fruitless (gene)

The fruitless gene (fru) is a Drosophila melanogaster gene that encodes several variants of a putative transcription factor protein. Normal fruitless function is required for proper development of several anatomical structures necessary for courtship, including motor neurons which innervate muscles needed for fly sexual behaviors.[1] The gene does not have an obvious mammalian homolog, but appears to function in sex determination in species as distant as the mosquito Anopheles gambiae.[2]

fruitless
Identifiers
OrganismDrosophila melanogaster
Symbolfru
Entrez42226
RefSeq (mRNA)NM_169821.1
RefSeq (Prot)NP_732349.1
UniProtQ8IN81
Other data
Chromosome3R: 14.22 - 14.39 Mb

fruitless serves as an example of how a gene or a group of genes may regulate the development and/or function of neurons involved in innate behavior. Research on fruitless has received attention in the popular press, since it provokes discussion on genetics of human sexual orientation,[3][4] and behaviors such as gender-specific aggression.[5]

Function

Male flies with mutations in the fruitless gene display altered sexual behavior. Fruitfly courtship, which involves a complex male-initiated ritual, may be disrupted in many ways by mutated fru alleles; fru is necessary for every step in the ritual. Some alleles prevent courting entirely, while others disrupt individual components. Notably, some loss-of-function alleles change or remove sexual preference.[1]

Although many genes are known to be involved in male courtship behavior, the fruitless gene has been considered noteworthy because it exhibits sex-specific alternative splicing. When females produce the male-spliced gene product, they behave as males. Males that do not produce the male-specific product do not court females and are infertile.[1] In the brain, a subset (ca. 2,000) of neurons express fruitless[6] and fruitless expression is sufficient to instruct sexually dimorphic connectivity. [7][8]

fruitless has at least four promoters, each encoding proteins containing both a BTB (Broad complex/tramtrack/bric-a-brac) domain and a zinc finger motif. Alternative splicing occurs at both the 5' and 3' ends, and there are several variants (other than the male- and female-specific splicing patterns).[1] The fruitless gene locus also controls the expression of hundreds of other genes,[9] any subset of which may actually regulate behavior.

Name

Early work refers to the gene as fruity, an apparent pun on both the common name of D. melanogaster, the fruit fly, as well as a slang word for homosexual. As social attitudes towards homosexuality changed, fruity came to be regarded as offensive, or at best, not politically correct. Thus, the gene was re-dubbed fruitless, alluding to the lack of offspring produced by flies with the mutation.[10] However, despite the original name and a continuing history of misleading inferences by the popular media, fruitless mutants primarily show defects in male-female courtship, though certain mutants cause male-male or female-female courtship.[11]

References
  1. Demir E, Dickson BJ (June 2005). "fruitless splicing specifies male courtship behavior in Drosophila". Cell. 121 (5): 785–94. doi:10.1016/j.cell.2005.04.027. PMID 15935764. S2CID 14663286.
  2. Gailey DA, Billeter JC, Liu JH, Bauzon F, Allendorfer JB, Goodwin SF (March 2006). "Functional conservation of the fruitless male sex-determination gene across 250 Myr of insect evolution". Molecular Biology and Evolution. 23 (3): 633–43. doi:10.1093/molbev/msj070. PMID 16319090.
  3. Burr C (June 1997). "Homosexuality and Biology, The Genetic Quest". The Atlantic.
  4. Wade N (December 13, 1996). "Mating Game of Fruit Fly Is Traced to a Single Gene". The New York Times.
  5. Sample, Ian (November 20, 2006). "Flies reveal gene that makes girls fight like boys". The Guardian.
  6. Cachero S, Ostrovsky AD, Yu JY, Dickson BJ, Jefferis GS (September 2010). "Sexual dimorphism in the fly brain". Current Biology. 20 (18): 1589–601. doi:10.1016/j.cub.2010.07.045. PMC 2957842. PMID 20832311.
  7. Kohl J, Ostrovsky AD, Frechter S, Jefferis GS (December 2013). "A bidirectional circuit switch reroutes pheromone signals in male and female brains". Cell. 155 (7): 1610–23. doi:10.1016/j.cell.2013.11.025. PMC 3898676. PMID 24360281.
  8. Ruta V, Datta SR, Vasconcelos ML, Freeland J, Looger LL, Axel R (December 2010). "A dimorphic pheromone circuit in Drosophila from sensory input to descending output". Nature. 468 (7324): 686–90. Bibcode:2010Natur.468..686R. doi:10.1038/nature09554. PMID 21124455. S2CID 4412743.
  9. Goldman TD, Arbeitman MN (November 2007). "Genomic and functional studies of Drosophila sex hierarchy regulated gene expression in adult head and nervous system tissues". PLOS Genetics. 3 (11): e216. doi:10.1371/journal.pgen.0030216. PMC 2082469. PMID 18039034.
  10. Gailey DA, Hall JC (April 1989). "Behavior and cytogenetics of fruitless in Drosophila melanogaster: different courtship defects caused by separate, closely linked lesions". Genetics. 121 (4): 773–85. PMC 1203660. PMID 2542123.
  11. "GeneBrief - fruitless". InteractiveFly. Society for Developmental Biology.
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