Sex chromosome evolution: life, death and repetitive DNA.
Dimorphic sex chromosomes create problems. Males of many species, including Drosophila, are heterogametic, with dissimilar X and Y chromosomes. The essential process of dosage compensation modulates the expression of X-linked genes in one sex to maintain a constant ratio of X to autosomal expression. This involves the regulation of hundreds of dissimilar genes whose only shared property is chromosomal address. Drosophila males dosage compensate by up regulating X-linked genes 2 fold. This is achieved by the Male Specific Lethal (MSL) complex, which is recruited to genes on the X chromosome and modifies chromatin to increase expression. How the MSL complex is restricted to X-linked genes remains unknown. Recent studies of sex chromosome evolution have identified a central role for 2 types of repetitive elements in X recognition. Helitrons carrying sites that recruit the MSL complex have expanded across the X chromosome in at least one Drosophila species. (1) Our laboratory found that siRNA from an X-linked satellite repeat promotes X recognition by a yet unknown mechanism. (2) The recurring adoption of repetitive elements as X-identify elements suggests that the large and mysterious fraction of the genome called "junk" DNA is actually instrumental in the evolution of sex chromosomes.
a Department of Biological Sciences ; Wayne State University ; Detroit , MI USA.
Nikita
N
Deshpande
Victoria H
VH
Meller
D000818:Animals; D005075:Biological Evolution; D002843:Chromatin; D004247:DNA / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation; D050172:Genes, X-Linked; D016678:Genome; D008297:Male; D012091:Repetitive Sequences, Nucleic Acid; D012730:Sex Chromosomes / Q000235:genetics*
D002843:Chromatin; D004247:DNA
1.688X repeats; 359 bp repeats; dosage compensation; helitrons; satellite repeats; sex chromosomes