Biology and Anatomy of Mouse Taxonomy Order Rodentia

Biology and Anatomy of Mouse

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

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 Importance ■ ■ 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 ■ ■ ■ ■ ■ These mice are glowing because scientists inserted a gene found in certain bioluminescent jellyfish into their DNA ■ ■ ■ Genetic Research Breeding research Cancer Drug testing Alzheimer’s Virology Histocompatability (tissue transfer) Congenital defects Aging Radiobiology Diabetes Behavior

Physiology ■ ■ ■ Life span: ○ 2 to 3 years Adult weight: ○ 20 to 40 gm Birth weight/condition: ○ 1 to 5 gm ○ blind ○ naked ○ Altricial ■ ■ Weaning age: ○ 21 to 28 days Temperature: ○ 97. 5 – 100. 4 °F HR: ○ 325 -780 beats/min RR: ○ 60 -220/min Urine p. H 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 Asian species. The taxonomic designation Mus musculus, as commonly applied, is a composite designation for several interbreeding species.

■ ■ ■ As early as the 17 th and 18 th centuries, mice were already being used in studies of anatomy and respiration. The breeders and fanciers of 19 th 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 C 3 H 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 socalled “Swiss mice” widely used today in research.