Fig. 4

Driver-effector trans-activation. Two independent driver lines with different LexPR transactivator expression patterns were studied: (A) — represents the driver line shown in Fig. 2A, (B) — the driver line shown in Fig. 2D. Each driver line was crossed with a transgenic effector line (different effector lines were used in panels A and B), which carried mCherry gene under control of the LexOP. The hybrid F₃ embryos that were double transgenic for the driver and effector cassettes were treated with 1 μM mifepristone from 24 hpf onwards. Bottom panel is a combined image showing both reporters EGFP and mCherry: green indicates excess of EGFP fluorescence, red — excess of mCherry fluorescence, yellow — similar levels of mCherry and EGFP fluorescence (notice that these colors do not constitute true molar ratios between the reporters). Although, most positive cells express both reporters, there are cells that yield brighter mCherry fluorescence than the EGFP and vice-versa. mCherry fluorescence is not detected in the effector lines containing only the effector cassette upon treatment with mifepristone. No background EGFP/mCherry fluorescence was detected in the control populations of double transgenic fish that were not treated with mifepristone (not shown). Images were captured at 96 hour post-fertilization. (A) Strong expression is in the cell layer at the bottom of the ear (possibly sensory patches), at the olfactory bulb region and in various neurons (head, dorsal view). Notice the autofluorescence from the iridophores in the eye that is visible only through the EGFP filter set. (B) Expression is detected in the specific subtype of muscle cells (lateral view). Two lines of dots show autofluorescence from the iridophores.