Updated: May 16, 2022
Caenorhabditis elegans, science's favorite nematode. Whether you're a lab student looking for some quick facts or just interested in worms, here's a post about the wiggly ones.
Scoop up a random pile of dirt, inspect it under the microscope, and chances are you'll see a bunch of tiny, clear, squiggly lines wriggling around. These are C. elegans worms. The soil is their home, where they spend their time feasting on soil bacteria. Being hidden from the sun in the dirt, they have no need for protective pigments and thus are clear in in color.
C. elegans is one of the most popular model organisms among biologists studying genetics, cell and molecular biology, and neurology. In the lab, worms are typically raised on nematode growth medium (NGM), which is coated with E. coli bacteria for them to eat. Their clear skin provides scientists an easy way to view their cells' development and behavior directly.
C. elegans worms come in two sexes: male and hermaphrodite. The male produces sperm. The hermaphrodite produces both sperm and eggs. Because of this, hermaphrodites can undergo self-fertilization and produce around 300 offspring. Sexual reproduction produces over 1000 offspring.
A worm begins its life as an egg. It hatches as a larva. If conditions are good, it will go through four larval stages: L1, L2, L3, and L4. Finally, after passing through an adolescent stage, it becomes an adult. If conditions are poor, the larva will enter a dauer state, in which it goes into remission, unable to eat. The young worm can remain in this state for several months and rejuvenate when conditions are good again.
In labs, worms may be stored in freezers for incubation. The optimal storage temperature is 20°C, in which incubation takes about 3-3.5 days.
The adult worm is 1-1.2 mm long, just visible to the naked eye. The body is a system of ~1000 somatic (body) cells, with hermaphrodites having fewer cells than males.
Both sexes have a distinct head and tail end, with the tail extending into a thin appendage just past the anus. The body is unsegmented and is built like a tube within a tube. The outer tube contains muscles and nerves. The inner tube contains the intestine, gonads, and pharynx, which is located toward the mouth. Between the two tubes is the pseudocoelomic cavity, which contains the pseudocoeloem fluid.
The main difference between the sexes is their reproductive system. The hermaphrodite has two gonads and a uterus. The gonad arms produce spermatocytes and oocytes, and the eggs are stored in the uterus until hatching. The male has a testis, seminal vesicle, and vans deferens for gonads. Again, the distal (far) end of the gonad produces spermatocytes.
Below is a detailed diagram of hermaphrodite anatomy, in case the words confuse you.
The entire genome of C. elegans has been sequenced, which contains 100 megabases and 20000 genes. All kinds of experiments are done where genes are edited and replaced and removed and added using biotechnologies such as CRISPR-Cas9, and in the process numerous mutant strains have been created. Wormbase contains a record of all mutants thus far made.
I myself have worked with C. elegans. In our most recent experiment, I and my lab partners studied the effect of the deb-1 gene on thrashing ability. Below is the poster we put together describing the experiment and our results.
So, that's a little bit about my favorite multicellular invertebrate animal. Next time you step on the soils of your backyard or the city park or any place with dirt, think about these little guys and all their microscopic buddies working to keep our soils fertile and fit for the trees and flowers that decorate our homes and streets.