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Fig. 3. aCC develops dendrites as collateral processes in the embryonic CNS.
(A) Schematic of aCC motoneuron in a late-stage embryo. The aCC cell
body (aCC) is present near the dorsal midline at each hemisegment in the
Drosophila embryonic CNS (CNS). The aCC extends a single axon (axon)
laterally that cuts across the longitudinal connective, exits the CNS, grows
past proximal muscles including muscle-12, then terminates at its target,
muscle-1. As its axon approaches the target, aCC begins to develop ipsilateral
dendrites (dendrite) as collateral processes from the CNS portion of the axon.
A medially directed dendritic growth cone (gc) extends across the midline,
which later develops into contralateral dendrites. A neuropil (neuropil)
emerges within the longitudinal connective. (B,C) Tracings of
DiI-labeled aCC motoneuron in wild-type embryos at hours 14 (B) and 17 (C). A
dotted circle surrounds the main dendrite, and an arrowhead points to the
dendritic growth cone that crosses the midline. A star indicates where distal
portion of the axon is cropped. Behind the aCC tracing, a shaded region
indicates where there is strong anti-HRP staining (see, for example,
Fig. 5C left). The width of
neuropil is measured as the mean distance between the edges of the
HRP-positive longitudinal connective at a point between the centers of
anterior and posterior commissures (ac and pc). (D,E) Histogram
of the number of aCC dendritic tips (mean±s.e.m. number per 4 µm) at
hours 14 (D, n=6 neurons) and 17 (E, n=14) along the
medial-lateral axis. Arrow indicates the mean position. Scale bar: 5
µm.
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