Collaboration between a Conserved RNA-Binding Protein and a Specific Protein Partner Restricts Stem Cell Differentiation in the Germline of C. Elegans

An important question in stem cell biology is understanding the molecular factors that maintain stemness. The cells that remain in a proliferative state at the distal tip produce daughters that differentiate into mature gametes as they progress proximally. The stem cell niche is controlled in part by the notch signaling pathway, but the molecular details are opaque. Here we address the role of a recently discovered gene lst-1 and its interaction with FBF-2. FBF maintains the stem cell pool in C. elegans, but we don’t understand the mechanisms involved. LST-1 and FBF are downstream targets of Notch signaling. We studied the physical interaction between LST-1 and FBF to identify the amino acid residues that are important for interaction. Leucine at 153 in LST1 and Tyrosine at 479 in FBF-2 are required for the interaction to take place. The site of interaction on FBF is shared between multiple protein partners. To determine if the interaction between FBF and LST-1 is relevant in animals, we applied CRISPR genome editing to incorporate the L153A mutation. Gld-1 is an mRNA target of FBF in the stem cell region. We measured GLD-1 protein abundance in the absence of either lst-1 or sygl-1 or both. We see that there is much higher expression of GLD-1 protein when both lst-1 and sygl-1 are absent, suggesting a lack of repression by FBF. Similar results were observed in the case of our LST L153A mutant worm. This makes us believe that LST-1 facilitated repression by FBF. We envisage that this knowledge provides an essential step towards the discovery of repressive mechanisms through which LST-1 engages mRNA destabilization, decay, or localization machinery.