X chromosome inactivation during Drosophila spermatogenesis.
Genes with male- and testis-enriched expression are under-represented on the Drosophila melanogaster X chromosome. There is also an excess of retrotransposed genes, many of which are expressed in testis, that have "escaped" the X chromosome and moved to the autosomes. It has been proposed that inactivation of the X chromosome during spermatogenesis contributes to these patterns: genes with a beneficial function late in spermatogenesis should be selectively favored to be autosomal in order to avoid inactivation. However, conclusive evidence for X inactivation in the male germline has been lacking. To test for such inactivation, we used a transgenic construct in which expression of a lacZ reporter gene was driven by the promoter sequence of the autosomal, testis-specific ocnus gene. Autosomal insertions of this transgene showed the expected pattern of male- and testis-specific expression. X-linked insertions, in contrast, showed only very low levels of reporter gene expression. Thus, we find that X linkage inhibits the activity of a testis-specific promoter. We obtained the same result using a vector in which the transgene was flanked by chromosomal insulator sequences. These results are consistent with global inactivation of the X chromosome in the male germline and support a selective explanation for X chromosome avoidance of genes with beneficial effects late in spermatogenesis.
Hense
Winfried
W
Department of Biology II, University of Munich, Planegg-Martinsried, Germany.
Baines
John F
JF
Parsch
John
J
D000818:Animals; D002874:Chromosome Mapping; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D017344:Genes, Insect; D017930:Genes, Reporter; D008040:Genetic Linkage; D007763:Lac Operon; D008297:Male; D030781:Organisms, Genetically Modified; D013091:Spermatogenesis / Q000235:genetics*; D013737:Testis / Q000378:metabolism; D014960:X Chromosome; D049951:X Chromosome Inactivation