Figure 5.
fkh-6 acts downstream of
tra-1 in the early gonad. (A) Simplified version of C. elegans sex-determination pathway (Hodgkin et al., 1986). The ratio of X chromosomes to autosomes (Madl and Herman, 1979) signals via a regulatory cascade and regulates
tra-1, such that high
tra-1 activity promotes female somatic development and represses male development. Early genes in the pathway and some genetic interactions are not shown. (B) Gonad is severely underdeveloped in
fkh-6;
tra-1 XX adult (broken line indicates gonadal boundary). (C-E) Comparison of Z4 daughters in
fkh-6,
tra-1, and
fkh-6;
tra-1 mutants. Z4.a and Z4.p are similar in size in
fkh-6(
q641) XO L1 male, whereas Z4.a is larger than Z4.p in
tra-1(
e1099) XX L1 pseudomale. In
fkh-6;
tra-1 double mutant XX L1 pseudomales, Z4.a and Z4.p are similar in size. Z1 daughters (out of focal plane) have the same size polarities. (F) Summary of early events of gonadogenesis in
fkh-6 and
tra-1 single mutants and
fkh-6;
tra-1 double mutants. Relative sizes of Z1 and Z4 daughters and male-specific anterior migration of Z1.p and Z4.a were scored. Eight Z1/Z4 divisions were scored for each mutant class (
fkh-6 XO,
tra-1 XX, and
fkh-6;
tra-1 XX). (G,H) DIC and fluorescence images showing
tra-1::gfp expression in the gonadal primordium of
fkh-6(
q641) XO L1 male. Arrowhead indicates Z4. Reporter also is expressed in Z1, which is out of focal plane. Other brightly expressing nuclei are intestinal. (I,J) DIC and fluorescence images showing
fkh-6(pro)::gfp expression in the gonadal primordium of
tra-1(
e1099) XX L1 pseudomale. Z1 (arrow) and Z4 daughters (arrowheads) express
fkh-6::gfp. Z4 daughters are displaced to the dorsal side of the gonad, a common
tra-1 defect (L.M. and J.K., unpublished). (K) Summary of
fkh-6::gfp and
tra-1::gfp expression. Wild-type timing of Z1/Z4 division and anterior migration of Z1.p/Z4.a is indicated at top (unbroken lines). Periods of GFP reporter expression in wild-type and mutant transgenic animals are indicated (broken-ended lines indicate imprecision in timing of expression).