Bantam regulates the adult sleep circuit in Drosophila
Sleep is a highly conserved feature of animal life characterized by dramatic changes in behavior, neural physiology and gene expression. The gene regulatory factors responsible for these sleep-dependent changes remain largely unknown. microRNAs are post-transcriptional modulators of gene expression which have been implicated in sleep regulation. Our previous screen identified 25 sleep-regulating microRNAs in Drosophila melanogaster, including the developmental regulator bantam (ban). Here we show that ban promotes early nighttime sleep through a population of glutamatergic neurons- the {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral Mushroom Body Output Neurons (MBONs). We found that knockdown of ban in these neurons led to a reduction in early night sleep. The {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral MBONs were previously shown to be wake-promoting, suggesting that ban acts to inhibit these neurons. GCaMP calcium imaging revealed that bantam inhibits the neural activity of the {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral MBONs during the night but not the day. Blocking synaptic transmission in the {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral MBONs rescued the effect of ban knockdown on sleep. Together these results suggest that ban promotes night sleep via the inhibition of the {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral MBONs. RNAseq further revealed that bantam negatively regulates the wake-promoting mRNAs Kelch and CCHamide-2 receptor in the {gamma}5{beta}'2a/{beta}'2mp/{beta}'2mp_bilateral MBONs. These experiments establish bantam as an active regulator of sleep and neural activity within the fly brain.