The Role of Doublesex and Intersex in the Serotonergic Innervation of the Male Drosophila Genitalia.

TitleThe Role of Doublesex and Intersex in the Serotonergic Innervation of the Male Drosophila Genitalia.
Publication TypeThesis
Year of Publication2004
AuthorsPlame, Rachel Lee
Academic DepartmentBiology
Thesis AdvisorTaylor, Barbara J.
DegreeHonors Baccalaureate of Arts in Biology in International Studies
Number of Pages33
Date Published06/2005
UniversityOregon State University
Thesis TypeUndergraduate
Keywordsexpression, fruit flies, genitalia, neurons

The fruitless (fru) gene in Drosophila produces a male-specific protein, FRUM, which is expressed in a small number of neurons in the central nervous system (CNS) and is responsible specifically for building the potential for male sexual behavior. A set of neurons that innervate male reproductive organs require FRUM to produce serotonin, a neurotransmitter. The gene doublesex (dsx) is necessary for the development of both maleand female reproductive tissues, and in females, intersex (ix) also plays a role in the repression of male structures. Serotonergic innervation was examined in a variety of genotypes. These genotypes included dsx and ix mutants, as well as previously studied fru mutants. The animals examined were dsx loss or gain of function male and female mutants, ix loss of function female and male mutants, and fru male mutants. Both homozygous and heterozygous mutants exhibited a similar range of defects. Female dsx null and dsxDom/dsx+ heterozygotes develop with both male and female reproductive
tracts. In the loss of function mutants, dsx1/dsx1 or dsx1/dsxM+R15, we found
serotonergic innervation to the male reproductive structures that develop in the mutants.
They also contain nerve terminals are present which contain serotonergic terminals which innervate the male reproductive tract. These mutant females did not have serotonergic
innervation on their female reproductive structures, and instead had the same expression pattern found in wild-type female fruit flies. DSXF has a role in preventing the development of 5HT innervation of male reproductive structures. To further examine the function of DSXF, another set of genotypes were examined. It is possible to make a chromosomally female (XX) fly develop as male (pseudomale) or an intersex by using a dsxDom (doublesex Dominant allele), such as dsxM. In these pseudomales, 5HT innervation was found on all of the male reproductive structures as found in wild-type males. However, as we saw in the dsx male mutants, we saw fewer boutons expressing 5HT. This allele allows us to examine the role of dsxM protein expressed in a female. In XX dsxD/dsx1 animals, only DSXM protein is produced. Intersexes were made with a doublesex dominant allele dsxM/+; and XX pseudomales dsx1/dsxM, and dsx1/dsxM+R15, which had only male structures. The other genotype we looked at with a dominant male allele was dsxM/+ intersexes; these XX animals develop as intersexes because both DSXM and DSXF proteins are present in this intersexual genotype. 5HT boutons innervated the male reproductive tissues but no the female reproductive tract.
The IX protein is known to assist DSXF protein in the repression of the development of the male-specific part of the genital disc. In female flies mutant for ix, we tested for serotonergic terminals using DAB. We found serotonergic terminals on the reproductive organs in a handful of flies that were looked at, though further research will need to be conducted to make a strong conclusion. This research also proposes that DSXF may be able to act alone or with a different partner than ix for this suppression of a set of motor neurons that innervate the male reproductive system or their ability to express serotonin for this suppression of male differentiation.