Identifying Specific Light Inputs for Each Subgroup of Brain Clock Neurons inDrosophilaLarvae

Abstract

In Drosophila, opsin visual photopigments as well as blue-light-sensitive cryptochrome (CRY) contribute to the synchronization of circadian clocks. We focused on the relatively simple larval brain, with nine clock neurons per hemisphere: five lateral neurons (LNs), four of which express the pigment-dispersing factor (PDF) neuropeptide, and two pairs of dorsal neurons (DN1s and DN2s). CRY is present only in the PDF-expressing LNs and the DN1s. The larval visual organ expresses only two rhodopsins (RH5 and RH6) and projects onto the LNs. We recently showed that PDF signaling is required for light to synchronize the CRY Ϫ larval DN2s. We now show that, in the absence of functional CRY, synchronization of the DN1s also requires PDF, suggesting that these neurons have no direct connection with the visual system. In contrast, the fifth (PDF Ϫ ) LN does not require the PDF-expressing cells to receive visual system inputs. All clock neurons are light-entrained by light-dark cycles in the rh5 2 ;cry b , rh6 1 cry b , and rh5 2 ;rh6 1 double mutants, whereas the triple mutant is circadianly blind. Thus, any one of the three photosensitive molecules is sufficient, and there is no other light input for the larval clock. Finally, we show that constant activation of the visual system can suppress molecular oscillations in the four PDF-expressing LNs, whereas, in the adult, this effect of constant light requires CRY. A surprising diversity and specificity of light input combinations thus exists even for this simple clock network.

Synergistic induction of the clock protein PERIOD by insulin-like peptide and prothoracicotropic hormone in Rhodnius prolixus (Hemiptera): implications for convergence of hormone signaling pathways

“…One group of clock cells in Drosophila (LNs) is photosensitive (Klarsfeld et al, 2011) and is traditionally regarded as the pacemaker (Vossall and Young, 1995). Rhodnius LNs exhibit circadian cycling of PER (Vafopoulou et al, 2010) and also express the neuropeptide PDF, which fills their axonal projections (Vafopoulou et al, 2007, 2010; Vafopoulou and Steel, 2012a).…”

Circadian light-input pathways inDrosophila

“… 47,48 Bolwig´s organs, together with CRY, are essential for light entrainment of the larval clock neurons. 49 However, it remains unclear how significantly HB eyelets contribute to light entrainment of the adult clock. Two studies have investigated the roles of the Rh5 and Rh6 proteins that are expressed in the HB eyelets and in photoreceptor cell R8 of the compound eyes.…”

“…This has already been shown for the larval brain, which has simpler circadian circuits involving only 18 clock neurons and only 2 light-input pathways: Bolwig´s organs and the CRY protein. 49 …”

Balance of Activity between LNvs and Glutamatergic Dorsal Clock Neurons Promotes Robust Circadian Rhythms in Drosophila

“…This requires both the larval visual system (Bolwig's Organ) and clock neurons (Keene et al, 2011). Bolwig's Organ likely innervates the 5 larval Lateral neurons (LN v s) (Keene et al, 2011; Klarsfeld et al, 2011), including the 4 LN v s which express the neuropeptide Pigment Dispersing Factor (PDF). Consistent with direct innervation, light transmitted via Bolwig's Organ rapidly increases neuronal activity of the PDF-expressing LN v s (Yuan et al, 2011).…”