[
International Worm Meeting,
2007]
Stem cells are defined by their unlimited or prolonged capacity for self-renewal and ability to produce at least one differentiated cell type. Their decision between self-renewal and differentiation is governed by both intrinsic signals and extrinsic stimuli from the surrounding microenvironment, or niche. The niche for C. elegans germline stem cells is provided by the distal tip cell (DTC) since it is both necessary and sufficient for maintenance of cells in the mitotic region. The DTC controls germline stem cells by Notch signaling (Crittenden et al. 2003). Specifically, germ cells in the mitotic region express the GLP-1 Notch receptor and respond to the LAG-2 DSL ligand expressed by the DTC. However, there may be additional factors required in the DTC for LAG-2 signaling and maintenance of germline stem cells. We have taken several approaches to further dissect the molecular and cellular properties of the DTC that enable it to function as a niche for the germline stem cells. Using a candidate gene approach, we are screening for genes required in the DTC for fertility by tissue-specific RNAi. To both narrow down the list of candidate genes and to determine the gene expression profile of the DTC, we have used a microarray approach, enriching for DTC transcripts by immunoprecipitation of Flag-tagged PAB-1 (poly-A binding protein) with associated RNAs (Roy et al. 2002). To investigate the cellular characteristics of the DTC that may contribute its role as a stem cell niche, we made a panel of fluorescent protein markers to examine the subcellular structure of the DTC in vivo. These include markers for the nuclear envelope, endoplasmic reticulum, Golgi, endosomes, and plasma membrane. Using a membrane marker, we found that contact between the DTC niche and germ cells in the mitotic region is extensive and dynamic. The DTC extends membrane processes that surround adjacent germ cells. The intimate contact between the niche and germ cells may provide a mechanism to physically anchor the distal-most germ cells within the niche and/or provide more localized signaling to maintain the germline stem cells.
[
Development & Evolution Meeting,
2008]
A stem cell's decision between self-renewal and differentiation is governed by extrinsic stimuli from the surrounding microenvironment, or niche, as well as by intrinsic cues. In C. elegans, the distal tip cell (DTC) provides the niche for germline stem cells and maintains a "mitotic region" by Notch signaling (e.g. Kimble and Crittenden 2007). DTC number and dosage of the LAG-2 DSL ligand, which is expressed by the DTC, can affect the number of germ cells in the mitotic region (Dyan Vogel and Myon-Hee Lee). To investigate DTC niche function, we made a panel of fluorescent protein markers to visualize its subcellular structure in vivo. These include markers for the nuclear envelope, endoplasmic reticulum, Golgi, endosomes, and plasma membrane. Using membrane markers, we found that contact between the DTC niche and germ cells in the mitotic region is extensive. The DTC extends membrane processes that surround adjacent germ cells. The intimate contact between the niche and germ cells may provide a mechanism to physically anchor the distal-most germ cells within the niche and/or provide more localized signaling to maintain the germline stem cells. With a combination of DTC, sheath cell, and germ cell markers, we are examining the relationship between the extent of niche contact and the region of cells with stem cell potential. We are also using tissue-specific RNAi to test which genes are required in the DTC for regulation of germline stem cells.