Analysis of P[gal4] insertion lines of Drosophila melanogaster as a route to identifying genes important in the follicle cells during oogenesis.

We report the analysis of a number of lines of Drosophila melanogaster containing insertions of the yeast gal4 gene. By crossing a UAS-lacZ fusion gene as a reporter into these lines, we analysed the expression patterns of beta-galactosidase during oogenesis. Since there is no expression of GAL4 in the germ-line in these experiments, this is an ideal system for the analysis of expression patterns in sub-sets of follicle cells. These lines provide ideal markers for sets of follicle cells, e.g. anterior or posterior polar cells for studying genetic interactions in oogenesis; however, they can also be used in the same way as conventional enhancer traps to clone nearby genes with similar expression patterns. The advantages of this dual gal4/UAS system over conventional enhancer trapping includes the possibility of GAL4-directed misexpression and antisense expression studies to establish the function of the genes we identified during follicle cell determination and differentiation. These studies could lead to the isolation of homologous genes crucial in mammalian oogenesis. Understanding how the somatic cells and germ cells interact to promote growth and maturation of the mammalian follicle and oocyte could well be crucial for improving the fertility of eggs used for in-vitro fertilization programmes, and could provide methods for assessing the quality of eggs.