Abstract
Author SummaryMany species have heteromorphic sex chromosomes (XY males or ZW females) where one sex chromosome (the Y or W) has degenerated. In the somatic cells of mammals, worms, and flies, the X-to-autosome ratio of expression is equalized between the sexes by dedicated sex chromosome-specific dosage compensation systems. In the germline cells of male mammals and worms, however, the X chromosome is transcriptionally silenced early in meiosis. Here we have analyzed gene expression in Drosophila testes and show that the X chromosome lacks both of these types of chromosomal regulation. We find that X chromosome-wide dosage compensation is absent from most cells in the Drosophila male germline, and there is little or no evidence for X chromosome-specific inactivation during meiosis. However, another kind of sex-chromosome-specific regulation occurs. Testes-specific transgene reporters show much weaker expression when inserted on the X chromosome versus the autosomes, suggesting that some other, uncharacterized mechanism limits their expression from the X during spermatogenesis. The strong suppression of X-linked transgenes—but not X-linked endogenous genes—suggests that endogenous X-linked testes-specific promoters might have adapted to a suppressive X chromosome environment in the Drosophila male germline.
Highlights
MethodsFly Strains WOL and YLZ transgene insert lines (described in [37]) were generously provided by John Parsch
In the somatic cells of mammals, worms, and flies, the X-to-autosome ratio of expression is equalized between the sexes by dedicated sex chromosome-specific dosage compensation systems
We find that X chromosome-wide dosage compensation is absent from most cells in the Drosophila male germline, and there is little or no evidence for X chromosome-specific inactivation during meiosis
Summary
Fly Strains WOL and YLZ transgene insert lines (described in [37]) were generously provided by John Parsch. Sample Preparation for Microarrays Wild-type individuals of the OreR lab strain were used for tissue dissection and RNA extraction. Testis apical tips were dissected in Ringer’s solution following [41], except that the surrounding testes sheath was removed. All dissected tissue was frozen at 280 until RNA extraction. Tissue from approximately 40 testis dissections and 100 thoraxes was used per extraction column, and approximately 760 testis apical tips, 100 male thoraxes, and 100 female thoraxes were used for each microarray hybridization. RNA extractions were pooled into four independent samples, and 1 mg of total RNA was used as a template for cRNA synthesis with Ambion’s Amino Allyl MessageAmp aRNA amplification protocol. CRNA synthesis and array hybridization were done at the Cornell Microarray Core Facility. Array data are available at the NCBI GEO under accession # GSE30850
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