FGF and TGF-β signaling pathways and a gene defined by the sy170 locus, respectively.

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