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Fig. 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unpublished).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).
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