Miles C I, Booker R
Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853-2702.
Dev Biol. 1993 Jan;155(1):147-60. doi: 10.1006/dbio.1993.1014.
Several aspects of leg development in the moth Manduca sexta were examined using the homeotic mutation Octopod (Octo). This mutation causes a transformation of the ventral epidermis of the first abdominal segment (A1) to that of the third thoracic segment (T3), resulting in the presence of thoracic-like legs on A1. The degree of transformation of A1 is variable, ranging from bumps on the cuticle to fully segmented thoracic-like legs. In the normal thoracic legs, clusters of undifferentiated cells known as differentiation centers are located around the coxal-trochanteral, femoral-tibial, and tibial-tarsal joints. The adult thoracic legs develop from the differentiation centers at metamorphosis. The homeotic legs of the Octopod larvae also have differentiation centers at comparable positions in the homeotic leg. As a result, the number of leg segments in a mutant adult is correlated with the number of segments and differentiation centers that animal had in its larval homeotic leg. Our data suggest that the differentiation center located at the coxal-trochanteral joint forms the adult coxa and trochanter, the center at the larval femoral-tibial joint the adult femur and tibia, and the differentiation center at the larval tibial-tarsal joint the adult tarsus. Homeotic larval legs which include at least a femur have supernumerary muscles, while adult homeotic legs rarely show discrete muscle. The homeotic larval muscles appear to have thoracic identities, based on their attachment points and the timing of their degeneration at the larval-pupal transition. They are innervated by a motoneuron that is normally present in A1 where it innervates the ventral lateral external muscle (VLE). In mutant animals, the same motoneuron innervates all of the homeotic muscles and the VLE. We consider possible mechanisms underlying the development of homeotic muscles and their innervation. At the larval-pupal transition, the VLE in mutant animals degenerates at its normal time, which is 3 days after the degeneration of the homeotic muscles. Thus, despite their common innervation, the two muscle types degenerate according to their own schedules, indicating that the developmental fates of the muscles are not dictated by their innervating neuron but are intrinsic to the muscles themselves.
利用同源异型突变体“八足（Octopod，Octo）”对烟草天蛾腿部发育的几个方面进行了研究。这种突变导致第一腹节（A1）的腹侧表皮转变为第三胸节（T3）的腹侧表皮，从而使A1上出现类似胸足的结构。A1的转变程度各不相同，从表皮上的凸起到完全分节的类似胸足的结构都有。在正常的胸足中，被称为分化中心的未分化细胞簇位于基节 - 转节、股节 - 胫节和胫节 - 跗节关节周围。成虫的胸足在变态发育过程中由这些分化中心发育而来。Octopod幼虫的同源异型足在同源异型足的相应位置也有分化中心。因此，突变体成虫腿部节段的数量与该动物幼虫同源异型足中的节段数量和分化中心数量相关。我们的数据表明，位于基节 - 转节关节处的分化中心形成成虫的基节和转节，幼虫股节 - 胫节关节处的分化中心形成成虫的股节和胫节，幼虫胫节 - 跗节关节处的分化中心形成成虫的跗节。包含至少一个股节的同源异型幼虫足有额外的肌肉，而成虫同源异型足很少有离散的肌肉。基于同源异型幼虫肌肉的附着点以及它们在幼虫 - 蛹期转变时退化的时间，这些肌肉似乎具有胸肌的特征。它们由通常存在于A1中的运动神经元支配，该运动神经元在A1中支配腹外侧外肌（VLE）。在突变体动物中，同一个运动神经元支配所有同源异型肌肉和VLE。我们考虑了同源异型肌肉及其神经支配发育的潜在机制。在幼虫 - 蛹期转变时，突变体动物中的VLE在其正常时间退化，即在同源异型肌肉退化3天后。因此，尽管这两种肌肉类型由共同的神经元支配，但它们根据各自的时间表退化，这表明肌肉的发育命运不是由支配它们的神经元决定的，而是肌肉自身固有的。
