PROJECTION PATTERN OF SENSORY NEURONS IN THE CENTRAL-NERVOUS-SYSTEM OF A HOMEOTIC MUTATION OF THE MOTH MANDUCA-SEXTA

Octopod (Octo) is a mutation of the moth Manduca sexta, which transfor ms the first abdominal segment (Al) 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 b e used in specifying the fates of sensory neurons located on the body surface of larval Manduca, Mechanical stimulation of homeotic leg sens illa did not cause reflexive movements of the homeotic legs, but elici ted responses similar to those observed following stimulation of ventr al Al body wall hairs, Intracellular recordings demonstrated that seve ral of the motoneurons in the Al ganglion received inputs from the hom eotic sensory hairs, The responses of these motoneurons to stimulation of homeotic sensilla resembled their responses to stimulation of vent ral body wall sensilla, Cobalt fills revealed that the mutation transf ormed the segmental projection pattern of only the sensory neurons loc ated 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 l egs had intersegmental projection patterns typical of abdominal sensor y neurons: an anteriorly directed projection terminating in the third thoracic ganglion (T3). Once this projection reached T3, however, it m imicked the projections of the thoracic leg sensory neurons. These res ults 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 sens ory neurons of Manduca, whereas the leg-specific projections are consi stent with a role for positional information in determining their patt ern. (C) 1995 John Wiley & Sons, Inc.