The primary goal of my project is to better understand how forward locomotion is driven in the nematode, Caenorhabditis elegans. Previous research I have performed on this model organism was aimed at discovering which neurons in C. elegans act as central pattern generators during swimming and crawling. This summer, I developed new, unique strains of C. elegans to be used in further experiments, and tested isolated aspects of the worm’s locomotory circuit to discover how changing neuronal and muscular features affect the worm’s overall behavior.
The first half of the summer was focused on integrating wild-type worms with trans genes that modify the worm’s muscular or neuronal network. Integrating trans genes is accomplished through UV irradiating worms that have been injected with extra-chromosomal trans genes, then selectively breeding the progeny that exhibit the desired phenotype until the trait is homozygous in a population. More complex tasks required me to cross integrated worms with different phenotypes to create offspring that had multiple useful traits for experiment (e.g. creating a strain that has both red fluorescent muscle cells while also expressing halorhodopsin in the neurons). I greatly expanded my understanding of practical genetics, and it was extremely rewarding to put the knowledge I would gained in my university classes to use in lab.
The second half of the summer was spent carrying out experiments on the worm strains I had created and analyzing the data from those experiments. One of the more exciting results came from an experiment where we ablated (killed) the muscle cells in the head region of the worm and used optogenetics to depolarize the head neurons with blue light. We observed that in many cases this induced tail bending in the subjects. The literature on C. elegans agrees that the bending wave during swimming and crawling is heavily influenced by proprioceptive feedback, but our experiment strongly supports the idea that a bending wave can also be propagated non-proprioceptively.
We built upon this conclusion in a later experiment and tested whether one could entrain the worm’s tail to undulate at a certain frequency by using timed hyperpolarizations of the head region. The worm’s head muscles were again ablated, completely preventing any movement from occurring in the head. We then used optogenetics to pulse illuminate the same ablated head region and observed that the tail undulation consistently paused during head illumination. In other words, the tail moved naturally when light was not being shone on the worm, and pulsing a blue laser at the head caused the tail to stop its regular movement at the same frequency as the laser (2 Hz). This data provides strong evidence in support of a non-proprioceptive model for propagation of bending waves in C. elegans, and enhances the scientific community’s understanding of forward locomotion in this model organism.