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Mol. Cell. Biol., 02 1995, 904-917, Vol 15, No. 2
PA Estes, LN Keyes and P Schedl
The choice of sexual identity in somatic tissues of the fruit fly
Drosophila melanogaster is determined early in embryogenesis by the X-
chromosome-to-autosome (X/A) ratio. The system that signals the X/A ratio
selects the sexual development pathway by determining the activity state of
the binary switch Sex-lethal (Sxl). In 2X/2A animals, the X/A signalling
system turns the Sxl gene on, ultimately activating an RNA-splicing
autoregulatory feedback loop which serves to maintain the female state
during the remainder of development. In 1X/2A animals, this autoregulatory
feedback loop is not activated and the male state is subsequently
maintained by the default splicing machinery. In the studies reported here,
we have examined how the X/A signalling system controls the initial choice
of sexual identity through its action on a special early embryonic Sxl
promoter, Sxl-Pe. We show that in the early embryo, the activity of Sxl-Pe
is controlled in a highly dose-sensitive fashion by the genes on the X
chromosome that function as numerator elements and by genes located on the
autosomes that function as denominator elements. Functional dissection of
Sxl-Pe indicates that activating the promoter in females requires the
cumulative action of multiple numerator genes which appear to exert their
effects through reiterated cis-acting target sites in the promoter.
Conversely, maintaining the promoter silent in males requires the
repressive activities of denominator genes, and at least one of the
denominator genes also appears to function through target sequences within
the promoter.
Copyright © 1995, American Society for Microbiology
Multiple response elements in the Sex-lethal early promoter ensure its female-specific expression pattern
Department of Molecular Biology, Princeton University, New Jersey 08544.
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