GFP Expression inDrosophilaTissues: Time Requirements for Formation of a Fluorescent Product

We analyzed the acquisition of fluorescence of a GFP fusion protein expressed from gene constructs designed to regulate either the time of translation of the protein or the time of gene transcription. Both gene constructs expressed a fusion protein with wild-type GFP appended to the N-terminus of the Bicoid (Bcd) transcription factor. One gene construct, P[gfp-bcd] expressed an mRNA that was initially translated at the time of egg deposition. GFP-Bcd fluorescence could first be detected in anterior nuclei in the embryo at syncytial blastoderm stage, within 1.5-2.5 h after translation commenced. The second gene construct, P[hs-gfp-bcd], utilized the hsp70 promoter to regulate the induction of gene expression. In larval salivary glands, GFP-Bcd fluorescence could first be detected in nuclei after a 40-min recovery period following a 10-min heat shock induction of gene expression. These estimates of the time required for the acquisition of a fluorescent GFP product in Drosophila tissues are less than suggested by previously published reports.