Tetrahymena as a model system to study phagocytosis

Module 2 – Week 1

Before we start this week…

• We have assigned new 4-person lab groups for everyone

• You will be doing much of the work in pairs today

• Half of class will start exercise #1: pipetting• Other half will start exercise #2: microscopy

Goals

1) Become competent in the use of micropipettors to deliver very small volumes of liquids.

2) Develop the ability to use the Olympus CH-2 brightfield microscope for studying single-celled organisms.

Next week…3) Explore how polystyrene microbeads can be used to

identify subcellular structures and organelles.4) Develop an experimental strategy to test a hypothesis

related to the phagocytotic mechanism of Tetrahymena.

Gilson Pipetman

• Identity of pipet on top button• P20 and P200 use yellow tips• P1000 uses blue tips• Two stop positions on piston– 1st: to fill– 2nd: to expel remaining liquid

during dispensing• The numbers on the dial

depends on the pipet in use

Pipetting exercise• P-1000 pipettor set to 500 μl (water weight = 500 mg = 0.500 g)• P200 set to 200 μl (water weight = 200 mg)• P20 set to 20 μl (water weight = 20 mg)

• Empty 1.7 ml centrifuge tube on a 3-place pan balance. Tare (zero) the balance so the weight of the tube is zeroed out.

• Pipette water into the tube. Weigh the tube and record the weight.

• Repeat five times.• Repeat this exercise with all three pipets.• Using Excel, calculate the average and standard deviation of your

three different pipettors.Pipette Volume set Approx. wt. Precision Precision

(ul) (mg) (%) range (mg)P-1000 1000 1000 0.15 998-1002

500 500 0.2 499-501P-200 200 200 0.15 199.7-200.3

100 100 0.25 99.7-100.3P-20 20 20 0.3 19.9-20.1

Olympus CH-2 microscope

Introduction to the microscope• Place sample slide with coverslip facing up on specimen holder.• Turn the light intensity dial to the zero position.• Turn the main power switch on and increase the light level. • Adjust specimen stage so that edge of glass is in beam.• Make sure the condenser is all the way down.• Rotate the 10x objective into position for viewing.• Turn the coarse focus knob to a position so that the specimen is basically in focus.• Adjust the distance between two eyepieces (interpupillary distance) so that you

see through both eyes.– Use the fine-focus knob to achieve optimum focus through the right ocular.– Use the diopter adjustment ring to focus the image through the left ocular, so that both

eyes see the image properly focused.• Adjust the aperture iris (using its lever) for optimum contrast. The iris aperture

must be adjusted each time you switch to a different objective.• After focusing with the 10x objective, you can increase total magnification with

the 40x objective. You will need to adjust the fine-focus each time you change. • Don’t let any objective lens contact the slide.

– Adjust the light intensity when you change objectives, and then re-adjust the iris aperture.

Viewing Tetrahymena in the microscope

• Tetrahymena cell culture prepared for you• Three 1.7 ml microtubes: A, B, and C.• A = 50 μl of Tetrahymena + 50 μl of 3 micron polystyrene beads. • B = 50 μl of Tetrahymena + 50 μl of 0.2% glutaraldehyde.

– PERFORM IN FUME HOOD; CAUTION: glutaraldehyde is highly toxic. • Mix both tubes gently. • C = 20 μl of cells from Tube “A” (~10 min bead exposure) + 20 μl of

glutaraldehyde, then mix. Record the duration of ink exposure.– PERFORM IN FUME HOOD

• Observe three Tetrahymena samples in the microscope

Glutaraldehyde

• Hazard Statements: • H302: Harmful if swallowed• H315: Causes skin irritation• H317: May cause an allergic skin reaction• H318: Causes serious eye damage• H330: Fatal if inhaled• H334: May cause allergy or asthma symptoms or

breathing difficulties if inhaled• H400: Very toxic to aquatic life• If you would like to review the complete MSDS, please

consult with your TA

Proper Personal Protective Equipment (PPE)

• All Glutaraldehyde must be handled in the fume hood

• Every student must wear a lab coat, gloves, and safety glasses when working with 2.5% glutaraldehyde or samples treated with glutaraldehyde

Disposal of Tips, Slides, and Tubes• Tips that have not come in contact with glutaraldehyde can be placed

in the coffee can labeled “Tips Only” located on your lab bench.• Slides that have not been contaminated with glutaraldehyde can be

put in the red “sharps” container on the side bench.• All tubes containing liquid with trace glutaraldehyde must be emptied

into the container in the fume hood labeled “Liquid Waste.”• Tips, tubes, and slides contaminated with glutaraldehyde must go in

the container in the fume hood labeled “Solid Waste.”• Gloves and kimwipes must go in the Biohazard Box located by the

hood• Wipe down your bench before leaving and put paper towel in

Biohazard Box• Don’t touch computers with gloved hands

Write up your work today

• Pipetting exercise– Calculate mean and S.D. for each pipet verification– Determine whether pipetting technique was precise or imprecise

• Initial observations of Tetrahymena– Drawing of typical cell– Describe swimming and eating behaviors

• Effects of glutaraldehyde

– For fixed cells exposed to beads, count number of beads per cell for ten cells. Mean and S.D.

• Turn in your observations, results and conclusions for Exercise #1 and #2 next lab session.

Next week’s experiment?

• From your initial observations, consider exploring the following:– What do Tetrahymena consider food?– What is the cellular mechanism by which food is

ingested?– ???

• Fill out the “My Proposed Experiment” form and turn in with summary of today’s work on flip side