title: Sex chromosome-specific regulation in the Drosophila male germline but little evidence for chromosomal dosage compensation or meiotic inactivation.
abstract: The evolution of heteromorphic sex chromosomes (e.g., XY in males or ZW in females) has repeatedly elicited the evolution of two kinds of chromosome-specific regulation: dosage compensation--the equalization of X chromosome gene expression in males and females--and meiotic sex chromosome inactivation (MSCI)--the transcriptional silencing and heterochromatinization of the X during meiosis in the male (or Z in the female) germline. How the X chromosome is regulated in the Drosophila melanogaster male germline is unclear. Here we report three new findings concerning gene expression from the X in Drosophila testes. First, X chromosome-wide dosage compensation appears to be absent from most of the Drosophila male germline. Second, microarray analysis provides no evidence for X chromosome-specific inactivation during meiosis. Third, we confirm the previous discovery that the expression of transgene reporters driven by autosomal spermatogenesis-specific promoters is strongly reduced when inserted on the X chromosome versus the autosomes; but we show that this chromosomal difference in expression is established in premeiotic cells and persists in meiotic cells. The magnitude of the X-autosome difference in transgene expression cannot be explained by the absence of dosage compensation, suggesting that a previously unrecognized mechanism limits expression from the X during spermatogenesis in Drosophila. These findings help to resolve several previously conflicting reports and have implications for patterns of genome evolution and speciation in Drosophila.
authors.affiliation: Department of Biology, University of Rochester, Rochester, New York, United States of America. cmeiklej@mail.rochester.edu
authors.forename: Colin D
authors.initials: CD
authors.lastname: Meiklejohn
authors.forename: Emily L
authors.initials: EL
authors.lastname: Landeen
authors.forename: Jodi M
authors.initials: JM
authors.lastname: Cook
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Kingan
authors.forename: Daven C
authors.initials: DC
authors.lastname: Presgraves
mesh_terms: D000818:Animals; D004303:Dosage Compensation, Genetic / Q000235:genetics*; D004330:Drosophila / Q000235:genetics*; D005260:Female; D005854:Germ Cells / Q000378:metabolism; D008297:Male; D008540:Meiosis / Q000235:genetics*; D012730:Sex Chromosomes / Q000235:genetics*; D013091:Spermatogenesis / Q000235:genetics; D013737:Testis / Q000378:metabolism; D049951:X Chromosome Inactivation / Q000235:genetics