Education Resource from the Society for Endocrinology
Dr Tony Coll
Summer School 11-14 July 2006
The Møller Centre, Storeys Way, Cambridge, UK
Mouse models have proven invaluable in dissecting out the components of a range of physiological systems. This session aims to illustrate the power of murine genetics by reviewing techniques and models, which have been pivotal in our current understanding of mechanisms controlling energy homeostasis.
The anatomical and physiological similarity to humans, plus their rapid breeding cycle and ease of handling, make mice an excellent experimental model. A number of inbred strains of mice also naturally develop diseases and conditions which affect humans too. Indeed many of these spontaneous mutants have proven invaluable in the study of metabolic disease. However, it is really since the early pioneering work on mouse embryonic stem (ES) cells in the 1980s that the use of murine models has expanded, due primarily to the huge advances in the ability to manipulate the mouse genome.
For example, homologous recombination (the recombining of an exogenous piece of DNA with its endogenous homologous sequence in vivo) within ES cells has now made it possible to make virtually any mutation in the germ line of mice. Thus, when asking “Is this gene and its product involved in a disease process?” one of the most common experimental strategies employed is to ablate the function of a target gene, generating a null allele and a so-called “knockout mouse”. Mice with such targeted deletions have been invaluable in parsing elements of the intricate system that controls food intake.
It is also possible to monitor the expression pattern of a gene from early development onwards, both in a temporal and spatial manner, by adding in an easily detectable reporter gene, which is expressed only when and where the gene of interest is expressed. For example, transgenic mice expressing green fluorescent protein (GFP) in such a way have greatly aided the isolation and subsequent study of distinct populations of neurons within the hypothalamus, an area critical in integrating peripheral signals of nutrition.
Advances in molecular biology have also allowed more sophisticated questions like "How is this gene involved in this disease?” to be directly addressed. It is now possible to produce mice with modified endogenous genes that can be acted on by recombinases expressed under the control of tissue-specific promoters. Such site-specific recombination can be used to conditionally activate ("gain-of-function") or inactivate ("loss-of-function") gene expression in a highly targeted, tissue- or cell- specific manner.
Again mice generated using these techniques have been invaluable in characterising neuronal pathways controlling appetite and energy expenditure.
Advances in molecular biology continue apace, with “recombineering” technology allowing rapid and accurate manipulation of the murine genome. Such strategies will continue to have utility in addressing fundamental questions in any integrated biological system.
The opinions expressed in this paper are those of the speaker and do not
necessarily reflect the views of the Society
Revised:
23-Aug-2006