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 formatio n controlled by homeotic and segmentation genes in early embryogenesis . We are studying the genetic regulation of embryogenesis in the red f lour 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 functi on of homeotic and segmentation gene homologs. Our analyses of the gen es in the HOM-C suggest many similarities in structure and function wi th the well-characterized Drosophila genes. Abdominal resembles its Dr osophila homolog abdominal-A in functioning to establish segmental ide ntities in the abdomen, such that in each case mutations result in hom eotic transformations to PS6. Although the anterior functional boundar y of abdominal-A homologs is precisely conserved, the domain within wh ich Abdominal is important extends more posterior than that of abdomin al-A. The final expression pattern of the segmentation gene engrailed in Tribolium is identical to Drosophila, suggesting that these homolog s are involved in a conserved developmental process. However, as expec ted the development of that pattern is different; engrailed stripes an ticipate the formation of each new segment as they appear sequentially in the elongating germ band. Although the grasshopper even-skipped an d fushi tarazu homologs are not apparently important in segmentation, the expression patterns of the Tribolium homologs strongly suggest tha t they have gained a role in segmentation in the lineage leading to be etles and flies. Nevertheless, differences between Tribolium and Droso phila in the dynamics of even-skipped expression and the fushi tarazu mutant phenotype indicate divergence in the regulation and roles of th ese genes.