studies with bacteria proved that DNA is genetic material · Xenopus laevis (African clawed frog) Xenopus laevis (African clawed frog) Advantages of using this organism: females can

Model Organisms/

Animal Research

How can we learn about humans by studying non-humans?

Evolutionary conservation of DNA and protein structure and functions

Examples:

a. human genes function in yeast

b. human disease genes found in other organisms

c. developmental processes are very similar

http://www.ceolas.org/VL/mo/

For lots of information about model organisms, see:

Model Organisms

1. small size (so you can grow lots of them in the lab)

2. short life cycle (so you can study many generations)

3. be able to generate a clonal population of organisms

4. ability to make mutations

5. ability to identify the mutated genes (inserting foreign DNA)

6. start with an organism that’s not too complicated

7. easy to watch development as it happens

8. lots of others using that model also so tools are developed

9. inexpensive to maintain

Model Organism TraitsEscherichia coli (E. coli, bacteria, “bugs”)

Basic characteristics:

rod shaped (2µm X 1µm; ~500 times smaller than an animal cell

lives in the intestine of many animals

grows in the lab on defined medium at 37ºC

divides every 20 minutes

Eukaryotic cell

(Animal or plant)* 10-100 µm in diameter

* linear DNA in nucleus

* has organelles

Prokaryotic cell

(Bacteria)* 1 µm in length

* circular DNA, no nucleus

* no organelles

Escherichia coli (E. coli, bacteria, “bugs”)

Advantages of using this organism:

very inexpensive

easy to mutagenize and introduce foreign DNA

used extensively as a tool for manipulation of DNA from all organisms

easily frozen to maintain stocks

Disadvantages:

much simpler than animal cells

single celled, so does not go through development

Significant Contributions to science:

metabolism, DNA replication, transcription, translation mechanisms very similar to

those in animals

studies with bacteria proved that DNA is genetic material

***nearly everyone uses E. coli: an essential tool for research

Grow on a plate

Bacteria as a tool Saccharomyces cerevisiae (yeast)


approximately 3µm in diameter

same yeast as used in bread and beer

grows in lab in defined medium at 30°C

divides every 90 minutes

Saccharomyces cerevisiae (yeast)


easy to mutagenize and introduce foreign DNA

can be induced to mate, so you can do genetics

entire genome sequence is known

easily frozen to maintain stocks

it is a Eukaryote

Limitations:

not multicellular

small size limits cell biological analyses

Significant contributions to science:

cell division control, gene regulation, DNA replication

functional studies of human genes can often be done in yeast

Caenorhabditis elegans (worms)


adult is about 1mm in length

in the wild lives in the dirt

in the lab is grown in petri dishes and fed E. coli at room temp.

life cycle is 3 days

2 sexes: self-fertilizing hermaphrodite and male

Caenorhabditis elegans (worms)


only 1000 cells, yet has skin, neurons, muscle, intestine, and gonads

embryos, larvae, and adults are clear, making studies of development straightforward

genome sequence is complete (done at Washington University)

easy to introduce foreign DNA and knock out genes

can easily be frozen to maintatin mutant stocks

Limitations:

although multicellular, not a vertebrate


studies of cell fate determination (how a cell “knows” what type of cell to become)

nervous system development

control of programmed cell death (2002 Nobel prize to Sulston, Brenner, and Horvitz)

Drosophila melanogaster (flies)


adult is about 3mm in length

in the wild is seen around rotting fruit

in the lab is fed on yeast at 25°C

life cycle takes about 12-14 days

Drosophila melanogaster (flies)Advantages of using this organism:

complex multicellular structures make it good for studying development

mutant flies often have defects that are very easy to see

well-developed nervous system allows for studies of behavior and learning

sequenced genome

Limitations:

not a vertebrate

don’t freeze well


identification of many genes that control development in flies and higher organisms

understanding of circadian rhythms

genes involved in learning

Arabidopsis thaliana (mustard weed, plant)

Basic characteristics

adult plant is about 6-10 inches tall

life cycle is 4-6 weeks

grown in the lab in small pots in dirt or defined medium

Arabidopsis thaliana (mustard weed, plant)


short generation time for a plant; small, sequenced genome

seeds of mutant stocks can be stored long-term

can introduce foreign DNA, easy to make mutants

Limitations:

not an economically relevant crop


first plant genome sequenced

analysis of plant specific biology relevant to crops

aid development of genetically modified crops

1. Animal Welfare Act

first written in 1966, amended several times since then

covers all warm-blooded animals except: horses not used for reseach;

animals raised for food; and mice, rats, and birds (2002 amendment)

regulates the proper treatment of these animals: food, housing, anesthesia

use, enrichment, record keeping

each institution must have an internal animal care and use committee

regulated by the United States Department of Agriculture

Laws Governing the Use of Animals in Research

http://www.nabr.org/AnimalLaw/AWA/TheAct.htm

Laws Governing the Use of Animals in Research

2. Health Research Extension Act of 1985, "Animals In Research”

Covers research funded by the National Institutes of Health (NIH)

Covers all vertebrates

Must consider whether the research is relevant to advancement of human

and/or animal health, knowledge, and the good of society

Must consider whether other non-animal approaches are possible

Must use the most relevant animal lowest on the phylogenetic tree (ie

lease like humans)

Avoid pain and distress to animals, use anaesthesia; euthanize animals

that are in pain

Investigators must be properly trained

http://grants2.nih.gov/grants/ol

aw/references/phspol.htm#Hea

lth%20Research%20Extension

%20Act%20of%201985

Danio rerio (zebrafish, fish)


adults are about 4cm long

originally isolated from rivers in India and Pakistan

grows in the lab in aquariums at 28ºC

young fish in the lab eat ciliates

adults eat brine shrimp (sea monkeys!)

Danio rerio (zebrafish, fish)Advantages of using this organism:

easy to mutagenize for genetic screens

embryos are clear, so developmental processes can easily be watched

is a vertebrate

small size and large brood size allows for extensive mutant analysis not possible in mice

Limitations:

relatively long generation time of 10-12 weeks

not a mammal


mutations identified affecting neuronal, muscular, cardiovascular, and bone

development

may prove to be the best genetic system for studying vertebrate development

Xenopus laevis (African clawed frog)

Xenopus laevis (African clawed frog)


females can be induced to lay hundreds of eggs

embryos are very large, so easy to surgically manipulate

is a vertebrate

eggs are large, so great for doing biochemistry experiments

Limitations:

long generation time of 1-2 years; breeding mutants not really feasible

not a mammal


basic understanding of vertebrate embryo development

cell cycle studies performed on egg extracts

http://www.xenbase.org/index.html

Mus musculus (mouse)


adults are about 10cm long

live in the lab in cages in special animal facilities

generation time is about 6 months

animals used in research are specifically bred for that purpose



mammal, vertebrate, very close to humans evolutionarily

fairly straightforward to “knock out” a gene of interest

Limitations:

long generation time and large space requirements make large scale genetic

experiments unwieldy

quite expensive to maintain (mouse costs can be up to $2 per mouse per day)


used especially in studies of the immune system

good model for cancer studies


Washington University Animal Studies Committee Requirements

food and water must be available constantly and changed twice a week

bedding and cages must be changed twice a week

must be on 12 hour light: 12 hour dark cycle

up to 5 mice per cage

animals must be observed daily, including weekends and holidays

cages can not be stacked

no other animal can be present when a mouse is euthanized

animals given tumors must be checked daily

animals showing signs of duress must be

euthanized

must follow guidelines for surgeries

must use approved euthanizing procedures

Dogs (canis familiaris)

Some important discoveries made using dogs:

1888: vaccine for rabies

1923: insulin discovered

1943: vitamin K discovered

1956: open heart surgery and cardiac pacemakers developed

1957: first successful human bone marrow transplant based on years of

experiments in dogs

Current Research using dogs

refining transplant technologies

blindness (many dog breeds are susceptible to eye disorders that very closely

resemble human disorders

gene therapy

*dogs used for research are specifically bred for that purpose, usually beagles

Dogs (canis familiaris)


dogs must be provided with exercise:

either be in a cage 2X the size required by Animal Welfare Act

or get 30 minutes of exercise three times per week on alternating days

dogs housed in isolation must get exercise and human interaction every day

group housed dogs must have at least a minimum amount of floor space

determined by the size of the dog

Dog size! !Floor Area (sq. ft.)

< l5kg !8

!15-30 kg !12.1

!> 30 kg ! 2 x (body length from tip of nose to tail base + 6”) 2 /144

Macaca mulatta (macaque, rhesus monkey)


Originate from India

Reach sexual maturity at 3-4 years

Live on average 16 years

Eat vegetation, insects, and small animals

Advantages of studying this organism:

very closely related to man

Limitations

extremely long life cycle makes genetic experiments nearly impossible

very expensive to maintain (at least $15 per day per animal)


these and a few other monkeys are the only animal models for studying HIV

very good model for neurobiology

used for studies of vaccines such as for ebola and anthrax

Macaca mulatta (macaque, rhesus monkey)

The National Sanctuary for Retired Research Primates

http://www.primatesanctuarynsrrp.org/

Non-human primates


*must provide enrichment:

social grouping required for some species

for some, other enrichement can be provided if research requires isolation

enrichment: cage complexities, toys (rotated every 2 weeks), varied food

items, foraging opportunities (ie puzzle feeders), interaction with

humans

*can not be restrained unless

directed by vet or in approved

protocol

*quarterly psychological well-

being assessment

*surgery guidelines must be

followed

*multiple surgeries can only be

done with ASC approval

studies with bacteria proved that DNA is genetic material · Xenopus laevis (African clawed frog) Xenopus laevis (African clawed frog) Advantages of using this organism: females can

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