Barbara J. Taylor

Control of Male Sexual Behavior and Sexual Orientation in Drosophila by the fruitless Gene

Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 10(5) neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

Male-specific fruitless specifies the neural substrates of Drosophila courtship behaviour

Robust innate behaviours are attractive systems for genetically dissecting how environmental cues are perceived and integrated to generate complex behaviours. During courtship, Drosophila males engage in a series of innate, stereotyped behaviours that are coordinated by specific sensory cues. However, little is known about the specific neural substrates mediating this complex behavioural programme. Genetic, developmental and behavioural studies have shown that the fruitless (fru) gene encodes a set of male-specific transcription factors (FruM) that act to establish the potential for courtship in Drosophila. FruM proteins are expressed in ∼2% of central nervous system neurons, at least one subset of which coordinates the component behaviours of courtship. Here we have inserted the yeast GAL4 gene into the fru locus by homologous recombination and show that (1) FruM is expressed in subsets of all peripheral sensory systems previously implicated in courtship, (2) inhibition of FruM function in olfactory system components reduces olfactory-dependent changes in courtship behaviour, (3) transient inactivation of all FruM-expressing neurons abolishes courtship behaviour, with no other gross changes in general behaviour, and (4) ‘masculinization’ of FruM-expressing neurons in females is largely sufficient to confer male courtship behaviour. Together, these data demonstrate that FruM proteins specify the neural substrates of male courtship.

Spatial, temporal, and sexually dimorphic expression patterns of the fruitless gene in the Drosophila central nervous system.

The fruitless (fru) gene of Drosophila produces both sex-specifically and non-sex-specifically spliced transcripts. Male-specific fru products are believed to regulate male courtship. To further an understanding of this genes behavioral role, we examined the central nervous system (CNS) for temporal, spatial, and sexually dimorphic expression patterns of sex-specific fru products by in situ hybridization and immunohistochemistry. For the latter, antibodies were designed to detect only male-specific forms of the protein (FRU(M)) or amino acid sequences that are in common among all translated products (FRU(COM)). Sex-specific mRNAs and male-specific proteins were first observed in mature larvae and peaked in their apparent abundances during the first half of the pupal period. At later stages and in adults, faint mRNA signals were seen in only a few neural clusters; in contrast, relatively strong FRU(M) signals persisted into adulthood. Twenty neuronal groups composed of 1700 fru-expressing neurons were identified in the midpupal CNS. These groups overlap most of the neural sites known to be involved in male courtship. Anti-FRU(COM) led to widespread labeling of neural and nonneural tissues in both sexes, but in the female CNS, only in developing ganglia in a pattern different from that of the males FRU(M) cells. Expression of sex-specific fru mRNAs in the CNS of males analyzed from the earliest pupal stages indicated that sex-specific alternative splicing is not the exclusive mechanism regulating expression of fruitless transcripts.

Are Complex Behaviors Specified by Dedicated Regulatory Genes? Reasoning from Drosophila

We thank S. McConnell, R. Lewontin, R. Sapolsky, M. Siegal, W. Newsome, W. Baker, I. Herskowitz, I. Marin, and E. Kiesman for valuable comments on the manuscript and discussions. This work was supported by a grant from the NIH.

A Broadly Implementable Research Course in Phage Discovery and Genomics for First-Year Undergraduate Students

ABSTRACT Engaging large numbers of undergraduates in authentic scientific discovery is desirable but difficult to achieve. We have developed a general model in which faculty and teaching assistants from diverse academic institutions are trained to teach a research course for first-year undergraduate students focused on bacteriophage discovery and genomics. The course is situated within a broader scientific context aimed at understanding viral diversity, such that faculty and students are collaborators with established researchers in the field. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunters Advancing Genomics and Evolutionary Science (SEA-PHAGES) course has been widely implemented and has been taken by over 4,800 students at 73 institutions. We show here that this alliance-sourced model not only substantially advances the field of phage genomics but also stimulates students’ interest in science, positively influences academic achievement, and enhances persistence in science, technology, engineering, and mathematics (STEM) disciplines. Broad application of this model by integrating other research areas with large numbers of early-career undergraduate students has the potential to be transformative in science education and research training. IMPORTANCE Engagement of undergraduate students in scientific research at early stages in their careers presents an opportunity to excite students about science, technology, engineering, and mathematics (STEM) disciplines and promote continued interests in these areas. Many excellent course-based undergraduate research experiences have been developed, but scaling these to a broader impact with larger numbers of students is challenging. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunting Advancing Genomics and Evolutionary Science (SEA-PHAGES) program takes advantage of the huge size and diversity of the bacteriophage population to engage students in discovery of new viruses, genome annotation, and comparative genomics, with strong impacts on bacteriophage research, increased persistence in STEM fields, and student self-identification with learning gains, motivation, attitude, and career aspirations. Engagement of undergraduate students in scientific research at early stages in their careers presents an opportunity to excite students about science, technology, engineering, and mathematics (STEM) disciplines and promote continued interests in these areas. Many excellent course-based undergraduate research experiences have been developed, but scaling these to a broader impact with larger numbers of students is challenging. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunting Advancing Genomics and Evolutionary Science (SEA-PHAGES) program takes advantage of the huge size and diversity of the bacteriophage population to engage students in discovery of new viruses, genome annotation, and comparative genomics, with strong impacts on bacteriophage research, increased persistence in STEM fields, and student self-identification with learning gains, motivation, attitude, and career aspirations.

Genetic tools for studying adaptation and the evolution of behavior

The rapid expansion of genomic and molecular genetic techniques in model organisms, and the application of these techniques to organisms that are less well studied genetically, make it possible to understand the genetic control of many behavioral phenotypes. However, many behavioral ecologists are uncertain about the value of including a genetic component in their studies. In this article, we review how genetic analyses of behavior are central to topics ranging from understanding past selection and predicting future evolution to explaining the neural and hormonal control of behavior. Furthermore, we review both new and old techniques for studying evolutionary behavior genetics and highlight how the choice of approach depends on both the question and the organism. Topics discussed include genetic architecture, detecting the past history of selection, and genotype‐by‐environment interactions. We show how these questions are being addressed with techniques including statistical genetics, QTL analyses, transgenic analyses, and microarrays. Many of the techniques were first applied to the behavior of genetic model organisms such as laboratory mice and flies. Two recent developments serve to expand the relevance of such studies to behavioral ecology. The first is to use model organisms for studies of the genetic basis of evolutionarily relevant behavior and the second is to apply methods developed in model genetic systems to species that have not previously been examined genetically. These conceptual advances, along with the rapid diversification of genetic tools and the recognition of widespread genetic homology, suggest a bright outlook for evolutionary genetic studies. This review provides access to tools through references to the recent literature and shows the great promise for evolutionary behavioral genetics.

dissatisfaction Encodes a Tailless-like Nuclear Receptor Expressed in a Subset of CNS Neurons Controlling Drosophila Sexual Behavior

The dissatisfaction (dsf) gene is necessary for appropriate sexual behavior and sex-specific neural development in both sexes. dsf males are bisexual and mate poorly, while mutant females resist male courtship and fail to lay eggs. Males and females have sex-specific neural abnormalities. We have cloned dsf and rescued both behavioral and neural phenotypes. dsf encodes a nuclear receptor closely related to the vertebrate Tailless proteins and is expressed in both sexes in an extremely limited set of neurons in regions of the brain potentially involved in sexual behavior. Expression of a female transformer cDNA under the control of a dsf enhancer in males leads to dsf-like bisexual behavior.

Lethality and developmental delay in Drosophila melanogaster larvae after ingestion of selected Pseudomonas fluorescens strains.

Background The fruit fly, Drosophila melanogaster, is a well-established model organism for probing the molecular and cellular basis of physiological and immune system responses of adults or late stage larvae to bacterial challenge. However, very little is known about the consequences of bacterial infections that occur in earlier stages of development. We have infected mid-second instar larvae with strains of Pseudomonas fluorescens to determine how infection alters the ability of larvae to survive and complete development. Methodology/Principal Findings We mimicked natural routes of infection using a non-invasive feeding procedure to study the toxicity of the three sequenced P. fluorescens strains (Pf0-1, SBW25, and Pf-5) to Drosophila melanogaster. Larvae fed with the three strains of P. fluorescens showed distinct differences in developmental trajectory and survival. Treatment with SBW25 caused a subset of insects to die concomitant with a systemic melanization reaction at larval, pupal or adult stages. Larvae fed with Pf-5 died in a dose-dependent manner with adult survivors showing eye and wing morphological defects. In addition, larvae in the Pf-5 treatment groups showed a dose-dependent delay in the onset of metamorphosis relative to control-, Pf0-1-, and SBW25-treated larvae. A functional gacA gene is required for the toxic properties of wild-type Pf-5 bacteria. Conclusions/Significance These experiments are the first to demonstrate that ingestion of P. fluorescens bacteria by D. melanogaster larvae causes both lethal and non-lethal phenotypes, including delay in the onset of metamorphosis and morphological defects in surviving adult flies, which can be decoupled.

Drosophila retained/dead ringer is necessary for neuronal pathfinding, female receptivity and repression of fruitless independent male courtship behaviors

Mutations in the Drosophila retained/dead ringer (retn) gene lead to female behavioral defects and alter a limited set of neurons in the CNS. retn is implicated as a major repressor of male courtship behavior in the absence of the fruitless (fru) male protein. retn females show fru-independent male-like courtship of males and females, and are highly resistant to courtship by males. Males mutant for retn court with normal parameters, although feminization of retn cells in males induces bisexuality. Alternatively spliced RNAs appear in the larval and pupal CNS, but none shows sex specificity. Post-embryonically, retn RNAs are expressed in a limited set of neurons in the CNS and eyes. Neural defects of retn mutant cells include mushroom body β-lobe fusion and pathfinding errors by photoreceptor and subesophageal neurons. We posit that some of these retn-expressing cells function to repress a male behavioral pathway activated by fruM.

Rhizoxin analogs, orfamide A and chitinase production contribute to the toxicity of Pseudomonas protegens strain Pf-5 to Drosophila melanogaster.

Pseudomonas protegens strain Pf-5 is a soil bacterium that was first described for its capacity to suppress plant diseases and has since been shown to be lethal to certain insects. Among these is the common fruit fly Drosophila melanogaster, a well-established model organism for studies evaluating the molecular and cellular basis of the immune response to bacterial challenge. Pf-5 produces the insect toxin FitD, but a ΔfitD mutant of Pf-5 retained full toxicity against D. melanogaster in a noninvasive feeding assay, indicating that FitD is not a major determinant of Pf-5s oral toxicity against this insect. Pf-5 also produces a broad spectrum of exoenzymes and natural products with antibiotic activity, whereas a mutant with a deletion in the global regulatory gene gacA produces none of these exoproducts and also lacks toxicity to D. melanogaster. In this study, we made use of a panel of Pf-5 mutants having single or multiple mutations in the biosynthetic gene clusters for seven natural products and two exoenzymes that are produced by the bacterium under the control of gacA. Our results demonstrate that the production of rhizoxin analogs, orfamide A, and chitinase are required for full oral toxicity of Pf-5 against D. melanogaster, with rhizoxins being the primary determinant.