Breeding stock for the Snell Dwarf colony was generously provided by The Jackson Laboratory (JAX catalog number 000643). The Snell Dwarf carries a recessive mutation in the Pit 1 gene (strain designation DW/JMlphlnPit1dw/J, updated in 2010 to DW/J Mlph <In>Pou1f1<dw/>J). Heterozygotes are normal in size while homozygotes are about 1/3 normal size and exhibit extended lifespan. In the NIA mutant mouse aging colony, the Snell Dwarf mice are bred from a heterozygous female crossed to a homozygous mutant male. Therefore, one half of the offspring will be heterozygous and one half will be homozygous mutants. Normal sized control mice available from this colony will all be heterozygous. These mice are not genotyped as the homozygotes are clearly distinguished from heterozygotes by size.
Dwarf mice have difficulty maintaining their body temperature so it is essential that they are housed with normal sized mice. They are housed with heterozygous mice in the NIA colony and must also be shipped with normal sized mice and housed with normal sized mice upon receipt. Therefore, there is a requirement when ordering Snell Dwarf mice that at least one normal-sized control (heterozygote) must be ordered for each dwarf mouse (homozygote) ordered. There will be no exceptions to this requirement.
Other husbandry issues are that a 6% fat diet is better for the dwarf mice than a 4% fat diet and powdered food should be placed in the bottom of the cage.
Li S, Crenshaw BE III, Rawson EJ, Simmons DM, Swanson LW, Rosenfeld MG, Dwarf locus mutants lacking three pituitary cell types result from mutations in the POU-domain gene pit-1. Nature 347, 528-533 (1990).
Flurkey K, Papaconstantinou J, Miller RA, Harrison DE, Lifespan extension and delayed immune and collagen aging in mutant mice with defects in growth hormone production. Proc Natl Acad Sci USA 98, 6736-6741 (2001).
Flurkey K, Papaconstantinou J, Harrison DE, The Snell dwarf mutation Pit1(dw) can increase lifespan in mice. Mech Ageing Dev 123, 121–130 (2002).