3. Genome
Mammalian
20 chromosomes
2.6 Gb
~25000 genes
99% have human counterpart
Strains
Inbred
Outbred
Recombinant inbred
Consomic
Fluorescent
Life Cycle
4-day oestrus
20-day gestation
4-8 pups per litter
2-8 litters per female
7 weeks to sexual maturity
2-3 year lifespan
Reverse genetics
Knockouts
Transfenics
Conditional expression
Inducible expression
Retroviral vectors
siRNA
The Mouse as an Experimental
System
Assisted reproduction
Cryopreservation
Embryo rederivation
In vitro fertilization
Intracytoplasmic sperm injection
Cloning
Tools
Genome sequence
Embryonic stem cells
Expression arrays
Gene-trap libraries
Insertional vector libraries
BAC libraries
4.
5. Basic questions to be asked
1. The mouse model is the one most commonly used for studies of human physiology
and disease, but is it the best one?
2. How useful and valid are these models for mimicking human disease?
3. What characterises mouse models that have proven useful for basic
science, clinical research and drug discovery?
4. What measures are needed to improve new and existing mouse models?
6. Out of the model organisms which may be
genetically modified, the mouse is:
•Best model for mammalian development
•Closely related to humans (mammals)
•10-15 offspring per litter and approximately one litter every month.
•Genome sequenced
•Many inbred strains characterized (450 available)
•Genetic manipulations well developed
•Mice are small, have a short generation time and an accelerated
lifespan (one mouse year equals about 30 human years)
8. Genomics
99% of mouse genes
have an equivalent in
humans making mice
ideal for the studying
the functions human
genes in health as
well as in diseases.
For significant genetic
changes, mouse
orthologs were close
to random in
matching to their
human counterparts
i.E the E-Value is
higher for the
alignment
Human
Mouse
11. • Gestation: Mouse: 18 days; Human:
270 Days
• Different hormonal regulation in
development of embryos
• Human: hCG; mouse: mPRL
• Human : Pituitary gland secretion not
required
Hum. Reprod. Update (2003) 9 (6):531-539.
Development
12. Manipulations at the embryo level
• Allows genetic manipulation of embryo possible
• Early embryo can be split to yield two “twins”
• Two morulas can be combined to form a chimera
• Cells from an embryo can be injected into another
blastocyst to form a chimera
• Embryonic manipulation difficult
inside the mother
• Extra-uterine embryo culture is
difficult.
• Need to cut open the uterus - ethical
issue
13. • Similarity
Genes responsible for building and
operating both organs are 90% identical--
which means that the mouse brain can be a
powerful tool for unravelling the mystery of
human mental disorders, memory and
intelligence related phenomenon.
• Difference
Human Vs Mouse Brain
Smooth surface-
less memory
More convulsions –
higher order
memory
14. Glia appear to play a more significant role in various brain
functions
70% neurons +30% glia 30% neuron+70% glia
Proportion of Neuron and Glial cells varies between Mouse and Humans
15. Transgenic Mouse
• Advantages :
• Contain extra genetic material integrated
into the genome in every cell.
• Generated to carry cloned oncogenes
provide good model for human cancer
• Good models for muscle growth study by
overexpressing the transgene insulin-like
Growth factor in differentiated muscle
fibers.
• Disadvantages:
• Transgene integration is apparently random ;
• Many experiments reveal that the genetic
surrounding of the inserted transgenic
construct is modulating the expression pattern
of the transgene itself both qualitatively and
quantitatively.
• Transgenic rescue of knockout mice is time-
consuming, expensive and labour intensive.
16. Knock-out mouse
Disadvantages:
• About 15% of Knock-outs are
developmentally lethal. This limits
studies to only embryonic development.
• It is difficult to determine a gene’s
function in relation to human diseases.
• Custom knock-out mice is very expensive
($3000 -$30,000)
Advantages :
• Very specific endogenous gene has
been altered in such a way that
interferes with normal expression.
• To study effects of gene
products, biochemical
pathways, alternative (compensatory)
pathways, and developmental
pathways
• Models to test the beneficial effects of
drugs or gene therapy
17. Behavioural studies
Disadvantages :
• Lab Environment Vs Natural environment
• Animals lack self- consciousness, self-reflection and
consideration
• Hallmarks of behavioural disorder such as
Depressed mood, Low-self esteem, suicidal
tendency are hardly accessible in mice
• Hence behaviours like Depression, Autism, suicidal
tendency can not be studied in mouse models.
(wikipedia)
Advantages :
• Mouse model shares many Features with
human brain functions like
Anxiety, Hunger, circadian rhythm, memory and
other emotional responses (Peter van Meer and
Jacob Raber)
• Robust phenotypes in mouse models -effective
treatments for components of Autism spectuam
disorders (Jill L. Silverman et.al 2010)
• Effects of alcoholism
18. Neurodegenerative disorders
1. Mice live only about two years, while people
can live for 80 years or more.
2. Neurodegenrative disorders are normally late
onset disorders.
3. Hence not a good model to study parkinson’s
and alzheimer’s disease and other diseases of
aging.
4. Incapable of expressing some cognitive
human disease symptoms.
21. Few more Limitations:
1. Early acting mutant phenotype difficult to study
2. Poor models to study inflammation in humans, a condition present in many
humans
3. Research mice are inbred and do not capture the genetic variation existing in
human population.
4.The research works have found that the responses in mice correlated poorly not
with those in humans but also with one another.
5.Drugs that have shown promise in mice have done poorly in humans.
6.Forward genetics : To identify novel gees involved in embryogenesis is difficult as
it is prohibitively expensive.
22. Poor models to study inflammation in humans, a
condition present in many humans
• Mice are resistant to infections and inflammations.
• Mice have lived for millennia in environments
teaming with microbes and they short gestation
periods and large litters. This shows they have
evolved with different strategies for dealing with
infections
23. Research mice are inbred and do not capture the
genetic variation existing in human population
• The research works have found that the
responses in mice correlated poorly not
with those in humans but also with one
another.
Proc Natl Acad Sci U S A. Feb 26, 2013; 110(9): 3507–3512.
26. Humanised mouse
A mouse's liver reacts differently to drugs as compared to the liver of humans.
This makes it difficult to predict whether or not the potential drug being tested will be
toxic in humans.
Various types of human cells and tissues are
engrafted and function, as they would in
humans are considered extremely useful in
basic and applied human disease research
28. Brown Norway
Rat
• Similarities to human sensitization
• Serotonergic bronchoconstriction
• IgE mediated
• Early and late phase reactions
• Airway hyperreactivity
• Tissue + BAL accumulation of
neutrophils, eosinophils, lymphocytes
• Good inflammatory responses
29. Concluding remarks
Just as no one human is representative of an entire population of humans, no one
strain of mouse is representative of all mice or much less, humans.
Although each of these systems can provide valuable insight, as researchers, we
know that the models are just that: models.
The only perfect model of human disease would be humans themselves, but
performing many kinds of research on humans is an ethical and practical
impossibility.
30. But,
Thanks to animal research, primarily in mice, cancer survival rates have continued
to rise.
Herceptin – a humanised mouse protein – has helped to increase the survival rate
of those with breast cancer; it could not have been attained without animal
research in mice.
While Fleming discovered penicillin without using animals, he shared the Nobel
Prize with Florey and Chain who, by testing it on mice, discovered how penicillin
could be used to fight infections inside the body.
http://www.understandinganimalresearch.org.uk/about-us/the-science-action-network/forty-reasons-why-we-
need-animals-in-research/
31. Alternatives for Human models other than mouse/ any
model organism
Human, inducible pluripotent stem cells can also elucidate new
mechanisms for understanding cancer and cell regeneration.
Imaging studies (such as MRI or PET scans) enable non-invasive study of
human subjects.
Recent advances in genetics and genomics can identify disease-associated
genes, which can be targeted for therapies.
