1997 WWLPT Biology Institute:
Life Cycles: Reproduction &
BARNSTABLE HIGH SCHOOL
744 WEST MAIN STREET
HYANNIS, MA. 02563
Teacher demonstration or group/cooperative activity.
Notes to the
Teacher: to top
The major focus of this activity is for students to see embryogenesis in action. If eggs can be found in early stages of development ( 1 - 8 cells, for example) cleavage can be witnessed and nuclei can be observed to divide in as little as 10 -15 minutes. For interested students and teachers, this can be a very exciting and inspiring experience.
For group work, students must be able to use dissecting and compound microscopes. Cultures should be ordered at least 2 weeks in advance from the Caenorhabditis Genetics Center from the University of Minnesota (see references) or from local research centers or universities that use C. elegans. Worms should be kept at 20 - 22 degrees Celsius, and temperatures above 25 result in sterility.
This activity may be done as a demonstration or group lab. For demonstrations, one slide may be set up on a demonstration microscope and displayed on the video monitor. Embryogenesis may be viewed for several minutes or several hours, and may extend for several days, if additional media is available, so that development into the adult form can be observed.
If students are working individually or in groups,
appropriate precautions should be taken when using single-edged razor
blades. No special problems are presented with the use C.
elegans or the medium in which it is cultured.
Caenorhabditis elegans wild type (N2 strain)
C. elegans media
Compound and dissecting microscopes
Video camera attachment for microscope and monitor screen*
Single-edged razor blades
Slides and coverslips
Hermaphrodites carry out self-fertilization, or, preferentially, are fertilized by males. Over 300 eggs are produced by a single hermaphrodite, and embryogenesis and may be viewed in various stages while still in the body cavity of the parent. The fertilized egg undergoes the first cleavage within 40 minutes, in which the anterior and posterior regions are formed. Successive cell divisions may occur at intervals of 15 minutes or less. Transparent bodies and eggs allow structures to be easily seen when viewed with a light microscope under high power. Micrographs showing the various stages of embrogenesis (Schierenberg, 1986) are available at .
Worms are available on a culture dish of medium with a lawn of E. coli, the primary food for the nematode. Individual worms may be transferred by gently picking them up with a "worm pick" made by melting fine platimum wire on the end of a pasteur pipette. Another method of harvesting many worms is to flood the culture dish with water and transfer the worm suspension to a petri plate. Using the dissecting microscope, hermaphrodites may be selected and trasferred on to a small drop of water on a glass slide.
The eggs are more easily studied after removal from the parent body. Using the dissecting microscope, locate the hermaprodites. With a new single-edged razor or scalpel blade, cut the worm into two or more pieces. The internal pressure will force eggs out. Cover with a cover slip and examine under the compound microscope.
How do organisms develop from a fertilized egg?
How long does it take for a cell to divide?
How does a zygote develop into an embryo?
Observe the stages of
development of the eggs of C. elegans, a common
Part I : Getting to know your worms.
Obtain a culture of C. elegans and examine under the dissecting microscope. Notice the movement of the worms over the media and try to determine the anterior and posterior ends from the direction of movement. Carefully, using the pick, transfer some worms from the culture dish to a drop of water on a slide and place a cover slip over the specimen. Examine the slide under the compound microscope, first under low power, then under increased magnification. Watch the behavior of worms and identify hermaphrodites and males.
Part II. Examination and study of eggs.
Using the dissecting microscope, select 3 or 4 hermaphrodites from your cultures. Transfer them to a small drop of water on a glass slide. Place the slide uncovered on the stage of the dissecting microscope. While looking through the microscope, locate your worms. With a new single-edged razor or scalpel blade, carefully cut the worms into two or more pieces. The internal pressure will force eggs out. When you have finished cutting the worms, add a cover slip and tranfer the slide to the compound microscope. Examine them first under low power to locate individual eggs, then increase magnification.
Locate an egg and determine the number of cells it contains. Try to find one with a very few visible nuclei. Determine what other cellular structures are visible. If a 2-celled stage has been located, one cell should be larger than the other. The larger cell will divide first to form the anterior region of the worm.
Make a sketch of your egg and note the time. Record any details. Check your eggs every few minutes and look for changes. Record them and make additional drawings. Compare your egg with those of other students.
When the period is over, save your eggs for later observation
or clean up your materials as directed.
For Films and Cultures of C. elegans:
Caenorhabditis Genetics Center
University of Minnesota
St. Paul, MN 55108.
attention: Theresa Stiernagle
Riddle D.L, Blumenthal, T., Meyer, B.J. and Priess, J.R.
1997. C. elegans II.
Cold Spring Harbor Laboratory Press.
Wood, W.B. and the Community of C. elegans researchers.
1998. The nematode Caenorhabditis elegans.
Cold Spring Harbor Laboratory Press.
Embryonic Development of the Nematode C. elegans. Einhard Schienberg/IWF. 12 minutes.
A Nematode as a Model Organism. The Genetics of Programmed
Cell Death. 30 minutes.
H. Robert Horvitz, Howard Hughes Med. Inst. MIT. 1966. Cognito Learning Media Inc.