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Judith Kimble - One of the best experts on this subject based on the ideXlab platform.
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germ line regulation of the caenorhabditis elegans sex determining gene tra 2
Developmental Biology, 1998Co-Authors: Patricia E Kuwabara, Peter G Okkema, Judith KimbleAbstract:The Caenorhabditis elegans sex-determining gene tra-2 promotes female development of the XX Hermaphrodite soma and germ line. We previously showed that a 4.7-kb tra-2 mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of the tra-2 locus. This paper focuses on the germ-line activity and regulation of tra-2. First, we characterize a 1.8-kb tra-2 mRNA, which is Hermaphrodite-specific and germ-line-dependent. This mRNA encodes TRA-2B, a protein identical to a predicted intracellular domain of TRA-2A. We show that the 1.8-kb mRNA is oocyte-specific, suggesting that it is involved in germ-line or embryonic sex determination. Second, we identify a tra-2 maternal effect on brood size that may be associated with the 1.8-kb mRNA. Third, we investigate seven dominant tra-2(mx) (for mixed character) mutations that sexually transform Hermaphrodites to females by eliminating Hermaphrodite spermatogenesis. Each of the tra-2(mx) mutants possesses a nonconserved missense change in a 22-amino-acid region common to both TRA-2A and TRA-2B, called the MX region. We propose that the MX region mediates a posttranslational regulation of tra-2 essential for the onset of Hermaphrodite spermatogenesis. Finally, we discuss aspects of tra-2 function and regulation that are specific to the unusual control of cell fate in the Hermaphrodite germ line. © 1998 Academic Press
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translational regulation of tra 2 by its 3 untranslated region controls sexual identity in c elegans
Cell, 1993Co-Authors: E B Goodwin, Peter G Okkema, Thomas C Evans, Judith KimbleAbstract:Summary C. elegans Hermaphrodites make sperm and then oocytes in an otherwise female animal. Gain-of-function mutations in the sex-determining gene tra-2 (tra-2(gf)) transform Hermaphrodites into females (spermless Hermaphrodites). The tra-2(gf) mutations map to a perfect direct repeat in the 3′ untranslated region; each repeat is called a direct repeat element (DRE). Three experiments demonstrate that DREs repress tra-2 at the translational level. First, tra-2(gf) mRNAs are associated with larger polysomes than are their wild-type counterparts. Second, translation of a reporter RNA is inhibited by DREs. Third, disruption of DREs does not increase tra-2 mRNA levels. An RNA binding activity specifically associates with the DREs. We propose that tra-2 translation is inhibited by association of an RNA binding-factor with the DREs and that this translational control is essential for development of C. elegans as a Hermaphrodite/male species.
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control of the sperm oocyte switch in caenorhabditis elegans Hermaphrodites by the fem 3 3 untranslated region
Nature, 1991Co-Authors: Julie Ahringer, Judith KimbleAbstract:IN the Caenorhabditis elegans Hermaphrodite germ line, sperm and then oocytes are made from a common pool of germ-cell precursors. The decision to differentiate as a sperm or an oocyte is regulated by the sex-determining gene,fem-3. Expression of fem-3 in the Hermaphrodite germ line directs spermatogenesis and must be negatively regulated to allow the switch to oogenesis1,2. In adult Hermaphrodites (which are producing oocytes), mostfem-3 RNA is found in the germ line3, consistent with both the requirement for fem-3 in Hermaphrodite spermatogenesis and the maternal effects of fem-3 on embryonic sex determination1,2Whereas loss-of-function mutants in fem-3 produce only oocytes, Hermaphrodites carrying any of nine fem-3 gain-of-function (gf) mutations make none; instead sperm are produced continuously and in vast excess over wild-type amounts1Genetic analyses suggest that fem-3(gf) mutations have escaped a negative control required for the switch to oogenesis1. Here we report that all nine fem-3(gf) mutants carry sequence alterations in the fem-3 3′ untranslated region (3′ UTR). There is no increase in the steady-state level of fem-3(gf) RNA over wild-type, but there is an increase in the polyadenylation of fem-3(gf) RNA that is coincident with the unregulated fem-3 sactivity. Results of a titration experiment support the hypothesis that a regulatory factor may bind the fem-3 3′ UTR. We speculate that fem-3 RNA is regulated through its 3′ UTR by binding a factor that inhibits translation, and discuss the idea that this control may be part of a more general regulation of maternal RNAs.
J. Antonio Baeza - One of the best experts on this subject based on the ideXlab platform.
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Population dynamics, sex ratio and size at sex change in a protandric simultaneous Hermaphrodite, the spiny shrimp Exhippolysmata oplophoroides
Marine Biology, 2010Co-Authors: J. Antonio Baeza, A. A. Braga, L. S. López-greco, Maria Lucia Negreiros-fransozo, E. Pérez, Adilson FransozoAbstract:One of the main goals of sex allocation theory is understanding sex ratio evolution. However, theoretical studies predicting sex ratios in species with unusual sexual systems, such as protandric simultaneous (PS) hermaphroditism, are rare. In PS Hermaphrodites, juveniles first develop into functional males that mature into simultaneous Hermaphrodites later in life. Here, we report on the sex ratio (males/males + Hermaphrodites) in the PS hermaphroditic shrimp Exhippolysmata oplophoroides . A 2-year study demonstrated that Hermaphrodites dominated the population in two different bays. This skewed sex ratio may be explained by limited encounter rates among conspecifics. In agreement with this idea, the density of shrimps was extremely low (≤1 shrimp km^−2) at the two study sites. Size at sex phase change and sex ratios remained relatively stable through time at the two bays. The stability of these parameters might be explained by the rather steady population structure of this species during the study period. A review of sex ratios in PS hermaphroditic shrimps ( Lysmata and Exhippolysmata ) revealed considerable variation; some species have male- and others Hermaphrodite-skewed sex ratios. The conditions explaining inter- and intra-specific sex ratio variation in protandric simultaneous hermaphroditic species remain to be addressed.
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The symbiotic lifestyle and its evolutionary consequences: social monogamy and sex allocation in the hermaphroditic shrimp Lysmata pederseni
Naturwissenschaften, 2010Co-Authors: J. Antonio BaezaAbstract:Sex allocation theory predicts female-biased sex allocation for simultaneous Hermaphrodites with a monogamous mating system. Mating systems theory predicts that monogamy is advantageous in environments where refuges are discrete, scarce, relatively small, and when predation risk is high outside of these refuges. These predictions were tested with the Caribbean shrimp Lysmata pederseni , a simultaneous Hermaphrodite which has an early male phase and lives inside tubes of the sponge Callyspongia vaginalis . This host sponge is a scarce resource that, together with the high predation risk typical of tropical environments, should favor monogamy in the shrimp. Field observations demonstrated that shrimps were frequently encountered as pairs within these tube sponges. Pairs were equally likely to comprise two Hermaphrodites or one Hermaphrodite and one male. Several of these pairs were observed for long periods of time in the field. Experiments demonstrated that Hermaphrodites tolerated other Hermaphrodites but not males in their host sponge. These results suggest that pairs of hermaphroditic L. pederseni are socially monogamous; they share the same host individual and might reproduce exclusively with their host partners for long periods of time. Nevertheless, males appeared less likely to establish long-term associations with Hermaphrodites as indicated by the rate of their disappearance from their hosts (greater than that of Hermaphrodites). Sex allocation was female biased in monogamous Hermaphrodites. On average, Hermaphrodites invested 34 times more to female than to male reproductive structures. Monogamy and female-biased sex allocation seem to be evolutionary consequences of adopting a symbiotic lifestyle in simultaneous Hermaphrodites.
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Male mating opportunities affect sex allocation in a protrandric-simultaneous hermaphroditic shrimp
Behavioral Ecology and Sociobiology, 2007Co-Authors: J. Antonio BaezaAbstract:Sex allocation theory predicts phenotypic adjustments by individuals in their investments into the male and female reproductive function in response to environmental conditions. I tested for phenotypically plastic shifts in sex allocation in a protandric simultaneous Hermaphrodite, in which individuals mature and reproduce as males first, and later in life, as simultaneous Hermaphrodites. I predicted that initially maturing males should adjust the timing of maturation as Hermaphrodites according to male mating opportunities mediated by population size of Hermaphrodites. In a first experiment, males maintained with only one Hermaphrodite reduced the time they spent as males in comparison to males maintained with no conspecifics, presumably because total reproductive output is maximized by two individuals being simultaneous Hermaphrodites when the mating system is a pair. Conversely, males maintained in groups with two or more Hermaphrodites increased the time they spent as males in comparison to single males. This delay in maturation was not an effect of resource depletion with increasing shrimp density because the growth rate of males did not differ among most of the experimental treatments. One hypothesis to explain this social mediation of sex allocation is that the smaller males are more successful in mating as males than are the larger Hermaphrodites: it will pay reproductively for males to delay maturation as Hermaphrodites in large but not in small groups. In agreement with this notion, a second experiment demonstrated that smaller males were four times more successful than were larger Hermaphrodites in inseminating shrimps reproducing as females. The informative cue that males may use to perceive different group sizes deserves further attention.
Charles F. Baer - One of the best experts on this subject based on the ideXlab platform.
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The mutational decay of male-male and Hermaphrodite-Hermaphrodite competitive fitness in the androdioecious nematode C. elegans
Heredity, 2018Co-Authors: Ayush Shekhar Saxena, Timothy A. Crombie, Dorian Feistel, Lindsay M. Johnson, Sayran Saber, Charles F. BaerAbstract:Androdioecious Caenorhabditis have a high frequency of self-compatible Hermaphrodites and a low frequency of males. The effects of mutations on male fitness are of interest for two reasons. First, when males are rare, selection on male-specific mutations is less efficient than in Hermaphrodites. Second, males may present a larger mutational target than Hermaphrodites because of the different ways in which fitness accrues in the two sexes. We report the first estimates of male-specific mutational effects in an androdioecious organism. The rate of male-specific inviable or sterile mutations is ⩽5 × 10^−4/generation, below the rate at which males would be lost solely due to those kinds of mutations. The rate of mutational decay of male competitive fitness is ~ 0.17%/generation; that of Hermaphrodite competitive fitness is ~ 0.11%/generation. The point estimate of ~ 1.5X faster rate of mutational decay of male fitness is nearly identical to the same ratio in Drosophila. Estimates of mutational variance (V_M) for male mating success and competitive fitness are not significantly different from zero, whereas V_M for Hermaphrodite competitive fitness is similar to that of non-competitive fitness. Two independent estimates of the average selection coefficient against mutations affecting Hermaphrodite competitive fitness agree to within two-fold, 0.33–0.5%.
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the mutational decay of male and Hermaphrodite competitive fitness in the androdioecious nematode c elegans in which males are naturally rare
bioRxiv, 2017Co-Authors: Ayush Shekhar Saxena, Timothy A. Crombie, Dorian Feistel, Lindsay M. Johnson, Sayran Saber, Charles F. BaerAbstract:Androdioecious Caenorhabditis have a high frequency of self-compatible Hermaphrodites and a low frequency of males. The effects of mutations on male fitness are of interest for two reasons. First, when males are rare, selection on male-specific mutations is less efficient than in Hermaphrodites. Second, males may present a larger mutational target than Hermaphrodites because of the different ways in which fitness accrues in the two sexes. We report the first estimates of male-specific mutational effects in an androdioecious organism. The rate of male-specific inviable or sterile mutations is ≤ 5 x 10-4/generation, below the rate at which males would be lost solely due to those kinds of mutations. The rate of mutational decay of male competitive fitness is ~0.17%/generation; that of Hermaphrodite competitive fitness is ~0.11%/generation. The point estimate of ~1.5X faster rate of mutational decay of male fitness is nearly identical to the same ratio in Drosophila. Estimates of mutational variance (VM) for male mating success and competitive fitness are not significantly different from zero, whereas VM for Hermaphrodite competitive fitness is similar to that of non-competitive fitness. The discrepancy between the two sexes is probably due to the greater inherent variability of mating relative to internal self-fertilization.
Patricia E Kuwabara - One of the best experts on this subject based on the ideXlab platform.
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germ line regulation of the caenorhabditis elegans sex determining gene tra 2
Developmental Biology, 1998Co-Authors: Patricia E Kuwabara, Peter G Okkema, Judith KimbleAbstract:The Caenorhabditis elegans sex-determining gene tra-2 promotes female development of the XX Hermaphrodite soma and germ line. We previously showed that a 4.7-kb tra-2 mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of the tra-2 locus. This paper focuses on the germ-line activity and regulation of tra-2. First, we characterize a 1.8-kb tra-2 mRNA, which is Hermaphrodite-specific and germ-line-dependent. This mRNA encodes TRA-2B, a protein identical to a predicted intracellular domain of TRA-2A. We show that the 1.8-kb mRNA is oocyte-specific, suggesting that it is involved in germ-line or embryonic sex determination. Second, we identify a tra-2 maternal effect on brood size that may be associated with the 1.8-kb mRNA. Third, we investigate seven dominant tra-2(mx) (for mixed character) mutations that sexually transform Hermaphrodites to females by eliminating Hermaphrodite spermatogenesis. Each of the tra-2(mx) mutants possesses a nonconserved missense change in a 22-amino-acid region common to both TRA-2A and TRA-2B, called the MX region. We propose that the MX region mediates a posttranslational regulation of tra-2 essential for the onset of Hermaphrodite spermatogenesis. Finally, we discuss aspects of tra-2 function and regulation that are specific to the unusual control of cell fate in the Hermaphrodite germ line. © 1998 Academic Press
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a novel regulatory mutation in the c elegans sex determination gene tra 2 defines a candidate ligand receptor interaction site
Development, 1996Co-Authors: Patricia E KuwabaraAbstract:Sex determination in the nematode C. elegans is dependent on cell-to-cell communication, which appears to be mediated by the predicted membrane protein TRA-2A and the secreted protein HER-1. In XO males, HER-1 is hypothesised to function as a repressive ligand that inactivates the TRA-2A receptor. In XX animals, HER-1 is absent and TRA-2A promotes Hermaphrodite development by negatively regulating the FEM proteins. This paper describes the molecular and genetic characterisation of a novel class of feminising mutations called tra-2(eg), for enhanced gain-of-function. In XX animals, mutant tra-2(eg) activity promotes entirely normal Hermaphrodite development. However, the tra-2(eg) mutations generate an XO-specific gain-of-function phenotype, because they transform XO mutants from male into Hermaphrodite. Therefore, the tra-2(eg) mutations identify a major regulatory site, which may be the TRA-2A/HER-1 interaction site. All ten tra-2(eg) mutations encode identical missense changes in a predicted extracellular domain of TRA-2A, named the EG site. It is proposed that the tra-2(eg) mutation encodes a TRA-2A protein that functions constitutively in XO animals, because it is defective in HER-1 binding. Phenotypic characterisation of sexually transformed XO tra-2(eg) Hermaphrodites reveals that their fertility is strongly affected by dosage compensation mutations, suggesting that dosage compensation plays a role in normal gametogenesis.
Lukas Scharer - One of the best experts on this subject based on the ideXlab platform.
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phenotypically plastic adjustment of sex allocation in a simultaneous Hermaphrodite
Proceedings of The Royal Society B: Biological Sciences, 2003Co-Authors: Lukas Scharer, Peter LadurnerAbstract:Sex allocation theory for simultaneous Hermaphrodites predicts an influence of the mating group size on sex allocation. Mating group size may depend on the size of the group in which an individual lives, or on the density, but studies to date have not distinguished between the two factors. We performed an experiment in which we raised a transparent simultaneous Hermaphrodite, the flatworm Macrostomum sp., in different group sizes (pairs, triplets, quartets and octets) and in different enclosure sizes (small and large). This design allows us to differentiate between the effects of group size and density. After worms reached maturity we determined their reproductive allocation patterns from microscopic images taken in vivo. The results suggest that the mating group size is a function of the group size, and not of the density. They support the shift to higher male allocation in larger mating groups predicted by sex allocation theory. To our knowledge, this is the first study that unambiguously shows phenotypically plastic sex allocation in response to mating group size in a simultaneous Hermaphrodite.
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size dependent sex allocation in a simultaneous Hermaphrodite parasite
Journal of Evolutionary Biology, 2001Co-Authors: Lukas Scharer, Lars M Karlsson, Mira Christen, Claus WedekindAbstract:Most models of sex allocation distinguish between sequential and simultaneous Hermaphrodites, although an intermediate sexual pattern, size-dependent sex allocation, is widespread in plants. Here we investigated sex allocation in a simultaneous Hermaphrodite animal, the tapeworm Schistocephalus solidus, in which adult size is highly variable. Sex allocation was determined using stereological techniques, which allow measuring somatic and reproductive tissues in a common currency, namely volume. We investigated the relationships between individual volume and allocation to different reproductive tissues using an allometric model. One measure of female allocation, yolk gland volume, increased more than proportionally with individual volume. This is in contrast to the measure of male allocation, testis volume, which showed a strong tendency to increase less than proportionally with individual volume. Together these patterns led to sex allocation being strongly related to individual volume, with large individuals being more biased towards female allocation. We discuss these findings in the light of current ideas about size-dependent sex allocation in, primarily, plants and try to extend them to simultaneous Hermaphrodite animals.