title: Incomplete meiotic sex chromosome inactivation in the domestic dog.
abstract: BACKGROUND
  In mammalian meiotic prophase, homologous chromosome recognition is aided by formation and repair of programmed DNA double-strand breaks (DSBs). Subsequently, stable associations form through homologous chromosome synapsis. In male mouse meiosis, the largely heterologous X and Y chromosomes synapse only in their short pseudoautosomal regions (PARs), and DSBs persist along the unsynapsed non-homologous arms of these sex chromosomes. Asynapsis of these arms and the persistent DSBs then trigger transcriptional silencing through meiotic sex chromosome inactivation (MSCI), resulting in formation of the XY body. This inactive state is partially maintained in post-meiotic haploid spermatids (postmeiotic sex chromatin repression, PSCR). For the human, establishment of MSCI and PSCR have also been reported, but X-linked gene silencing appears to be more variable compared to mouse. To gain more insight into the regulation and significance of MSCI and PSCR among different eutherian species, we have performed a global analysis of XY pairing dynamics, DSB repair, MSCI and PSCR in the domestic dog (Canis lupus familiaris), for which the complete genome sequence has recently become available, allowing a thorough comparative analyses.
  
  
  RESULTS
  In addition to PAR synapsis between X and Y, we observed extensive self-synapsis of part of the dog X chromosome, and rapid loss of known markers of DSB repair from that part of the X. Sequencing of RNA from purified spermatocytes and spermatids revealed establishment of MSCI. However, the self-synapsing region of the X displayed higher X-linked gene expression compared to the unsynapsed area in spermatocytes, and was post-meiotically reactivated in spermatids. In contrast, genes in the PAR, which are expected to escape MSCI, were expressed at very low levels in both spermatocytes and spermatids. Our comparative analysis was then used to identify two X-linked genes that may escape MSCI in spermatocytes, and 21 that are specifically re-activated in spermatids of human, mouse and dog.
  
  
  CONCLUSIONS
  Our data indicate that MSCI is incomplete in the dog. This may be partially explained by extensive, but transient, self-synapsis of the X chromosome, in association with rapid completion of meiotic DSB repair. In addition, our comparative analysis identifies novel candidate male fertility genes.
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. f.federici@erasmusmc.nl.
authors.forename: Federica
authors.initials: F
authors.lastname: Federici
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. eskeatnaf.mulugeta@curie.fr.|Present address: Institut Curie, Genetics and Developmental Biology, Unit 11 et 13 rue Pierre et Marie Curie, 75248, Paris, Cedex 05, France. eskeatnaf.mulugeta@curie.fr.
authors.forename: Eskeatnaf
authors.initials: E
authors.lastname: Mulugeta
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. s.schoenmakers@erasmusmc.nl.|Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. s.schoenmakers@erasmusmc.nl.
authors.forename: Sam
authors.initials: S
authors.lastname: Schoenmakers
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. e.wassenaar@erasmusmc.nl.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Wassenaar
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. johobrug@xs4all.nl.
authors.forename: Jos W
authors.initials: JW
authors.lastname: Hoogerbrugge
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. g.vanderheijden@erasmusmc.nl.|Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. g.vanderheijden@erasmusmc.nl.
authors.forename: Godfried W
authors.initials: GW
authors.lastname: van der Heijden
authors.affiliation: Department of Pathology, Erasmus Optical Imaging Centre, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. w.vancappellen@erasmusmc.nl.
authors.forename: Wiggert A
authors.initials: WA
authors.lastname: van Cappellen
authors.affiliation: Department of Pathology, Erasmus Optical Imaging Centre, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. j.slotman@erasmusmc.nl.
authors.forename: Johan A
authors.initials: JA
authors.lastname: Slotman
authors.affiliation: Erasmus Center for Biomics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. w.vanijcken@erasmusmc.nl.
authors.forename: Wilfred F J
authors.initials: WF
authors.lastname: van IJcken
authors.affiliation: Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. j.laven@erasmusmc.nl.
authors.forename: Joop S E
authors.initials: JS
authors.lastname: Laven
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. j.a.grootegoed@erasmusmc.nl.
authors.forename: J Anton
authors.initials: JA
authors.lastname: Grootegoed
authors.affiliation: Department of Developmental Biology, Erasmus MC, University Medical Center, PO BOX 2040, 3000 CA, Rotterdam, The Netherlands. w.baarends@erasmusmc.nl.
authors.forename: Willy M
authors.initials: WM
authors.lastname: Baarends
mesh_terms: D000818:Animals; D000829:Animals, Domestic; D033481:Chromosomes, Mammalian / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004285:Dogs / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D008540:Meiosis; D051379:Mice; D012730:Sex Chromosomes / Q000378:metabolism*; D013090:Spermatocytes / Q000166:cytology / Q000378:metabolism; D013091:Spermatogenesis; D013737:Testis; D049951:X Chromosome Inactivation