A fruitless upstream region that defines the species specificity in the male-specific muscle patterning in Drosophila

Abstract

The muscle of Lawrence (MOL) is a male-specific muscle present in the abdomen of some adult Drosophila species. Formation of the MOL depends on innervation by motoneurons that express fruitless, a neural male determinant. Drosophila melanogaster males carry a pair of MOLs in the 5th abdominal segment, whereas D. subobscura males carry a pair in both the 5th and 4th segments. We hypothesized that the fru gene of D. subobscura but not that of D. melanogaster contains a cis element that directs the formation of the additional pair of MOLs. Successively extended 5’ DNA fragments to the P1 promoter of D. subobscura or the corresponding fragments that are chimeric (i.e., containing both melanogaster and subobscura elements) were introduced into D. melanogaster and tested for their ability to induce the MOL to locate the hypothetical cis element. We found that a 1.5–2-kb genomic fragment located 4–6-kb upstream of the P1 promoter in D. subobscura but not that of D. melanogaster permits MOL formation in females, provided this fragment is grafted to the distal ∼4-kb segment from D. melanogaster, demonstrating that this genomic fragment of D. subobscura contains a cis element for the MOL induction.

Keywords:

• Evolution
• neuromuscular system
• sex determination gene
• enhancers
• D. subobscura

Acknowledgements

We thank the Arizona Species Stock Center for fly stocks, Satoshi Nomoto for technical suggestions and Mayura Suyama for secretarial assistance.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

This work was supported in part by Grants-in-Aid for Scientific Research (23220007, 26113702 and 26114502 to D.Y. and 23500380 and 26430001 to G.T.) from the Japanese Government Ministry of Education, Culture, Sports, Science and Technology (MEXT), a Life Science Grant from the Takeda Science Foundation to D.Y., and a Grant-in-Aid for JSPS fellows (#21-6797) to S.T.