Shedl, T. & Kimble, J. fog-2, a germ-line specific sex determination gene required for hermaphrodite spermatogenesis in Caenorhabditis elegans. Genetics 119, 43-61

Laboratory of Cell and Molecular Biology, Graduate School, Univesity of Wisconsin, Madison 53706.
Genetics (Impact Factor: 5.96). 06/1988; 119(1):43-61.
Source: PubMed


This paper describes the isolation and characterization of 16 mutations in the germ-line sex determination gene fog-2 (fog for feminization of the germ line). In the nematode Caenorhabditis elegans there are normally two sexes, self-fertilizing hermaphrodites (XX) and males (XO). Wild-type XX animals are hermaphrodite in the germ line (spermatogenesis followed by oogenesis), and female in the soma. fog-2 loss-of-function mutations transform XX animals into females while XO animals are unaffected. Thus, wild-type fog-2 is necessary for spermatogenesis in hermaphrodites but not males. The fem genes and fog-1 are each essential for specification of spermatogenesis in both XX and XO animals. fog-2 acts as a positive regulator of the fem genes and fog-1. The tra-2 and tra-3 genes act as negative regulators of the fem genes and fog-1 to allow oogenesis. Two models are discussed for how fog-2 might positively regulate the fem genes and fog-1 to permit spermatogenesis; fog-2 may act as a negative regulator of tra-2 and tra-3, or fog-2 may act positively on the fem genes and fog-1 rendering them insensitive to the negative action of tra-2 and tra-3.

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Available from: Tim Schedl, Aug 05, 2015
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    • "After 48 hours of recovery, worms displayed stacked oocytes (arrowhead in 31°C 48 hours) in one or both gonadal arms. Stacked oocytes are characteristic of a gonad that is producing oocytes but no longer has functional sperm to induce oocyte maturation and ovulation [40], [42], [43]. After 72 hours of recovery, almost all of the worms treated at 31°C had stacked oocytes in both gonads. "
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    ABSTRACT: To ensure long-term reproductive success organisms have to cope with harsh environmental extremes. A reproductive strategy that simply maximizes offspring production is likely to be disadvantageous because it could lead to a catastrophic loss of fecundity under unfavorable conditions. To understand how an appropriate balance is achieved, we investigated reproductive performance of C. elegans under conditions of chronic heat stress. We found that following even prolonged exposure to temperatures at which none of the offspring survive, worms could recover and resume reproduction. The likelihood of producing viable offspring falls precipitously after exposure to temperatures greater than 28°C primarily due to sperm damage. Surprisingly, we found that worms that experienced higher temperatures can recover considerably better, provided they did not initiate ovulation. Therefore mechanisms controlling this process must play a crucial role in determining the probability of recovery. We show, however, that suppressing ovulation is only beneficial under relatively long stresses, whereas it is a disadvantageous strategy under shorter stresses of the same intensity. This is because the benefit of shutting down egg laying, and thus protecting the reproductive system, is negated by the cost associated with implementing this strategy - it takes considerable time to recover and produce offspring. We interpret these balanced trade-offs as a dynamic response of the C. elegans reproductive system to stress and an adaptation to life in variable and unpredictable conditions.
    Full-text · Article · Aug 2014 · PLoS ONE
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    • "More importantly, fem-3(q96) sperm-only adults raised at 22° possessed SP56 but not RME-2 (Figure 1B), and fog-2(q71) oocyte-only adults raised at 22° had RME-2 but not SP56 (Figure 1C). Yet these two XX mutants have morphologically indistinguishable somatic tissues, including the somatic gonad (Barton et al. 1987; Schedl and Kimble 1988). We note that use of mutants was essential for this analysis and caution that a mutant transcriptome may include changes not found in wild-type and that XX sperm are only a proxy for XO sperm. "
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    ABSTRACT: The nematode Caenorhabditis elegans is an important model for studies of germ cell biology, including the meiotic cell cycle, gamete specification as sperm or oocyte and gamete development. Fundamental to those studies is a genome-level knowledge of the germline transcriptome. Here we use RNA-Seq to identify genes expressed in isolated XX gonads, which are roughly 95% germline and 5% somatic gonadal tissue. We generate data from mutants making either sperm [fem-3(q96)] or oocytes [fog-2(q71)], both grown at 22°. Our dataset identifies a total of 10,754 mRNAs in the polyadenylated transcriptome of XX gonads, with 2,748 enriched in spermatogenic gonads, 1,732 enriched in oogenic gonads and the remaining 6,274 not enriched in either. These spermatogenic, oogenic and gender-neutral gene datasets compare well with those of earlier studies, but double the number of genes identified. A comparison of the additional genes found in our study with in situ hybridization patterns in the Kohara database suggests that most are expressed in the germline. We also query our RNA-Seq data for differential exon usage and find 351 mRNAs with sex-enriched isoforms. We suggest that this new dataset will prove useful for studies focusing on C. elegans germ cell biology.
    Full-text · Article · Jul 2014 · G3-Genes Genomes Genetics
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    • "Outcrossing rates are be calculated as twice male frequencies (r = 2 m, [33]). Male fitness assays involved placing an equal proportion of late L4 staged wild type experimental and GFP tester males in competition for mating and fertilization of fog-2(q71/q71) females (strain JK574; [62]), during the 24 h preceding the usual passage of experimental evolution. This assay was thus also a head-to-head competition assay, as the assay of population-wide fitness and hermaphrodite fitness. "
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    ABSTRACT: Background Why most organisms reproduce via outcrossing rather than selfing is a central question in evolutionary biology. It has long ago been suggested that outcrossing is favoured when it facilitates adaptation to novel environments. We have previously shown that the experimental evolution of increased outcrossing rates in populations of the male-hermaphrodite nematode Caenorhabditis elegans were correlated with the experimental evolution of increased male fitness. However, it is unknown whether outcrossing led to adaptation, and if so, which fitness components can explain the observed increase in outcrossing rates. Results Using experimental evolution in six populations with initially low standing levels of genetic diversity, we show with head-to-head competition assays that population-wide fitness improved during 100 generations. Since outcrossing rates increased during the same period, this result demonstrates that outcrossing is adaptive. We also show that there was little evolution of hermaphrodite fitness under conditions of selfing or under conditions of outcrossing with unrelated tester males. We nonetheless find a positive genetic correlation between hermaphrodite self-fitness and population-wide fitness, and a negative genetic correlation between hermaphrodite mating success and population-wide fitness. These results suggest that the several hermaphrodite traits measured are fitness components. Tradeoffs expressed in hermaphrodites, particularly noticed between self-fitness and mating success, may in turn explain their lack of change during experimental evolution. Conclusions Our findings indicate that outcrossing facilitates adaptation to novel environments. They further indicate that the experimental evolution of increased outcrossing rates depended little on hermaphrodites because of fitness tradeoffs between selfing and outcrossing. Instead, the evolution of increased outcrossing rates appears to have resulted from unhindered selection on males.
    Full-text · Article · Jun 2014 · BMC Evolutionary Biology
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