Booker R, Miles C I
Division of Biological Sciences, Cornell University, Ithaca, New York 14853, USA.
J Neurobiol. 1995 Nov;28(3):281-96. doi: 10.1002/neu.480280303.
Octopod (Octo) is a mutation of the moth Manduca sexta, which transforms the first abdominal segment (A1) in the anterior direction. Mutant animals are characterized by the appearance of homeotic thoracic-like legs on A1. We exploited this mutation to determine what rules might be used in specifying the fates of sensory neurons located on the body surface of larval Manduca. Mechanical stimulation of homeotic leg sensilla did not cause reflexive movements of the homeotic legs, but elicited responses similar to those observed following stimulation of ventral A1 body wall hairs. Intracellular recordings demonstrated that several of the motoneurons in the A1 ganglion received inputs from the homeotic sensory hairs. The responses of these motoneurons to stimulation of homeotic sensilla resembled their responses to stimulation of ventral body wall sensilla. Cobalt fills revealed that the mutation transformed the segmental projection pattern of only the sensory neurons located on the ventral surface of A1, resulting in a greater number with intersegmental projection patterns typical of sensory neurons found on the thoracic body wall. Many of the sensory neurons on the homeotic legs had intersegmental projection patterns typical of abdominal sensory neurons: an anteriorly directed projection terminating in the third thoracic ganglion (T3). Once this projection reached T3, however, it mimicked the projections of the thoracic leg sensory neurons. These results demonstrate that the same rules are not used in the establishment of the intersegmental and leg-specific projection patterns. Segmental identity influences the intersegmental projection pattern of the sensory neurons of Manduca, whereas the leg-specific projections are consistent with a role for positional information in determining their pattern.
章鱼足（Octo）是烟草天蛾的一种突变体，它使第一腹节（A1）向前转变。突变动物的特征是在A1节出现类似胸足的同源异型腿。我们利用这种突变来确定在指定烟草天蛾幼虫体表感觉神经元命运时可能使用了哪些规则。对同源异型腿感觉毛的机械刺激不会引起同源异型腿的反射性运动，但会引发与刺激A1腹侧体壁毛后观察到的类似反应。细胞内记录表明，A1神经节中的几个运动神经元从同源异型感觉毛接收输入。这些运动神经元对同源异型感觉毛刺激的反应类似于它们对腹侧体壁感觉毛刺激的反应。钴填充显示，该突变仅改变了位于A1腹面的感觉神经元的节段投射模式，导致更多的感觉神经元具有胸壁上典型的节间投射模式。同源异型腿上的许多感觉神经元具有腹部感觉神经元典型的节间投射模式：向前投射终止于第三胸神经节（T3）。然而，一旦这个投射到达T3，它就模仿胸腿感觉神经元的投射。这些结果表明，在建立节间和腿部特异性投射模式时使用了不同的规则。节段身份影响烟草天蛾感觉神经元的节间投射模式，而腿部特异性投射与位置信息在确定其模式中的作用一致。
