The retarded hair growth ( rhg ) mutation in mice is an allele of ornithine aminotransferase ( Oat )

Abstract

Because of the similar phenotypes they generate and their proximate reported locations on Chromosome 7, we tested the recessive retarded hair growth (rhg) and frizzy (fr) mouse mutations for allelism, but found instead that these defects complement. To discover the molecular basis of rhg, we analyzed a large intraspecific backcross panel that segregated for rhg and restricted this locus to a 0.9 Mb region that includes fewer than ten genes, only five of which have been reported to be expressed in skin. Complementation testing between rhg and a recessive null allele of fibroblast growth factor receptor 2 eliminated Fgfr2 as the possible basis of the retarded hair growth phenotype, but DNA sequencing of another of these candidates, ornithine aminotransferase (Oat), revealed a G to C transversion specifically associated with the rhg allele that would result in a glycine to alanine substitution at residue 353 of the gene product. To test whether this missense mutation might cause the mutant phenotype, we crossed rhg/rhg mice with mice that carried a recessive, perinatal-lethal, null mutation in Oat (designated OatΔ herein). Hybrid offspring that inherited both rhg and OatΔ displayed markedly delayed postnatal growth and hair development, indicating that these two mutations are allelic, and suggesting strongly that the G to C mutation in Oat is responsible for the retarded hair growth phenotype. Comparisons among +/+, rhg/+, rhg/rhg and rhg/OatΔ mice showed plasma ornithine levels and ornithine aminotransferase activities (in liver lysates) consistent with this assignment. Because histology of 7- and 12-month-old rhg/rhg and rhg/OatΔ retinas revealed chorioretinal degeneration similar to that described previously for OatΔ/OatΔ mice, we suggest that the rhg mutant may offer an ideal model for gyrate atrophy of the choroid and retina (GACR) in humans, which is also caused by the substitution of glycine 353 in some families.

Auxotrophy-Based Detection of Hyperornithinemia in Mouse Blood and Urine

“…Amino acids were separated by high-resolution ion-exchange chromatography, subjected to postcolumn ninhydrin derivatization, and detected by spectrophotometry at 570 and 440 nm. Plasma ornithine concentrations found in this survey have been reported previously by Bisaillon et al 10 and are cited again in this text for the reader’s convenience; plasma arginine and citrulline concentrations are reported here for the first time.…”

“…found in this survey have been reported previously by Bisaillon et al 10 and are cited again in this text for the reader's convenience; plasma arginine and citrulline concentrations are reported here for the first time.…”

“…Indeed, the levels of ornithine measured by this approach in mutant mouse blood were comparable to levels previously found for these subjects by direct chemical analysis. 9,10 Similar results were obtained in microtiter culture experiments that used E coli strain BW6165 (Coli Genetic Stock Center, Stock Number 6760, Yale University) 28 instead of CAG12185 (see Figure 6), but this lacY mutant strain yielded inconsistent results in top agar assays (data not shown).…”

“…All animals were housed and fed according to federal guidelines, and the Institutional Animal Care and Use Committee at Central Connecticut State University (CCSU) approved all procedures involving mice (animal protocol applications #131, 134, and 136). Segregating inbred B6Ei;AKR- Oat rhg / J mice (carrying the spontaneous retarded hair growth mutation, herein referred to as rhg ) were obtained from The Jackson Laboratory (Bar Harbor, Maine) and are described by Bisaillon et al 10 Mice carrying the Oat tm1Dva targeted mutation (designated herein as Oat Δ ) were kindly provided by Dr David Valle (Institute of Genetic Medicine and Departments of Pediatrics, Ophthalmology, and Molecular Biology & Genetics, The Johns Hopkins University School of Medicine, Baltimore, Maryland). The creation of the Oat Δ mutation is described by Wang et al 9 DNA tests for distinguishing these mutant Oat alleles ( Oat Δ and rhg ) from wild type are described in Bisaillon et al 10 Both mutant Oat alleles were maintained as C57BL/6J congenic stocks, and C57BL/6J mice provided our wild-type controls.…”

“…These mouse mutants, the engineered Oat knockout 9 and the spontaneous missense variant called retarded hair growth, 10 have been shown to be excellent models for the inherited human condition known as gyrate atrophy of the choroid and retina (GACR, Online Mendelian Inheritance in Man (OMIM) #258870), which results in visual impairment that begins in childhood with myopia and night blindness and progresses to complete blindness by the fourth or fifth decade of life. [11][12][13] Dietary restriction of arginine has been shown to prevent (but not reverse) retinal degeneration in OAT-deficient mice.…”