| Summary: | In Drosophila, XX embryos express Sxl from the early promoter, SxlPe, and
become females. At the same time, XY embryos with only one X chromosome become
males.
I investigated the role of repression in the establishment of the strict regulation of
SxlPe. I found that the co-repressor Groucho, is responsible for amplification of the
two-fold difference in X-encoded activator genes into an all-or-nothing difference in Sxl
expression. Three new basic helix-loop-helix repressors of Sxl were identified: Hey,
Cwo and the prooncogene Myc, all of which are maternally supplied. I have shown that
Myc specific repression is important as early as cycle 10, which is 2 cycles earlier than
the onset of normal Sxl expression.
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