Sarkissian, T. | Search bioRxiv

bioRxiv2020

Connectomics analysis reveals first, second, and third order thermosensory and hygrosensory neurons in the adult Drosophila brain

Animals exhibit innate and learned preferences for temperature and humidity - conditions critical for their survival and reproduction. Here, we leveraged a whole adult brain electron microscopy volume to study the circuitry associated with antennal thermosensory and hygrosensory neurons, which target specific ventroposterior (VP) glomeruli in the Drosophila melanogaster antennal lobe. We have identified two new VP glomeruli, in addition to the five known ones, and the projection neurons (VP PNs) that relay VP information to higher brain centres, including the mushroom body and lateral horn, seats of learned and innate olfactory behaviours, respectively. Focussing on the mushroom body lateral accessory calyx (lACA), a known thermosensory neuropil, we present a comprehensive connectome by reconstructing neurons downstream of heating- and cooling-responsive VP PNs. We find that a few lACA-associated mushroom body intrinsic neurons (Kenyon cells) solely receive thermosensory inputs, while most receive additional olfactory and thermo- or hygrosensory PN inputs in the main calyx. Unexpectedly, we find several classes of lACA-associated neurons that form a local network with outputs to other brain neuropils, suggesting that the lACA serves as a general hub for thermosensory circuitry. For example, we find DN1 pacemaker neurons that link the lACA to the accessory medulla, likely mediating temperature-based entrainment of the circadian clock. Finally, we survey strongly connected downstream partners of VP PNs across the protocerebrum; these include a descending neuron that receives input mainly from dry-responsive VP PNs, meaning that just two synapses might separate hygrosensory inputs from motor neurons in the nerve cord. (249) HIGHLIGHTSO_LITwo novel thermo/hygrosensory glomeruli in the fly antennal lobe C_LIO_LIFirst complete set of thermosensory and hygrosensory projection neurons C_LIO_LIFirst connectome for a thermosensory centre, the lateral accessory calyx C_LIO_LINovel third order neurons, including a link to the circadian clock C_LI

neuroscience↗

bioRxiv2018

A Cut/cohesin axis alters the chromatin landscape to facilitate neuroblast death

Precise control of cell death in the nervous system is essential for development. Spatial and temporal factors activate the death of Drosophila neural stem cells (neuroblasts) by controlling the transcription of multiple cell death genes through a shared enhancer, enh1. The activity of enh1 is controlled by abdominalA and Notch, but additional inputs are needed for proper specificity. Here we show that the Cut DNA binding protein is required for neuroblast death, acting downstream of enh1. In the nervous system, Cut promotes an open chromatin conformation in the cell death gene locus, allowing cell death gene expression in response to abdominalA. We demonstrate a temporal increase in global H3K27me3 levels in neuroblasts, which is enhanced by cut knockdown. Furthermore, cut regulates the expression of the cohesin subunit Stromalin in the nervous system. The cohesin components Stromalin and NippedB are required for neuroblast death, and knockdown of Stromalin increases repressive histone modifications in neuroblasts. Thus Cut and cohesin regulate apoptosis in the developing nervous system by altering the chromatin landscape.\n\nSummary statementCut regulates the programmed death of neural stem cells by altering cohesin levels and promoting a more open chromatin conformation to allow cell death gene expression.

developmental biology↗