To test whether peak NAS-37 expression coincided with ecdysis in each larval stage, a PEST protein degradation signal was fused onto the C-terminus of the pWD90 GFP construct. This sequence increases protein turnover and should rapidly eliminate GFP fluorescence after expression has stopped. As expected, bright fluorescence was observed in the Hyp5 cell at the anterior tip of the animal and in the rectal epithelial cells at ecdysis. After the molt,
nas-37 expression was very low in all cells, although expression continued in Hyp5 and the rectal epithelial cells. GFP expression driven by the
nas-37 promoter (Pnas-37::GPF) began to rise about 6 hours before ecdysis, with peak
nas-37 expression in hypodermal cells (and seam cells exclusively in the L4 stage) about 4 hours before each molt.