The C. elegans left and right AWC olfactory neurons display stochastic asymmetry: one AWC subtype adopts the default AWCOFF identity and the contralateral neuron is specified as the induced AWCON subtype. We previously showed that the TIR-1 (Sarm1) scaffold protein assembles a Ca2+-regulated signaling complex at synaptic regions in the AWC axons, in a microtubule-dependent mechanism, to specify AWCOFF. We also showed that proper localization of the TIR-1 Ca2+ signaling complex at the AWC synapses is important for precise AWC asymmetry.
To identify additional molecules required for the localization of TIR-1 in AWC subtype choice, we performed unbiased forward genetic screens to identify mutants with defective TIR-1 localization and AWC diversity. We screened through 8,560 genomes and identified six TIR-1 localization defective (tld) mutants with reduced localization of TIR-1 at synapses in the AWC axons, and/or accumulation of TIR-1 in the AWC cell body. Most of the tld mutants alone do not show a defect in AWC asymmetry. However, some tld mutants enhance the tir-1(ky388) reduction of function 2AWCON phenotype, supporting an important role of these tld genes in regulating TIR-1 trafficking and /or stability to specify AWCOFF. We have identified the mutations responsible for the tld mutant phenotypes using whole genome sequencing (kindly performed by Alexander Boyanov in Oliver Hober’s lab). Our study of the tld genes will provide insights into how cell-specific Ca2+ signaling proteins such as TIR-1 are linked to the conserved synaptic assembly in neuronal diversification. In addition to neuronal diversification, TIR-1 (Sarm1) is also implicated in innate immunity and axon degeneration. Identification and characterization of the genes, such as tld, that interact with tir-1 in AWC asymmetry may advance our understanding of how TIR-1 (Sarm1) functions in other biological contexts including innate immunity and axon degeneration.