Abstract
Dosage compensation equates between the sexes the gene dose of sex chromosomes that carry substantially different gene content. In Drosophila, the single male X chromosome is hypertranscribed by approximately two-fold to effect this correction. The key genes are male lethal and appear not to be required in females, or affect their viability. Here, we show these male lethals do in fact have a role in females, and they participate in the very process which will eventually shut down their function—female determination. We find the male dosage compensation complex is required for upregulating transcription of the sex determination master switch, Sex-lethal, an X-linked gene which is specifically activated in females in response to their two X chromosomes. The levels of some X-linked genes are also affected, and some of these genes are used in the process of counting the number of X chromosomes early in development. Our data suggest that before the female state is set, the ground state is male and female X chromosome expression is elevated. Females thus utilize the male dosage compensation process to amplify the signal which determines their fate.
Highlights
When the sex chromosomes carry substantially different gene numbers, dosage compensation is necessary to equalize gene expression between the two sexes
The first male specific lethal identified, maleless, is involved in dosage compensation as are the identified male lethals, msl-1 and msl-2 [3]. msl-3 identified by Uchida et al [4] and males absent on the first complete the proteins collectively known as the male specific lethals
Dosage compensation refers to the process which equates gene dose between the sexes
Summary
When the sex chromosomes carry substantially different gene numbers, dosage compensation is necessary to equalize gene expression between the two sexes. In the three best studied model systems Drosophila, C. elegans and mammals where males are XY and females XX, this involves targeting X-specific components which modify the chromatin and transcription of X-linked genes In each of these cases the end result is different; Drosophila upregulates transcription of the male X by about two-fold, C. elegans downregulates transcription of both X chromosomes in the hermaphrodite by approximately half, and mammals generally shut down transcription of one of the two female X chromosomes (reviewed in [1]). Msl-3 identified by Uchida et al [4] and males absent on the first (mof; [5]) complete the proteins collectively known as the male specific lethals (msls; reviewed in [1,6,7]) In addition to these proteins, two RNAs on the X chromosome (the roX RNAs), which are not present in females, are essential for dosage compensation [8]. JIL is enriched on the male X chromosome but its loss leads to lethality in both sexes [10]
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