Vanderbilt Summer Science Academy

Identifying Molecular Targets of UNC-4 That Maintain Synaptic Specificity in the C. elegans Motor Neuron Circuit

Synaptic specificity is essential for motor neuron circuit functionality in all organisms. Compared to chemical synapses that utilize neurotransmitters, far less is known about the genetic regulation of electrical synapses, which are composed of gap junctions that depend on ion flow to send signals. Our model organism, the nematode Caenorhabditis elegans, allows us to investigate the genetic regulation of gap junction-mediated electrical synapses in a fully mapped nervous system.

In wild-type worms, backward movement is directed by the proper electrical connections between A-class interneurons and VA motor neurons, while forward movement is directed by B-class interneurons onto VB motor neurons. The transcriptional repressor UNC-4 acts in VA neurons to prevent VB-type inputs. Thus, unc-4 mutants lose proper VA inputs and cannot move backwards. RNA Sequencing analysis has identified hundreds of possible molecular targets of UNC-4 in its maintenance of correct synaptic specificity. Two targets are likely candidates based on RNAi results: the GPCR frpr-17, and the phosphodiesterase pde-1. Using mutant screens, I am testing whether frpr-17 and pde-1 knockouts suppress the unc-4 backward defect. I am creating these knockouts using genetic crosses and the CRISPR/Cas9 system, made possible by a variety of cloning techniques. With this approach, my project in this simple organism can identify novel molecular components that also regulate synapse specificity in more complex nervous systems. The discovery of key determinants of synaptic specificity could lead to improved treatment of neurogenic disorders arising from altered connectivity in the developing human brain.