Maternal control of Drosophila segmentation gene expression.

Several genes have been identified that are involved in establishing the segmented body pattern during development of the fruit-fly Drosophila melanogaster. These fall into several classes on the basis of the kind of alteration to the wild-type segmentation pattern observed in mutant embryos. For example, mutations of the pair-rule class, such as fushi tarazu (ftz), cause the deletion of pattern elements with a two-segment periodicity; those of the gap class, such as knirps, cause the deletion of contiguous groups of segments. The availability of antibodies against the ftz protein has allowed its spatial pattern of expression to be studied during the development of wild-type and mutant embryos. The aim of the latter kind of experiment is to investigate possible interactions between these important genes. We have recently reported that knirps mutations cause a striking alteration to the pattern of transverse stripes of ftz expression usually seen during embryogenesis. Knirps is a zygotically-expressed gene, but recently a class of maternally-active genes has been identified that causes similar defects in pattern formation. We have now investigated the pattern of ftz expression in mutants of this class and have found that while they do have features seen in knirps mutants, they also exhibit significant differences between the different mutations reflecting the distinct but overlapping domains of gene activity. These observations demonstrate that maternally-active segmentation genes regulate zygotic gene expression, and that some of their effects on ftz may be directed through the knirps gene.