Abstract
Various neuronal intermediate filament defects are associated with neurological disorders, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). To study how human diseases develop, scientists frequently employ model organisms, such as zebrafish, fruit flies, and worms. However, whether a neurofilament homolog exists in the nematode Caenorhabditis elegans remains unclear. In this study, we investigated a candidate gene, temporarily assigned gene-63 (tag-63), which we hypothesized to be a homolog to human neurofilament heavy polypeptide (nefh) according to WormBase BLASTP. We established a stable transgenic worm line expressing the tag-63 transcriptional reporter and found that tag-63 expresses in some neurons showing partial co-occurrence with the pan-neuronal reporter UNC-104. Additionally, we sequenced and outcrossed the deletion mutant strain VC275 tag-63(ok471) and separately crossed it with the translational reporters UNC-104/KIF1A (kinesin-3 motors) and SNB-1/VAMP1 (synaptobrevin-1 synaptic vesicles). We verified the crossing through genotyping PCR and Western blotting and examined anterograde motor UNC-104 and corresponding cargo SNB-1 fast axonal transport dynamics in the mechanosensory neuron ALM by using time-lapse imaging in live worms. Intriguingly, we found that worms carrying the TAG-63 mutation significantly activate the retrograde machinery and deactivate the anterograde machinery of UNC-104 and SNB-1 by acting on differential transport parameters. Moreover, the TAG-63 mutation causes similar motility schemes between UNC-104 and SNB-1 in anterograde but not retrograde transport directions. Based on these results, we propose a novel model that neurofilament homolog TAG-63 affecting fast axonal transport in C. elegans via transient interactions between TAG-63 and the motor-cargo complex.