Isolating the neural circuitry of prickle-mediated epilepsy
Creators: name: Lilienthal, Anthony
Publisher: name: University of Iowa
Year: 2023
Subjects: PRICKLE
public abstract
Epilepsy
Neurobiology

description: Epilepsy is a neurological condition characterized by recurring seizures and is estimated to affect 50 million individuals worldwide; however, one in three epilepsy patients are unable to find antiepileptic medications which can reliably alleviate their symptoms. This highlights a need for the development of new treatment options for epilepsy patients. Previous work in the Manak lab identified a mutation in the Drosophila planar cell polarity (PCP) gene prickle which models the myoclonus epilepsy and ataxia (uncoordinated gait) symptoms found by human patients with mutations in their PRICKLE1 &amp; PRICKLE2 genes. These mutations specifically affect one of the two adult prickle gene isoforms, prickle-spiney-legs (pksple). Our goal was to determine the mechanism of this atypical epilepsy; however, work in our lab found that Drosophila pk mutations can result in many more neurological conditions. We found that mutations which reduce expression of the pksple isoform also led to olfactory learning defects and an increased nociceptive sensitivity. Conversely, we found that mutations which reduce expression of the other adult pk isoform, prickle-prickle (pkpk), are associated with increased neurodegeneration and innate immune response. Therefore, to determine the mechanisms specific to the pricklemediated seizures, we recognized that we needed to further characterize and localize the neuronal circuitry responsible for the myoclonic seizure phenotype.
description: We first defined a spontaneous seizure assay to model the myoclonic epilepsy phenotype. Using this behavioral assay, we determined that the spontaneous seizures were neuronal in origin. We then determined when pksple expression is required for proper neuronal development. This was achieved through immunohistochemistry - mapping Pk proteins expression throughout postembryonic neuron development in the fly brain and ventral nerve cord (VNC) and through the TARGET system. With this analysis, we have narrowed the critical window for the spontaneous seizure phenotype to post-embryonic neurogenesis from L2 larvae through 24 hours postpuparium formation.
description: We then used a combination of behavioral and immunohistochemical tools to further isolate the prickle-seizure circuitry. First, using the Gal4/UAS system, we found that the myoclonic seizures likely originate from neurons in the fly brain, similar to what has been previously observed in humans. To our knowledge, this is a first in Drosophila epilepsy field. We then characterized the seizure circuitry based on neurotransmitter, as multiple forms of epilepsy (for example, Dravet syndrome) are linked to specific neuron subsets. From these experiments, we found that glutamatergic neurons likely play a role in the seizure phenotype. These findings also suggested the circuitry underlying the myoclonic epilepsy is complex, thus requiring a broader approach to isolating the prickle-mediated neuron circuitry. Using the Gal4/UAS systems curated in databases such as FlyLight and FlyBowl, we screened areas of the larval brain, the larval nerve cord, and the adult central complex for associations with the myoclonic epilepsy phenotype. From this analysis, we found that neurons in the larval subesophageal zone (SEZ) likely require pksple expression to properly develop during post-embryonic neurogenesis.
description: In conclusion, we have isolated likely parts of the neuronal circuitry responsible for the myoclonic seizure phenotype in pksple loss of function mutations. Although this is unlikely to be the complete seizure circuit, these findings provide a novel system to understand the mechanisms underlying prickle-mediated epilepsy. Furthermore, looking at additional systems in different prickle mutant models may provide additional insight into other conditions including autism spectrum disorders. Further research can build on these model systems to develop novel treatments for epileptic patients.