Omura, C. | bioRxiv Science

bioRxiv2021

Pharmacologic rescue of circadian β-cell failure through P2Y1 purinergic receptor identified by small-molecule screen

The mammalian circadian clock drives daily oscillations in physiology and behavior through an autoregulatory transcription feedback loop present in central and peripheral cells. Ablation of the core clock within the endocrine pancreas of adult animals impairs the transcription and splicing of genes involved in hormone exocytosis and causes hypoinsulinemic diabetes. However, identification of druggable proteins and pathways to ameliorate the burden of circadian metabolic disease remains a challenge. Here, we generated {beta} cells expressing a nano-luciferase reporter within the proinsulin polypeptide to screen 2,640 pharmacologically-active compounds and identify insulinotropic molecules that bypass the secretory defect in clock mutant {beta} cells. We validated lead compounds in primary mouse islets and identified known modulators of ligandgated ion channels and G-protein coupled receptors, including the antihelmintic ivermectin. Single-cell electrophysiology in circadian mutant mouse and human cadaveric islets validated ivermectin as a glucose-dependent secretagogue. Genetic, genomic, and pharmacologic analyses established that the molecular clock controls the expression of the purinergic P2Y1 receptor to mediate the insulinotropic activity of ivermectin. These findings identify the P2Y1 purinergic receptor as a target to rescue circadian {beta}-cell failure and establish a chemical genetic screen for endocrine therapeutics.

cell biology↗

bioRxiv2021

Evolution of maternal and early zygotic transcript regulation across Drosophila

The complements of mRNAs in early embryonic development are crucial for setting up developmental trajectories across all animals. The earliest stages of development are regulated by mRNAs deposited into the egg by the mother, until the zygote can become competent to transcribe its own genome. Previously, we showed that the set of maternally deposited and early transcribed zygotic mRNAs in Drosophila are generally conserved across species, but with some notable variation. We also showed that a majority of regulators of these two types of transcripts are shared. In this study, we examine the differences in regulatory motifs associated with maternal deposition and early zygotic transcription across species of Drosophila. For maternal transcripts, while the regulators are mostly conserved, we find the Drosophila pseudoobscura species subgroup appears to contain numerous novel regulatory motifs unique to these species. These novel motifs are enriched in transposable elements exclusive to this group. As this species group had been previously identified as having an exceptional amount of divergence in early embryonic transcripts, this change in regulation may be responsible. However, transcripts that are present at the maternal stage only in these species are equally enriched in novel (group-specific) and conserved binding sites, so the novel regulation is not the sole cause of regulatory divergence in these species. At the zygotic stage, we observe a wide variety of species-specific motifs. Additionally, at both stages we observe motifs conserved across species having different effects on gene expression in different species, and regulating different sets of genes in different species. By examining changes in motif content across species, we find that changes in motif content alone is generally insufficient to drive gene expression changes across species.

evolutionary biology↗