Phenylalanine hydroxylase (PAH) is central to phenylalanine metabolism and defects in this gene underlie phenylketonuria. This ENU-induced T835C missense mutation yields an F263S single amino acid substitution that causes severely diminished PAH catalytic activity in homozygotes and provides a model of severe phenylketonuria.
Dr. Alexandra Shedlovsky, University of Wisconsin , Madison
Phenylketonuria (PKU) in humans results from a deficiency in phenylalanine hydroxylase (PAH), which normally converts phenylalanine to tyrosine. If untreated, phenylketonuria results in severe and irreversible mental retardation. While the Pahenu1 mutation, a conservative V106A substitution, provides a mild phenotype and model for hyperphenylalaninemia, this Pahenu2 mutation is an F263S single amino substitution that causes a much more severe phenotype and model for phenylketonuria. Homozygous Pahenu2 mice show severe hyperphenylalanemia with serum phenylalanine levels elevated 10-20 fold and urinary ketone concentrations significantly increased in adults. They have PAH protein evident by Western blot but almost no enzyme activity, consistent with disruption of the catalytic domain. Homozyogtes typically have small heads and display behavioral abnormalities starting at about 2 weeks and lasting into adulthood. Under conditions of elevated phenylalanine (e.g. at 25 g/dl in drinking water), Pahenu2 animals sicken within days. Homozygous Pahenu2 females are fertile but have smaller and fewer litters and pups generally die perinatally. Consistent with maternal PKU in humans, this effect depends entirely upon the genotype of the mother. (Shedlovsky et al., 1993; Sarkissian et al., 2000)
As in human patients, the mutant mice are hypopigmented unless maintained on a low phenylalanine diet. The coat color of the background strain, BTBR T+ Itpr3tf/J (Stock No. 002282) is black and tan (at/at), but Pahenu2 homozygosity results in hypopigmentation evident in the dorsal coat of homozygotes generally by 4 to 6 weeks of age. This strain is also homozygous for the tufted mutation (Itpr3tf) resulting in various molting patterns in the mouse coat. These effects, limited to the mouse coat, may make the mice appear malformed. In The Jackson Laboratory colony, homozygous prewean pups are black and tan then molt at 3-4 weeks of age, but when the fur grows back the mice are brown and tan. When breeders lose their fur at an older age, it does not generally grow back. Our colony shows a very low percentage of mice that appear black and tan after 6-7 weeks of age.
Of note, the Pahenu2 mutation is also available on a congenic C57BL/6J background as Stock No. 029218.
A BTBR T+ Itpr3tf male was treated with ENU and mated to normal BTBR females. Their offspring were screened for mutations in Pah by breeding with mice homozygous for the Pahenu1 mutation and looking for non-complementation in the offspring. The breeders found to carry mutations in Pah were then bred to normal BTBR mates and the mutant sublines maintained thereafter. BTBR T+ Itpr3tf is homozygous for at, Itpr3tf, Disc1del, and Cox7a2ll, but wildtype for brachyury. Because Pahenu2 homozygous females are not appropriate breeders this strain was generally maintained by breeding heterozygous females with heterozygous or homozygous males. This strain was imported into The Jackson Laboratory in 1994 from Dr. Alexandra Shedlovsky and Dr. William Dove at the McArdle Laboratory for Cancer Research, University of Wisconsin. Embryos were initially cryopreserved within a few additional generations of sibling intercrosses.
|Allele Name||phenylalanine hydroxylase enu 2|
|Allele Type||Chemically induced (ENU)|
|Gene Symbol and Name||Pah, phenylalanine hydroxylase|
|Strain of Origin||BTBR|
|Molecular Note||A T835C missense mutation in exon 7 results in a phenylalanine to serine substitution at amino acid 263 (F263S).|
|Mutations Made By|| |
Dr. William Dove, University of Wisconsin- Madison
Crosses of heterozygous females with homozygous males are recommended. Homozygous females are fertile but do not rear their young when maintained on a standard mouse diet; none of their pups survive beyond several hours.
Technician's Note: This strain breeds well and does not require any special husbandry. The Jackson Laboratory maintains their colony on a 6% fat diet. The average litter size is 8-12 pups. The expected coat color from breeding is Black with Brown.
When using the PAHenu2 mouse strain in a publication, please cite the originating article(s) and include JAX stock #002232 in your Materials and Methods section.