Analysis of function of the pair-rule genes hairy, even-skipped and fushi tarazu in mosaic Drosophila embryos.

We report the first attempt of its kind to study genetic interactions using young Drosophila embryos that are mosaic for wildtype and mutant cells. Using nuclear transplantation we make mosaic embryos in which a patch of cells lacks a particular segmentation gene, A. With antibodies, we than look at the expression of another gene that is known to be downstream of gene A, with respect to the cells in the patch. We have examples of patches of hairy cells (where we monitor the effect on fushi tarazu (ftz) expression), even-skipped (monitoring ftz) and ftz (monitoring engrailed and Ultrabithorax). Our main finding is that the dependence of engrailed expression on the ftz gene is strictly cell-autonomous. This result goes some way towards explaining the dependence of Ultrabithorax expression on ftz, a dependence we show to be locally cell-autonomous within parts of parasegments 6 and 8 but non autonomous within parasegment 7.