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A Newsletter Exploring Science 
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Behind the Species... Mouse
I love Mickey Mouse more than any woman I have ever known. We all know what a mouse is. At the most basic level, a mouse is a small, furry quadruped with a long, hairless tail and big ears. Although there are 38 different species of mice (genus Mus), the species we are most familiar with is the common house or laboratory mouse (Mus musculus), a ubiquitous little rodent that appears everywhere from the laboratory to cartoons to the inside of our walls. But what is a mouse? What lies beneath the fuzzy exterior, the sharp eyes, and the twitching nose? What is it about mice that contains so much power over the workings of the human race? How can such a tiny, shy little creature influence us so much, for better or for worse? To truly understand the mouse and its mysterious inner workings, we should begin with the species name itself, Mus musculus. The word mus, which means "mouse" in Latin, has a double meaning in Old English; it stands for both "small rodent" and "muscle". Similarly, musculus in Latin means "muscle" and also "little mouse!" In Greek, the word mys means both "mouse" and "muscle" as well, and gives us the origin of the prefix myo-, which in medical terminology refers to "muscle". What is the rationale behind the seemingly bizarre association between mice and musculature? Apparently it arose from the thought that certain muscles resembled mice in shape and movement! Another theory places the origin of mus as deriving from the old Sanskrit term mush, which means "to steal", as mice are wont to do when they happen across a store of grain. Thus, mice are in name "little thieving muscles!" The predisposition to pilfering actually works in the mouse's favor. Mice are very resourceful creatures; mammalian ancestors to mice most likely survived the cataclysmic event that wiped out the dinosaurs and much of the plant life on Earth by surviving on a diet of hardy seeds. Mice first appeared about ten thousand years ago in southeastern Asia and India, and about four thousand years ago they took advantage of the development of human agriculture, surviving off of stolen grains and other stored foods. As human populations migrated to other parts of the world, mice went along with them as stowaways. It is mainly due to the commensal nature of the mouse's life with human beings that different species of mice were able to spread to all four corners of the globe. In some ways we can track the movement of our ancestors based on the species of mouse that has colonized a certain geographical area. Mice belong to the order Rodentia (rodents), a group of mammals that are characterized by upper and lower incisors that continue to grow throughout the animal's lifetime. Eating seeds and hard, pelleted rodent chow helps wear down the teeth so they do not grow too long. Mice are classic omnivores; they can and do eat almost anything, a trait that has allowed them to survive in any environment, on any continent. Grains, seeds, bread, dandelion heads, fruit, vegetables, worms, grasshoppers, and spiders have all filled the belly of the hungry mouse. Mice may also exhibit cannibalistic behavior, feasting on the carcasses of other dead mice or stillborn pups, or consuming their own tails if facing starvation. They don't, however, enjoy cheese more than other foods; the stereotype of the cheese-glutton mouse arose because cheese was frequently used as bait for mousetraps, due to its soft and smelly nature. Of course, when it comes to a mouse's teeth, most of us are concerned with whether or not those teeth are going to pierce through our skin. Mice don't generally bite; if you ran into a mouse, its first response would be flight rather than fight. Of course, there are times when you may be bitten; a mouse may bite if it is cornered and feels threatened, if you are handling it roughly, or if it is protecting its pups. If you handle mice gently and carefully and get them accustomed to being handled from an early age, they are far less likely to bite you than your average pet hamster. It is interesting, though, to note that you will find more cases of people being afraid of mice than of hamsters. In spite of everything, people still find it in their hearts to admire the little fellow, even allowing him into their homes as a pet. Pet mice have been around in Europe and Asia for thousands of years, dating back at least as far as ancient Greece and Rome. Asian mouse fanciers (hobbyists) began to experiment with selective breeding, aiming for the development of new and different coat colors. The British eventually jumped on the breeding bandwagon with the Americans soon to follow; the now-defunct American Mouse Club, which was the first fancy mouse association in the United States, formed in the 1950s. Mouse clubs operate much in the same way as dog or cat fancy clubs; they set standards for breeding and conformation and sponsor purebred mouse shows. Though we most often think of the agouti wild mouse or white lab mouse as being standard representations of mice, they do come in a whole assortment of coat colors and patterns, from white to gray to bluish to black, speckled and spotted, tricolor and brindle. Coats are most often smooth and shorthaired, though some purebreds have long coats, curly coats, or no coat at all! Many exotic coat phenotypes are characteristic of purebred or genetically engineered strains, though you'll still see some variety in conventional mice. Historically, mouse fanciers and laboratories have benefited mutually from breeding and trading mice with unique traits; the fanciers would obtain unique purebred (fancy) mice to show and the researchers would gain models with certain genetic traits for study. In fact, several common laboratory strains used today can trace their ancestry back to turn-of-the-century schoolteacher Abbie Lathrop, a mouse fancier and breeder who supplied scientists with purebred mice. Clarence Cook Little, a Harvard University scientist who later became president of the University of Michigan (1925–1929) and founder of Jackson Labs in Maine, began the practice of inbreeding to produce genetically identical mice, which involves mating sibling pairs for at least 20 generations. Nowadays most laboratory mice come from specialist companies or labs that maintain huge, complex breeding colonies. You can get conventional mice, germ-free mice, nude mice, knockout mice, and a whole host of other variations. Early geneticists such as Cuenot and William Ernest Castle used fancy mice in their studies of Mendelian genetics, thus applying Mendel's theories on plant genetics to mammals. While fruit flies and nematodes have eclipsed the mouse in research into genetic variation over the years, the mouse is still a useful model for studying how genetic traits affect cancer and the immune system, as well as for studying traits that are purely mammalian. In the last 20 years mice have climbed to the top of the list of most used laboratory animal species. This is partly due to the development of recombinant DNA technology and genetic engineering, which allows for practices like genetic manipulation on the embryonic level, creation of chimeras, and the "knocking out" of specific genes. Since mice from inbred strains are virtually identical to each other, scientists can easily eliminate unwanted variables and produce data that is consistent and easy to reproduce. Of course, inbred animals of any species will show certain defects and odd characteristics that are not found in normal breeding populations, mainly due to the expression of recessive alleles that normally would be masked by dominant genes from a mate that is genetically different. These strange traits, which can include anything from a head tilt to a completely nude body to immunity against a certain disease, are helpful in studying the disease process and how the body reacts to it. The drawback to using genetically engineered or inbred strains is that it is not necessarily representative of the traits manifested in wild or "normal" mice, or in mammals as a whole. In general, mice are ideal laboratory animals. As mammals, they are genetically related to humans, but unlike larger species they are relatively low maintenance, require much less space and food, and scientists can breed many generations in a relatively short period of time. Mice typically have 8–12 pups per litter; one breeding pair and its progeny can produce up to 5,000 mice by the time the year is out! Mouse group dynamics also make for relatively easy breeding colony management. Mice raised together can cohabit quite peacefully, especially if they are all females, though males that were not raised together may fight if housed with each other. Breeding pairs can remain together even after the birth of the pups. But before they produce one big, happy family, there is the old-fashioned courtship; the University of Washington recently discovered that male mice create high frequency song-like vocalizations in order to "serenade" their intended ladyloves! Now that we know real mice "sing" to each other, the idea of the operatically inclined superhero crooner Mighty Mouse is not that far off base. What is interesting about Mighty Mouse and other fictional mice is the fact that they often dominate the environment and situations that they are in, and they often possess a very intelligent, brave, and self-assured air about them. Who could forget the plucky warrior Reepicheep and his little sword from The Chronicles of Narnia? Mice in cartoons seem to always remain one step ahead of cats, brooms, mousetraps, and other obstacles, relying on speed and cunning to carry them through any ordeal unharmed. Jerry from Tom and Jerry and Speedy Gonzales from the Looney Tunes cartoons always came out on top, leaving their feline adversaries suffering the humiliation of defeat. A little field mouse is said to have inspired Robert Burns to write his ode To A Mouse as an apology for having disturbed its nest. And who would have guessed that a tiny little creature running around Walt Disney's studio inspired him to create Mickey Mouse, arguably the most beloved and well known cartoon character of all time? Walt Disney imagined the possibilities, and so began the creation of his magical world and our love affair with all things Mickey. In many ways these anthropomorphic characters embody the hope we all have for ourselves, that the little guy can triumph and accomplish great things in spite of all the roadblocks life throws at us. Human beings and mice have a very unique, special relationship. We love them and loathe them, fear them and foster them. They take from us our food and stow away in our homes, delivering diseases to us in return for our inadvertent hospitality. Yet the little freeloaders endlessly amuse us and provide us with artistic inspiration. We invite them into our homes as pets, honoring them with human names, and become their voluntary caretakers. We proudly display them, resplendent in their purebred coats, in mouse shows and fairs. They use us and we use them; it is hard to imagine mice without human interactions. In some ways we give them life, whether we are willing or even conscious of it, by supplying them with food and shelter and immortalizing them in art. And they may just save our lives; one day we may cure cancer and other diseases, and the little lab mouse will have been an integral part of it all.
Continued on page 2... page one page two You may download a PDF format of the actual newsletter. |
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We Want to Hear From You! We want to include your stories, comments, or questions relating to animals in your classroom in upcoming editions of BioFocus. Please email stories to mismr@umich.edu. |