Experimental Animal Models Flashcards
(36 cards)
Methods of developing animal models
- Spontaneously occurring variations
- Selective breeding
- Genetic modifications
- Drug effects
- Environmental effects
- Surgical & physical alterations
What were the earliest animal models available?
Spontaneously occurring variations within the animal population
What does selective breeding allow?
To keep a trait within a population
Examples of breeding colonies
- Leptin deficient mouse - occurred spontaneously, mice develop symptoms similar to obesity & T2DM
- SHR - selective breeding of WK rats which naturally have HBP
- Nude mouse (athymic mice) - immunocompromised
How is an animal model created by drug effects?
An otherwise healthy animal is treated with a compound known to induce a disease condition or symptoms that closely mimic the disease
Common way to model depression
Chronic mild stress test - animals are subjected to unpredictable stressors resulting in a variety of behavioural deficits: food & water deprivation, small temp reductions, changes of cage mates, changes in light/dark cycles
Examples of drug-induced animal models of disease
- Streptozotocin induced diabetes in rats - IV injection, makes pancreas swell & causes degeneration of islet of Langerhans’ beta cells
- Deoxycorticosterone induced HT in rats, dogs, pigs - prolonged mineralocorticoid admin
- MPTP for PD in primates, nice - admin triggers rapid destruction of DA-synthesising neurons in SN
What is a common model of early life stress?
Maternal separation model - pups separated from mother for several hrs per day over a period i.e. 3hr/day during 1st 2 wks of life
Adults then present with depressive behaviour
How is obesity and metabolic syndrome induced by diet?
- High fat diet fed to rats
- Cafeteria diet: regular chow + ad libitum access to energy dense foods e.g. cookies, cheese, processed meats etc.
Examples of surgical and physical alterations to create animal models of disease
- Ligating or cutting structures - e.g. LCA to generate MI
- Banding or constricting structures - aortic banding leads to cardiac overload, hypertrophy and eventually HF
- Removing organs - pancreatectomy to induce diabetes
Examples of genetic models of disease
- Forward vs reverse genetics
- Microinjection- induced transgenics
- Cre-lox system
Forward vs reverse genetics
Forward: generating spontaneous mutations - not ideal, you can’t target anything, unfair for the animals
Reverse: target specific genes, delete them, see the effects of that change on the phenotype
How does reverse genetics work?
- Inject stem cells into an egg grown by a donor mother
- Mutation incorporated into genome by homologous recombination
- Injected into a foster mother
- Offspring are chimeras - have original and GM genes
- Use selective breeding to get the line you want
How does microinjection-induced transgenics work?
- Obtain eggs
- Eggs fertilised
- Microinjection of manipulated DNA into pronucleus
- If prior to cell division, contributes to all cells of organism
- Fertilised egg then inserted into pseudo pregnant foster mothers
- Mated with vasectomised males - their body then preps for pregnancy
- Offspring are transgenic
Example of a transgenic mouse used in research
SOD1-G93A transgenic mouse model used in ALS (amyotrophic lateral sclerosis) research - display neurodegeneration and symptomatology consistent with ALS
the Cre-lox system
- Cre recombinanse gene is there
- LoxP sequences flank the DNA you want to delete (the gene is then called ‘floxed’)
- Add Cre recombinase, causes deletion of the floxed gene
When is the Cre-lox system used?
Can be used to generate general knockouts, but used more often to generate conditional mutations
What can be linked to Cre recombinase gene?
Promoter
Cre-lox can be either
Conditional on time or tissue-specific
Example of a knockout generated by the Cre-lox system
Cardiomyocyte-specific STAT-3 knockout - whole body STAT-3 k/o results in rapid degeneration of STAT-3 k/o embryos between days 6.5 and 7.5 in mice
How to get heterozygote STAT-3 k/o mouse
Cross STAT-3 floxed mouse (STAT-3 gene with LoxP either side) with a mouse with normal STAT-3 genes and Cre recombinase genes with heart-specific promoter
How to get a STAT-3 complete k/o
Cross STAT-3 floxed mouse and Cre-recom mouse
What is a mouse model of hyperlipidaemia and what can it be used to study?
Apolipoprotein E knockout mouse model, used to study atherosclerosis
What are usually used when generating new genetically altered mouse strains?
Usually wild type inbred strains or F1 crosses between two strains are used