Timing and location of period and timeless gene activity in developing fruit fly nervous system reveal new internal clock cells and patterns

Period (per) and timeless (tim) genes are rhythmically expressed in larval Drosophila neurons throughout development.

• Rhythmic expression of per and tim occurs in several groups of neurons in the larval central nervous system under both light/dark cycles and constant dark conditions.
• Lateral neurons (LNs) in larvae, similar to those in adults, are immunoreactive to pigment-dispersing hormone and maintain strong cycling of PER from the first larval instar onward.
• LNs are positioned close to the terminals of Bolwig's nerve, suggesting they may receive light input from the larval eyes.
• A subset of dorsal neurons (DNLs) also expresses per and tim but shows differential cycling patterns in PER and TIM compared to LNs.
• The light sensitivity associated with TIM protein levels differs in larval Drosophila compared to adults.

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