Gap junctions form between BDU and PLM neurons.

<p>(A) Time-lapse images of BDU and PLM cells and gap junction plaques. BDU and PLM cells were stained by mCherry. Gap junctions were stained by P<i>unc-53</i>::UNC-9::GFP. Images were collected every 90 seconds. Yellow arrows indicate the possible BDU-PLM membrane contact sites. Arrowheads indicate the putative gap junction plaques. (B) No gap junction plaques are formed in unconnected BDU and PLM neurites in <i>unc-34</i> mutants. BDU and PLM cells were stained by P<i>unc-86</i>::mCherry. Gap junctions were stained by P<i>unc-86</i>::UNC-9::GFP. Arrows indicate the BDU and PLM neurites. (C) UNC-9 antibody staining (red) on BDU and PLM cells (labeled green by P<i>unc-86</i>::MYR::GFP). Dashed boxes indicate co-localization of UNC-9 with the BDU-PLM junction. (D) Enlarged images of dashed boxes in (C). Scale bars represent 10 µm. (E) Low power TEM image of a wild type L4 animal in the anterior midbody region. Scale bar is 10 µm. Int: intestine; Go: gonad; VC: ventral cord; DC: dorsal cord. Boxed region is shown in the inset on the right, from a nearby section where the posterior BDUR process reaches laterally towards the cuticle to make direct contact with the anterior limit of the PLMR dendrite. Arrow points to a large gap junction. This single junction continued for 37 serial thin sections, roughly 2.5 microns along the body axis. Double asterisk (**) marks the mantle protein that is secreted on the right edge of PLMR, facing the cuticle. One large (15 protofilament) microtubule can be seen in cross-section within the PLMR dendrite; such large diameter microtubules and mantle protein are characteristic only of the “touch dendrites” of ALM, PLM, AVM and PVM. Scale bar in the inset is 0.5 µm. A second inset to the extreme right shows the gap junction at even higher power from another section. Scale bar is 0.1 µm.