Multicellular organisms can form patterns using self-assembly

In self-assembly, each cell (or organism) has a small set of instructions, but those instructions help organize the entire group

There is no “organizer” or “manager” in self-assembly. The instructions inside each cell are carefully designed so the cells can organize themselves.

Self assembly

Endoderm

Ectoderm

Multicellular

Tentacles

• Disecting Scope (E069, E070, E071, E073, E074, E075, E075, E076, E077, E078, E079, E080, E082, E083, E084, E088)Budding hydra, living (Carolina, item 155996)
• Media (available from Taylor Skokan at UCSF, contact Jessica Allen)
  • Hydra Medium (in 100 ml Deionized Water)
    • 44 mg CaCl2
    • 2 mg MgSO4
    • 2 mg K2CO3
    • 4 mg NaHCO3
  • Dissociation Medium (in 100 ml Deionized Water)
    • 5 mg CaCl2
    • 7 mg MgSO4
    • 85 mg KCl
    • 274 mg HEPES
    • 51 mg Na2HPO4
    • 0 mg KH2PO4
    • 5 mg NaPyruvate
    • 0 mg Na3Citrate
  • Microcentrifuge tubes
  • Centrifuge (set to speed 800 x G)
  • Glass pipets
  • Ice in ice buckets
  • Rubber bulbs (SEP has extra)
  • 35mm petri dishes (SEP has extra)
  • Dissecting scopes
  • Chartboard paper
  • Markers
  • Post-it notes

Daly Ralson Resource Center:

Dissecting Scope (E069, E070, E071, E073, E074, E075, E075, E076, E077, E078, E079, E080, E082, E083, E084, E088)

Groups of 3-4 students

5 days

15 min – Intro

30 min – Dissociation

Check hydra:

4-6 hours later (15 mins)

1 day later (15 mins)

2 days later (15 mins)

3 days later (15 mins)

4 days later (15 mins)

40 min – Wrap-up/Closure

As this activity requires more complex knowledge of cell biology and DNA, basics of biology should be introduced before attempting this activity. Students should have an understanding that single cells have programming in the form of DNA. This “programming” can be used to sense and respond to its environment or other cells.

• Identify hydra, its parts, and the two layers of cells that form its inside and outside
• Understand that self-assembly is one way that multicellular organisms for complex structures out of a group of cells
• Consider what sort of programming cells would need to form an inside an outside layer
• Develop students ability to collect evidence through observation.

Hydra’s ability to reassemble itself after being broken down into single cells is unique in the animal world. That ability is attractive to scientists as it might hold the answer to how life evolved from single celled organisms, how might we unlock hydra-healing powers to heal human wounds.

Hydra self-assembly into a whole organism from a clump of cells is an example of emergence ( where an entity has properties its parts do not) or self organization (spontaneous order arise from local interactions between parts and requiring no external organizing agent). Some examples include swarming of insects, fish, or birds, crystallization, protein folding, or formation of lipid bilayers.

More info: https://www.wired.com/2004/02/machines/

When ordering hydra from Carolina, they will ask for a delivery date. Make sure to have your hydra delivered 1 or 2 days before your activity. It is even advisable to have two cultures delivered, one 1 or 2 days before, and 1 the day of (just in case something goes wrong with the first culture).

Be sure to have your hydra medium and dissociation solution prepared in advance. For this activity, each group needs a microcentrifuge tube filled with hydra (25 organisms or so), a glass pipette with a rubber bulb, and three empty micropipettes. They will also need a tube of dissociation media.

To allow for students to make observations of whole hydra before dissociation, make sure to have a petri dish of extra hydra on display at a dissecting scope, or give each group a small petri dish containing a few whole organisms.

(15 mins)

Remind students of observations so far using single-celled organisms. Each single-celled organism demonstrates complex behavior and we can use robotics to model those behaviors. But what about more complex organisms? How do they form from single cells?

Introduce the concept of self-organization or self-assembly, especially using organismal-level examples like flocks of birds or swarms of ants or bees. The important points to highlight are as follows:

• Combining individuals into a group, we can get more complex structures
• The complex structure can’t be made by one individual
• There is no external control, or one “organizer” or “manager”
• Each individual has a small bit of instructions, but, when combined, the larger structure is created from the group

For example, ants forage, build their nests, protect their homes, without any leadership, language, or memory. No one any is intelligent enough to complete all of the above tasks, but somehow, as a group, the ants are smarter than any one individual.

See more here: https://www.ted.com/talks/deborah_gordon_digs_ants?language=en#t-88009

More info: https://www.wired.com/2013/07/what-ants-yes-know-that-we-dont-the-future-of-networking/

Hydra are fairly simple organisms related to the jellyfish. They only have two layers of cells (inner, endoderm, and outer, ectoderm). They have tentacles that inject a neurotoxin into their prey.

Scientist are fascinated by these organisms because they are able to reform from a ball of single cells. Somehow the pattern for a hydra is hard coded into each individual cell.

Dissociation (30 mins):

Encourage student groups to follow the student handout. They will first need to make observations of whole hydra.

Have your student look at the liquid media in the tube containing the hydra about to be dissociated. It should be relatively clear. They will be using a glass pipette to shear the hydra and knock cells off of the larger organism. As they do this, the liquid will get cloudy (from bit of hydra floating in the liquid).

Student should be careful not to introduce bubbles and be sure to keep their hydra on ice as much as possible to prevent their cells from dying during the dissociation process. The easiest and quickest way to shear hydra seems to be to rest the glass pipette tip at the bottom of the microcentrifuge tube to create a smaller opening. When hydra are sucked up through this smaller opening, they are shredded into smaller pieces (It’s just as gruesome as it sounds).

After centrifuging their “hydra parts”, students should carefully loosen the clump of cells using a gentle jet of liquid from the glass pipette. Each clump of cells can then be placed into a small petri dish with a 50/50 mixture of dissociation solution and hydra medium.

Hydra Observation Schedule:

4-6 hours later (15 mins)

1 day later (15 mins)

2 days later (15 mins)

3 days later (15 mins)

4 days later (15 mins)

At each of the times above, have students use the dissecting scopes to look for: organization of the two cell layers (darker inside layer and clearer outside layer), hollowing out at the center of the clump (looks like little bubbles), tentacle buds, hydra develops more of a top and bottom, fully formed hydra (4 days)

If clumps do not look smooth by the 4-6 hour checkpoint, the hydra may be dying. Sometimes the clumps look almost fuzzy (with bits of cell debris falling off of clumps of cells). This is not a great sign, but sometime hydra clumps can recover.

The organization of the clumps into an inner and outer layer is hard to see without a high powered dissecting scope. Using the black background setting for the dissecting scopes helps. Tentacle budding and hollowing out are more obvious.

As hydra are reforming, check in with students to see how they think this is occurring? What is controlling this process? How do hydra know how to reform? Is there something that is giving each cell instructions? Remind them that self-assembly happens without an “organizer” or “manager”.

(40 mins)

To connect this activity to robotics, we find a good closing activity to be to develop a hypothetical program for robot self-assembly.

Give each group a piece of chart board paper (or other large sheet) and markers. Ask each group to develop a program that would get 5 robots to create an organized structure, whereby one robot is in the center (inner robot) surrounded by 4 robots (outer robots). They are allowed to propose sensor that haven’t been invented yet (or aren’t currently on the robot) such as different kinds of touch sensors, cameras, microphones, etc.

Once completed, have each group place their poster on the wall. Everyone participates in a gallery walk with post-it notes, leaving questions, suggestions, and comments for other groups on their respective posters

Coming soon

Structure and Function

ETS2 Links Among Engineering, Technology, Science, and Society

HS-LS1-1 From Molecules to Organisms: Structures and Processes

(Hydra contain DNA that controls the specilized function of particular kinds of cells, specifically the endoderm (inner layer) and ectoderm (outerlayer). DNA likely contains the instructions for self-assembly.)

HS-LS1-2 From Molecules to Organisms: Structures and Processes

(Hydra are multicellular organisms made up of many cells. These cells can be dissociated, but they (somehow) retain a knowledge of their function and can self-assemble into the correct pattern to recreate hydra.)

HS LS1.A Structure and Function

ETS2.A Interdependence of Science, Engineering, and Technology

(By modeling hydra self-assembly in robots (using the thought experiment), students are connectig scientific observation with engineering design.)

Practice 3. Planning and Carrying Out Investigations

Practice 4. Analyzing and Interpreting Data

Practice 6. Constructing Explanations and Designing Solutions

Patterns

Systems and System Models

Structure and Function

Stability and Change