Nakao Hajime
Insect Growth Regulation Research Unit, Division of Insect Sciences, National Institute of Agrobiological Sciences, 1-2 Oowashi, Tsukuba, Ibaraki 305-8634, Japan.
Dev Biol. 2016 May 15;413(2):207-16. doi: 10.1016/j.ydbio.2016.03.024. Epub 2016 Mar 22.
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.
同一物种内昆虫的体节数量似乎是固定的，与胚层类型无关：长胚层与短/中胚层。本研究表明，通过敲低家蚕驼背基因（Bm-hb）可诱导额外体节形成，推测是通过末端体节添加，这是一种在正常家蚕胚胎发育中未观察到的短/中胚层样的体节形成模式。这表明Bm-hb抑制体节形成。所得结果还表明，间隙基因Bm-Kr（家蚕Krüppel）通过抑制终止体节形成的Bm-hb的表达，为体节形成的进程提供了一个允许的环境。这表明了间隙基因参与体节形成的一种新机制。似乎Bm-Kr和Bm-hb参与体节计数，它们的相互作用有助于在家蚕中形成正确数量的体节。类似的机制可能在采用非果蝇模式的体节形成方式的昆虫中起作用，比如短/中胚层昆虫。
