Abstract
Stem cell systems are essential for development and maintenance of polarized tissues. Intercellular signaling pathways control stem cell systems, where niche cells signal stem cells to maintain the stem cell fate/self renewal and inhibit differentiation. In the C. elegans germline stem cell system, GLP-1 Notch signaling specifies the stem cell fate. However, the downstream transcriptional targets of GLP-1 signaling that mediate the stem cell fate have not been fully enumerated. We employed a genome-wide approach to uncover transcriptional targets of GLP-1 signaling - the intersection of genes identified as directly bound by LAG-1, the C. elegans Notch pathway sequence-specific DNA binding protein, from ChIP-seq experiments, with genes identified as requiring GLP-1 signaling for RNA accumulation, from RNA-seq analysis. lst-1 and sygl-1, genes previously identified as transcriptional targets from a bioinformatic candidate gene approach, were bound by germline LAG-1 and their expression dependent on glp-1 and germline lag-1 activity. No additional genes were identified as both bound by LAG-1 and whose mRNA level was dependent on glp-1 and lag-1. Genes were identified as likely secondary effects of GLP-1 signaling with the properties that their glp-1 dependent mRNA accumulation could be explained by a requirement for lst-1 and sygl-1 activity and their lack of LAG-1 binding. Furthermore, glp-1 dependent peak accumulation of FBF-2, which promotes the stem cell fate, is explained by a requirement for lst-1 and sygl-1 activity. Finally, we showed that lag-1 is germline autonomously required for the stem cell fate and that elevated LAG-1 accumulation is spatially limited to the stem cell region by posttranscriptional regulation that, in part, requires lst-1 and sygl-1. These findings are consistent with the possibility that lst-1 and sygl-1 are the sole germline GLP-1 signaling mRNA transcriptional targets, which largely or completely mediate the stem cell fate.
