Investigating the coordinate regulation of stem cell proliferation and differentiation by FBF proteins

Balance of stem cell proliferation and differentiation is important for maintaining tissue homeostasis, and uncovering the mechanisms regulating the balance of proliferation and differentiation of stem cells helps us understand the causative factors for ageing, cancer and various degenerative disorders. Pumilio and FBF (PUF) family RNA-binding proteins are conserved mRNA regulators controlling stem cell development in eukaryotes. FBF-1 and FBF-2, two PUF family proteins in C. elegans, are expressed in the mitotic region of the germline and are important for maintaining germline stem cells. FBF-1 and FBF-2 are very similar in primary sequence and share most of the target mRNAs, but they localize to distinct RNA granules and have different effects on target mRNAs and stem cell maintenance. This dissertation studies how FBFs mediate the coordinate regulation of germline stem cell proliferation and differentiation and the mechanisms allowing differential activities of FBF homologs in stem cells. This work has, for the first time, demonstrated that FBF-1 and FBF-2 have distinct effects on stem cell dynamics: FBF-1 restricts the rate of stem cell meiotic entry, while FBF-2 promotes both rates of proliferation and meiotic entry. Based on our findings, we propose that FBFs’ coordinate regulation contributes to maintaining the balance of stem cell proliferation and differentiation in the germline. In addition, this work has also identified CCR4-NOT deadenylation machinery as an FBF-1-specific cofactor, DLC-1 as an FBF-2-specific cofactor, and five splicing factors as potential specific cofactors for FBF-2. PUF proteins are conserved stem cell regulators in eukaryotes, from yeast to humans, and they share conserved mechanisms that affect stem cell proliferation and differentiation. This dissertation offers new mechanistic insights into PUF function in C. elegans that are likely relevant for other organisms