C. elegans as a biological model
Caenorhabditis elegans has first been studied in 1900 by Emile Maupas and half a century later by Victor Nigon. Sydney Brenner’s group used the roundworm for genetic and neuronal studies and it became a wider biological model during the following decades. It had led to 13,000+ publications, and contributed to 5 Nobel Prizes (Brenner for pioneering genetic studies, Suiston for elucidating the exact cell lineage from one fertilized egg to 959 cells in the adult and Horvitz for investigation of programmed cell death, which later turned out to be very important in the development of cancer in 2002; Fire and Mello in 2006 for their discovery of RNA interference during translation; Chalfie in 2008). Nobelized Sydney Brenner named it “Nature’s gift to science” because of its versatility and proposed this elegant worm as a model organism in 1965.
Temperature has a major impacts on C. elegans life cycle
C. elegans life cycle consists in 4 larval stages, L1 to L4 with molting after each stage, plus one mature stage. This cycle is very sensitive to temperature and other microenvironmental factors. For example, if the embryos are grown at 15°C they will reach the mature stage within 6 days but if their environmental temperature is increased to 25°C, the time needed to reach the mature stage is reduced by more than 50% and they become mature worms after 2.5 days. Interestingly, if the microenvironment conditions are not stable enough during L1 and L2, larvae enter into a “Dauer” (dormant) developmental stage, where the worms can survive up to 4 months (instead of a more typical 2-3 weeks lifespan) . Molecularly speaking this Dauer phase occurs when two genes called daf-2 and daf-23  are down regulated as a result of the temperature changes.
Generating and using TS mutations in C. elegans
Although still possible with traditional techniques (random mutagenesis), it is now easier than ever to create thermo-sensitive nematodes thanks to the development of DNA engineering techniques such as TALEN or CRISPR/Cas9, temperature- sensitive C. elegans worms have been used to study the genes that act on the growth and development .
This study shows ways to avoid the lethal effect of zygotic, maternal effects or sterile mutations. It also allows the identification of 24 thermo-sensitive alleles of a group of 13 genes. Some of them like the mex-1 mutation have direct effects on the embryo polarity development. LEARN MORE.