Model Systems in Cell Biology

What is a model system?

A cell or organism commonly used for research (observations or experiments) as an example to understand the biology of cells and organisms more generally

Key characteristics of model systems

• Relatively easy to maintain and grow in a laboratory setting

• Amenable to experimental manipulation and/or observation

• Subject of existing biological data

• Existing experimental tools and protocols

• Minimal genetic variation within the population

Choosing a model system for cell biology

• Does the model exhibit the behaviors or features of interest?

• Are appropriate tools, techniques and biological information available to study the scientific question or phenomenon in the model system?

• Is the timescale required for the experiments suitable?

• What is the cost of using the system?

• Is using the model system for the experiments ethical?

• Are the results applicable to other systems?

• Is the model system the simplest option that is sufficient for the work?

• Based on the advantages and limitations, is the system better than other systems (or equal to) for the proposed research?

Common model systems in cell biology

Budding Yeast (Saccharomyces cerevisiae)

Roundworm (Caenorhabiditis elegans)

Fruit fly (Drosophila melanogaster)

Zebrafish (Danio rerio)

African Clawed Frog (Xenopus laevis)

Mouse (Mus musculus)

Human (Homo sapiens)

Budding Yeast (S. Cerevisiae)

Unicellular eukaryote

Budding Yeast (S. Cerevisiae) Size

~5-10 μM

Budding Yeast (S. Cerevisiae) Cost

Very inexpensive and easy to maintain and grow

Budding Yeast (S. Cerevisiae) Generation time

Cells can divide about every 90 min

Budding Yeast (S. Cerevisiae)growth

Can be grown as haploids (one copy of genome) or diploids (2 copies of genome)

Budding Yeast (S. Cerevisiae) other perks

Easy to genetically manipulate, Many existing tools, mutants, and modified strains exist, Distinct cell morphologies at different phases of the cell cycle

Roundworm (C. elegans) :Multicellular (~1,000 cells)

Roundworm (C. elegans) Size

~1mM in length

Roundworm (C. elegans) Cost

Relatively inexpensive and easy to maintain and grow

Roundworm (C. elegans) Generation time

3-4 days

Roundworm (C. elegans) other stuff

Produces many offspring, Easily observable behavior, Transparent, Development process is well understood

Fruit Fly (Drosophila melanogaster)

Multicellular (More complex than worms)

Fruit Fly (Drosophila melanogaster) Size

~3 mM length

Fruit Fly (Drosophila melanogaster) Cost

More expensive and labor-intensive to maintain than worms

Fruit Fly (Drosophila melanogaster) Generation time

10 days

Fruit Fly (Drosophila melanogaster) other stuff

Produces many offspring, Genetic tools available to target specific genes, Many mutant lines, including models of some human diseases, are available

Zebrafish (Danio rerio)

Vertebrate

Zebrafish (Danio rerio) Size

~4 cm in length

Zebrafish (Danio rerio) Cost

Expensive and labor-intensive to maintain

Zebrafish (Danio rerio) Generation time

3 months

Zebrafish (Danio rerio) other stuff

Produces many offspring, Embryos are transparent, Embryonic development is very rapid

African Clawed Frog (Xenopus laevis)

Vertebrate

African Clawed Frog (Xenopus laevis) Size

10 cm in length

African Clawed Frog (Xenopus laevis) Cost

Expensive and labor-intensive to maintain

African Clawed Frog (Xenopus laevis) Generation time

1-2 years

African Clawed Frog (Xenopus laevis) other stuff

Can be induced to lay eggs which are large and easily observable, Cell cycle is very rapid during early development

Mouse (Mus musculus)

Mammal

Mouse (Mus musculus) Size

10 cm in length

Mouse (Mus musculus) Cost

Very expensive and labor-intensive to maintain

Mouse (Mus musculus) Generation time

10 weeks

Mouse (Mus musculus) other stuff

Average 6-8 mice per litter, Many different tools and mutant lines, including disease models, already exist, Similar to humans in many ways

Humans (Homo sapiens)

Most research using humans consists of observations of existing biological characteristics in the human population. Considered unethical to perform experiments on humans (with the exception of approved clinical trials). Common approach for experiments is to use isolated human cells that are maintained and grown in the lab ("cell culture")

Cell culture

• Cells are removed from a multicellular organism and grown in the lab • Cell culture allows the study of cell behavior and experiments outside of the organism and in a simplified context • Researchers can manipulate cell behavior without affecting a person or organism (however, informed consent and privacy are important considerations) • Immortalized cell lines (often derived from human tumors) allow indefinite replication • Cell behavior may differ when out of the context of the organism • Some types of cells are challenging to maintain or grow in culture

Summary

• Model systems allow researchers to use established tools and knowledge as a starting point and context for observations or experiments • Model systems are used to study biological phenomena that may be generalizable to other organisms • Researchers choose a model system by evaluating the characteristics of available model systems and considering the requirements or priorities for their research question • The simplest model system that has the appropriate biological characteristics and allows the research to be completed quickly and at a low cost is an ideal choice • Considering the model system is an important part of evaluating and interpreting research in cell biology