Zygotic expression and activity of the Drosophila Toll gene, a gene required maternally for embryonic dorsal-ventral pattern formation.

Maternal expression of the Toll gene is required for the production and the correct spatial organization of all lateral and ventral structures of the Drosophila embryo. We show here that the Toll gene is transcribed zygotically in the embryo and that zygotic expression is important for the viability of the larva. Both genetic and molecular data indicate that the zygotic Toll product has the same biochemical activity as the maternal product. The spatial distribution of the Toll transcript in the embryo was analyzed. In contrast to the uniform distribution of the maternal RNA, the zygotic Toll RNA is present in a complex spatial and temporal pattern in the embryo. A striking feature of this pattern is the correlation of the regions of invaginating cells with sites of accumulation of zygotic Toll RNA.