Fruitless (gene)

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The fruitless gene (fru) is a Drosophila melanogaster gene that encodes several variants of a 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 is not present in mammals. Nor do many other Drosophilid flies contain clear homologs, suggesting that the specifics of fruitless function are unlikely to carry over to other animals. Despite the narrow applicability of research on the fruitless gene, it has historically served as a popular example of how changes in gene expression can lead to changes in behavior, and increasingly as case study for genetic control of nervous system development. Research on fruitless has received attention in the popular press, since it is seen to be connected to the issue of the genetics of human sexual orientation,[2] [3] and behaviors such as gender-specific aggression.[4]

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[edit] 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 a number of 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 with the female-spliced gene product exhibit complete loss of male courtship behavior and sexual orientation.[1] Unfortunately, some of these findings cannot be replicated and the mechanisms by which fruitless controls sex-specific cell differentiation and behavior are controversial [5].

Some of the controversy may be due to the complexity of the fruitless gene locus, which is still incompletely understood. fruitless has at least four promoters, each encoding proteins with a beta-turn-beta domain containing 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 [6], any subset of which may actually regulate behavior.

[edit] 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.[7] However, it should be noted that -- despite the original name and a continuing history of misleading inferences by some researchers and science reporters -- fruitless mutants primarily show defects in male-female courtship, with no significant alteration in male-male or female-female courtship. Thus, evidence is not consistent with the idea that fruitless is any sort of 'gay gene'.

[edit] External links

[edit] References

  1. ^ a b c d Demir E and Dickson BJ (2005). "fruitless splicing specifies male courtship behavior in Drosophila." Cell 121: 785-794.
  2. ^ The Atlantic Homosexuality and Biology, The Genetic Quest June 1997, Chandler Burr
  3. ^ The New York Times Mating Game of Fruit Fly Is Traced to a Single Gene December 13, 1996, Nicholas Wade
  4. ^ The Guardian Flies reveal gene that makes girls fight like boys November 20, 2006, Ian Sample
  5. ^ Ferri et al (2008) fruitless Gene products truncated of their male-like qualities promote neural and behavioral maleness in Drosophila if these proteins are produced in the right places at the right times J. Neurogenetics 22(1):17-55
  6. ^ Goldman and Arbeitman (2007) Genomic and functional studies of Drosophila sex hierarchy regulated gene expression in adult head and nervous system tissues PloS Genetics 3(11):e216
  7. ^ Gailey DA and Hall JC (1989). "Behavior and cytogenetics of fruitless in Drosophila melanogaster: different courtship defects caused by separate, closely linked lesions." Genetics 121: 773-785.
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