Biology and Anatomy of Mouse

A brief history of rodent welfare The word mouse in the English language can be traced back to the Latin mus, then to the Greek mys,and finally to the ancient Sanskrit mush meaning "to steal”.

Taxonomy Order: Rodentia Sub-Order: Myomorpha Family: Muridae Sub-Family: Murinae Genus: Mus Species: Mus musculus

21st century rodents: pets or pests? nuisance animals fancy breeds

Human values determine animal welfare When a mouse is being used for research on cancer, it is highly valued and a range of standards and legislation governs its care and management. Once a mouse escapes from its cage, invades human space or presents a threat to economically important crops, its status changes and it becomes a pest that can be trapped or poisoned with little concern for its welfare. The value of the animal determines the way in which people treat animals, and what constitutes an acceptable level of welfare.

Animal value factors Factors about animals that may affect how people regard them: A species that gets high media coverage, publicity Cute and cuddly Similar to humans, so that we relate to it Of use to us A danger to us or to other animals A species that is endangered or near extinction

Animal values: mice in research Today, the mouse is recognized by the scientific community as the most important model for human diseases and disorders Mice account for the majority (98%) of procedures involving genetically modified animals.

Reasons for use Inexpensive Small size Short life span (2-3 years Can study many generations in short time period

Reasons for use Rapid Reproduction (G.P. 19-21 days) Large litter size

Mice uses Genetic Research Breeding research Cancer Drug testing Cosmetics Virology Histocompatability (tissue transfer) Congenital defects Aging Radiobiology Diabetis Behavior These mice are glowing because scientists inserted a gene found in certain bioluminescent jellyfish into their DNA

Physiology Life span: 2 to 3 years Adult weight: 20 to 40 gm Birth weight/condition: 1 to 5 gm blind naked Weaning age: 21 to 28 days Temperature: 97.5 – 100.4 F HR: 325-780 beats/min RR: 60-220/min Urine pH is 7.3-8.5, with a mean specific gravity of 1.08 “highly concentrated”

Reproduction Puberty: 6-8 weeks Estrous cycle: 4-5 days Spontaneous ovulation: polyestrus Gestation: 19-21 days Litter size: 1-20 (average is 6-12) Eyes open: 12-13 days Vaginal plugs persist for 18-24 hours

Reproduction cont. Breeding duration 7-9 months Breeding onset Male 50 days Female 50-60 days

Breeds

Mus musculus The laboratory strains of mice used today are descendants of the western European house mouse (Mus domesticus), with some genes from Asianspecies. The taxonomic designation Mus musculus, as commonly applied, is a composite designation for several interbreeding species.

As early as the 17th and 18th centuries, mice were already being used in studies of anatomy and respiration. The breeders and fanciers of 19th century Europe developed the albino and color mutants, and they began the investigations of varietal characteristics and inheritance that provided stocks for later research. This yellow mutant is used in studies of pigmentation, implantation, obesity, and sterility.

Rex (Frizzie)

Spotted

Inbred mouse strains From left to right in this photograph are the BALB/c, DBA/2, and C3H strains. In 1907 Clarence Cook Little, then a Harvard undergraduate, began studying the inheritance of coat color in mice. Two years later he began inbreeding mice. Little was also interested in studying neoplastic diseases. He recognized that inbreeding mice eliminated the genetic diversity in unrelated animals and facilitated his study of tumors.

Mouse strains* (inbred, mutant, and genetically engineered mice) http://www.informatics.jax.org/external/festing/mouse/STRAINS.shtml A genetically defined strain is any strain in which the genetic background is known, is similar or identical from one mouse to another, and can be faithfully reproduced over time (Davisson, 1999) Where previously there were only 140,000 variations in DNA sequence described, it turns out there are 8.3 million. *inbred animal used for experimental purposes

Albino mouse This image shows a Swiss mouse. In 1926 Dr. Clara Lynch of the Rockefeller Institute obtained two male and seven female albino mice from a colleague in Switzerland. These were the ancestors of the so-called “Swiss mice” widely used today in research.

Anatomy

External Vibrissae.

Harderian Gland behind eye

Left forepaw

Right hind paw.

Genitalia External genitalia. Female External genitalia. Male.

Skull.

Right mandible Dental formula is 2(I 1/1, M 3/3) = 16. The incisors are open-rooted and grow continuously. Mice will bite or "pinch" with their sharp incisors if mishandled

Viscera - Neck dissected

Ventral aspect of female. Mammary tissue in situ

Thoracic Cavity Abdominal Cavity

Sexing Ano-genital distance Females closer than male Adult male testes below tail but retractable Female Male

Female Male