Chromatin structural changes around satellite repeats on the female sex chromosome in Schistosoma mansoni and their possible role in sex chromosome emergence

In the leuphotrochozoan parasitic platyhelminth Schistosoma mansoni, male individuals are homogametic (ZZ) whereas females are heterogametic (ZW). To elucidate the mechanisms that led to the emergence of sex chromosomes, we compared the genomic sequence and the chromatin structure of male and female...

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Bibliographic Details
Published in:Genome biology 2012-02, Vol.13 (2), p.R14-R14
Main Authors: Lepesant, Julie M J, Cosseau, Céline, Boissier, Jérome, Freitag, Michael, Portela, Julien, Climent, Déborah, Perrin, Cécile, Zerlotini, Adhemar, Grunau, Christoph
Format: Article
Language:English
Subjects:
Animals
Chromatin - chemistry
Chromatin - genetics
DNA, Satellite - genetics
Evolution, Molecular
Female
Larva - genetics
Larva - growth & development
Male
Recombination, Genetic
Schistosoma mansoni - genetics
Schistosoma mansoni - growth & development
Sequence Analysis, DNA
Sex Chromosomes - genetics
Sex Determination Processes - genetics
Transcription, Genetic
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Summary:In the leuphotrochozoan parasitic platyhelminth Schistosoma mansoni, male individuals are homogametic (ZZ) whereas females are heterogametic (ZW). To elucidate the mechanisms that led to the emergence of sex chromosomes, we compared the genomic sequence and the chromatin structure of male and female individuals. As for many eukaryotes, the lower estimate for the repeat content is 40%, with an unknown proportion of domesticated repeats. We used massive sequencing to de novo assemble all repeats, and identify unambiguously Z-specific, W-specific and pseudoautosomal regions of the S. mansoni sex chromosomes. We show that 70 to 90% of S. mansoni W and Z are pseudoautosomal. No female-specific gene could be identified. Instead, the W-specific region is composed almost entirely of 36 satellite repeat families, of which 33 were previously unknown. Transcription and chromatin status of female-specific repeats are stage-specific: for those repeats that are transcribed, transcription is restricted to the larval stages lacking sexual dimorphism. In contrast, in the sexually dimorphic adult stage of the life cycle, no transcription occurs. In addition, the euchromatic character of histone modifications around the W-specific repeats decreases during the life cycle. Recombination repression occurs in this region even if homologous sequences are present on both the Z and W chromosomes. Our study provides for the first time evidence for the hypothesis that, at least in organisms with a ZW type of sex chromosomes, repeat-induced chromatin structure changes could indeed be the initial event in sex chromosome emergence.
ISSN:1465-6906
1474-760X
1465-6914
DOI:10.1186/gb-2012-13-2-r14