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. 2016 Jan 11;202(3):1085–1103. doi: 10.1534/genetics.115.185678

Figure 9.

Figure 9

Control of GLD-1 accumulation in coordination with germline stem cell differentiation. (A) Model for control of GLD-1 accumulation in the adult hermaphrodite is split into regions called GLD-1 repression and GLD-1 activation. Approximate positions of stem cell pool, progenitors completing their current mitotic cell cycle (terminal mitosis), meiotic S pool, and leptotene/zygotene region are based on previous work (Fox and Schedl 2015). Switch, germ cells exit GLD-1 repression and enter the activation region in coordination with germ cell commitment to meiotic development. IC, irreversible commitment, as experimentally defined by glp-1(bn18) temperature shift, occurs after germ cell commitment and entry into GLD-1 activation. CDmaxR, where rate of GLD-1 accumulation change is maximum closely follows IC as germ cells progress toward sME and eME, where GLD-1 levels plateau. (B) Genetic control of GLD-1 repression region. Germ cells in GLD-1 repression are mostly stem cells, GLD-1 modestly accumulates, and GLD-1 accumulation change is equal or, more proximally, greater than 0. Reduction of GLP-1 signaling activity along the DTC plexus could account for the modestly increased GLD-1 accumulation. (C) Genetic control of GLD-1 activation region is split into two subregions: (1) GLD-1 rapidly accumulates, progenitors complete terminal mitosis and/or initiate meiotic S, and GLD-1 accumulation change is maximum/much greater than 0. (2) GLD-1 levels plateau at peak once all germ cells enter meiosis, and GLD-1 accumulation change = 0. Genes that promote GLD-1 accumulation act in both subregions, but unknown gene(s), Y, downregulates GLD-1 accumulation in subregion 2. Although we measured GLD-1 steady-state levels, we infer that final GLD-1 accumulation output is the ratio of GLD-1 synthesis and GLD-1 turnover, such that when GLD-1 accumulation is >0, then synthesis exceeds turnover, and when GLD-1 accumulation = 0, then GLD-1 synthesis and turnover are equal. (D) GLD-1 levels within germ cells of the same gcd position are similar, even though germ cells are at different stages of the mitotic cell cycle (S or G2), in meiotic S, or in leptotene/zygotene, the proportions of which depend on distance from the distal tip. Germ cells in M phase are low frequency and G1 is short or nonexistent (Fox et al. 2011) therefore not shown.