Multiple mechanisms cooperate to control PUF protein FBF-1 and FBF-2 accumulation in Caenorhabditis elegans germline

The RNA-binding proteins, FBF-1 and FBF-2 (FBFs) are essential regulators of germline stem cell maintenance in Caenorhabditis elegans, yet the mechanisms controlling their protein abundance remain poorly defined. We implicate the ubiquitin-proteasome system in limiting FBF accumulation within mitotic stem cells and identify a C-terminal peptide of FBF-2, termed VR4, that functions as a degron to promote protein clearance. Through a targeted screen, we define a network comprising fourteen genes that constrain FBF levels in germline progenitor cells, affecting both FBF-1 and FBF-2. While VR4 mediates degradation by a subset of FBF regulators, additional degrons or indirect mechanisms also limit FBF levels. Several FBF regulators operate in a context-dependent manner to mediate FBF turnover. Together, this work reveals a multifaceted regulatory network that tightly controls FBF protein levels in mitotic germline cells, preventing aberrant accumulation and enabling responses to developmental and physiological cues.