title: Chromatin structural changes around satellite repeats on the female sex chromosome in Schistosoma mansoni and their possible role in sex chromosome emergence.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Université de Perpignan Via Domitia, CNRS, UMR 5244 Ecologie et Evolution des Interactions (2EI), 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France. julie.lepesant@univ-perp.fr
authors.forename: Julie M J
authors.initials: JM
authors.lastname: Lepesant
authors.forename: Céline
authors.initials: C
authors.lastname: Cosseau
authors.forename: Jérome
authors.initials: J
authors.lastname: Boissier
authors.forename: Michael
authors.initials: M
authors.lastname: Freitag
authors.forename: Julien
authors.initials: J
authors.lastname: Portela
authors.forename: Déborah
authors.initials: D
authors.lastname: Climent
authors.forename: Cécile
authors.initials: C
authors.lastname: Perrin
authors.forename: Adhemar
authors.initials: A
authors.lastname: Zerlotini
authors.forename: Christoph
authors.initials: C
authors.lastname: Grunau
mesh_terms: D000818:Animals; D002843:Chromatin / Q000737:chemistry / Q000235:genetics; D004276:DNA, Satellite / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D007814:Larva / Q000235:genetics / Q000254:growth & development; D008297:Male; D011995:Recombination, Genetic; D012550:Schistosoma mansoni / Q000235:genetics* / Q000254:growth & development; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D004276:DNA, Satellite