2. The Need for Model Organisms Flashcards Preview

BMS336 - Modelling Human Disease and Dysfunction > 2. The Need for Model Organisms > Flashcards

Flashcards in 2. The Need for Model Organisms Deck (27)
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1
Q

What is a model organism?

A

A non-human species studied to understand biological phenomena, with the expectation that findings in the model will provide insight into workings of humans

2
Q

When are model organisms used to study human disease?

A

When human experimentation is unfeasible/unethical

3
Q

Why are we able to use model organisms to study human disease?

A

Due to common descent of all living organisms and the conservation of developmental and metabolic pathways through evolution

4
Q

Why are particular organisms selected as models?

A
  1. By chance (what was available at time)
  2. Inbred populations within species to decrease genetic variation (allows rapid genome sequencing)
  3. Low cost and short lifespan
  4. Easy to induce mutations
  5. Easy to score phenotypes
  6. Easy to analyse disease traits
  7. Easy to manipulate
5
Q

Why are Drosophila, Zebrafish and Mouse used as models to study human disease?

A
  • All share a degree of gene conservation with humans
  • Basic mechanisms of gene action (proteins and pathways) are conserved
  • Development and maintenance of body and core metabolic pathways are conserved
  • Easy to interfere with gene function in model organisms
  • Can study gene expression in real time (e.g. optic clarity in zebrafish)
6
Q

What are the 6 opportunities afforded by model organisms?

A
  1. Provide models where it is possible to examine individual over life course
  2. Provide models where it is possible to examine genetic x environmental interactions
  3. Can understand mechanisms from correlation to cause
  4. Allow us to make transgenic reporter lines
  5. Large numbers of animals and reporter lines aid the development of new therapeutics
  6. Enable a whole organism or systems approach to studying disease states
7
Q

What is the significance that most diseases studied are chronic diseases that develop over time?
What does this mean for model organisms?

A
  • Need to study disease in relation to ageing process

- Require model organisms with short lifespans to trace progression of disease through life

8
Q

What does an individual’s genotype confer?

A

Genotype confers the potential for health across life course and the high likelihood of developing a specific disease - e.g. BRCA2 mutation confers high susceptibility of developing breast cancer

9
Q

How do environmental factors interact with the genotype?

A

Interact with genotype to trigger/exacerbate disease

10
Q

What are diseases likely to arise from?

A

Gene x environment interactions

11
Q

Why are animal models useful for modelling complex diseases with many variables?

A
  • Genetically tractable - CRISPR can make transgenic animal with specific mutation in specific gene to model human susceptibility genes
  • Can be examined in large numbers - outcomes can be concluded as statistically significant
12
Q

What do genome-wide association studies (GWAS) identify?

A

Mutations that correlate with disease susceptibility

13
Q

Give an example of a GWAS

A
  • 10 individuals, 5 healthy and 5 with T2D
  • Sequence genomes and identify mutations that correlate with T2D individuals but not healthy individuals
  • Identifies correlation between genome variation and T2D susceptibility
14
Q

What do GWAS studies not show?

What can be used for this?

A
  • When and where gene is expressed or how gene product may trigger/exacerbate disease
  • Use an animal model
15
Q

What techniques can be used to identify which cells/tissues express a specific gene?
What does this tell us in relation to disease?

A
  • In situ hybridisation shows where and when mRNA is expressed
  • Immunohistochemistry shows where and when protein is synthesised
  • Can then infer from location of expression what may be happening in dysfunction, e.g. if expressed in hypothalamus, disease may be caused by hypothalamus dysfunction
16
Q

What techniques can be used to identify gene function?

What does this tell us in relation to disease?

A
  • Loss/Gain of function genetic approaches

- Function of cells/tissues that is controlled by the gene product

17
Q

What is the process for generating a tissue-specific (conditional) knockout?

A
  1. Gene to be KO’d is flanked by lox sites and 1st transgenic mouse is made in which WT gene is replaced with engineered gene
  2. Identify tissue-specific promoter governing expression of gene that is specifically expressed in the cells in which you wish to KO gene
  3. Clone the coding sequence of the enzyme Cre recombinase downstream of this promoter and 2nd transgenic mouse is made in which Cre recombinase is expressed only in the required cells
  4. Cross 2 transgenic mice - Cre recombinase acts on lox sites like scissors and removes flowed allele so that gene is KO’d only in cells expressing Cre recombinase
18
Q

What are transgenic reporter lines?

A

Animals whose genomes have been engineered to give a colour report of expression of a specific gene

19
Q

What is the main advantage of reporter lines?

A

Animal is alive therefore can visualise gene expression in real time

20
Q

What do reporter lines enable?

A
  • Visualisation of cells expressing specific gene in real time
  • Isolation of labelled cells by FACS
21
Q

What do reporter lines depend on?

A

The fact that genes are differentially transcribed as a function of the interaction of their promoter/enhancers and cell-specific transcription factors

22
Q

What is the process for generating a transgenic reporter line?

A
  • Identify a tissue-specific promoter in cells to be followed
  • Clone coding sequences of fluorescent reporter proteins (e.g. GFP, Kaede, RFP) downstream of this tissue-specific promoter
  • Make transgenic animal in which this transgene is stably incorporated into the genome and reporter will be expressed only in cells which have correct transcription factors for the promoter
23
Q

What can transgenic reporter lines be used for?

A
  • Follow cells over time in health, disease, after insult or drug administration
  • Analysis of cell behaviour (proliferation, migration)
  • Analysis of cell function (hormone secretion, response to signalling)
24
Q

What does understanding of disease and deterioration require?

A

A comprehensive understanding of the whole organism and the complex and dynamic interactions between different systems, organs and cells

25
Q

What is a technique for studying cells in their normal environments?

A

Generate multiplex transgenic reporter lines, where different cells express a different reporter colour

26
Q

What are in vitro cell lines used for?

A
  • Drug screening for new therapeutics
  • Single cell type studies
  • Generation of organoids
27
Q

What do the opportunities afforded through model organisms allow us to do?

A
  • Identify molecular pathways in normal cells/tissues
  • Identify normal and aberrant cellular outputs e.g. proliferation
  • Identify disease progression e.g. primary cause and secondary consequences
  • Perform high-throughput screens for drug development