title: Hunchback knockdown induces supernumerary segment formation in Bombyx.
abstract: Insect segment number within species appears to be fixed irrespective of germ types: long vs. short/intermediate. The present study showed induction of supernumerary segment formation by the knockdown of Bombyx hunchback (Bm-hb), presumably by terminal segment addition, a short/intermediate-like-segmentation mode that is not observed in normal Bombyx embryogenesis. This suggests that Bm-hb suppresses segmentation. The results obtained also suggest that the gap gene Bm-Kr (Bombyx Krüppel) provides a permissive environment for the progression of segmentation by suppressing the expression Bm-hb, which terminates segmentation. This indicates a novel mechanism by which the gap gene is involved in segmentation. It appears that Bm-Kr and Bm-hb are involved in segment counting and their interplay contributes to the correct number of segments being formed in Bombyx. Similar mechanisms may be operating in insects that employ the non-Drosophilan mode of segmentation such as in short/intermediate-germ insects.
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@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; D055785:Gene Knockdown Techniques; D017344:Genes, Insect
keywords: Bombyx; Hunchback; Krüppel; Segmentation clock; Supernumerary segment formation