brief about Caenorhabditis elegans

2. Kingdom Animalia
Phylum Nematoda
Class Chromadorea
Order Rhabditida
Family Rhabditidae
Genus Caenorhabditis
Species C elegans
A tiny nematode; lives in garden soil, feeding on
bacteria

3.  Free-living, transparent nematode, about 1 mm
in length, lives in temperate soil environments.
 Unsegmented, vermiform, and bilaterally
symmetrical.
 Has cuticular integument, four main epidermal
cords, and a fluid-filled pseudocoelomate cavity
 Generally feeds on bacteria.
 C. elegans has two sexes: hermaphrodites and
males

4.  Males have a single-lobed gonad, vas
deferens, and a tail specialized for
mating.
 Hermaphrodites have two ovaries,
oviducts, spermatheca, and a single
uterus.
 The hermaphrodite gonad produces first
sperm and then oocytes

8. Hermaphrodites have about 10
eggs inside--the older eggs are laid
about as fast as new eggs are
made
Oocytes pass into the spermatheca and are
fertilized. Embryos develop in the uterus, and
have a few cleavages before the eggs are laid,
so the embryos have a few dozen cells when
the embryos are laid. The embryos develop
into worms over the next 8-18 hours

9.  Simple body organization
 Easy to grow
 Short life cycle: 3 days per generation
 Powerful genetics (both self-fertile and cross-fertile)
 Transparent body wall
 Small size
 Invariant
 Fully described anatomy and development
 Post-genomic tools -- RNAi

10.  Simplest organisms with a nervous system.
 It is an eukaryote, shares cellular and molecular structures and control
pathways with higher organisms.
 It goes through a complex developmental process, including
embryogenesis, morphogenesis, and growth to an adult.
 The biological information obtained from C. elegans may be directly
applicable to more complex organisms.
 About 35% of C. elegans genes have human homologs.

11.  C. elegans was the first multicellular organism to have its genome
completely sequenced
 Young, freshly starved larvae best survive freezing in 15% glycerol
solution, can also be stored at −80 °C for over ten years
 About 35% to 45% of the worms stored in liquid nitrogen survive.

12.  There are six chromosomes: five pairs of autosomes and the sex
chromosome, X
 Hermaphrodites have two X chromosomes (XX).
 Males have one X chromosome (XO); having only one chromosome
instead of a pair is called the hemizygous state.

13.  It lives a total of about 2 weeks.
 The eggs are fertilized within the adult
hermaphrodite and laid at about the 40 cell
stage
 They hatch and it proceeds through 4 larval
stages
 C. elegans can adopt an alternative life
form, called the dauer larval stage in
unfavorable conditions.
 Dauer larvae are thin and can move but
their mouths are plugged and they cannot
eat & can remain viable for three months.
General form of life cycle of
C elegans

14. LIFE CYCLE OF
C elegans
Daurer larvae appear to be
non-aging: they can roam
around for months and then
re-enter the L4 stage when
they encounter a food
source and live about 15
more days

15.  RNA interference (RNAi) has been extensively used on C. elegans
 C. elegans are fed with transgenic bacteria or injected with RNA into
the body cavity that express double-stranded RNA that complements
the gene of interest, thereby causing RNA silencing.
 Live samples of C. elegans used to explore the effects of zero gravity on
muscle development and physiology.
 The research was primarily about genetic basis of muscle atrophy,
which relates to space travel

16.  Studying meiosis is considerably simplified in the sperm and egg nuclei
in the gonads, the difficulties of heterogeneous cellular populations are
eliminated because every nucleus at a given position in the gonad
therefore is at roughly the same step in meiosis.
 It can also be used to study nicotine dependence because it exhibits
behavioral responses to nicotine that parallel those of mammals; e.g.,
acute response, tolerance, withdrawal, and sensitization.