The core clock gene, Bmal1, and its downstream target, the SNARE regulatory protein secretagogin, are necessary for circadian secretion of glucagon-like peptide-1

•Murine GLP-1 secretion is circadian and is regulated by the clock gene Bmal1.•The regulatory SNARE protein, secretagogin, is expressed in all intestinal L-cells.•Secretagogin expression is circadian and regulated by BMAL1 in intestinal L-cells.•Secretagogin translocates to the cell membrane upon L-cell stimulation.•Secretagogin knockdown impairs rhythmic secretion of glucagon-like peptide-1.