C. elegans (nematode)

(Caenorhabditis elegans)

Samantha Myers



external image 0002-nematode.jpg
Diagram depicting the internal structure of Caenorhabditis [[#|elegans]]
http://lysozyme.co.uk/news-2.html
(Alexander Soloviev)

Classification/ Diagnostic characteristics
A close up of a nematode.
A close up of a nematode.

-type of worm
-first organism studied with microRNA (noncoding regions of RNa that are transcribed)
-1 mm long nematode
-favorite model organism of developmental biologists
-one of the first eukaryotic genomes to be sequenced


C. elegans is a free-living as opposed to parasitic roundworm. They usually live in soil, where it can feed on bacteria and fungi. In the labs, it is grown by feeding the organism on a bacterial lawn of E. coli. Its small size allows scientists to study its anatomy very closely, making it an excellent model for study of neurodevelopment.
http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html (Bhu)

They represent, for example, 90% of all life forms on the ocean floor. Their numerical dominance, often exceeding more than a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity in lifestyles, and their presence at various trophic levels point at an important role in many ecosystems.Their many parasitic forms include pathogens in most plants and animals (including humans). [3]

Relationship to Humans

-CED-3 protein that is involved in cell death is similar to the gene controlling cell death in humans
-CED-4 which is involved in apoptosis pathway has relatives in humans
-shows these proteins are helpful and favorable-years of evolution and these genes are still present
nematodes

They are parasites which often inhabit humans. They can be detrimental to their [[#|hosts]] both due to the diseases that they may carry in addition to the detrimental effect of them living off their hosts,

These can also be parasitic towards crops grown by humans, hurting crop production. However, different groups of nematodes are instead predators towards crop pests, actually serving as an [[#|effective pest control]], in some cases.
http://en.wikipedia.org/wiki/Nematode#Agriculture_and_horticulture

Habitat/ Niche

-normally lives in temperate soil environments
-can also live in the laboratory


Nematodes are known to be found in virtually every habitat on earth, aquatic and on land. However, the majority of Nematode species are aquatic. They are the most numerous organisms on earth.

http://classes.seattleu.edu/biology/biol235/hodin/nematodePriapulidGroup/nematodes/ecology.htm


Predator Avoidance
-trasnparent covering

When threatened by a predator, C. elegans will execute a series of evasive maneuvers such as omega bends and reversals in order to evade being eaten. (Colin Gray)
http://www.genetics-gsa.org/celegans2011/abstracts/fulltext/f71088.htm

Nutrient Aquisition

-digests food
-feeds on small aniamls and protists, includiong other roundworms
-feed on bacteria that develop on decaying vegetable matter
-exchanges nurtients with environment through cuticle and gut

Reproduction/Life Cycle

c. elegans life cycle.gif
http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html

-reproduces sexually
-lays eggs through vulva located on the lower surface
-several larval stages
-pass through 4 juvenile stages-in 4th produce all their sperm, then start to produce oocytes
-contains both male and female reproductive organs
-Short life cycle (about two weeks)
-The life cycle is temperature dependent which is within the 20C - 25C range.
-C. elegans can adopt an alternate life form if food is too scarce. This is called the dauer larval stage.
http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html
- Within two hours fertilization is [[#|completed]] and the eggs are laid.
- After about 12 hours the eggs [[#|begin]] to hatch and the offspring are born.
- The offspring for both males and females reach maturity within 3 days from their birth.
- The average Caenorhabditis elegans live about 58 days before it dies.
http://animaldiversity.ummz.umich.edu/accounts/Caenorhabditis_elegans/

C. elegans is extremely fecund; a hermaphrodite can produce about 300 to 350 offspring under self-fertilization and more if it mates with males. This ability to reproduce such great numbers, makes it easy to produce numerous genotypes and phenotypes.
http://www.wormclassroom.org/short-history-c-elegans-research

There are two genders of C. Elegans, males and hermaphrodites.
https://en.wikipedia.org/wiki/C_elegans

C. Elegans males have a specilized tale for mating. The eggs are laid by the hermaphrodite which have two ovaries, oviducts, and a single uterus.
http://en.wikipedia.org/wiki/Caenorhabditis_elegans

external image reprodSystemSmall.gif
The Sexual Organs of a C. elegans (GC)
http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html

Growth/Development

-develops from a fertilized egg to larva in 8 hours, reaches adult stage in 3.5 days
-goes through vulval development
-development is controlled by molecular switches that allow a cell to go down one of two tracks
-produce 1,090 somatic cells as it develops into an adult,
131 die
-sheds it cuticle 4 times as it grows


Caption: C. elegans Life Cycle

C. elegans Life Cycle
C. elegans Life Cycle

http://www.wormclassroom.org/image/c-elegans-life-cycle

external image Celegans.gif

^The male and female anatomy of C.elegans
Integument
Nematodes a thick, transparent outer cuticle that is durable and flexible in order to accommodate the organism's movements. The cuticle is a multi-layered structure composed of cross-linked collagen proteins along with other organic materials, and it is important because it provides the worm support and leverage. This cuticle integument can be likened to an exoskeleton and is shed at certain periods during a nematode's life cycle as the organism grows. (2) [GW]

Movement

C. elegans move by contracting their longitudinal muscles.

Hillis, David M. Principles of Life. Sunderland, MA: Sinauer Associates, 2012. Print.
C.Eleagns most commonly move in what are known as sinusoidal movements, movements which resemble very much the shape of a curve. Although that is common, events such as mating, feeding and other environmental influences can disrupt the muscle contractions, thus ruing the sinusoidal movement.-
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013914

C.elegans contracting their muscles
C.elegans contracting their muscles


Locomotion:
external image NematodeLocomotion.gif
Nematodes move by undulations or wave-like motions of the body. This produces a thrashing movement. The body's contractions are according to dorsal/ventral contractions of the body. As one segment of the body contracts, it "pulls" the remainder of the body forward. Therefore, the contracting/relaxing alternations provide a locomotion style for the nematode. The muscles are able to "manipulate" each other to contract/relax accordingly by use of the pressure changes through the fluid skeletal space of the pseudocoel. As the muscles are contracted, to relax and extend the "stressed" muscles by means of the stiff cuticle and high pressure which forces the organism to take form of its longitudinal characteristic.

Picture taken from the website:
http://classes.seattleu.edu/biology/biol235/hodin/nematodePriapulidGroup/nematodes/locomotion.htm



Sensing the Environment

-two lateral nerves which receive sensory information
-sense of touch is provided by sensory bristles and papillae

Gas Exchange

-exchange oxygen with environment through cuticle and gut (one cell layer thick)
-materials are moved through the gut by contraction of pharynx
- Nematodes exchange gases with their environment through simple diffusion across their exterior cell walls and similarly excrete gases through simple diffusion according to differences in concentration gradients. (4)

Waste Removal

C. elegans remove waste through the use of four cells: the pore, duct, canal and the gland cell. This excretory system removes metabolic waste and excess fluids. This system is also responsible for maintaining the organism's salt concentration.

http://www.wormatlas.org/ver1/handbook/excretory.htm

Environmental Physiology

Nemotods are ectothermic meaning their temperature depends on their environment instead of internally regulating it. Different types of nemotodes have different optimal temperatures. For example the optimal temperature for C. elegans is 25 degrees Celcius. (http://www.biocontrol.entomology.cornell.edu/pathogens/nematodes.html)

Internal Circulation

- lacks skeletal elements and has no [[#|circulatory system]]
- Due to small size oxygen is diffused from the air through the body
(Cam Somers)
http://www.sfu.ca/biology/faculty/hutter/hutterlab/research/Celegans.html

Chemical Control


Review:
Where are nematodes more prevelant?
How many days does it take a larva to reach adult stage?
3. Because nematodes are ectotherms and have a regulated temperature depending on the outside environment, how do they work to control this internal temperature? For example, if it is too hot out, would the nematodes know to go under a rock or find some shade? (evan).
How does the nematode's transparent covering help it move, hide from preditors, and sustain its structure?
4. Explain nematode's usefulness to humans in modern society. (Prashant)
5. Reflect on the nematodes ability to reproduce both sexually and asexually, the number of offspring it is capable of producing, and the offspring "retention-rate", and explain it's connection to it's lifespan.

References

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.

‚Äč2. http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html

http://nematode.unl.edu/wormgen.htm
4. http://www.darwinsgalapagos.com/animals/nematoda_roundworms.htm