Abstract:

Notch-type signaling plays a fundamental role in regulating the development of metazoans. In the gonad of nematode Caenorhabditis elegans, the germline mitosis/meiosis decision is regulated by somatic gonadal cells, including the distal tip cell (DTC) and the proximal anchor cell (AC), via GLP-1/Notch signaling. Although this signaling has four main components, more have been isolated that regulate GLP-1 signaling activity, one of which is the ego-2 (e nhancer of glp-1 ) gene, a genetic enhancer of a glp-1 loss-of-function (lf) mutation. GLP-1 signaling also regulates embryonic development. Another Notch receptor in C. elegans, LIN-12, functions in the soma.

My dissertation research has focused on the molecular identification of the ego-2 gene, characterization of its molecular structure and functions, and description of its relationship with its paralog, alx-1, and other components of the GLP-1/LIN-12/Notch pathway. EGO-2 not only promotes GLP-1 signaling in both germline and embryonic development, but also positively regulates the Z1.ppp-Z4.aaa interaction via LIN-12 during somatic gonad development, suggesting that EGO-2 is a general regulator of Notch signaling. ego-2 activity is mainly required in the soma to promote germline proliferation, consistent with the genetic data showing that it acts upstream or in parallel with glp-1. The ego-2(lf) also causes Spe (Spe rmatogenesis) defect in the germ line and many other somatic phenotypes. Therefore, EGO-2 activity is involved in many aspects of development, which may or may not involve GLP-1/Notch signaling. EGO-2 and ALX-1 have opposite functions with respect to GLP-1 signaling in germline proliferation, but act in concert during spermatogenesis, suggesting their relationship is complex.

The EGO-2 protein is predicted to contain a Bro1 domain, which has been shown to be involved in endocytosis, a process which can positively regulate Notch signaling in many species. Based on our data, we hypothesize that in the DTC, as well as some other somatic gonadal and germ cells, EGO-2 functions in the endosomal process(es) to promote Notch signaling. To further analyze EGO-2 function, I first assembled a wildtype ego-2 hybrid genomic/cDNA construct, which can rescue some ego-2(lf) phenotypes. I tagged this construct with green fluorescent protein to examine the EGO-2 expression pattern in the future.