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Initiation of recombination suppression and PAR formation during the early stages of neo-sex chromosome differentiation in the Okinawa spiny rat, Tokudaia muenninki.

Murata C, Kuroki Y, Imoto I, Tsukahara M, Ikejiri N, Kuroiwa A - BMC Evol. Biol. (2015)

Bottom Line: In contrast, the sequence evolution toward AT-richness was observed in those pericentromeric regions.Furthermore, we showed genetic differentiation between the pericentromeric regions as well as an accelerated rate of evolution in the neo-Y region through the detection of male-specific substitutions by gene sequencing in multiple males and females, and each neo-sex-derived BAC sequencing.Our results suggest that recombination has been suppressed in the pericentromeric region of neo-sex chromosomes without chromosome rearrangement, whereas high levels of recombination activity is limited in the peritelomeric region of almost undifferentiated neo-sex chromosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, Institute of Health Biosciences, Tokushima University Graduate School, 3-18-15, Kuramoto-cho, Tokushima, Japan. murata.chie@tokushima-u.ac.jp.

ABSTRACT

Background: Sex chromosomes of extant eutherian species are too ancient to reveal the process that initiated sex-chromosome differentiation. By contrast, the neo-sex chromosomes generated by sex-autosome fusions of recent origin in Tokudaia muenninki are expected to be evolutionarily 'young', and therefore provide a good model in which to elucidate the early phases of eutherian sex chromosome evolution. Here we describe the genomic evolution of T. muenninki in neo-sex chromosome differentiation.

Results: FISH mapping of a T. muenninki male, using 50 BAC clones as probes, revealed no chromosomal rearrangements between the neo-sex chromosomes. Substitution-direction analysis disclosed that sequence evolution toward GC-richness, which positively correlates with recombination activity, occurred in the peritelomeric regions, but not middle regions of the neo-sex chromosomes. In contrast, the sequence evolution toward AT-richness was observed in those pericentromeric regions. Furthermore, we showed genetic differentiation between the pericentromeric regions as well as an accelerated rate of evolution in the neo-Y region through the detection of male-specific substitutions by gene sequencing in multiple males and females, and each neo-sex-derived BAC sequencing.

Conclusions: Our results suggest that recombination has been suppressed in the pericentromeric region of neo-sex chromosomes without chromosome rearrangement, whereas high levels of recombination activity is limited in the peritelomeric region of almost undifferentiated neo-sex chromosomes. We conclude that PAR might have been formed on the peritelomeric region of sex chromosomes as an independent event from spread of recombination suppression during the early stages of sex chromosome differentiation.

No MeSH data available.


Related in: MedlinePlus

Evolution of neo-sex chromosomes. In the early stages of sex-chromosome differentiation, a putative PAR with recombination activity might have been formed prior to the spread of recombination suppression. Red: ancestral X region; blue: ancestral Y region; pink: neo-X region diverged from neo-Y; sky blue: neo-Y region diverged from neo-X; white: undifferentiated neo-sex chromosomal region; yellow: putative PAR. MYA: million years ago
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Fig3: Evolution of neo-sex chromosomes. In the early stages of sex-chromosome differentiation, a putative PAR with recombination activity might have been formed prior to the spread of recombination suppression. Red: ancestral X region; blue: ancestral Y region; pink: neo-X region diverged from neo-Y; sky blue: neo-Y region diverged from neo-X; white: undifferentiated neo-sex chromosomal region; yellow: putative PAR. MYA: million years ago

Mentions: Our research showed that recombination might have been suppressed and activated in the pericentromeric and peritelomeric region of almost homologous neo-sex chromosomes without distinct chromosome rearrangement in T. muenninki. We conclude that the PAR might have been formed independently of the spread of recombination suppression at the same time as the initiation of recombination suppression during an early stage of sex-chromosome differentiation (Fig. 3). T. muenninki neo-sex chromosomes are excellent models for the very early stages of sex-chromosome differentiation, and further analysis of them should provide new insights into eutherian sex-chromosome evolution.Fig. 3


Initiation of recombination suppression and PAR formation during the early stages of neo-sex chromosome differentiation in the Okinawa spiny rat, Tokudaia muenninki.

Murata C, Kuroki Y, Imoto I, Tsukahara M, Ikejiri N, Kuroiwa A - BMC Evol. Biol. (2015)

Evolution of neo-sex chromosomes. In the early stages of sex-chromosome differentiation, a putative PAR with recombination activity might have been formed prior to the spread of recombination suppression. Red: ancestral X region; blue: ancestral Y region; pink: neo-X region diverged from neo-Y; sky blue: neo-Y region diverged from neo-X; white: undifferentiated neo-sex chromosomal region; yellow: putative PAR. MYA: million years ago
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4625939&req=5

Fig3: Evolution of neo-sex chromosomes. In the early stages of sex-chromosome differentiation, a putative PAR with recombination activity might have been formed prior to the spread of recombination suppression. Red: ancestral X region; blue: ancestral Y region; pink: neo-X region diverged from neo-Y; sky blue: neo-Y region diverged from neo-X; white: undifferentiated neo-sex chromosomal region; yellow: putative PAR. MYA: million years ago
Mentions: Our research showed that recombination might have been suppressed and activated in the pericentromeric and peritelomeric region of almost homologous neo-sex chromosomes without distinct chromosome rearrangement in T. muenninki. We conclude that the PAR might have been formed independently of the spread of recombination suppression at the same time as the initiation of recombination suppression during an early stage of sex-chromosome differentiation (Fig. 3). T. muenninki neo-sex chromosomes are excellent models for the very early stages of sex-chromosome differentiation, and further analysis of them should provide new insights into eutherian sex-chromosome evolution.Fig. 3

Bottom Line: In contrast, the sequence evolution toward AT-richness was observed in those pericentromeric regions.Furthermore, we showed genetic differentiation between the pericentromeric regions as well as an accelerated rate of evolution in the neo-Y region through the detection of male-specific substitutions by gene sequencing in multiple males and females, and each neo-sex-derived BAC sequencing.Our results suggest that recombination has been suppressed in the pericentromeric region of neo-sex chromosomes without chromosome rearrangement, whereas high levels of recombination activity is limited in the peritelomeric region of almost undifferentiated neo-sex chromosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, Institute of Health Biosciences, Tokushima University Graduate School, 3-18-15, Kuramoto-cho, Tokushima, Japan. murata.chie@tokushima-u.ac.jp.

ABSTRACT

Background: Sex chromosomes of extant eutherian species are too ancient to reveal the process that initiated sex-chromosome differentiation. By contrast, the neo-sex chromosomes generated by sex-autosome fusions of recent origin in Tokudaia muenninki are expected to be evolutionarily 'young', and therefore provide a good model in which to elucidate the early phases of eutherian sex chromosome evolution. Here we describe the genomic evolution of T. muenninki in neo-sex chromosome differentiation.

Results: FISH mapping of a T. muenninki male, using 50 BAC clones as probes, revealed no chromosomal rearrangements between the neo-sex chromosomes. Substitution-direction analysis disclosed that sequence evolution toward GC-richness, which positively correlates with recombination activity, occurred in the peritelomeric regions, but not middle regions of the neo-sex chromosomes. In contrast, the sequence evolution toward AT-richness was observed in those pericentromeric regions. Furthermore, we showed genetic differentiation between the pericentromeric regions as well as an accelerated rate of evolution in the neo-Y region through the detection of male-specific substitutions by gene sequencing in multiple males and females, and each neo-sex-derived BAC sequencing.

Conclusions: Our results suggest that recombination has been suppressed in the pericentromeric region of neo-sex chromosomes without chromosome rearrangement, whereas high levels of recombination activity is limited in the peritelomeric region of almost undifferentiated neo-sex chromosomes. We conclude that PAR might have been formed on the peritelomeric region of sex chromosomes as an independent event from spread of recombination suppression during the early stages of sex chromosome differentiation.

No MeSH data available.


Related in: MedlinePlus