Sex determination by multiple sex chromosomes in
            <i>Xenopus tropicalis</i>

Schartl, Manfred

doi:10.1073/pnas.1513518112

Cited by 12 publications

(8 citation statements)

References 20 publications

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“…In laboratory triploids, ZZW genotypes developed as females, but YWW into males, showing the Y is a much stronger male determiner than the Z; while the Z of X. tropicalis can determine maleness only in the absence of W [ 131 ]. Importantly, commenting on the relative ‘strength' of sex chromosomes, Schartl [ 133 ] concluded that this hierarchy in multiple sex-chromosome systems is context-dependent and can vary in different organisms. Recently, nucleotide polymorphisms of expressed transcripts suggested genetic degeneration on the W chromosome, emergence of a new Y chromosome from an ancestral Z chromosome, and natural co-occurrence of the W, Z and Y chromosomes in the same X. tropicalis population [ 134 ].…”

Section: Sex Chromosomes In Hybrids Along the Speciation Continuummentioning

confidence: 99%

Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the ‘extended speciation continuum'

Stöck

Dedukh

Reifová

et al. 2021

Phil. Trans. R. Soc. B

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We review knowledge about the roles of sex chromosomes in vertebrate hybridization and speciation, exploring a gradient of divergences with increasing reproductive isolation (speciation continuum). Under early divergence, well-differentiated sex chromosomes in meiotic hybrids may cause Haldane-effects and introgress less easily than autosomes. Undifferentiated sex chromosomes are more susceptible to introgression and form multiple (or new) sex chromosome systems with hardly predictable dominance hierarchies. Under increased divergence, most vertebrates reach complete intrinsic reproductive isolation. Slightly earlier, some hybrids (linked in ‘the extended speciation continuum') exhibit aberrant gametogenesis, leading towards female clonality. This facilitates the evolution of various allodiploid and allopolyploid clonal (‘asexual’) hybrid vertebrates, where ‘asexuality' might be a form of intrinsic reproductive isolation. A comprehensive list of ‘asexual' hybrid vertebrates shows that they all evolved from parents with divergences that were greater than at the intraspecific level (K2P-distances of greater than 5–22% based on mtDNA). These ‘asexual' taxa inherited genetic sex determination by mostly undifferentiated sex chromosomes. Among the few known sex-determining systems in hybrid ‘asexuals', female heterogamety (ZW) occurred about twice as often as male heterogamety (XY). We hypothesize that pre-/meiotic aberrations in all-female ZW-hybrids present Haldane-effects promoting their evolution. Understanding the preconditions to produce various clonal or meiotic allopolyploids appears crucial for insights into the evolution of sex, ‘asexuality' and polyploidy. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.

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Section: Sex Chromosomes In Hybrids Along the Speciation Continuummentioning

confidence: 99%

Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the ‘extended speciation continuum'

Stöck

Dedukh

Reifová

et al. 2021

Phil. Trans. R. Soc. B

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“…Very recently, Roco et al [2015] provided evidence that in S. tropicalis at least 3 sex chromosomes exist, leading to YZ, YW, and ZZ males and ZW and WW females. The fact that 3 sex chromosomes coexist in the same population suggests a recent emergence of the third sex chromosome and an ongoing process of homologous transition [Schartl, 2015].…”

Section: Sex Chromosomesmentioning

confidence: 99%

Sex Reversal in Amphibians

Flament¹

2016

Sex Dev

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Amphibians have been widely used to study developmental biology due to the fact that embryo development takes place independently of the maternal organism and that observations and experimental approaches are easy. Some amphibians like Xenopus became model organisms in this field. In the first part of this article, the differentiation of the gonads in amphibians and the mechanisms governing this process are reviewed. In the second part, the state of the art about sex reversal, which can be induced by steroid hormones in general and by temperature in some species, is presented. Also information about pollutants found in the environment that could interfere with the development of the amphibian reproductive apparatus or with their reproductive physiology is given. Such compounds could play a part in the amphibian decline, since in the wild, many amphibians are endangered species.

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“…In theory, reuse of the sex chromosomes, termed homologous turnover, is possible if the new sex-determining locus is established on an existing sex-chromosome through mechanisms (1) or (2). There is no empirical evidence for it in vertebrates [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

Identification of the sex-determining locus in grass puffer (Takifugu niphobles) provides evidence for sex-chromosome turnover in a subset of Takifugu species

et al. 2018

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There is increasing evidence for frequent turnover in sex chromosomes in vertebrates. Yet experimental systems suitable for tracing the detailed process of turnover are rare. In theory, homologous turnover is possible if the new sex-determining locus is established on the existing sex-chromosome. However, there is no empirical evidence for such an event. The genus Takifugu includes fugu (Takifugu rubripes) and its two closely-related species whose sex is most likely determined by a SNP at the Amhr2 locus. In these species, males are heterozygous, with G and C alleles at the SNP site, while females are homozygous for the C allele. To determine if a shift in the sex-determining locus occurred in another member of this genus, we used genetic mapping to characterize the sex-chromosome systems of Takifugu niphobles. We found that the G allele of Amhr2 is absent in T. niphobles. Nevertheless, our initial mapping suggests a linkage between the phenotypic sex and the chromosome 19, which harbors the Amhr2 locus. Subsequent high-resolution analysis using a sex-reversed fish demonstrated that the sex-determining locus maps to the proximal end of chromosome 19, far from the Amhr2 locus. Thus, it is likely that homologous turnover involving these species has occurred. The data also showed that there is a male-specific reduction of recombination around the sex-determining locus. Nevertheless, no evidence for sex-chromosome differentiation was detected: the reduced recombination depended on phenotypic sex rather than genotypic sex; no X- or Y-specific maker was obtained; the YY individual was viable. Furthermore, fine-scale mapping narrowed down the new sex-determining locus to the interval corresponding to approximately 300-kb of sequence in the fugu genome. Thus, T. niphobles is determined to have a young and small sex-determining region that is suitable for studying an early phase of sex-chromosome evolution and the mechanisms underlying turnover of sex chromosome.

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Sex determination by multiple sex chromosomes in Xenopus tropicalis

Cited by 12 publications

References 20 publications

Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the ‘extended speciation continuum'

Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the ‘extended speciation continuum'

Sex Reversal in Amphibians

Identification of the sex-determining locus in grass puffer (Takifugu niphobles) provides evidence for sex-chromosome turnover in a subset of Takifugu species

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