Genetic control of early embryogenesis in the red flour beetle, Tribolium castaneum.

The power of genetic analysis possible with the fruit fly, Drosophila melanogaster, has yielded a detailed understanding of pattern formation controlled by homeotic and segmentation genes in early embryogenesis. We are studying the genetic regulation of embryogenesis in the red flour beetle, Tribolium castaneum. The dynamic process of germ rudiment formation and sequential segmentation exhibited by Tribolium provides a context different than Drosophila within which to assess the function of homeotic and segmentation gene homologs. Our analyses of the genes in the HOM-C suggest many similarities in structure and function with the well-characterized Drosophila genes. Abdominal resembles its Drosophila homolog abdominal-A in functioning to establish segmental identities in the abdomen, such that in each case mutations result in homeotic transformations to PS6. Although the anterior functional boundary of abdominal-A homologs is precisely conserved, the domain within which Abdominal is important extends more posterior than that of abdominal-A. The final expression pattern of the segmentation gene engrailed in Tribolium is identical to Drosophila, suggesting that these homologs are involved in a conserved developmental process. However, as expected the development of that pattern is different; engrailed stripes anticipate the formation of each new segment as they appear sequentially in the elongating germ band. Although the grasshopper even-skipped and fushi tarazu homologs are not apparently important in segmentation, the expression patterns of the Tribolium homologs strongly suggest that they have gained a role in segmentation in the lineage leading to beetles and flies. Nevertheless, differences between Tribolium and Drosophila in the dynamics of even-skipped expression and the fushi tarazu mutant phenotype indicate divergence in the regulation and roles of these genes.