Animal Models

I've been trying to import a searchable database of animal models for a couple of years now, without success.

Following are some excerpts from Special Topic Overviews published in Laboratory Animal Science as well as articles from the ILAR Journal which are likely to be considered important animal model information on the ACLAM boards. More information has been added as it becomes convenient to do so, in lieu of placing it into the nonfunctional database. For lists of mouse mutants, click here.

Animal Models of Motor Neuron Disease

Brittany Spaniel Dog (Canis familiaris)

In dogs this is called Hereditary Canine Spinal Muscular Atrophy (HCSMA) and exists in a colony of Brittanies maintained since 1979. It is a very good model for Lou Gehrig's disease with the exception that the motor cortex is not affected in dogs. It is an autosomal dominant disease mapped to canine chromosomal linkage group 1. HCSMA is the only spontaneously-occurring, dominantly-inherited animal motor neuron disease in which the onset and severity varies with gene dose.{3926}

Horse

Thought to be caused by dietary vitamin E deficiency, this disease in horses mimics the most common (sporadic) form of amyotrophic lateral sclerosis (ALS). An important feature is that sometimes the disease burns itself out; after sudden onset and rapid progression, the disease stabilizes.{3926}

Mouse (Mus)

G93A-SOD 1

Transgenic mice with this particular mutation in the Cu/Zn SOD are the "best" model of ALS (Lou Gehrig's Disease) features. One of the Jax strains (B6SJL-Tg(SOD1*G93A)1Gur/J) expresses human G93A mutant SOD1 in neurons in the brain and spinal cord. It is autosomal recessive. There are differences in expression of signs depending on the backgroud strain and copy number of the transgene. There is much debate over whether the main defect in ALS is in superoxide dismutase, largely as a result of work with transgenic mice. It is possible that in ALS, the Cu/Zn SOD either is itself toxic or has a toxic function. In this mutant, Cu/Zn SOD is normal. Note that this is a model of motor neuron disease, and may affect both upper and lower motor neurons, not just those in the spinal cord. ALS is the most common motor neuron disease. About 10% are familial, and the rest are sporadic. Signs of upper MND include spasticity, hyperreflexia and plantar signs; signs of lower MND are muscle weakness, fasciculations and atrophy. A variety of knockouts have shown that motor neurons depend on neurotrophins and other factors (GDNF or glial-derived nerve growth factor and others).{3926}

Motor neuron degenerative (mnd)

The motor neuron degenerative (mnd) mouse is a spontaneous mutant that has late onset motor neuron degeneration and accumulation of neurofilaments and lipofuscin material like patients with Lou Gehrig's disease. However, they do not show skeletal muscle degeneration and motor neuron loss. They are therefore a better model for Batten's disease, the most common human neuronal lipofuscinosis. It is autosomal recessive.{3926} Current strains (i.e. B6.KB2-Cln8^mnd/MsrJ) develop hindlimb weakness between 5-11 months of age which progresses to severe spastic paralysis of all limbs and death by 9-14 months.

Wobbler

The wobbler mouse is a spontaneous mutant model for Lou Gehrig's disease, a motor neuron disease. They have anterior horn cell loss in the spinal cord and muscle denervation atrophy. The gene is on mouse chromosome 11. Affected progeny can be identified before clinical signs appear, a distinct advantage. It is autosomal recessive.{3926}

Wasted mutant

The wasted mutant mouse is different from other Lou Gehrig's disease models because the disease is very aggressive, with death by 28 days. It is autosomal recessive. There is vacuolar degeneration of anterior horn cells in the spinal cord and motor nuclei of the brainstem. The mutation is a lethal deletion of translation elongation factor 1.{3926}

Progressive motor neuronopathy (pmn)

The progressive motor neuronopathy mouse is an autosomal recessive mutant, like the others. They show muscular atrophy and paralysis with little loss of motor neurons in the spinal cord. This makes them a model for "dying-back axonal disease." The affected gene is on chromosome 13.{3926}

Since the above was written in 1999 based on a review article in LAS, the world has moved on. These days the Jackson lab is a better source for mouse model information. In the case of ALS, for example, they have produced a 28-page PDF document on mouse models, including guidelines for preclinical testing and colony management information for the various mouse strains.

Neurologic Disease Models

Alzheimer's Disease

Alzheimer's disease is characterized by memory loss and cognitive deficits. Pathology includes amyloid plaques, neurofibrillary tangles made of tau protein associated with microtubules, reactive gliosis by surrounding astrocytes, and conversion of microglial cells into macrophage-like cells. Lesions are confined to the cortex and hippocampus. Transgenic mice that over-express amyloid precursor protein (APP) produce more of the peptide in the amyloid plaques. In humans there are four alleles of the APP gene, and people with two copies of the E-4 allele have a higher risk of Alzheimer's. The APP gene product is cleaved into fragments; the A-beta fragment is found in CSF and plasma, and has a protease inhibitor function. A-beta is deposited in amyloid plaques, particularly the 42-peptide fragment (as opposed to the 40-peptide fragment). The plaques in mice expressing mutant APP protein very closely resemble the plaques in humans. Two other genes, encoding for presenilin-1 and PS-2, are also involved. In mice, APP, PS1 and PS2 mutations are all dominant. Mice that are double-transgenic for APP and PS1 show much greater plaque formation at an earlier age (~11 months) than those with mutant APP alone.

Lesions in mice that resemble those in humans include: (1) increased A-beta 42 in plaques (although mice also have the 40-peptide fragment); (2) dystrophic neurites; (3) activated astrocytes. Presence of plaques alone (in mice) doesn't seem to be the problem; it is the presenilin and APP combined that seem to be required. A news report in Lab Animal magazine (30(9):12, 2001)reported that the interaction of A-beta with tau leads to the formation of neurofibrillary tangles.

Mutant mice with these genes have not yet been behavior-tested. The background strain (presumably C57BL/6) has retinal degeneration and becomes blind by 2 months of age, making behavior evaluation more difficult.{4533}

Huntington's Disease

There is a transgenic mouse model of Huntington's Disease. The brain is small and there is other neuropathology. There are neuronal intracellular inclusions consisting of huntington and ubiquitin deposits which are also seen in human patients. Female mice are sterile, and only half the males are fertile, for 3 weeks; this creates a "unique breeding situation".{4530}

Nonhuman Primates in Current Disease Research {4152}

Avian models

Birds are naturally hypercholesterolemic, with cholesterol levels of 200-350mg/dl, but most of it is HDL. Chickens have been used for studies of viral effects (Marek's disease exacerbates it) on atherosclerosis. They were the first animal in which the effect of estrogens (which reduce coronary lesions with little effect on aortic lesions) was known. Turkeys develop natural atherosclerosis leading to dissecting aortic aneurysms. Japanese quail are small birds, and they develop significant lesions after only 2-3 months of cholesterol feeding.{4166}

Pigeons have been used a lot for atherosclerosis study. White Carneau birds are very susceptible with cholesterol feeding, while Show Racers are resistant. They all develop atherosclerosis in the same initial site, in the aorta at the bifurcation of the celiac artery. The predominant lipoproteins are b-VLDL and LDL in cholesterol-fed birds. The predominant apolipoproteins are apoB and apoA1; however birds do not produce apoE or apoB-48 and do not form chylomicrons during fat absorption. Egg-laying females have major changes in plasma lipoproteins associated with fat delivery to the eggs. Some pigeons are naturally infected with a pigeon herpesvirus which is perhaps similar to Marek's disease in chickens. When taken off cholesterol diets, pigeons return to normal cholesterol levels in a few weeks, in contrast to rabbits which take months. The early pathogenesis probably involves macrophages, as foam cells appear early; current studies involve bone marrow transplant between WC and SR pigeons.{4166}

Non-human primate models

New World monkeys aren't good models because they have chronic renal disease which modulates atherosclerosis and lipoprotein metabolism. Squirrel monkeys fed atherogenic diets develop lipid and then mineral accumulations in the glomeruli. A similar picture occurs in male cotton-top tamarins, which are more likely to have coronary atherosclerosis than females.

Old World monkeys have been studied a lot, particularly cynos. Females have protection from their estrogens; in fact high-ranking females have less disease because they produce more estrogen each cycle. In contrast, males of high rank have higher rates of disease whereas low-ranking males have less disease. Single-housed macaques have more extensive disease than group-housed. Monkeys tend to be hyper-responsive to dietary cholesterol, or hypo-responsive, and this is probably genetic. African green monkeys have been used in studies of saturated vs. polyunsaturated fats, clearly showing that saturated fat diets are the worst. Monkeys are also used to evaluate estrogen replacement in post-menopausal states. If a woman still has a uterus, a progestin must be added to her estrogen replacement to protect her from endometrial cancer. Medroxyprogesterone acetate (Provera^®) is most commonly used. Cynomolgus monkeys were used to demonstrate that addition of this progestin attenuated the positive effects of estrogen on atherosclerosis in the coronary arteries.{4167}

Mouse models

The modern theory of atherogenesis is that atherosclerosis is an excessive fibroproliferative response to an insult of the arterial wall. Lipoproteins are retained in the wall in the first step. Endothelial cells are activated and produce cell adhesion molecules, which attract macrophages. Macrophages become cholesterol-engorged foam cells causing the first grossly visible lesion, the fatty streak. The second lesion, the intermediate fibrous plaque, has smooth muscle cells covering the fatty streak. The dead cells in the center produce cholesterol crystals. The advanced complex lesion involves a thrombotic event after the rupture of plaque.

Differences between mice and humans are: lifespan, weight/size, mouse lipid profile (most cholesterol on HDLs, opposite from humans), ability to control environment and genetics. Mouse models are useful for identifying genes involved, identification of cell roles, and characterization of environment and dietary effects on lesion development.

The first model was the diet-induced model produced by feeding high fat/high cholesterol diets, which were toxic in the early years. The Paigen diet is 15% fat, 1.25% cholesterol, and 0.5% cholic acid. She also developed the cross-sectional lesion measurement method still used to quantify lesions. The gene for susceptibility was determined to be the Ath-1 locus on chromosome 1. Mouse strains were made by crossing susceptible C57BL/6 to resistant C3H and creating recombinant inbred strains by vertical brother-sister matings. There has been some challenge lately to this gene's true function. But using this model, the following were discovered: lesion size is decreased by over-expression of ApoA-I in HDL, apoE transgene, and alcohol feeding. Lesion size is increased by TNF; MHC class II deficiency has no effect. The Paigen diet itself is inflammatory, causing the expression of acute phase reactants such as serum amyloid A5.

The apoE knockout mouse has total cholesterol of 500 mg/dl composed mostly of bVLDL. A "western type" diet mimicking the American diet has been developed that is 21% fat, 0.15% cholesterol and no cholic acid. These mice develop later lesions than the first ones, going all the way to intermediate fibroproliferative stage. The candidate-gene approach is used to create double mutants on the apoE knockout mouse. Those with the human apoAI transgene have smaller lesions, with high HDL levels. The op (osteopetrotic) mouse has no macrophage colony-stimulating factor and therefore fewer monocytes. apoE/Op mice have decreased lesions. Further supporting the lack of an effect of the immune system, Rag-1 deficient mice (which can't mature their T or B cells) combined with apoE KO have only a 40% decrease of lesion size. Apparently the immune system plays an early role (with CD4 + T cells) but later the lesions develop anyway. Environmental effects studied with apoE KO mice include: decreased lesions induced by antioxidant drugs, estrogen, and bone marrow transplantation.

Comparison of atherosclerosis lesion pathology {4168}
Lesion	ApoE KO	Human
Fatty streaks	Yes	Yes
Fibrous plaques	Yes	Yes
Lesion calcification	Yes	Yes
Oxidized epitopes	Yes	Yes
Lesions form at sites of disturbed flow	Yes	Yes
Diet responsive	Yes	Yes
Aneurysms observed	Yes	Yes
Plaque rupture observed	No	Yes

Cancer Models

There is much interest in replacing the traditional "two-species" chronic carcinogenic assay with a second, shorter (2-year) bioassay using either the rat or the mouse, usually a genetically-modified strain. Some of the recommended modified strains are Tg.AC v-Ha-ras, rasH2, p53+/- heterozygotes, and XPA-/- mice.{4572}

Mice

p53 null strains: These mice develop tumors in as little as 60 days. Most human malignancies have mutations in p53.{4530}

p53+/- heterozygotes: Produced by introduction of a mutant allele into ES cells. The most common tumors in the mice are osteosarcomas and malignant lymphomas. They are also more susceptible to tumor induction by some carcinogens. They appear to be susceptible to tumor induction by mutagenic carcinogens, but not by non-mutagenic carcinogens. Users must be aware of some unique features of these mice: on a C57Bl/6 background, they tend to develop sarcomas at the site of microchip implants. On an FVB background, they develop sarcomas at the site of eartag application.{4572}

rasH2: Activated ras oncogenes are present in 30% of human cancers. Transgenic mice carrying the human ras gene are being evaluated as a model for rapid carcinogenicity testing. Transgenics carry 5-6 copies of the transgene per genome. Within 18 months, half of them develop spontaneous liver tumors, primarily angiosarcomas. A number of chemical carcinogens have been studied in this model.{4572}

Tg.AC v-Ha-ras: Useful for detection of "nongenotoxic" carcinogens and tumor promoters, such as the topical application of TPA (12-O-tetradecanoylphorbol-13-acetate) in skin papilloma and squamous cell carcinoma. They have an activated ras oncogene. The background strain is usually FVB/n. There is a carcinogen "non-responder" phenotype in this strain that resulted from a rearrangement of the promoter gene. Therefore, it is important to type all Tg.AC mice for homozygosity and the absence of this rearranged promoter. The most common spontaneous tumors are odontogenic tumors (13-17%). These may lead to weight loss in animals on pelleted diets. Animal caretakers must be aware that Tg.AC mice must be housed individually, as their skin damages easily with handling, grooming, or wounds. Differences in papilloma induction have been observed depending on whether they are housed on bedding or raised wire. Males have a high background incidence of genitourinary disease.{4572}

Tgfb1 Rag2 double null model: Mice transgenic for Tgfb1 all die. When crossed with mice with the Rag2 mutation (which have no mature T or B cells), they all develop tumors by 5 months. The outcome of intercrossing Tgfb1/+ x Rag-/- is highly dependent on the background strain, being worse if on a C57BL/6 background.{4530}

XPA-/-: Named after humans with hereditary xeroderma pigmentosum, these mice have a genetic defect in DNA repair at the damage recognition step. XPA mice develop normally, have no histological abnormalities, and are fertile. Their mortality rate is normal until 18 months of age. They are susceptible to UV light and dimethylbenzanthracene-induced skin cancers. Their fibroblasts are deficient in "unscheduled" DNA synthesis.

Breast Cancer{4753}

Two genes, TGF-alpha and c-erbB-2 (HER-2), predispose the mammary gland to cancer. Both transgenic mice and transgenic rats which overexpress one of these genes develop atypia in mammary tissues. Multiparous transgenic female offspring from c-erbB-2-expressing lines and MMTV-TGFalpha expressing lines develop a variety of focal hyperplastic and benign lesions that resemble lesions commonly found in human breasts. More malignant lesions, including ductal carcinoma in situ and carcinoma, also develop stochastically (randomly) at low frequency. In addition, multiparous TGFalpha-expressing female transgenics frequently develop severe pregnancy-dependent lactating hyperplasias as well as residual lobules of hyperplastic secretory epithelium and genuine lactating adenomas after weaning.

This image depicts diffuse lobular hyperplasia in an MMTV-TGFalpha transgenic rat. The same pattern appears in mice transgenic for TGFalpha. The pattern is consistent with lactation. Note that the cells and the lobules are not atypical.

Image from an MMTV-TGF-alpha mouse with adenosquamous carcinoma. The secretory (clear cytoplasmic vacuoles) papillary tumor (left) is adjacent to an area of squamous differentiation (red, right). Transgenic mice given a single oral dose of 0.5mg dimethylbenzanthacene (DMBA) develop tumors much faster.

To define the role of TGF alpha in normal tissue function and in pathogenesis, transgenic mice have been generated bearing a fusion gene of the mouse metallothionein 1 promoter and human TGF alpha cDNA. The effects of TGF alpha overproduction are pleiotropic and tissue specific. The liver frequently contains multifocal, well-differentiated hepatocellular carcinomas that express enhanced levels of human TGF alpha RNA. The mammary gland exhibits impeded morphogenetic penetration of epithelial duct cells into the stromal fat pad. The pancreas shows progressive interstitial fibrosis and a florid acinoductular metaplasia. TGF alpha therefore plays an important role in cellular proliferation, organogenesis, and neoplastic transformation.

Mammary adenocarcinoma from c-myc expressing transplant

Another gene, c-myc, is also involved in mammary tumor development. Transgenic mice (non-virgin females) carrying c-myc or TGFalpha under the influence of the whey acidic protein (WAP-TGFalpha x WAP-c-myc) all develop tumors. This is an invasive adenocarcinoma developing from a transplanted nodule, 16 days post-transplant. The transplant is growing into adjacent skeletal muscle (nest of dark pink). The tumor is seen as nests and cords of invasive cells. Many of the nests are forming glands. The dark chromatin and cytoplasm of these cells are typical of the myc type tumor. The myc type is a dominant phenotype that masks the TGFalpha.

Metabolic Disease Models

Hypothyroidism

The rdw rat is the first known rat mutant with hereditary congenital hypothyroidism. There are mouse mutants (hyt/hyt and cog/cog) with similar conditions. This rat mutant arose in 1990 from a colony of inbred Wistar-Imamichi rats in Japan and has been maintained and studied as a possible model for human hypothyroidism and associated diseases (cretinism, Hashimoto's thyroiditis, and myxedema). The trait is autosomal recessive, and affected animals are infertile; therefore F1 x F1 mating is used to produce animals for study. Animals treated with thyroxine are restored to normal parameters. Rdw rats have retarded organ development and subnormal function, anemia, altered protein metabolism, altered liver function (failure to convert cholesterol to bile acids), and repressed gluconeogenesis. Many of these effects are secondary to the hypothesized reduction of GH synthesis by the pituitary, which is caused by decreased thyroxine (T4). {3722}

Lipid Storage Diseases

Feline Niemann-Pick disease type C

A litter of cats was donated to Colorado State University because some were affected with early onset of tremor with rapid progression to ataxia and death at 7-10 months of age. It was determined that the defect was an autosomal recessive neurovisceral lysosomal storage disorder in which cholesterol lipidosis results from defective intracellular transport of unesterified cholesterol. The onset, clinical signs and progression are very similar to a human disease, Niemann-Pick disease type C (types A and B are primary sphingomyelinase deficiencies). Histologically, cells contain foamy material which is substrate. Serum abnormalities all refer to hepatic fibrosis that occurs later in the disease. The definitive histologic criterion in humans (which also occurs in cats) is accumulation of unesterified cholesterol in cultured skin fibroblasts that stains positive with the fluorescent polyene antibiotic called filipin.{2763}

Animal Models of Human Disease