Automating In Vivo Screens and Challenging Dogma

Caenorhabditis elegans is a tiny nematode species that makes big contributions to molecular research. These worms have simple genomes, well-delineated developmental processes, brief lifespans, and many conserved biological pathways across the animal kingdom, including human processes such as aging, reproduction, and neurodevelopment. Because they are easy and affordable to grow in a dish, they are exceptional model organisms for in vivo compound screens, but traditional C. elegans culture methods can hinder high throughput assays.¹

There are limitations to what you can do when you're looking on a plate, and with millions of worms.
- Coleen Murphy, Princeton University

“There are limitations to what you can do when you're looking on a plate, and with millions of worms,” said Coleen Murphy, a molecular biologist at Princeton University who studies aging processes using C. elegans models. Conventionally, scientists culture C. elegans on solid agar plates and visually screen the effects of genetic or environmental perturbations, seeking out and scoring phenotypic changes by watching the worms under a microscope. While this approach is robust and informative, it is tedious and groups many worms on the same plate, making it difficult for researchers to investigate related phenotypes in individual animals.¹

As a solution to conventional culture limitations, Murphy’s team built a new high throughput tool. In work published in Lab on a Chip, the researchers created and validated a lab-on-a-chip device called CeLab, which enabled them to automate worm assays for both individual- and population-level studies.² Designed by bioengineer Salman Sohrabi, who was a postdoctoral researcher in Murphy’s laboratory at the time of this work, CeLab contains 200 separate incubation areas connected to microfluidic ports for manipulations, compound screens, and phenotype analyses.

The researchers performed proof of principle experiments to validate their system, comparing plate-based lifespan, mating, reproductive span, and drug testing assays with CeLab techniques. They demonstrated comparable measurements between plates and CeLab, found that CeLab accelerated screening, and scored individual worm phenotypes that could not be captured in population plate assays.

“There are two sides to the screen: you need to have a good phenotype and a good way to do it. Because sometimes you have really nice phenotypes, but they're really hard to set up for automation,” said Alex Parker, a neuroscientist from the University of Montreal, who uses C. elegans models to screen neurodegenerative disease therapeutics and who was not involved in the study. C. elegans are excellent models for lifespan research, but their large brood size typically necessitates that researchers manually separate individual worms from their progeny while conducting lifespan studies on fertile organisms. Parker pointed to Murphy’s solid foundation in C. elegans research as key to CeLab’s automation success. “It's a very nice system because they had the benefit and the experience of knowing the field for a long time, and what are the problems with trying to automate.”

CeLab’s strengths also allowed Murphy’s team to investigate reproductive aging paradigms, such as the disposable soma hypothesis, which is the evolutionary concept of a trade-off between how long an animal lives versus how large it grows and how often it reproduces.³ Although some lifespan studies in C. elegans have supported the disposable soma hypothesis, the relationship between aging and reproduction remains contentious across the animal kingdom.³ Murphy and her team found that lifespan and reproductive span were uncoupled in worms cultured on CeLab chips, and individual lifespans were actually correlated with higher progeny numbers. “They've got a new way to study this, and it's already paying off in interesting observations,” said Parker.

Their observations support the idea that lifespan does not come at the cost of reproductive fitness, but rather that if an animal is healthy, it is more likely to live longer, reproduce longer, and produce more progeny. “This idea that at an individual level, the disposable soma hypothesis is incorrect, it was mind blowing because it's so well accepted in the field that there must be a trade-off,” Murphy said. “It's just so cool to observe … and it fits much better with all the observations in humans.”