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What can I learn from worms? Regeneration, stem cells, and models

Lesson 5: How can we see the worms’ cells during regeneration?

I. Overview In this lesson, students examine how scientists study cell growth and division using the incorporation of

5’-bromo-2-deoxyuridine (BrdU) and subsequent visualization. Students are introduced to a University

of Illinois scientist whose work uses this technique to investigate the process by which planarians

regenerate. At the end of the lesson, students make a hypothetical drawing of BrdU localization in their

cut planarians from the previous lesson, illustrating how stem cells have divided and migrated during

the process of regeneration.

Connections to the driving question This lesson connects to the driving question by showing how worms can be used to learn about

regeneration. Students learn how worms can be studied to provide insights on stem cell division and

migration.

Connections to previous lessons Students have made cuts to planarians in previous lessons, and they have been observing regeneration

in their planarians. This lesson provides a technique to visualize details of regeneration on a cellular

level. As a result, students understand the micro-level processes that contribute to the macro-level

regeneration that they observe.

II. Standards

National Science Education Standards

Content Standard A: Abilities necessary to do scientific inquiry. Formulate and revise scientific

explanations and models using logic and evidence. Student inquiries should culminate in

formulating an explanation or model. Models should be physical, conceptual, and mathematical.

IN the process of answering the questions, the students should engage in discussions and

arguments that result in the revision of their explanations. These discussions should be based

on scientific knowledge, the use of logic, and evidence from their investigation. (9-12 A: 1/4)

Content Standard A: Understandings about scientific inquiry. Scientific explanations must

adhere to criteria such as: a proposed explanation must be logically consistent; it must abide by

the rules of evidence; it must be open to questions and possible modification; and it must be

based on historical and current scientific knowledge. (9-12 A: 2/5)

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Content Standard C: The cell. Cells can differentiate, and complex multicellular organisms are

formed as a highly organized arrangement of differentiated cells. In the development of these

multicellular organisms, the progeny from a single cell form an embryo in which the cells

multiply and differentiate to form the many specialized cells, tissues and organs that comprise

the final organism. This differentiation is regulated through the expression of different genes.

(9/12 C: 1/6)

Benchmarks for Science Literacy The Living Environment: Heredity

The many body cells in an individual can be very different from one another, even though they

are all descended from a single cell and thus have essentially identical genetic instructions.

5B/H6a

The Living Environment: Cells

Before a cell divides, the instructions are duplicated so that each of the two new cells gets all

the necessary information for carrying on. 5C/H4c

Complex interactions among the different kinds of molecules in the cell cause distinct cycles of

activities, such as growth and division. Cell behavior can also be affected by molecules from

other parts of the organism or even other organisms. 5C/H5

III. Learning Objectives

Learning objective Assessment Criteria Location in Lesson

Describe how BrdU

can be used to

visualize cells.

Descriptions can include:

• Planarians are fed BrdU

• BrdU is incorporated into planarian DNA

• Planarians fixed and a BrdU-specific primary

antibody is applied

• A secondary antibody is applied which includes a

tag that is visible under a fluorescent microscope

Opening of lesson

discussion questions

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Use images of stained

planarians to predict

the time since

exposure to BrdU.

Drawn predictions can include:

• Day 3 drawing has less BrdU cells, and they are less

concentrated than Figure 5A.

• Day 7 drawing has more BrdU cells, and they are

more concentrated than Figure 5A.

Student packet Q. 9

Differentiate between

cells stained by BrdU

and those that are not

stained by BrdU.

Students make this distinction by counting the cells

that fluoresce in the pictures and not counting the

others.

Cell counting in

Activity 1

Identify evidence of

cell migration and

differentiation.

Explanation can include:

• The staining pattern moves anterior (toward the

front) over time

• The pattern changes because the differentiated

cells migrate to the area in front of the eyespots,

which does not have its own stem cells

Student packet Q. 6

Develop a scientific

explanation that

describes the stem cell

replication and

migration in recently

cut planarians.

Explanation should be supported by evidence and

reasoning. See CERR Rubric

(Resource_BaseRubricCERR.docx) for additional

assessment criteria.

Student packet Q. 3

Student packet Q. 12

IV. Adaptations and Accommodations For this lesson, the pre-reading on BrdU staining can be completed in class with the video shown

afterward to ensure that students complete the reading. The reading and video together should provide

the differentiation needed to help most students understand the technique for the rest of the lesson’s

activities. Another adaptation could be creating a class initial illustration explanation for how the cut

planarian should look with BrdU staining in Activity 1. Instead of having groups of students develop this

explanation, the class could come up with an initial explanation together using the claim, evidence,

reasoning framework and then revise the explanation after completing the activities in the Student

Packet.

Safety There are no additional safety concerns associated with this lesson.

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V. Timeframe for lesson

Opening of Lesson

Discussion of “Investigating Planarian Cell Regeneration using BrdU” reading – 5-10 minutes

Main Part of Lesson

Activity 1: BrdU Images and Animation – 15 minutes

Activity 2: Develop Revised Explanation Using Published Data – 20-25 minutes

Conclusion of Lesson

Closing Discussion – 5-10 minutes

VI. Advance prep and materials

Opening of Lesson

Materials:

Student pre-reading on BrdU Staining

(U2_L5_PreReading_InvestigatingPlanarianCellRegeneration.docx)

Activity 1: BrdU Images and Animation

Materials:

BrdU Animation Video

Time Course BrdU Images, 1 set/group of 4 students (U2_L5_Resource_BrdUImages.pdf)

Student Packet, 1 copy/student (U2_L5_StudentPacket.docx)

Preparation:

Preview video to make sure the technology is compatible with your computer

Activity 2: Develop Revised Explanation Using Published Data

Materials:

Student Packet, 1 copy/student (U2_L5_StudentPacket.docx)

Homework and Assessments

Materials:

Student pre-reading on RNAi (U2_L6_HW_PreReading_RNAi.docx, found in the Lesson 6 folder)

Checkpoint assessment, optional (U2_L5_StudentSheet_Checkpoint.docx)

VII. Resources and references

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Teacher resources McNeill, K. L., & Krajcik, J. S. (2012). Supporting Grade 5-8 Students in Constructing Explanations

in Science: The Claim, Evidence, and Reasoning Framework for Talk and Writing. Pearson.

Four-video series on cell migration:

o http://www.youtube.com/user/unclineberger#p/u/22/kRV7to3gst0

o http://www.youtube.com/user/unclineberger#p/u/21/hcw7bwA0dTA

o http://www.youtube.com/user/unclineberger#p/u/20/ixfOMFFaEzY

o http://www.youtube.com/user/unclineberger#p/u/19/2HRscyXEVj0

References Forsthoefel, D.J., Park, A.E., and Newmark, P.A. (2011). Stem cell-based growth, regeneration,

and remodeling of the planarian intestine. Developmental Biology. 356: 445-459.

Sánchez Alvarado A, Newmark PA, Robb SM, Juste R. (2002). The Schmidtea mediterranea

database as a molecular resource for studying platyhelminthes, stem cells and regeneration.

Development. 129(24): 5659-65.

Teacher Background

Regeneration & Cell Staining

Planarians are used as model organisms because of their high regenerative capacity. As the students

learned in Lesson 3, if a planarian is cut, it will re-grow the “missing” portion of its body. Under normal

circumstances, cell regeneration occurs in intact (uncut) planarians to replace old or damaged cells. In

fact, in all animals, cells are regularly replaced in many tissues. Planarians are unique because they have

stem cells that can be used to re-grow an entire organism as long as a portion of the planarian is present.

Newly generated cells have to differentiate and migrate to the area of the body or cell layer where they

belong. In planarians, stem cells are located throughout most parts of the body. However, not all parts

of the planarian’s body contain stem cells.

Scientists are interested in discovering more about the migration of these cells. They have developed

techniques to track newly divided cells. One such technique involves feeding planarians a compound

called 5’-bromo-2-deoxyuridine (BrdU), which is a thymidine analog. Because its chemical structure is

similar to that of thymidine (see chemical structure below), the BrdU will get incorporated into the DNA

during cell division.

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To introduce the BrdU into the planarians, the scientists dissolve the BrdU in 40% ethanol. This ethanol-

BrdU mixture is then added to a beef liver mix and fed to the planarians. Once the planarians have eaten

the BrdU, it is incorporated into the DNA of dividing cells along with the other normal DNA molecules. As

the cells divided, the BrdU was passed along to the daughter cells. After a certain period of time, the

scientists “fixed,” or preserved, the planarians and began a procedure that allowed them to detect the

cells containing the BrdU. This process is shown in the image below (Figure 1).

This same image is in the student materials for the students to read as well. In the images the students

receive as part of the activity packet, the planarians have been labeled with fluorescent antibody to

BrdU. To label only the molecule of interest, which in this case is BrdU, scientists create antibodies that

specifically bind the molecule of interest. To create the primary antibody, the molecule (or part of the

molecule) is injected into an animal, usually a rabbit or mouse. Scientists use the animal’s natural

immune system to create antibodies specific to the protein of interest. After the animal has produced a

large amount of antibodies, the scientists will take the blood and extract the antibodies. This antibody is

called the primary antibody, and it will bind to the molecule of interest. Next, the scientists use another

antibody called a secondary antibody. This secondary antibody generally binds the primary antibody

made by a specific animal described above. In addition, the secondary antibody may contain a special

tag that will fluoresce a certain color under a fluorescent microscope.

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Figure 1: Showing the procedure to localize BrdU in planarians

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Cell Migration

In planarians, like other organisms, chemical gradients are important to establish polarity such as the

position of the head and tail. Chemical gradients can also be used by newly generated cells to migrate

from the stem cell area, where they were born, to the tissue, where they are needed.

To migrate, these cells need two types of proteins on the outside of the cell membrane: 1) receptors

that recognize the chemicals in the gradient and 2) cell-adhesion molecules (CAMs). Because chemicals

present in the gradient have a specific shape they will fit in receptors that correspond to that shape.

The chemicals will bind to these receptors found on the cell membrane of the migrating cells. The

binding of the chemicals in the gradient to the migrating cell will orient the cell and will cause it to move

either towards a chemo-attractant or away from a chemo-repulsant. In this way chemical gradients can

guide migration.

CAMs are important for cell movement, as they are the primary molecules for cell-to-cell binding. The

CAMs on a migrating cell can bind to CAMs on the surface of another cell’s membrane to guide itself

along its path. With this cell-to-cell adhesion, the migrating cell can pull itself towards its destination –

the tissue where it will mature and function. Neurons not only need to get to their destination but also

have the extra challenge of getting their axons to grow into the proper target region or organ. Axon

guidance also relies on chemical gradients and CAMs.

Cell migration videos

Four-video series on cell migration:

http://www.youtube.com/user/unclineberger#p/u/22/kRV7to3gst0

http://www.youtube.com/user/unclineberger#p/u/21/hcw7bwA0dTA

http://www.youtube.com/user/unclineberger#p/u/20/ixfOMFFaEzY

http://www.youtube.com/user/unclineberger#p/u/19/2HRscyXEVj0

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VII. Lesson Implementation

Opening of Lesson: Ask the students to take out the “Investigating Planarian Cell Regeneration using BrdU” reading that was

used previously (in class or for homework). Engage the class in a discussion on the reading using the

following questions:

What is one thing you took away from the reading?

o After a student has initially shared what he or she learned, ask another student to repeat

what was just said by the first student, and then to add an additional piece of

information from the reading. Using this strategy of adding to previous comments,

students will be encouraged to listen to their classmates. Additionally, one can ask

students to make connections between students’ comments, ensuring that they develop

a deeper and more connected understanding of the reading.

How can you tell what is happening to the stem cells, or neoblasts, of the planarian using the

BrdU incorporation and detection technique?

o Ask an initial student to state his or her answer. Then ask the next student to agree or

disagree with the first statement and provide a supporting reason for agreeing or

disagreeing.

Why is it important that scientists are able to use BrdU incorporation and detection in the

laboratory? What can they study using this labeling technique?

o Ask students to share their ideas with their partner and then share out to the rest of the

class what they came up with for this question.

Teacher Content Knowledge The term neoblast refers to the undifferentiated cells of the planarian.

Following this discussion, tell the students that they will be watching a video about a scientist who uses

BrdU on a regular basis to study planarian regeneration. This video is meant to supplement the reading,

showing the process of BrdU incorporation and subsequent detection in an audiovisual manner.

Following this video, the students will investigate how stem cells grow, divide, and migrate to injured

parts of planarians and develop a claim based on evidence and reasoning on what their own cut

planarian’s stem cells might look like under a microscope.

Main Part of Lesson

Activity 1: BrdU Images and Animation

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In this initial activity, students watch a video of Dr. David Forsthoefel, a researcher at the University of

Illinois, explaining BrdU incorporation and detection using animations to supplement his narration.

Encourage students to take notes about the video on the back of their reading, particularly noting any

questions or anything that is confusing from the reading and the video. Ask the students:

Do the reading and the video complement each other? Are there any points where there is

disagreement on the technique?

o Allow the students to generate ideas and also answer their fellow classmates’ questions.

Scientific Practices: Analyzing and interpreting data. When students view the images in the next part of the activity below, they are

engaging in a scientific practice. By analyzing images from a primary research article,

students use the same skills that the original researchers used.

Then, arrange the students in groups of 4-5 and pass out the BrdU images from a recent paper by

Forsthoefel, Park, and Newmark (2011). Here, students view and analyze data from a recent research

paper in order to later make predictions about their own planarians’ cell growth and migration at

different time points (pg. 1 of the U2_L5_StudentPacket.docx). The students should count the number

of cells labeled in the highlighted area for each time period. At the front of the class, draw a data table

similar to the one below. Have each group write the number of labeled cells they see in each image:

24 hr 72 hr 5 day

Group 1’s count Group 1’s count Group 1’s count

Group 2’s count Group 2’s count Group 2’s count

… … …

Average= (~111 cells) Average= (~170 cells) Average= (~120 cells)

After each group enters their data in the table, generate an average number of cells for each of the time

periods. Engage in a conversation with the students, asking students to agree/disagree with one

another and to repeat what has been said by other students, as well as adding on to previous students’

statements or explaining what that student said with the following questions:

Was it difficult to count the cells? Were there differences in the brightness of the labeled cells?

Why do you think that occurred?

Why are there more cells at the 5-day compared to the 24 hr?

Do the cells stay in the same place? Why do you think they are/are not remaining in the same

place?

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Explain to the students that they will develop their own models of what their cut planarians’ stem cells

are doing during the regeneration. Hand out the BrdU student packet titled “How do scientists view

planarian stem cells?” and ask students to answer the first 3 questions based on their reading, the

video/animation, and the BrdU images they just analyzed. It is important that students understand that

this is just their initial explanation based on what they know up to this point; they will work through the

rest of the Student Packet (pg. 2-5) and then revise their explanation at the end of the packet.

Activity 2: Develop Revised Explanation Using Published Data

For this activity, the students work through the rest of the Student Packet (pg. 2-5). Students analyze

data from a 1999 paper written by Newmark and Sánchez that describes the cell labeling process that

Forsthoefel used in his work. To do this, students work in groups to answer questions based on the

scientific paper written by Newmark and Sánchez. Necessary portions of this paper are included in the

student materials.

Scientific Practices: Constructing explanations. Part of scientific practice includes developing scientific explanations in which a claim is

supported by evidence and reasoning. Students will have practice with this skill as the

activity continues below. Students will use evidence from primary research to support

a claim that they develop.

As the students work in groups, it is important to circulate around the classroom, evaluating the types of

conversations in each group. In addition to being used as an assessment, questions provide a way for

students to practice developing scientific explanations that include a claim, evidence to support the

claim, and reasoning to link the claim and evidence.

Teacher Pedagogical Content Knowledge Scientific explanations need to include a claim, evidence (data), and reasoning that link

the claim and evidence. The reasoning here would be the appropriate scientific

principles that were introduced through the video and initial pre-reading on BrdU

staining.

To support the students, the initial illustration and explanation can be developed as a

class, focusing on how evidence supports a claim and the reasoning links the claim and

evidence:

Claim: The BrdU staining would appear ____ at Day 0 and ____ at Day 7.

Evidence: In other examples of BrdU staining (evidence from student packet in Lesson

5) ___________.

Reasoning: This is because in the reading and video on BrdU staining (scientific

principles found in BrdU video, background reading, and student packet)

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______________.

Rebuttal: The staining could not appear as _________ at Day 0 or Day 7 because based

on information presented in the student packet __________, this staining is not

plausible.

As students develop their understanding of both what a scientific explanation is and

the necessary science, students should be encouraged to include a rebuttal in their

explanation. A rebuttal would be a statement describing why another claim is not as

“good” as the claim being championed in the explanation by the student. Each rebuttal

could include evidence and reasoning as well.

Conclusion of Lesson To conclude the lesson, have students complete the Student Packet including the revised explanation

included at the end of the packet. Allow students to complete this as homework if not completed in

class.

In a whole class discussion, ask students to share their revised explanations with the class. A

representative from each group should share the following with the class:

The initial explanation the group developed,

The ideas and thought processes that the group used to revise their explanation,

Their revised explanation based on the BrdU reading, video, and Student Packet.

Ask the students to think about why scientists study planarians using this technique:

What is useful about cell-count data to scientists?

How can this information help scientists understand more about human stem cell regeneration?

“Ask the Scientist” questions #9 (Now that you have the data, what do you do next?) and #11 (What is

the human connection to your research?) can be used here to show the students how one researcher is

using similar types of data to study how planarians regenerate.

Explain to the students that in the next lesson they will learn about another technique that scientists use

to study how planarians regenerate. This technique, RNA interference or RNAi, is important since it

allows scientists to “knock down” the amount of protein in a planarian and see what happens to the

behavior of the planarian, thereby determining a possible role of that protein.

The RNAi pre-reading, found in the Lesson 6 folder as U2_L6_HW_PreReading_RNAi.docx, can be

assigned as homework or completed the next day in class in a group reading format.

Assessments

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During this lesson, a variety of group and whole class discussions can be used to informally evaluate the

students. In Activity 1, students record the number of labeled cells they count for each planarian image

and discuss these results as a class. Then, they develop an initial explanation based on the claim,

evidence, reasoning framework to describe their own cut planarians’ cellular regeneration. This written

and illustrated explanation is used at the end of the lesson when students create a revised explanation,

based on their analysis of the figures in the Student Packet. This second revised explanation could be

done as an individual assessment or as a group activity.

Also, a “checkpoint” assessment (U2_L5_StudentSheet_Checkpoint.docx) can be assigned to evaluate

what students have learned about regeneration up to and including the content of Lesson 5. Here, have

students create a response based on the Claim, Evidence, Reasoning (CER) framework that is outlined in

the McNeill and Krajcik (2012) text Supporting Grade 5-8 Students in Constructing Explanations in

Science: The Claim, Evidence, and Reasoning Framework for Talk and Writing. A sample base rubric

(Resource_BaseRubricCERR.docx) is meant to serve as a starting point for more specific CER rubrics.

Depending on the activity, it is helpful for students to have a more precise idea of what is expected of

them for their CER response.