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| Direct Link Between Male-specific Neurons And Gender-specific Behaviors |
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| SciMed - Neuroscience | |||
| TS-Si News Service | |||
| Wednesday, 10 September 2008 17:30 | |||
 Hokkaido, Japan. New research has identified a few critical neurons that initiate sex-specific behaviors, observing that masculinization of a model organism elicits male-typical courtship behaviors from females. The study, published in the journal Neuron, demonstrates a direct link between sexual dimorphism in the  brain and gender differences in behavior. [C1] Research into sexual dimorphism includes consideration of sexually dimorphic mechanisms that trigger gender-specific behavior. The new findings represent one of only a few examples that present direct evidence for this phenomenon and the first to identify a specific cluster of cells that initiate courtship.
Fruitless and Doublesex Coordinate to Generate Male-Specific Neurons that Can Initiate Courtship. Ken-ichi Kimura, Tomoaki Hachiya, Masayuki Koganezawa, Tatsunori Tazawa, and Daisuke Yamamoto.
Neuron 59(5) 759-769. doi: 10.1016 / j.neuron.2008.06.007 Scientists regard sexual dimorphism within a species as the systematic difference in form between individuals into male and female sexes. In humans, it refers to obvious characteristics, such as the endocrine (hormonal) systems and their physiological and behavioural effects, as well as
differentiation of gonads, breasts, internal and external genitals, muscle mass differentiation, and hair. There are anomalous exceptions to this general observation that are statistically minute but instructive in developmental terms. Lead study author Professor Ken-ichi Kimura of the Hokkaido University of Education in Japan. [N1]
"Although previous studies have identified a few key brain areas, such as the
dorsal posterior brain, that appear to play a pivotal role in initiating male sexual behavior, nothing is known about the identity of neurons and their circuits in the brain sites which are central to the generation of male courtship behavior," says Kimura.In the fruit fly, Drosophila melanogaster, males display a series of complex and stereotypic behaviors when they are courting a female. Males chase the female while vibrating their wings, producing a love song that has an aphrodisiac influence on the female, who would otherwise take action to escape the male's advances. Later steps in the male courtship behavior involve the initiation and completion of copulation.
Professor Kimura and colleagues made use of a sophisticated technique that allowed them to identify, manipulate, and study small groups of cells in the fruit fly brain.
Studies have indicated that fru functions in parallel with another sex-determination gene called doublesex (dsx) and that fru may function as a kind of master control gene to direct organization of brain centers for sexual behavior.
A fru/dsx-expressing cell cluster, known as P1, was identified as an important site for initiating male courtship behavior. P1 cells are fated to die in females through the action of a feminizing protein called DsxF. Interestingly, genetic manipulation of females so that they possessed male P1 neurons effectively provoked male-typical courtship behavior in the females, even when other parts of the brain were not masculinized.
"P1 is located in the dorsal posterior brain and is composed of 20 neurons that have projections which communicate with the bilateral protocerebrum," explains Professor Kimura. "We found that the masculinizing protein Fru is required in the male brain for correct positioning of the projections from the P1 neurons."
Taken together, these findings demonstrate that the coordinated action of sex-determination genes dsx and fru confer the unique ability to initiate male-typical sexual behavior on P1 neurons.
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