Trailblazers: Investigating Chemotaxis with C.elegans
Growth and Development of C.elegans There are two naturally occurring sexes in C.elegans . The vast majority of worms are self-fertile hermaphrodites, meaning that they produce both the sperm and the eggs used for reproduction. Free-living males represent <1% of the total nematode population. However, free-living males plus a hermaphrodite can produce over 1000 offspring in a generation; in contrast, self-fertilized hermaphrodite worms will produce about 300. Because their sperm will preferentially fertilize a hermaphrodite’s eggs and produce more offspring, free-living males are often used to introduce specific genetic mutations into a worm population to be studied. C.elegans develop from embryo to adult in four days, allowing for rapid studies in the laboratory (Figure 3). The worms are grown on agar plates or in liquid culture and they feed on E. coli . After being laid, the worm embryo will develop for approximately 14 hours before hatching. Juvenile worms progress through four larval stages (L1-L4) over the next two days, increasing in size with each stage. After the fourth larval molt (L4), the worms are reproductively mature, meaning that they can be used for further genetic studies. Adults will live for 2-3 weeks, over which time they gradually age and lose vigor.
Adult (1110-1150 µm) (capable of egg laying)
Young Adult (900-940 µm)
8 hr.
ex utero development (9 hours)
Egg Hatching
10 hr.
molt
L4 (620-650 µm)
L1 (250 µm)
molt
up to 4 months
8 hr.
13 hr. Predauer (L2d)
12 hr.
Dauer (400 µm)
molt
L3 (490-510 µm)
molt
L2 (360-380 µm)
molt
8 hr.
Figure 3: Life Cycle of C.elegans
SNIFFER WORMS - THE CHEMOSENSORY SYSTEM OF C.elegans C.elegans have sophisticated sensory capabilities that allow them to navigate chemically diverse environments. They also use chemical cues to temporarily survive harsh conditions by going into an alternate low energy larval state. When finding food and avoiding danger, C.elegans maneuver using a biased random walk or pirouette model (Figure 4). Rather than moving directly toward or away from a chemical an individual will alternate between long forward movements and random changes in directions. In the presence of attractants, much more time is spent moving forward.
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