![]() (I) Pairwise comparisons of neurite proximity for the PVD 1° dendrite, ALA axon, and the CAN process. The location of optical cross sections in the lateral nerve tract are indicated by dashed lines with corresponding cross sections shown below (H’, H” or H”’). (H) Fluorescent image showing the processes of ALA (dzEx1766), CAN (otIs33), and the PVD 1° dendrite (dzIs53) using the same color code as in (A). Additional examples of gap junctions (arrowheads) between members of the left lateral nerve are shown in (E)–(G). Arrowheads show gap junctions in CAN processes close to its cell body, contacting with either epidermis or the excretory canal (EXC). (D) A mid-body section where the right-side ALA axon (identified by large dense core vesicles and a large smooth ER compartment) and a PVD dendrite are enveloped by epidermis. (D-G) TEM micrographs showing electrical synapses between the processes of ALA, CAN and PVD, and surrounding tissues. The presence of dense core vesicles in an ALA axon in (C) is indicated by arrowheads. (B and C) TEM image of lateral nerve tract cross-sections. (A) Schematics of PVD (green), ALA (blue), CAN (red) neurons, and the excretory canal (yellow) in adult animals. L1CAM Menorin Netrin Papilin activity-dependent activity-independent axon dendrite maintenance self-assembly.Ĭopyright © 2018 Elsevier Inc. Thus, axons can serve as critical scaffolds to pattern and maintain dendrites through contact-dependent but activity-independent mechanisms. We found that the SAX-7/L1CAM cell adhesion molecule engages in distinct molecular mechanisms to mediate extensions of PVD 1° dendrites and maintain the ALA-PVD axon-dendritic fascicle, respectively. PVD 1° dendrites mimic ALA axon guidance defects in loss-of-function mutants for the extracellular matrix molecule MIG-6/Papilin or the UNC-6/Netrin pathway, suggesting that axon-dendrite adhesion is important for dendrite formation. ![]() Here, we show that in Caenorhabditis elegans, the axons of the ALA neuron control guidance and extension of the 1° dendrites of PVD somatosensory neurons independently of ALA activity. The activity of presynaptic axons has long been known to shape dendrites, but activity-independent functions of axons in this process have remained elusive. The mechanisms that pattern and maintain dendritic arbors are key to understanding the principles that govern nervous system assembly.
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