Knockout Mice: The Real Heroes of Genetic Research

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The most famous knockout mice are designed to lack genes that control appetite.  The knockout mouse on the left has become morbidly obese, despite being raised in the same conditions as the mouse on the right

Research in genetics would not be the same without our little friend Mus musculus, otherwise known as the common house mouse.  Mice are the heart and soul of many research projects, and it is through our toying with their genomes that much of our knowledge of genetics and mammalian physiology have come from the examination of these furry little guys.

Mice are a common sight in many laboratories because their little bodies function much in the same way that human bodies (and those of other mammals) do.  Mice are small and easy to handle, they breed quickly so many generations can be observed over a relatively short period of time, and they mature quickly, allowing researchers to observe the entire lifespan of a mouse over the course of just a year or two.  Mice are also easy to care for and they thrive in very controlled environments, making them absolutely perfect for their role as test subjects.

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Image taken from University of Australia; protected under Fair Use

Now, you’re probably wondering why some lab mice are called “knockout” mice.  No, it’s not because they can land an amazing uppercut in the ring, it’s actually because a single gene or a group of genes have been removed or altered within the mouse genome, effectively knocking out that/those gene(s).  This allows researchers to see the effects of removing a gene, and by analyzing these effects and changing which genes are removed from which mice, the function of a gene and which genes it interacts with can be studied.

The mice that I work with have three altered genes, Tsc1, P0cre, and lacZ.  Tsc1 is the gene whose function I am trying to uncover, while P0cre allows me to turn on and off the function of Tsc1 by simply changing the type of food that I feed the mice.  You see, the way that the genomes of these mice have been designed, the gene P0cre is located next to Tsc1, and by feeding the mice a food which contains specific proteins designed to stick to the P0cre DNA, I can activate and inactivate Tsc1 whenever I like.  lacZ is a gene which codes for a protein designed to digest the sugar lactose.  When this gene is knocked out of the mouse genome I am able to use a special type of chemical staining to turn certain cell types blue, allowing me to detect the presence of certain cells in the mice.

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This is a sample of agarose gel which has had DNA passed through it.  The dark bands are areas where DNA segments of certain lengths have gathered

To find out which genes a certain mouse has (i.e. figuring out its genotype), I perform a process known as genotyping.  This process involves the amplification of mouse DNA through a series of chemical reactions designed to replicate DNA dozens of times.  DNA is negatively charged, so after a sufficient amount of DNA matching the mouse’s DNA has been replicated, I place it inside of a thick gel and run electricity through the gel.  The negatively-charged DNA is pulled through the gel, with smaller DNA segments being pulled further than longer ones.  By looking at the gel after the DNA has separated by size within it, we can identify which genes are present or not present within the mouse.

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