FROM BEHAVIOR TO DEVELOPMENT - GENES FOR SEXUAL-BEHAVIOR DEFINE THE NEURONAL SEXUAL SWITCH IN DROSOPHILA

The isolation and analysis of Drosophila mutants with altered sexual o rientation lead to the identification of novel branches in the sex-det ermination cascade which govern the sexually dimorphic development of the nervous system. One such example is the fruitless (fru) gene, the mutation of which induces male-to-male courtship and malformation of a male-specific muscle, the muscle of Lawrence (MOL). Since the MOL is formed in wild-type flies when the innervating nerve is male, regardle ss of the sex of the MOL itself, the primary site of Fru function is l ikely to be the motoneurons controlling the MOL. The fru gene produces multiple transcripts including sex-specific ones. A female-specific m RNA from the fru locus has a putative Transformer (Tra) binding site i n its 5' untranslated region, suggesting that fru is a direct target o f Tra. The fru transcripts encode a set of proteins similar to the BTB (Bric a brac, Tramtrack and Broad-complex)-Zn finger family of transc ription factors. Mutations in the dissatisfaction (dsf) gene result in male-to-male courtship and reduced sexual receptivity of females. The dfs mutations also give rise to poor curling of the abdomen in males during copulation and failure of egg-laying by females. The latter phe notypes are ascribable to aberrant innervation of the relevant muscles . A genetic analysis reveals that expression of the dsf phenotypes dep ends on Tra but not on Doublesex (Dsx) or Fru, suggesting that dsf rep resents another target of Tra, Taken together, these findings suggest that the sex-determination protein Tra has at least three different ta rgets, dsx, fru and dsf, each of which represents the first gene in a branch of the sex-determination hierarchy functioning in a mutually-ex clusive set of neuronal cells in the Drosophila central nervous system . (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.