Defining the role of Drosophila lateral neurons in the control of circadian rhythms in motor activity and eclosion by targeted genetic ablation and PERIOD protein overexpression

The ventral lateral neurons (LN(v)s) of the Drosophila brain that express t he period (per) and pigment dispersing factor (pdf) genes play a major role in the control of circadian activity rhythms. A new P-gal4 enhancer trap l ine is described that is mostly expressed in the LN(v)s This P-gal4 line wa s used to ablate the LN(v)s by using the pro-apoptosis gene bax, to stop PE R protein oscillations by overexpressing per and to block synaptic transmis sion with the tetanus toxin light chain (TeTxLC). Genetic ablation of these clock cells leads to the loss of robust 24-h activity rhythms and reveals a phase advance in light-dark conditions as well as a weak short-period rhy thm in constant darkness. This behavioural phenotype is similar to that des cribed for disconnected(1) (disco(1)) mutants, in which we show that the ma jority of the individuals have a reduced number of dorsally projecting late ral neurons which, however, fail to express PER. In both LNv-ablated and di sco(1) flies, PER cycles in the so-called dorsal neurons (DNs) of the super ior protocerebrum, suggesting that the weak short-period rhythm could stem from these PDF-negative cells. The overexpression of per in LNs suppresses PER protein oscillations and leads to the disruption of both activity and e closion rhythms, indicating that PER cycling in these cells is required for both of these rhythmic behaviours. Interestingly, flies overexpressing PER in the LNs do not show any weak short-period rhythms, although PER cycles in at least a fraction of the DNs, suggesting a dominant role of the LNs on the behavioural rhythms. Expression of TeTxLC in the LN(v)s does not impai r activity rhythms, which indicates that the PDF-expressing neurons do not use synaptobrevin-dependent transmission to control these rhythms.