Functional Dissection of the Neural Substrates for Sexual Behaviors in Drosophila melanogaster

Abstract

The male-specific Fruitless proteins (FruM) act to establish the potential for male courtship behavior in Drosophila melanogaster and are expressed in small groups of neurons throughout the nervous system. We screened ∼1000 GAL4 lines, using assays for general courtship, male–male interactions, and male fertility to determine the phenotypes resulting from the GAL4-driven inhibition of FruM expression in subsets of these neurons. A battery of secondary assays showed that the phenotypic classes of GAL4 lines could be divided into subgroups on the basis of additional neurobiological and behavioral criteria. For example, in some lines, restoration of FruM expression in cholinergic neurons restores fertility or reduces male–male courtship. Persistent chains of males courting each other in some lines results from males courting both sexes indiscriminately, whereas in other lines this phenotype results from apparent habituation deficits. Inhibition of ectopic FruM expression in females, in populations of neurons where FruM is necessary for male fertility, can rescue female infertility. To identify the neurons responsible for some of the observed behavioral alterations, we determined the overlap between the identified GAL4 lines and endogenous FruM expression in lines with fertility defects. The GAL4 lines causing fertility defects generally had widespread overlap with FruM expression in many regions of the nervous system, suggesting likely redundant FruM-expressing neuronal pathways capable of conferring male fertility. From associations between the screened behaviors, we propose a functional model for courtship initiation.

Genetic and Neural Mechanisms that Inhibit Drosophila from Mating with Other Species

“…Flies were anesthetized by CO 2 , introduced into a humidified courtship chamber divided by a plastic film to separate experimental from target flies, and allowed to recover at rearing temperature for 3–4 hours prior to testing, as described before (Manoli et al, 2005; Meissner et al, 2011). …”

Genetic Manipulation of Genes and Cells in the Nervous System of the Fruit Fly

“…The FruM-positive median bundle neurons were shown to be critical for correct behavioral sequence generation using RNAi against FruM (Manoli and Baker, 2004). A screen using the intersection between FruM and GAL4 neuronal expression facilitated identification of additional brain regions involved in male courtship (Meissner et al, 2011). Statistical analysis of courtship behavior when randomly generated subsets of the FruM expression pattern were feminized or inhibited suggested brain regions key for courtship initiation (Kimura et al, 2008).…”

Author response: Neuron hemilineages provide the functional ground plan for the Drosophila ventral nervous system

“…As proof of principle, we demonstrated that a previously identified subset of the fruitless (fru)-expressing neurons involved in courtship song are all produced in hemilineage 12A and cleanly isolated this fru+ cluster. The fru-expressing neurons are necessary and sufficient to drive most aspects of male courtship behavior, and their anatomy, genetics, and function have been dissected in detail (e.g., Manoli and Baker, 2004;Yu et al, 2010b;Meissner et al, 2011). The fru expression pattern can be divided into ∼100 groups of cells, including ∼40 in the VNS (Yu et al, 2010).…”