Epileptic-like convulsions associated with LIS-1 in the cytoskeletal control of neurotransmitter signaling in Caenorhabditis elegans

Abstract

Cortical malformations are a collection of disorders affecting brain development. Mutations in the LIS1 gene lead to a disorganized and smooth cerebral cortex caused by failure in neuronal migration. Among the clinical consequences of lissencephaly are mental retardation and intractable epilepsy. It remains unclear whether the seizures result from aberrant neuronal placement, disruption of intrinsic properties of neurons, or both. The nematode Caenorhabditis elegans offers an opportunity to study such convulsions in a simple animal with a defined nervous system. Here we show that convulsions mimicking epilepsy can be induced by a mutation in a C. elegans lis-1 allele (pnm-1), in combination with a chemical antagonist of gamma-aminobutyric acid (GABA) neurotransmitter signaling. Identical convulsions were obtained using C. elegans mutants defective in GABA transmission, whereas none of these mutants or the antagonist alone caused convulsions, indicating a threshold was exceeded in response to this combination. Crosses between pnm-1 and fluorescent marker strains designed to exclusively illuminate either the processes of GABAergic neurons or synaptic vesicles surprisingly showed no deviations in neuronal architecture. Instead, presynaptic defects in GABAergic vesicle distribution were clearly evident and could be phenocopied by RNAi directed against cytoplasmic dynein, a known LIS1 interactor. Furthermore, mutations in UNC-104, a neuronal-specific kinesin, and SNB-1, a synaptic vesicle-associated protein termed synaptobrevin, exhibit similar convulsion phenotypes following chemical induction. Taken together, these studies establish C. elegans as a system to investigate subtle cytoskeletal mechanisms regulating intrinsic neuronal activity and suggest that it may be possible to dissociate the epileptic consequences of lissencephaly from the more phenotypically overt cortical defects associated with neuronal migration.

prickle modulates microtubule polarity and axonal transport to ameliorate seizures in flies

“…The first possibility is that neuronal and/or axonal migration defects might play a role, because it has been observed that LIS1 mutations are associated with migration defects (33), although this has not been observed in worms (25). While we cannot firmly rule this out, we do not observe obvious defects in neuronal positioning, nor do we see defects in axonal pathfinding to the somatic musculature in pk sple mutant larval filet preparations.…”

“…Although this is to our knowledge the first direct genetic evidence demonstrating that mutations in an ortholog of a known human epilepsy gene produce seizures through altered vesicle transport, mutations in genes encoding motor or motor-associated proteins (such as Kinesin-1 family member KIF5A or lissencephaly 1 (LIS1), a gene encoding a factor that clamps dynein to MTs) have been shown to produce seizure activity in mice, worms, and sometimes humans (24)(25)(26)(27)(28)(29), suggesting that vesicle transport defects, normally linked to a variety of neurodegenerative diseases, can also be associated with seizures. In the case of KIF5A, it was shown that a conditional knockout of the gene led to impaired GABA A receptor-mediated synaptic transmission in inhibitory neurons, thus producing epileptic phenotypes, and KIF5A (but neither KIF5B nor KIF5C, the two other Kinesin-1 family members) was shown to directly interact with a GABA A receptor-associated protein (26).…”

“…Additionally, rescue experiments showed that expression of KIF5A (but neither KIF5B nor KIF5C) was able to rescue the GABA A receptor transport defect, demonstrating that only one of the three Kinesin-1 family members was required for this specific transport function. In the case of LIS1, a presynaptic defect was observed such that synaptic vesicles were improperly distributed in GABAergic neurons (25). Although such data point toward motor-associated transport problems as being correlated with seizures, defects in the ability to properly recycle synaptic vesicles via dynamin/shibire in mice/flies, or amphiphysin in mice, can also cause seizure activity, suggesting that overall control of vesicle trafficking in neurons is critical for suppressing seizures (30)(31)(32).…”

Pharmacogenetic Analysis Reveals a Post-Developmental Role for Rac GTPases inCaenorhabditis elegansGABAergic Neurotransmission

“…Behavioral and pharmacological assays: Convulsion assays were performed, as previously described (Williams et al 2004;Locke et al 2008). Concentrations of PTZ (Sigma) employed are indicated in the text.…”

“…We also observed anterior ''epileptic-like'' convulsions, which were intense, frequent, and repetitive, with lis-1(t1550) homozygotes in the presence of pentylenetetrazole (PTZ; Williams et al 2004), an epileptogenic GABA A receptor antagonist (Huang et al 2001;Fernandez et al 2007). PTZ sensitivity was also increased in heterozygous lis-1(t1550) mutants following RNA interference (RNAi) against worm orthologs of associated cortical malformation genes, such as cdk-5 and nud-2, which are known to interact with LIS1 and the dynein motor complex.…”