The mRNA Decay Factor CAR-1/LSM14 Regulates Axon Regeneration via Mitochondrial Calcium Dynamics

Ngang Heok Tang,Brian A Yee,Gene W Yeo,Suhong Xu,Yishi Jin,Andrew D Chisholm,Stephen M Blazie,Kyung Won Kim

doi:10.1016/j.cub.2019.12.061

Ngang Heok Tang, Brian A Yee + Show 6 more

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https://doi.org/10.1016/j.cub.2019.12.061

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Abstract

mRNA decay factors regulate mRNA turnover by recruiting non-translating mRNAs and targeting them for translational repression and mRNA degradation. How mRNA decay pathways regulate cellular function invivo with specificity is poorly understood. Here, we show that C.elegans mRNA decay factors, including the translational repressors CAR-1/LSM14 and CGH-1/DDX6, and the decapping enzymes DCAP-1/DCP1, function in neurons to differentially regulate axon development, maintenance, and regrowth following injury. In neuronal cell bodies, CAR-1 fully colocalizes with CGH-1 and partially colocalizes with DCAP-1, suggesting that mRNA decay components form at least two types of cytoplasmic granules. Following axon injury in adult neurons, loss of CAR-1 or CGH-1 results in increased axon regrowth and growth cone formation, whereas loss of DCAP-1 or DCAP-2 results in reduced regrowth. To determine how CAR-1 inhibits regrowth, we analyzed mRNAs bound to pan-neuronally expressed GFP::CAR-1 using a crosslinking and immunoprecipitation-based approach. Among the putative mRNA targets of CAR-1, we characterized the roles of micu-1, a regulator of the mitochondrial calcium uniporter MCU-1, in axon injury. We show that loss of car-1 results increased MICU-1 protein levels, and that enhanced axon regrowth in car-1 mutants is dependent on micu-1 and mcu-1. Moreover, axon injury induces transient calcium influx into axonal mitochondria, dependent on MCU-1. In car-1 loss-of-function mutants and in micu-1 overexpressing animals, the axonal mitochondrial calcium influx is more sustained, which likely underlies enhanced axon regrowth. Our data uncover a novel pathway that controls axon regrowth through axonal mitochondrial calcium uptake.

Highlights

C. elegans expresses many conserved mRNA decay factors, whose functions have been mostly characterized in the germline and in early embryos [7,8,9,10]
The interaction between CAR-1/LSM14 and CGH-1/DDX6 regulates the formation of endoplasmic reticulum and anaphase spindle network; loss of function in car-1 or cgh-1 leads to sterility and embryonic lethality due to defects in germline apoptosis and embryonic cytokinesis [7, 8, 10]
We examined functional transgenes of full-length DCAP-1 or CGH-1 expressed under their respective promoters [12, 13] and observed expression in many neurons including touch receptor neurons (TRNs) and motor neurons, localizing to cytoplasmic puncta in neuronal cell bodies (Figures 1B and S2A)

Summary

Introduction

C. elegans expresses many conserved mRNA decay factors, whose functions have been mostly characterized in the germline and in early embryos [7,8,9,10]. The CAR-1 protein family includes yeast Scd, Drosophila Tral (Trailer hitch), Xenopus RAP55, and mammalian LSM14 [11]. The interaction between CAR-1/LSM14 and CGH-1/DDX6 regulates the formation of endoplasmic reticulum and anaphase spindle network; loss of function in car-1 or cgh-1 leads to sterility and embryonic lethality due to defects in germline apoptosis and embryonic cytokinesis [7, 8, 10]. Loss of function in cgh-1 has recently been shown to affect dendrite development in PVD neurons [6]. The neuronal mRNA targets of CAR-1 or CGH-1 have not yet been identified

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