<i>fruitless</i> tunes functional flexibility of courtship circuitry during development.

Abstract

Drosophila male courtship is controlled by the male-specific products of the <i>fruitless</i> (<i>fru^M</i>) gene and its expressing neuronal circuitry. <i>fru^M</i> is considered a master gene that controls all aspects of male courtship. By temporally and spatially manipulating <i>fru^M</i> expression, we found that <i>fru^M</i> is required during a critical developmental period for innate courtship toward females, while its function during adulthood is involved in inhibiting male-male courtship. By altering or eliminating <i>fru^M</i> expression, we generated males that are innately heterosexual, homosexual, bisexual, or without innate courtship but could acquire such behavior in an experience-dependent manner. These findings show that <i>fru^M</i> is not absolutely necessary for courtship but is critical during development to build a sex circuitry with reduced flexibility and enhanced efficiency, and provide a new view about how <i>fru^M</i> tunes functional flexibility of a sex circuitry instead of switching on its function as conventionally viewed.