Fig. 3

NB7–1 derived Nkx6⁺ motor neuron projects axon to ventral oblique muscles and dendrites to the dorsal neuropil. (A-A"‘) Single cell flip out labels a single VO motor neuron with HA (red) within the NB7–1 lineage (green). Note the single VO neuron has an axon projection to the ISNd nerve branch known to innervate the ventral oblique muscle group, and a dendritic projection to the midline (yellow arrowhead). FasII staining shows the ISN and ISNd nerves (blue). Stage 16 embryo; ventral midline, dashed line. Scale bar: 7 μm. (B-B″) Single cell flip out labels a single Eve⁻ VO motor neuron (green) with an axon projection exiting the CNS and its dendrites projecting to the dorsal-most region of the neuropil. Eve⁺ U3/U4 motor neurons, magenta; white arrows in B. Newly hatched larva; posterior (cross-section) view; dorsal up, ventral midline, dashed line; neuropil boundary, dashed circle. VO motor neuron cell body lies between the U3 and U4 neuron cell bodies (white arrows), similar to its position in the late embryo (see Fig. 1). Scale bar: 10 μm. (C,C′) The VO motor neuron (green) is identifiable in a TEM reconstruction of the newly hatched larval CNS, previously named MN15/16/17 [26]. Note that the VO has similar morphology in both light and TEM volumes (compare panels B and C), and that the VO has a similar cell body position between U3/U4 (compare panels B′ and C′). Posterior (cross-section) view; dorsal up, ventral midline, dashed line; approximate neuropil boundary, translucent shading; only neurons in A1R are shown. Dashed box, region enlarged in D,D’. (D,D’) VO and U3/U4 form postsynapses in different regions of the neuropil. Dorsal up, midline, white dashed line; only neurons in A1R are shown