Dendrite regeneration in C. elegans is controlled by the RAC GTPase CED-10 and the RhoGEF TIAM-1

Abstract

Neurons are vulnerable to physical insults, which compromise the integrity of both dendrites and axons. Although several molecular pathways of axon regeneration are identified, our knowledge of dendrite regeneration is limited. To understand the mechanisms of dendrite regeneration, we used the PVD neurons in C. elegans with stereotyped branched dendrites. Using femtosecond laser, we severed the primary dendrites and axon of this neuron. After severing the primary dendrites near the cell body, we observed sprouting of new branches from the proximal site within 6 hours, which regrew further with time in an unstereotyped manner. This was accompanied by reconnection between the proximal and distal dendrites, and fusion among the higher-order branches as reported before. We quantified the regeneration pattern into three aspects–territory length, number of branches, and fusion phenomena. Axonal injury causes a retraction of the severed end followed by a Dual leucine zipper kinase-1 (DLK-1) dependent regrowth from the severed end. We tested the roles of the major axon regeneration signalling hubs such as DLK-1-RPM-1, cAMP elevation, let-7 miRNA, AKT-1, Phosphatidylserine (PS) exposure/PS in dendrite regeneration. We found that neither dendrite regrowth nor fusion was affected by the axon injury pathway molecules. Surprisingly, we found that the RAC GTPase, CED-10 and its upstream GEF, TIAM-1 play a cell-autonomous role in dendrite regeneration. Additionally, the function of CED-10 in epidermal cell is critical for post-dendrotomy fusion phenomena. This work describes a novel regulatory mechanism of dendrite regeneration and provides a framework for understanding the cellular mechanism of dendrite regeneration using PVD neuron as a model system.

Optimization of RNAi efficiency in PVD neuron ofC. elegans

“…Since the RNAi mediated knockdown of mec-3, tiam-1 and hpo-30 produced strong phenotype in nre1(-) lin-15b(-) , Pmec-3::sid-1[+] strain, we were encouraged to test whether one can optimally use this background in dendrite regeneration studies. Previous work showed that the primary dendrite of PVD upon laser injury shows regeneration response (15, 17). The dendrite regeneration depends on the RAC GTPase CED-10, GEF TIAM-1 (17) and the fusogen molecule AFF-1 (16).…”

“…Previous work showed that the primary dendrite of PVD upon laser injury shows regeneration response (15,17). The dendrite regeneration depends on the RAC GTPase CED-10, GEF TIAM-1 (17) and the fusogen molecule AFF-1 (16).…”

“…The selffusion process is dependent on epidermal secretion of AFF-1 fusogen (16). The regrowth and branching is dependent on neuron specific function of CED-10 RAC GTPase (17). Dendrite regeneration phenomenon is recently also discovered both in fly and vertebrate model systems (18)(19)(20).…”

“…Molecular control of these processes are poorly defined. It is also seen that upon laser mediated injury, the primary dendrites show various regeneration phenomena including the self-fusion between the proximal and distal dendrites, branching and regrowth (15-17). The self-fusion process is dependent on epidermal secretion of AFF-1 fusogen (16).…”

TIAM-1 differentially regulates dendritic and axonal microtubule organization in patterning neuronal development through its multiple domains

“…Although TIAM-1 is a GEF factor, its GEF activity is not required for normal dendritic development [ 46 ]. Instead, a recent study showed the GEF activity of TIAM-1 is required for dendritic regeneration after laser ablation [ 47 ]. Here, we further show that TIAM-1 patterns neuronal development through its different domains: N-terminal EVH1 domain, middle PDZ domain, C-terminal GEF domain.…”