title: Analyses of interactions among pair-rule genes and the gap gene Krüppel in Bombyx segmentation.
abstract: In the short-germ insect Tribolium, a pair-rule gene circuit consisting of the Tribolium homologs of even-skipped, runt, and odd-skipped (Tc-eve, Tc-run and Tc-odd, respectively) has been implicated in segment formation. To examine the application of the model to other taxa, I studied the expression and function of pair-rule genes in Bombyx mori, together with a Bombyx homolog of Krüppel (Bm-Kr), a known gap gene. Knockdown embryos of Bombyx homologs of eve, run and odd (Bm-eve, Bm-run and Bm-odd) exhibited asegmental phenotypes similar to those of Tribolium knockdowns. However, pair-rule gene interactions were similar to those of both Tribolium and Drosophila, which, different from Tribolium, shows a hierarchical segmentation mode. Additionally, the Bm-odd expression pattern shares characteristics with those of Drosophila pair-rule genes that receive upstream regulatory input. On the other hand, Bm-Kr knockdowns exhibited a large posterior segment deletion as observed in short-germ insects. However, a detailed analysis of these embryos indicated that Bm-Kr modulates expression of pair-rule genes like in Drosophila, although the mechanisms appear to be different. This suggested hierarchical interactions between Bm-Kr and pair-rule genes. Based on these results, I concluded that the pair-rule gene circuit model that describes Tribolium development is not applicable to Bombyx.
authors.affiliation: Insect Growth Regulation Research Unit, Division of Insect Sciences, National Institute of Agrobiological Sciences, 1-2 Oowashi, Tsukuba, Ibaraki 305-8634, Japan. Electronic address: nakaoh@nias.affrc.go.jp.
authors.forename: Hajime
authors.initials: H
authors.lastname: Nakao
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics*; D012831:Bombyx / Q000196:embryology* / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D004843:Epistasis, Genetic; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D017344:Genes, Insect; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D010641:Phenotype; D034622:RNA Interference; D012689:Sequence Homology, Nucleic Acid
chemical_list: D019476:Insect Proteins
keywords: Bombyx; Krüppel; Pair-rule gene circuit; RNAi; Segmentation