Evolutionarily conserved hedgehog proteins orchestrate the patterning of embryonic tissues, and dysfunctions in their signaling can lead to tumorigenesis. In vertebrates, Sonic hedgehog (Shh) is essential for nervous system development, but the mechanisms underlying its action remain unclear. Early electrical activity is another developmental cue important for proliferation, migration, and differentiation of neurons. Here we demonstrate the interplay between Shh signaling and Ca 2+ dynamics in the developing spinal cord. Ca 2+ imaging of embryonic spinal cells shows that Shh acutely increases Ca 2+ spike activity through activation of the Shh coreceptor Smoothened (Smo) in neurons. Smo recruits a heterotrimeric GTP-binding protein-dependent pathway and engages both intracellular Ca 2+ stores and Ca 2+ influx. The dynamics of this signaling are manifested in synchronous Ca 2+ spikes and inositol triphosphate transients apparent at the neuronal primary cilium. Interaction of Shh and electrical activity modulates neurotransmitter phenotype expression in spinal neurons. These results indicate that electrical activity and second-messenger signaling mediate Shh action in embryonic spinal neurons.

SUMMARY The hormonal regulation of feeding behaviour is well known in vertebrates,whereas it remains poorly understood in insects. Here, we report that the takeout gene is an essential component of nutritional homeostasis in Drosophila. takeout encodes a putative juvenile hormone (JH)binding protein and has been described as a link between circadian rhythm and feeding behaviour. However, the physiological role of takeout and its putative link to JH remain unknown. In this study, we show that takeout (to1) flies failed to adapt their food intake according to food availability and that most defects could be genetically rescued. When food is abundant, to1 are hyperphagic, yielding to hypertrophy of the fat body. When food reappears after a starvation period, to1 flies do not increase their food intake as much as wild-type flies. This defect in food intake regulation is partly based on the action of Takeout on taste neurons, because the sensitivity of to1 gustatory neurons to sugars does not increase after starvation, as in wild-type neurons. This lack of regulation is also evident at the locomotor activity, which normally increases during starvation, a behaviour related to food foraging. In addition, to1 flies lack sexual dimorphism of locomotor activity,which has previously been linked to the JH circulating level. Moreover,application of the JH analog methoprene rescues the phenotype. These results suggest that takeout plays a central role as a feeding regulator and may act by modulating the circulating JH level.

Insulin signaling pathways are implicated in several physiological processes in invertebrates, including the control of growth and life span; the latter of these has also been correlated with juvenile hormone (JH) deficiency. In turn, JH levels have been correlated with sex-specific differences in locomotor activity. Here, the involvement of the insulin signaling pathway in sex-specific differences in locomotor activity was investigated in Drosophila. Ablation of insulin-producing neurons in the adult pars-intercerebralis was found to increase trehalosemia and to abolish sexual dimorphism relevant to locomotion. Conversely, hyper-insulinemia induced by insulin injection or by over-expression of an insulin-like peptide decreases trehalosemia but does not affect locomotive behavior. Moreover, we also show that in the head of adult flies, the insulin receptor (InR) is expressed only in the fat body surrounding the brain. While both male and female InR mutants are hyper-trehalosemic, they exhibit similar patterns of locomotor activity. Our results indicate that first, insulin controls trehalosemia in adults, and second, like JH, it controls sex-specific differences in the locomotor activity of adult Drosophila in a manner independent of its effect on trehalose metabolism.