Finding which light signals affect different groups of brain clock neurons in fruit fly larvae

In the absence of functional cryptochrome (CRY), synchronization of the DN1 neurons in Drosophila larvae requires the pigment-dispersing factor (PDF).

• Opsin visual photopigments and blue-light-sensitive cryptochrome contribute to the synchronization of circadian clocks in Drosophila.
• Five lateral neurons (LNs) express PDF, while CRY is present only in PDF-expressing LNs and DN1s.
• Synchronization of DN2 neurons requires PDF signaling when CRY is not functional.
• The fifth LN, which does not express PDF, can still receive visual input independently of PDF-expressing cells.
• Light-dark cycles entrain all clock neurons in specific mutant combinations, but a triple mutant lacks circadian responses.
• Constant activation of the visual system suppresses molecular oscillations in PDF-expressing LNs, a response that is CRY-dependent in adults.

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