Circadian regulation of egg-laying behavior in fruit flies Drosophila melanogaster.

Significant progress has been made in our understanding of the neurogenetics of circadian clocks in fruit flies Drosophila melanogaster. Several pacemaker neurons and clock genes have now been identified and their roles in the cellular and molecular clockwork established. Some recent findings suggest that the basic architecture of the clock is multi-oscillatory; the clock mechanisms in the ventral lateral neurons (LN(v)s) of the fly brain govern locomotor activity and adult emergence rhythms, while the peripheral oscillators located in antennal cells regulate olfactory rhythm. Among circadian phenomena exhibited by Drosophila, the egg-laying rhythm is unique in many ways: (i) this rhythm persists under constant light (LL), while locomotor activity and adult emergence become arrhythmic, (ii) its circadian periodicity is much longer than 24h, and (iii) while egg-laying is rhythmic under constant darkness, the expression of two core clock genes period (per) and timeless (tim), is non-oscillatory in the ovaries. In this paper, we review our current knowledge of the circadian regulation of egg-laying behavior in Drosophila, and provide some possible explanations for its self-sustained nature. We conclude by discussing the existing limitations in our understanding of the regulatory mechanisms and propose few approaches to address them.