Regulation of neurotransmitter vesicles by the homeodomain protein UNC-4 and its transcriptional corepressor UNC-37/groucho in Caenorhabditis elegans cholinergic motor neurons.
Motor neuron function depends on neurotransmitter release from synaptic vesicles (SVs). Here we show that the UNC-4 homeoprotein and its transcriptional corepressor protein UNC-37 regulate SV protein levels in specific Caenorhabditis elegans motor neurons. UNC-4 is expressed in four classes (DA, VA, VC, and SAB) of cholinergic motor neurons. Antibody staining reveals that five different vesicular proteins (UNC-17, choline acetyltransferase, Synaptotagmin, Synaptobrevin, and RAB-3) are substantially reduced in unc-4 and unc-37 mutants in these cells; nonvesicular neuronal proteins (Syntaxin, UNC-18, and UNC-11) are not affected, however. Ultrastructural analysis of VA motor neurons in the mutant unc-4(e120) confirms that SV number in the presynaptic zone is reduced ( approximately 40%) whereas axonal diameter and synaptic morphology are not visibly altered. Because the UNC-4-UNC-37 complex has been shown to mediate transcriptional repression, we propose that these effects are performed via an intermediate gene. Our results are consistent with a model in which this unc-4 target gene ("gene-x") functions at a post-transcriptional level as a negative regulator of SV biogenesis or stability. Experiments with a temperature-sensitive unc-4 mutant show that the adult level of SV proteins strictly depends on unc-4 function during a critical period of motor neuron differentiation. unc-4 activity during this sensitive larval stage is also required for the creation of proper synaptic inputs to VA motor neurons. The temporal correlation of these events may mean that a common unc-4-dependent mechanism controls both the specificity of synaptic inputs as well as the strength of synaptic outputs for these motor neurons.
Lickteig
K M
KM
Department of Cell Biology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
Duerr
J S
JS
Frisby
D L
DL
Hall
D H
DH
Rand
J B
JB
Miller
D M
DM
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins / Q000096:biosynthesis; D002795:Choline O-Acetyltransferase / Q000096:biosynthesis; D018507:Gene Expression Regulation, Developmental; D015801:Helminth Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009043:Motor Activity / Q000235:genetics; D009046:Motor Neurons / Q000378:metabolism* / Q000648:ultrastructure; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009687:Nuclear Proteins; D010750:Phosphoproteins; D050765:Qa-SNARE Proteins; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D015801:Helminth Proteins; D018398:Homeodomain Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D018377:Neurotransmitter Agents; D009687:Nuclear Proteins; D010750:Phosphoproteins; D050765:Qa-SNARE Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C082365:Unc-17 protein, C elegans; C082636:Unc-18 protein, C elegans; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins; C106184:unc-37 protein, C elegans; C073171:unc-4 protein, C elegans; D002795:Choline O-Acetyltransferase