Evolution of dosage compensation.
In polytene chromosome squashes from the fruit fly Drosophila melanogaster, the single, dosage-compensated X chromosome in males can be distinguished from the autosomes by the presence of an isoform of histone H4 acetylated at lysine 16, H4.Ac16. We have used H4.Ac16 as a marker to examine the evolving relationship between dosage compensation and sex chromosome composition in species of Drosophila with one (D. melanogaster), two (D. pseudoobscura) or three (D. miranda) identifiable X chromosome arms. In each case, we find that H4.Ac16 is distributed as discrete, closely spaced bands along the entire length of each X chromosome, the only exception being the X2 chromosome of D. miranda in which a terminal region constituting about 10% of the chromosome by length is not labelled with anti-H4.Ac16 antibodies. We conclude that, with this exception, dosage compensation extends along the X chromosomes of all three species. As D. pseudoobscura and D. miranda diverged only about 2 Mya, the spread of dosage-compensated loci along X2 has been rapid, suggesting that regional changes rather than piecemeal, gene-by-gene, changes may have been involved.
Steinemann
M
M
Institut für Genetik, Heinrich Heine Universität Düsseldorf, Germany. steinem@mail.rz.uni-duesseldorf.de
Steinemann
S
S
Turner
B M
BM
D000107:Acetylation; D000818:Animals; D004303:Dosage Compensation, Genetic; D004330:Drosophila / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D004331:Drosophila melanogaster / Q000235:genetics / Q000254:growth & development; D019143:Evolution, Molecular; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006657:Histones / Q000032:analysis / Q000378:metabolism; D007814:Larva; D008297:Male; D011499:Protein Processing, Post-Translational; D013045:Species Specificity; D014960:X Chromosome / Q000737:chemistry / Q000235:genetics*
D006657:Histones