Trends in Genetics
ReviewSex comes in from the cold: the integration of sex and pattern
Section snippets
Interactions of regulatory genes at the bottom of the hierarchy
In females, dsx acts with two other genes, hermaphrodite (her) 13., 14., 15., 16. and intersex (ix) 17., 18. to control sexual development. The her gene encodes a zinc finger protein [16], whereas ix encodes a protein that has no obvious DNA-binding domain but has homology to a region that functions as a transcriptional activator in several mammalian proteins that function as transcriptional activators [18], suggesting that ix might be a transcriptional activator. As described below, both her
On the nature of sexual dimorphism in Drosophila
Because investigators of the sex hierarchy have previously focused on regulatory gene interactions, and because the aspects of sexual differentiation most evident to the general Drosophila researcher are sometimes viewed as relatively minor embellishments on the body plan (remove a little pigment here, sharpen up the bristles in that row a bit, add some yolk protein, etc., and Voila! – you have turned a male into a female), there has been a tendency to consider sex as a relatively superficial
Regulation of sexual dimorphism: early studies
Early studies of how sexual differentiation is controlled by the dsx branch of the hierarchy led to two significant generalizations [7]. First, dsx can act both negatively [26] and positively 8., 12. to regulate various target genes. For example, transcription of the Yp1 gene is repressed by the DSXM protein, but activated by the DSXF protein [12]. Second, genes expressed sex-specifically are controlled by the hierarchy in either of two ways. Some terminal differentiation genes are direct
The dsx gene in the genital disc and the fates of the repressed genital primordia
The genital disc gives rise to the genitalia and analia (Fig. 2g,h). By contrast to most imaginal discs, which are essentially two-dimensional [30], the genital disc is a three-dimensional structure with distinct dorsal and ventral epithelia, which generate the different adult genital and anal structures 31., 32. (Fig. 3). The genital disc is strikingly sexually dimorphic (Fig. 2e,f). The three primordia – female genital, male genital, and anal – that make up the genital disc originate from
Regulation of sexual dimorphism: recent studies
The past three years have seen the identification of five of the downstream genes through which dsx and its partners act. As these five genes encode well-known developmental regulatory proteins, the finding that sex modulates the activities of these genes has provided substantial insight into how sexual dimorphism is generated at the tissue and cellular level, as well as the levels at which information from the sex hierarchy and other patterning hierarchies is integrated.
Conclusion
The last three years have seen a revolution – both conceptually and factually – in our understanding of how the dsx branch of the sex hierarchy functions to control sexual development. One key conceptual change was the finding that the manner in which dsx modulates development can be explained in a unitary model in which dsx is instructive in all its known functions. In addition, our understanding of what the sex hierarchy does has been substantially broadened by demonstrations that this
Acknowledgements
We thank members of the Baker laboratory and Hank Bayle for their interest and helpful discussions, Guennet Bohm for technical support, and the helpful suggestions of the reviewers.
References (75)
- et al.
The regulation of the Drosophila msl-2 gene reveals a function for Sex-lethal in translational control
Cell
(1997) Are complex behaviors specified by dedicated regulatory genes? Reasoning from Drosophila
Cell
(2001)The regulation of sex determination and sexually dimorphic differentiation in Drosophila
Curr. Opin. Cell Biol.
(1993)Sex-specific regulation of yolk protein gene expression in Drosophila
Cell
(1985)Sequences expressed sex-specifically in Drosophila melanogaster adults
Dev. Biol.
(1987)- et al.
Determination of male-specific gene expression in Drosophila accessory glands
Dev. Biol.
(1988) - et al.
Genetic and developmental evidence for a repressed genital primordium in Drosophila melanogaster
Dev. Biol.
(1982) The sex determination gene doublesex regulates the A/P organizer to direct sex-specific patterns of growth in the Drosophila genital imaginal disc
Dev. Cell
(2001)Drosophila terminalia as an appendage-like structure
Mech. Dev.
(1999)- et al.
Expression of the caudal gene in the germ line of Drosophila: formation of an RNA and protein gradient during early embryogenesis
Cell
(1987)