The lin-4 microRNA targets the LIN-14 transcription factor to inhibit netrin-mediated axon attraction.
miR-125 microRNAs, such as lin-4 in Caenorhabditis elegans, were among the first microRNAs discovered, are phylogenetically conserved, and have been implicated in regulating developmental timing. Here, we showed that loss-of-function mutations in lin-4 microRNA increased axon attraction mediated by the netrin homolog UNC-6. The absence of lin-4 microRNA suppressed the axon guidance defects of anterior ventral microtubule (AVM) neurons caused by loss-of-function mutations in slt-1, which encodes a repulsive guidance cue. Selective expression of lin-4 microRNA in AVM neurons of lin-4-null animals indicated that the effect of lin-4 on AVM axon guidance was cell-autonomous. Promoter reporter analysis suggested that lin-4 was likely expressed strongly in AVM neurons during the developmental time frame that the axons are guided to their targets. In contrast, the lin-4 reporter was barely detectable in anterior lateral microtubule (ALM) neurons, axon guidance of which is insensitive to netrin. In AVM neurons, the transcription factor LIN-14, a target of lin-4 microRNA, stimulated UNC-6-mediated ventral guidance of the AVM axon. LIN-14 promoted attraction of the AVM axon through the UNC-6 receptor UNC-40 [the worm homolog of vertebrate Deleted in Colorectal Cancer (DCC)] and its cofactor MADD-2, which signals through both the UNC-34 (Ena) and the CED-10 (Rac1) downstream pathways. LIN-14 stimulated UNC-6-mediated axon attraction in part by increasing UNC-40 abundance. Our study indicated that lin-4 microRNA reduced the activity of LIN-14 to terminate UNC-6-mediated axon guidance of AVM neurons.
Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, OH 45229, USA.
Yan
Y
Zou
Hui
H
Chiu
Dorothée
D
Domenger
Chiou-Fen
CF
Chuang
Chieh
C
Chang
D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000378:metabolism / Q000502:physiology; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000254:growth & development*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D020439:Growth Cones / Q000378:metabolism / Q000502:physiology*; D007814:Larva / Q000254:growth & development; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D000075385:Netrins; D055495:Neurogenesis / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism*; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000502:physiology*
D029742:Caenorhabditis elegans Proteins; D015815:Cell Adhesion Molecules; D017931:DNA Primers; C102669:LIN-14 protein, C elegans; D035683:MicroRNAs; D009419:Nerve Tissue Proteins; D000075385:Netrins; D009687:Nuclear Proteins; C102174:UNC-40 protein, C elegans; C078146:UNC-6 protein, C elegans; C452194:lin-4 microRNA, C elegans