Germline stem cell differentiation in C. elegans is controlled by
glp-1 Notch signaling. Cell fate regulator GLD-1 is sufficient to induce meiotic entry and expressed at high level during meiotic prophase, inhibiting mitotic gene activity.
glp-1 signaling and other regulators control GLD-1 levels post-transcriptionally (low in stem cells, high in meiotic prophase) but many aspects of GLD-1 regulation are uncharacterized, including the link between
glp-1-mediated transcriptional control and post-transcriptional GLD-1 regulation. We established a sensitive assay to quantify GLD-1 levels across an ~35 cell diameter field where distal germline stem cells differentiate proximally into meiotic prophase cells in the adult C. elegans hermaphrodite and applied the approach to mutants in known or proposed GLD-1 regulators. In wild type GLD-1 levels elevated ~20 fold in a sigmoidal pattern. We found that two direct transcriptional targets of
glp-1 signaling,
lst-1 and
sygl-1, were individually required for repression of GLD-1. We determined that
lst-1 and
sygl-1 act in the same genetic pathway as known GLD-1 translational repressor
fbf-1, while
lst-1 also acts in parallel to
fbf-1, linking
glp-1-mediated transcriptional control and post-transcriptional GLD-1 repression. Additionally, we estimated the position in wild type gonads where germ cells irreversibly commit to meiotic development based on GLD-1 levels in worms where
glp-1 activity was manipulated to cause an irreversible fate switch. Analysis of known repressors and activators, as well as modeling the sigmoidal accumulation pattern, indicated that regulation of GLD-1 levels is largely regional, which we integrated with the current view of germline stem cell differentiation.