The TRIM-NHL protein LIN-41 and the OMA RNA-binding proteins antagonistically control the prophase-to-metaphase transition and growth of Caenorhabditis elegans oocytes.
Bottom Line: Instead, these cells activate CDK-1, enter M phase, assemble spindles, and attempt to segregate chromosomes.Translational derepression of the CDK-1 activator CDC-25.3 appears to contribute to premature M-phase entry in lin-41 mutant oocytes.Genetic and phenotypic analyses indicate that LIN-41 and OMA-1/2 exhibit an antagonistic relationship, and we suggest that translational regulation by these proteins could be important for controlling and coordinating oocyte growth and meiotic maturation.
Affiliation: Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455.Show MeSH
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Mentions: Our screen permitted the isolation of temperature-sensitive alleles, and we identified one lin-41 allele with temperature-sensitive sterility. lin-41(tn1487ts) animals are 100% fertile at 15° but almost completely sterile at 25° (Table 1). At the intermediate temperature of 22°, lin-41(tn1487ts) animals are mostly fertile but display reduced fecundity and embryonic viability, resulting in dramatically reduced brood sizes. These defects are likely caused by poor-quality oocytes. lin-41(tn1487ts) oocytes at 22° are often small and sometimes disorganized, but can make a relatively normal transition from pachytene into diakinesis, unlike lin-41(n2914) oocytes (compare Figure 7, D–I; Figure 8, I–L; and Figure S3G). Furthermore, the progeny of lin-41(tn1487ts) XX hermaphrodites raised at 22° are more frequently XO males, suggesting that there are elevated levels of chromosome nondisjunction during oocyte meiosis at this temperature (Table 1). Male frequency is ∼10- to 20-fold higher than in the wild type (Table 1) (Hodgkin et al. 1979; Rose and Baillie 1979). Increased numbers of males are also observed among the progeny of lin-41 alleles isolated as intragenic suppressors of lin-41(tn1487ts) sterility at 25° (Table 1). Males are most evident among the progeny of two relatively weak suppressors of tn1487ts with amino acid changes in the first B-box zinc-finger domain (tn1487tstn1536 and tn1487tstn1539), but are also notable among the progeny of two stronger suppressors with amino acid changes in the NHL-repeat domain (tn1487tstn1515 and tn1487tstn1516). It is presently unknown how these second-site mutations in the lin-41 gene suppress the temperature-sensitive sterility of tn1487ts. Temperature-sensitive alleles can cause protein destabilization and degradation at restrictive temperatures, but lin-41(tn1487ts) does not reduce LIN-41 protein accumulation in adult hermaphrodites raised at 25° (Figure 3L). Furthermore, LIN-41 expression and localization is relatively normal in lin-41(tn1487ts) germ lines at both 22° and 25°, although there appears to be a gradual, rather than dramatic, increase in LIN-41 protein levels during pachytene at both temperatures (Figure S3G; C. Spike, unpublished results). It is possible, therefore, that tn1487ts and its intragenic suppressor mutations identify LIN-41 residues with critical roles in regulating LIN-41 RNA binding or mRNA translation activities. Consistent with this possibility, the lin-41(tn1487ts) mutation in the NHL-repeat domain derepresses translation of several 3′ UTR reporter constructs, including the OMA mRNA targets, zif-1 and cdc-25.3 (Spike et al. 2014).
Affiliation: Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455.