- 1. Mouse Model: Pros and Cons Ankita Das Chetana Tamadaddi Prashant Waiker Indian Institute of Science Education & Research Bhopal
2. MOUSE : Mammalian model organism 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. 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? 5. 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) 6. Phylogenetic analysis Not so far Indeed they are 7. 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 8. Life cycle Fast Slow 9. Embryology HUMAN MOUSE 10. 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 11. 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 12. 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 13. 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 14. 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. 15. 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 genes 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 16. 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 17. 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 parkinsons and alzheimers disease and other diseases of aging. 4. Incapable of expressing some cognitive human disease symptoms. 18. Cancer Model 19. Drug Target Studies 20. 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. 21. 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 22. 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): 35073512. 23. Mice trials did not translated to human!!! 24. Cost-ineffectiveness of mouse models: http://www.ohsu.edu/xd/research/research-cores/transgenics/services-costs.cfm 25. 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 26. DRUG FACTORY FOR FUTURE Few more advantages of mouse model 27. 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 28. 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. 29. 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/ 30. 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.