Pair-rule and gap gene mutants in the flour beetle Tribolium castaneum

Early pattern formation in the Drosophila embryo occurs in a syncytial blas toderm where communication between nuclei is unimpeded by cell walls. Durin g the development of other insects, similar gene expression patterns are ge nerated in a cellular environment. In Tribolium, for instance, pair-rule st ripes are transiently expressed near the posterior end of the growing germ band. To elucidate how pattern formation in such a situation deviates from that of Drosophila, functional data about the genes involved are essential. In agenetic screen for Tribolium mutants affecting the larval cuticle patt ern, we isolated 4 mutants (from a total of 30) which disrupt segmentation in the thorax and abdomen. Two of these mutants display clear pair-rule phe notypes. This demonstrates that not only the expression, but also the funct ion of pair-rule genes in this short-germ insect is in principle similar to Drosophila. The other two mutants appear to identify gap genes. They provi de the first evidence for the involvement of gap genes in abdominal segment ation of short-germ embryos. However, significant differences between the p henotypes of these mutants and those of known Drosophila gap mutants exist which indicates that evolutionary changes occurred in either the regulation or action of these genes.