The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform

Ikuo Miura - One of the best experts on this subject based on the ideXlab platform.

  • Evolutionary Changes in Sensitivity to Hormonally Induced Gonadal Sex Reversal in a Frog Species.
    Sexual Development, 2016
    Co-Authors: Ikuo Miura, Hiromi Ohtani, Mitsuaki Ogata, Tariq Ezaz
    Abstract:

    The Japanese frog Glandirana rugosa is unique in that it shows geographic variation in Sex chromosome differentiation and Heterogametic Sex determination. To elucidate the cause of interpopulation differences in gonadal Sex differentiation, we investigated hormonally induced Sex reversal and the expression patterns of genes associated with Sex determination during early tadpole development. We found that Sex reversal was easily induced in XX females and XY males of 2 forms (West-Japan and East-Japan) of G. rugosa with the ancestral homomorphic Sex chromosomes under male Heterogametic Sex determination. During Sex reversal, expression of CYP19 and/or FOXL2 was dependent on the phenotypic Sex of the gonad. In contrast, Sex reversal was not induced in ZW females of a population with a heteromorphic ZW Sex chromosome system or in XX females or XY males in a population with a heteromorphic XY Sex chromosome system. The latter 2 populations are evolutionarily derived forms. These results indicate an evolutionary direction for the gonadal Sex differentiation mechanism. The original system was highly sensitive to Sex hormones and allowed almost complete Sex reversal. From this ancestral form, a new system evolved that was resistant to hormones and showed a change in the Heterogametic Sex and the Sex chromosome differentiation mechanism.

  • The ZZ/ZW Sex-determining mechanism originated twice and independently during evolution of the frog, Rana rugosa.
    Heredity, 2007
    Co-Authors: Mitsuaki Ogata, Hiromi Ohtani, Y. Hasegawa, M Mineyama, Ikuo Miura
    Abstract:

    The Japanese frog, Rana rugosa, has two distinct Sex chromosome types, XX/XY and ZZ/ZW. These two types are found in localized groups, separated geographically by a boundary area predicted to lie somewhere around Lake Biwa in central Japan. To determine this precise boundary, the Heterogametic Sex of 18 populations around Lake Biwa was examined by genotyping Sex-linked genes. Phylogenetic relationships between the populations were also analyzed using mitochondrial 12S rRNA gene. Results showed that the Suzuka-Kii mountain range located east of Lake Biwa separated the XX/XY populations from the ZZ/ZW populations. Unexpectedly, from a phylogenetic perspective, the ZZ/ZW populations around Lake Biwa belonged not to the main ZW group but to the XY group. The authors propose that the ZZ/ZW populations around Lake Biwa diverged secondarily from the XX/XY group through a change of Heterogametic Sex, eventually forming a new group. This group was thus named the ‘Neo-ZW group’. As the main ZW group inhabiting northwestern Japan is known to have a different male Heterogametic origin, this finding shows that change of Heterogametic Sex from male to female may have occurred twice, and independently, during the frog speciation.

  • an evolutionary witness the frog rana rugosa underwent change of Heterogametic Sex from xy male to zw female
    Sexual Development, 2007
    Co-Authors: Ikuo Miura
    Abstract:

    There are two basic types of heterogamety for genetic Sex determination in animals and plants: male heterogamety (XX/XY) and female heterogamety (ZZ/ZW). Although apparently in opposition, the two distinct types may in fact be interchangeable. For example, in amphibians it has been shown that the Heterogametic Sex was originally female and may have become male at some branching point in their phylogenetic evolution. In particular, there is evidence that the male Heterogametic Sex determination of the frog Rana rugosa returned to its previous female state during speciation that occurred when the distribution range of the frog expanded across Japan. This change is quite recent in the phylogenetic time scale. This paper presents a review of the Sex chromosomes and Sex determination in the frog R. rugosa, an evolutionary witness proving the viability of changing Heterogametic Sex, and introduces recent findings and on-going studies in the frog. Change of the Heterogametic Sex will also be discussed, relating data from frogs (Rana) and other animals to the replacement of a master Sex-determining gene in the course of speciation.

  • Change of the Heterogametic Sex from male to female in the frog.
    Genetics, 2003
    Co-Authors: Mitsuaki Ogata, Hiromi Ohtani, T. Igarashi, Y. Hasegawa, Youko Ichikawa, Ikuo Miura
    Abstract:

    Two different types of Sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male Heterogametic Sex determination and homomorphic Sex chromosomes. In this study, to find out how the different types of Sex chromosomes differentiated, particularly the evolutionary reason for the Heterogametic Sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that Sex ratio bias according to the maternal origin of the hybrid population was a trigger for the Sex chromosome differentiation and the change of Heterogametic Sex.

  • effects of dibutyl phthalate as an environmental endocrine disruptor on gonadal Sex differentiation of genetic males of the frog rana rugosa
    Environmental Health Perspectives, 2000
    Co-Authors: Hiromi Ohtani, Ikuo Miura, Youko Ichikawa
    Abstract:

    To examine the effects of dibutyl phthalate (DBP) on gonadal Sex differentiation, genetically male tadpoles of Rana rugosa were exposed to dilute solutions of DBP at concentrations of 0.1, 1, or 10 microM during days 19-23 after fertilization, which is the critical period of gonadal Sex differentiation in R. rugosa. Tadpoles were necropsied on day 40. The genetically male tadpoles were produced from crossings between males (ZZ) of one local population, in which females are the Heterogametic Sex, and females (XX) of another local population, in which males are the Heterogametic Sex. As positive control groups, tadpoles were exposed to dilute solutions of 17beta-estradiol (E(2)) at concentrations of 0. 01, 0.1, or 1 microM during the same period. The internal structure of the gonads was histologically examined in a total of 30 control tadpoles, 86 E(2)-treated tadpoles, and 90 DBP-treated tadpoles. The gonads of the control tadpoles all showed the typical structure of testes. In contrast, 0.01, 0.1, and 1 microM E(2) treatments caused the undifferentiated gonads of 18, 63, and 100% of the tadpoles, respectively, to develop into gonads of complete or partial ovarian structure. After 0.1, 1, and 10 microM DBP treatment, 0, 7, and 17% of tadpoles, respectively, were similarly affected. These findings suggest that DBP was about 1,000-fold less potent than E(2). Nevertheless, DBP is an environmentally dangerous hormone that disrupts the pathways of testicular differentiation in genetically male animals.

Urban Friberg - One of the best experts on this subject based on the ideXlab platform.

  • Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis.
    Evolution; international journal of organic evolution, 2018
    Co-Authors: Martin Brengdahl, Christopher M. Kimber, Jack Maguire-baxter, Urban Friberg
    Abstract:

    Life span differs between the Sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: Sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the Heterogametic Sex suffers a shortened life span because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (∼20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced life span or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the Heterogametic Sex appears too small to explain general Sex differences in life span.

David Laloi - One of the best experts on this subject based on the ideXlab platform.

  • The Sex chromosome system can influence the evolution of Sex-biased dispersal.
    Journal of evolutionary biology, 2018
    Co-Authors: Thomas Brom, Manuel Massot, David Laloi
    Abstract:

    Sex-biased dispersal is a much-discussed feature in literature on dispersal. Diverse hypotheses have been proposed to explain the evolution of Sex-biased dispersal, a difference in dispersal rate or dispersal distance between males and females. An early hypothesis has indicated that it may rely on the difference in Sex chromosomes between males and females. However, this proposal was quickly rejected without a real assessment. We propose a new perspective on this hypothesis by investigating the evolution of Sex-biased dispersal when dispersal genes are Sex-linked, that is when they are located on the Sex chromosomes. We show that individuals of the Heterogametic Sex disperse relatively more than do individuals of the homogametic Sex when dispersal genes are Sex-linked rather than autosomal. Although such a Sex-biased dispersal towards the Heterogametic Sex is always observed in monogamous species, the mating system and the location of dispersal genes interact to modulate Sex-biased dispersal in monandry and polyandry. In the context of the multicausality of dispersal, we suggest that Sex-linked dispersal genes can influence the evolution of Sex-biased dispersal.

Martin Brengdahl - One of the best experts on this subject based on the ideXlab platform.

  • Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis.
    Evolution; international journal of organic evolution, 2018
    Co-Authors: Martin Brengdahl, Christopher M. Kimber, Jack Maguire-baxter, Urban Friberg
    Abstract:

    Life span differs between the Sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: Sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the Heterogametic Sex suffers a shortened life span because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (∼20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced life span or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the Heterogametic Sex appears too small to explain general Sex differences in life span.

Hiromi Ohtani - One of the best experts on this subject based on the ideXlab platform.

  • Evolutionary Changes in Sensitivity to Hormonally Induced Gonadal Sex Reversal in a Frog Species.
    Sexual Development, 2016
    Co-Authors: Ikuo Miura, Hiromi Ohtani, Mitsuaki Ogata, Tariq Ezaz
    Abstract:

    The Japanese frog Glandirana rugosa is unique in that it shows geographic variation in Sex chromosome differentiation and Heterogametic Sex determination. To elucidate the cause of interpopulation differences in gonadal Sex differentiation, we investigated hormonally induced Sex reversal and the expression patterns of genes associated with Sex determination during early tadpole development. We found that Sex reversal was easily induced in XX females and XY males of 2 forms (West-Japan and East-Japan) of G. rugosa with the ancestral homomorphic Sex chromosomes under male Heterogametic Sex determination. During Sex reversal, expression of CYP19 and/or FOXL2 was dependent on the phenotypic Sex of the gonad. In contrast, Sex reversal was not induced in ZW females of a population with a heteromorphic ZW Sex chromosome system or in XX females or XY males in a population with a heteromorphic XY Sex chromosome system. The latter 2 populations are evolutionarily derived forms. These results indicate an evolutionary direction for the gonadal Sex differentiation mechanism. The original system was highly sensitive to Sex hormones and allowed almost complete Sex reversal. From this ancestral form, a new system evolved that was resistant to hormones and showed a change in the Heterogametic Sex and the Sex chromosome differentiation mechanism.

  • The ZZ/ZW Sex-determining mechanism originated twice and independently during evolution of the frog, Rana rugosa.
    Heredity, 2007
    Co-Authors: Mitsuaki Ogata, Hiromi Ohtani, Y. Hasegawa, M Mineyama, Ikuo Miura
    Abstract:

    The Japanese frog, Rana rugosa, has two distinct Sex chromosome types, XX/XY and ZZ/ZW. These two types are found in localized groups, separated geographically by a boundary area predicted to lie somewhere around Lake Biwa in central Japan. To determine this precise boundary, the Heterogametic Sex of 18 populations around Lake Biwa was examined by genotyping Sex-linked genes. Phylogenetic relationships between the populations were also analyzed using mitochondrial 12S rRNA gene. Results showed that the Suzuka-Kii mountain range located east of Lake Biwa separated the XX/XY populations from the ZZ/ZW populations. Unexpectedly, from a phylogenetic perspective, the ZZ/ZW populations around Lake Biwa belonged not to the main ZW group but to the XY group. The authors propose that the ZZ/ZW populations around Lake Biwa diverged secondarily from the XX/XY group through a change of Heterogametic Sex, eventually forming a new group. This group was thus named the ‘Neo-ZW group’. As the main ZW group inhabiting northwestern Japan is known to have a different male Heterogametic origin, this finding shows that change of Heterogametic Sex from male to female may have occurred twice, and independently, during the frog speciation.

  • Change of the Heterogametic Sex from male to female in the frog.
    Genetics, 2003
    Co-Authors: Mitsuaki Ogata, Hiromi Ohtani, T. Igarashi, Y. Hasegawa, Youko Ichikawa, Ikuo Miura
    Abstract:

    Two different types of Sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male Heterogametic Sex determination and homomorphic Sex chromosomes. In this study, to find out how the different types of Sex chromosomes differentiated, particularly the evolutionary reason for the Heterogametic Sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that Sex ratio bias according to the maternal origin of the hybrid population was a trigger for the Sex chromosome differentiation and the change of Heterogametic Sex.

  • effects of dibutyl phthalate as an environmental endocrine disruptor on gonadal Sex differentiation of genetic males of the frog rana rugosa
    Environmental Health Perspectives, 2000
    Co-Authors: Hiromi Ohtani, Ikuo Miura, Youko Ichikawa
    Abstract:

    To examine the effects of dibutyl phthalate (DBP) on gonadal Sex differentiation, genetically male tadpoles of Rana rugosa were exposed to dilute solutions of DBP at concentrations of 0.1, 1, or 10 microM during days 19-23 after fertilization, which is the critical period of gonadal Sex differentiation in R. rugosa. Tadpoles were necropsied on day 40. The genetically male tadpoles were produced from crossings between males (ZZ) of one local population, in which females are the Heterogametic Sex, and females (XX) of another local population, in which males are the Heterogametic Sex. As positive control groups, tadpoles were exposed to dilute solutions of 17beta-estradiol (E(2)) at concentrations of 0. 01, 0.1, or 1 microM during the same period. The internal structure of the gonads was histologically examined in a total of 30 control tadpoles, 86 E(2)-treated tadpoles, and 90 DBP-treated tadpoles. The gonads of the control tadpoles all showed the typical structure of testes. In contrast, 0.01, 0.1, and 1 microM E(2) treatments caused the undifferentiated gonads of 18, 63, and 100% of the tadpoles, respectively, to develop into gonads of complete or partial ovarian structure. After 0.1, 1, and 10 microM DBP treatment, 0, 7, and 17% of tadpoles, respectively, were similarly affected. These findings suggest that DBP was about 1,000-fold less potent than E(2). Nevertheless, DBP is an environmentally dangerous hormone that disrupts the pathways of testicular differentiation in genetically male animals.