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First published online 6 July 2005
doi: 10.1242/dev.01921
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1 Cellular and Molecular Biology Training Program, University of
Wisconsin-Madison, Madison, WI 53706, USA
2 Department of Biochemistry, University of Wisconsin-Madison, Madison, WI
53706, USA
3 Howard Hughes Medical Institute, University of Wisconsin-Madison, Madison, WI
53706, USA
* Author for correspondence (e-mail: jekimble{at}facstaff.wisc.edu)
Accepted 27 May 2005
RNA-binding proteins control germline development in metazoans. This work
focuses on control of the C. elegans germline by two RNA-binding
proteins: FOG-1, a CPEB homolog; and FBF, a PUF family member. Previous
studies have shown that FOG-1 specifies the sperm fate and that FBF promotes
proliferation. Here, we report that FOG-1 also promotes proliferation. Whereas
fbf-1 fbf-2 double mutants make 
120 germ cells, fog-1; fbf-1
fbf-2 triple mutants make only 10 germ cells. The triple mutant
germline divides normally until early L2, when germ cells prematurely enter
meiosis and begin oogenesis. Importantly, fog-1/+; fbf-1
fbf-2 animals make more germ cells than fbf-1 fbf-2 double
mutants, demonstrating that one dose of wild-type fog-1
promotes proliferation more effectively than two doses – at least in the
absence of FBF. FOG-1 protein is barely detectable in proliferating germ
cells, but abundant in germ cells destined for spermatogenesis. Based on
fog-1 dose effects, together with the gradient of FOG-1 protein
abundance, we suggest that low FOG-1 promotes proliferation and high FOG-1
specifies spermatogenesis. FBF binds specifically to regulatory elements in
the fog-1 3'UTR, and FOG-1 increases in animals lacking FBF.
Therefore, FBF represses fog-1 expression. We suggest that FBF
promotes continued proliferation, at least in part, by maintaining FOG-1 at a
low level appropriate for proliferation. The dose-dependent control of
proliferation and cell fate by FOG-1 has striking parallels with
Xenopus CPEB, suggesting a conserved mechanism in animal
development.
Key words: C. elegans, Germline, FBF, FOG-1, CPEB, Sex determination, Mitosis, Meiosis, Sperm, Oocyte
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