ego-1 and germline proliferation 1 EGO-1, a putative RNA-directed RNA polymerase, promotes germline proliferation in parallel with GLP-1/Notch signaling and regulates the spatial organization of nuclear pore complexes and germline P granules in C. elegans

1 EGO-1, a putative RNA-directed RNA polymerase, promotes germline proliferation in parallel with GLP-1/Notch signaling and regulates the spatial organization of nuclear pore complexes and germline P granules in C. elegans ego-1 and germline proliferation 2 ego-1 and germline proliferation ego-1 and germline proliferation 3 ABSTRACT C. elegans EGO-1, a putative cellular RNA-directed RNA polymerase, promotes several aspects of germline development, including proliferation, meiosis, and gametogenesis, and ensures a robust response to RNA interference. In C. elegans, GLP-1/Notch signaling from the somatic gonad maintains a population of proliferating germ cells, while entry of germ cells into meiosis is triggered by the GLD-1 and GLD-2 pathways. GLP-1 signaling prevents germ cells from entering meiosis by inhibiting GLD-1 and GLD-2 activity. We originally identified the ego-1 gene based on a genetic interaction with glp-1. Here, we investigate the role of ego-1 in germline proliferation. Our data indicate that EGO-1 does not positively regulate GLP-1 protein levels or GLP-1 signaling activity. Moreover, GLP-1 signaling does not positively regulate EGO-1 activity. EGO-1 does not inhibit expression of GLD-1 protein in the distal germ line. Instead, EGO-1 acts in parallel with GLP-1 signaling to influence the proliferation vs. meiosis fate choice. Moreover, EGO-1 and GLD-1 act in parallel to ensure germline health. Finally, the size and distribution of nuclear pore complexes and perinuclear P granules are altered in the absence of EGO-1, effects that disrupt germ cell biology per se and probably limit germline growth. ego-1 and germline proliferation 4 EGO-1, a putative cellular RNA-directed RNA polymerase (RdRP), is required for diverse aspects of germline function in C. elegans (Qiao et al. 1995; Smardon et al. 2000). The ego-1 gene was first identified because it interacts genetically with the Notch/GLP-1 signaling pathway that maintains germline proliferation (Qiao et al. 1995). However, ego-1 mutations affect not only germline proliferation, but also early meiosis and gametogenesis, suggesting that ego-1 activity is important for a variety of germline processes (Qiao et al. 1995; Smardon et al. 2000). Members of the RdRP family are implicated in RNA silencing phenomena in diverse organisms and in assembly of heterochromatin (reviewed by Meister and Tuschl 2004; Lippman and Martienssen 2004; Grewal and Rice 2004). The specific role of RdRP in these processes remains unclear. In vitro RdRP activity has been demonstrated for Neurospora QDE-1 and S. pombe RdP1 (Makayev and Bamford 2002; Motamedi et al 2004). Oher RdRPs, including EGO-1, are assumed …