Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation, affecting one in 800 live born human beings. Mice with segmental trisomy 16 (Ts65Dn mice) are at dosage imbalance for genes corresponding to those on human chromosome 21q21-22.3--which includes the so-called DS 'critical region'. They do not show early-onset of Alzheimer disease pathology; however, Ts65Dn mice do demonstrate impaired performance in a complex learning task requiring the integration of visual and spatial information. The reproducibility of this phenotype among Ts65Dn mice indicates that dosage imbalance for a gene or genes in this region contributes to this impairment. The corresponding dosage imbalance for the human homologues of these genes may contribute to cognitive deficits in DS.

The Jackson Laboratory, having the world's largest collection of mouse mutant stocks and genetically diverse inbred strains, is an ideal place to look for genetically determined eye variations and disorders. Through ophthalmoscopy, electroretinography and histology, we have discovered disorders affecting all aspects of the eye including the lid, cornea, iris, lens and retina, resulting in corneal disorders, cataracts, glaucoma and retinal degenerations. Mouse models of retinal degeneration have been investigated for many years in the hope of understanding the causes of photoreceptor cell death. Sixteen naturally occurring mouse mutants that manifest degeneration of photoreceptors in the retina with preservation of all other retinal cell types have been found: retinal degeneration (formerly rd, identical with rodless retina, r, now Pde6b(rd1)); Purkinje cell degeneration (pcd); nervous (nr); retinal degeneration slow (rds, now Prph(Rd2)); retinal degeneration 3 (rd3); motor neuron degeneration (mnd); retinal degeneration 4 (Rd4); retinal degeneration 5 (rd5, now tub); vitiligo (vit, now Mitf(mi-vit)); retinal degeneration 6 (rd6); retinal degeneration 7 (rd7, now Nr2e3(rd7)); neuronal ceroid lipofuscinosis (nclf); retinal degeneration 8 (rd8); retinal degeneration 9 (Rd9); retinal degeneration 10 (rd10, now Pde6b(rd10)); and cone photoreceptor function loss (cpfl1). In this report, we first review the genotypes and phenotypes of these mutants and second, list the mouse strains that carry each mutation. We will also provide detailed information about the cpfl1 mutation. The phenotypic characteristics of cpfl1 mice are similar to those observed in patients with complete achromatopsia (ACHM2, OMIM 216900) and the cpfl1 mutation is the first naturally-arising mutation in mice to cause cone-specific photoreceptor function loss. cpfl1 mice may provide a model for congenital achromatopsia in humans.

Misfolded proteins are associated with several pathological conditions including neurodegeneration. Although some of these abnormally folded proteins result from mutations in genes encoding disease-associated proteins (for example, repeat-expansion diseases), more general mechanisms that lead to misfolded proteins in neurons remain largely unknown. Here we demonstrate that low levels of mischarged transfer RNAs (tRNAs) can lead to an intracellular accumulation of misfolded proteins in neurons. These accumulations are accompanied by upregulation of cytoplasmic protein chaperones and by induction of the unfolded protein response. We report that the mouse sticky mutation, which causes cerebellar Purkinje cell loss and ataxia, is a missense mutation in the editing domain of the alanyl-tRNA synthetase gene that compromises the proofreading activity of this enzyme during aminoacylation of tRNAs. These findings demonstrate that disruption of translational fidelity in terminally differentiated neurons leads to the accumulation of misfolded proteins and cell death, and provide a novel mechanism underlying neurodegeneration.

Targeted mutagenesis in mice, a powerful tool for the analysis of gene function and human disease, makes extensive use of 129 mouse substrains. Although all are named 129, we document that outcrossing of these substrains, both deliberate and accidental, has lead to extensive genetic variability among substrains and embryonic stem cells derived from them. This clearer understanding of 129 substrain variability allows consideration of its negative impact on targeting technology, including: homologous recombination frequencies, preparation of inbred animals, and availability of appropriate controls. Based on these considerations we suggest a number of recommendations for future experimental design.

We report the chromosomal localization, mutant gene identification, ophthalmic appearance, histology, and functional analysis of two new hereditary mouse models of retinal degeneration not having the Pde6brd1("r", "rd", or "rodless") mutation. One strain harbors an autosomal recessive mutation that maps to mouse chromosome 5. Sequence analysis showed that the retinal degeneration is caused by a missense point mutation in exon 13 of the beta-subunit of the rod cGMP phosphodiesterase (beta-PDE) gene (Pde6b). The gene symbol for this strain was set as Pde6brd10, abbreviated rd10 hereafter. Mice homozygous for the rd10 mutation showed histological changes at postnatal day 16 (P16) of age and sclerotic retinal vessels at four weeks of age, consistent with retinal degeneration. Retinal sections were highly positive for TUNEL and activated caspase-3 immunoreactivity, specifically in the outer nuclear layer (ONL). ERGs were never normal, but rod and cone ERG a- and b-waves were easily measured at P18 and steadily declined over 90% by two months of age. Protein extracts from rd10 retinas were positive for beta-PDE immunoreactivity starting at about the same time as wild-type (P10), though signal averaged less than 40% of wild-type. Interestingly, rearing rd10 mice in total darkness delayed degeneration for at least a week, after which morphological and functional loss progressed irregularly. With the second strain, a complementation test with rd1 mice revealed that the retinal degeneration phenotype observed represents a possible new allele of Pde6b. Sequencing demonstrated a missense point mutation in exon 16 of the beta-subunit of rod phosphodiesterase gene, different from the point mutations in rd1 and rd10. The gene symbol for this strain was set as Pde6bnmf137, abbreviated nmf137 hereafter. Mice homozygous for this mutation showed retinal degeneration with a mottled retina and white retinal vessels at three weeks of age. The exon 13 missense mutation (rd10) is the first known occurrence of a second mutant allele spontaneously arising in the Pde6b gene in mice and may provide a model for studying the pathogenesis of autosomal recessive retinitis pigmentosa (arRP) in humans. It may also provide a better model for experimental pharmaceutical-based therapy for RP because of its later onset and milder retinal degeneration than rd1 and nmf137.

The signalling lipid PI(3,5)P 2 is generated on endosomes and regulates retrograde traffic to the trans-Golgi network. Physiological signals regulate rapid, transient changes in PI(3,5)P 2 levels. Mutations that lower PI(3,5)P 2 cause neurodegeneration in human patients and mice. The function of Vac14 in the regulation of PI(3,5)P 2 was uncharacterized previously. Here, we predict that yeast and mammalian Vac14 are composed entirely of HEAT repeats and demonstrate that Vac14 exerts an effect as a scaffold for the PI(3,5)P 2 regulatory complex by direct contact with the known regulators of PI(3,5)P 2 : Fig4, Fab1, Vac7 and Atg18. We also report that the mouse mutant ingls (infantile gliosis) results from a missense mutation in Vac14 that prevents the association of Vac14 with Fab1, generating a partial complex. Analysis of ingls and two additional mutants provides insight into the organization of the PI(3,5)P 2 regulatory complex and indicates that Vac14 mediates three distinct mechanisms for the rapid interconversion of PI3P and PI(3,5)P 2 . Moreover, these studies show that the association of Fab1 with the complex is essential for viability in the mouse.

Oculocutaneous albinism (OCA) affects approximately 1/20,000 people worldwide. All forms of OCA exhibit generalized hypopigmentation. Reduced pigmentation during eye development results in misrouting of the optic nerves, nystagmus, alternating strabismus, and reduced visual acuity. Loss of pigmentation in the skin leads to an increased risk for skin cancer. Two common forms and one infrequent form of OCA have been described. OCA1 (MIM 203100) is associated with mutations of the TYR gene encoding tyrosinase (the rate-limiting enzyme in the production of melanin pigment) and accounts for approximately 40% of OCA worldwide. OCA2 (MIM 203200), the most common form of OCA, is associated with mutations of the P gene and accounts for approximately 50% of OCA worldwide. OCA3 (MIM 203290), a rare form of OCA and also known as "rufous/red albinism," is associated with mutations in TYRP1 (encoding tyrosinase-related protein 1). Analysis of the TYR and P genes in patients with OCA suggests that other genes may be associated with OCA. We have identified the mouse underwhite gene (uw) and its human orthologue, which underlies a new form of human OCA, termed "OCA4." The encoded protein, MATP (for "membrane-associated transporter protein") is predicted to span the membrane 12 times and likely functions as a transporter.

Osteogenesis imperfecta (OI) is a heritable disorder ofconnective tissue associated with fractures, osteopenia, and short stature. 01 results from mutations affecting the proal or proa2 gene of type I collagen. We describe a strain of mice with a nonlethal recessively inherited mutation (oim) that results in phenotypic and biochemical features that simulate moderate to severe human 01. Although imperfect osteogenesis has been previously observed in bovine, feline, and murine species, none of these have duplicated both the biochemical and clinical findings associated with human OI (4-7). The Mov-13 mouse, which has a transcriptional block of the proal(I) collagen gene, has provided a potential model of human 01 type II (8-13). More recently, several transgenic variants of Mov-13 and normal mice have been created as useful models of mild 01 type I or lethal OI type II (tt, 14, 15).In this report we describe a naturally occurring mouse mutation that produces phenotypic and biochemical features similar to those seen in moderate to severe human OI. We have named this mutation osteogenesis imperfecta murine (oim). Homozygous oim mice have osteopenia, fractures, and progressive skeletal deformities. Our data indicate that these mice are deficient in proa2(I) collagen because of a G deletion at nucleotide 3983 of the Cola-2 gene. This mutation results in tissue accumulation of al(I) homotrimeric collagen in the extracellular matrix. Homozygous oim mice should permit the study of type I collagen pathophysiology in a manner not possible in humans. MATERIALS AND METHODSRadiographic and Microscopic Examination. Whole-body radiographs were taken in a Faxitron x-ray machine (34 keV for 1.5 min) using Kodak OM1 film. For light microscopy, excised femurs were fixed in neutral buffered Formalin for 24 hr, decalcified in 10% (wt/vol) EDTA in 0.1 M Tris'HCl buffer, pH 6.9, for 14 days at 4°C, embedded in paraffin, sectioned, and stained with hematoxylin and eosin.Isolation and Culture of Dermal Fibroblasts. Dermis was obtained from the back of 3-to 5-day-old homozygous oim and wild-type pups. The skin was rinsed with iodine then 70o (vol/vol) ethanol, excised, and minced to 1-to 3-mm2 pieces.Explants were grown for 2 weeks in Dulbecco's modified Eagle's medium supplemented with 10%o fetal bovine serum, streptomycin at 100 jug/ml, penicillin at 100 units/ml, and amphotericin B at 0.25 jig/ml. Cultures were assayed in the second passage.Collagen and Procollagen Analysis in Vitro. Fibroblast cultures were grown several days past visual confluence in 10-cm2 dishes. The medium was then supplemented with 150 ,uM sodium ascorbate and 24 hr later the cultures were incubated for 30 min in Dulbecco's modified Eagle's medium plus 1% dialyzed fetal bovine serum, antibiotics, 100 ,uM each nonessential amino acids but no proline, and 150 ,uM sodium ascorbate (starve medium). De novo synthesized proteins were radiolabeled for 2 hr (short-label analysis) or 24 hr (steady-state analysis) with starve medium containing 20 ,uCi (1 Ci = 37 ...