Figure 4.

The spinal motoneurons marked by the M602 insertions. (A–C) Lateral views of the M602A; UAS:GFP animals. At 20 hpf, GFP expression was detected in the ventral spinal cord and the rostral hindbrain (A,B). The dotted lines demarcate the dorsal and ventral limit of the spinal cord in (B). At 48 hpf, GFP is strongly detected in the ventral spinal cord and the rostral and caudal hindbrain, as well as weakly in other tissues. (D–F) Lateral view of the M602A;UAS:RFP; mnr2b-GFP triple transgenic animal at 48 hpf. Arrows indicate the myoseptal region in the dorsal musculature. (G) The plot of single GFP-labeled cells (open orange circles, N = 40 cells). For reference, the results from the experiment with mnGFF7 in Figure 2A are superimposed as gray circles. (H) Distribution of the GFP-labeled cells plotted with respect to the soma position along the RC axis on the horizontal axis and to the DV soma position on the vertical axis. The exit point of the ventral root from the spinal cord is indicated on the RC axis by the gray vertical line marked as vr (x = 0). The dorsally, laterally, and ventrally projecting cells are shown as red, green, and blue circles, respectively. The cells with bifurcating main axon and the vmS motoneurons are shown as gray squares and open triangles, respectively. (I) Cell counts of the neurons innervating the axial muscles based on the axon trajectory and muscle innervation pattern. P and S indicate primary and secondary motoneurons, respectively. Diagonally-striped bars indicate iS type neurons. “Bifurc” indicates the motoneurons with a bifurcating main axon. The bars indicate 20 μm in (B), and 50 μm in (F).