Fig. 1. Early gonadogenesis in wild-type and Sys mutant animals. See Kimble and Hirsh (Kimble and Hirsh, 1979) for more detail about wild type and see Miskowski et al. (Miskowski et al., 2001) for more detail about sys-1 mutants. (A) The gonadal primordium is morphologically indistinguishable in hermaphrodites and males (primordium symmetry represented by arrows beneath figure). The somatic gonadal precursors, Z1 and Z4, reside at the poles of the primordium; germline precursors, Z2 and Z3 (not shown), reside centrally between Z1 and Z4. (B) Z1 and Z4 divide asymmetrically in both sexes. When first born, their daughters are positioned with the same symmetry as the earlier primordium (arrows point towards proximal regions). In hermaphrodites, this symmetry is retained throughout gonadogenesis. (C) In males, the Z1/Z4 daughters rearrange (left figure, curved arrows) to generate an asymmetric structure (right figure, single arrow points towards proximal pole). (D) Fates of Z1/Z4 daughters in wild-type hermaphrodites. Z1.a and Z4.p give rise to DTCs (red), which have leader function and control germline proliferation. Z1.p and Z4.a give rise to AC/VU cells. Lateral signaling results in selection of one precursor as an AC (dark blue) and the other as a ventral uterine precursor (VU), one of nine somatic gonadal blast cells (light blue) that form the somatic gonadal primordium in hermaphrodites (SPh). gl, germline. (E) Fates of Z1/Z4 daughters in wild-type males (and most sys-1 mutant males). Z1.a and Z4.p give rise to DTCs (blue), which control germline proliferation, but do not have leader function. Z1.p and Z4.a give rise to cells with potential to become either a linker cell (LC) or a vas deferens blast cell (VD). Lateral signaling results in selection of one of these precursors as an LC (red), which has leader function; the other becomes a VD, one of seven somatic gonadal blast cells (light blue) that form the somatic gonadal primordium (SPm). gl, germ line. (F) Fates of Z1/Z4 daughters in sys-1 mutant hermaphrodites. All four Z1/Z4 daughters can give rise to AC/VU cells, and no DTCs are made. Furthermore, no SPh forms; instead, a ring of somatic gonadal cells encircles the germline (gl) at late L2/early L3. (G) Fates of Z1/Z4 daughters in 30% of sys-1 mutant males. Z1 and Z4 do not make DTCs; instead extra LCs and extra somatic gonadal cells are observed by late L2.
