Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant disorder characterized by the extracellular deposition of amyloid fibrils and by prominent peripheral and autonomic nerve involvement. The first symptoms usually appear in individuals between 20 and 45 years of age, and the disease is progressive and fatal in about 10 to 20 years. The amyloid protein is mainly composed of transthyretin (TTR; a protein formerly known as prealbumin) with a substitution of methionine for valine at position 30 (hMet30) in the FAP type I, as reported in Japan, Sweden, and Portugal. These amyloid deposits also contain a small but significant amount of SAP. The human TTR gene has been cloned and well characterized at molecular level. Using this gene as a probe, it is now possible to carry out DNA diagnosis of FAP. So far examined, all the Japanese FAP patients are either heterozygotes or homozygotes, carrying one or two mutant gene. Thus, it is clear that the main cause of this disease is the presence of the mutant TTR gene. However, many questions in relation to the disease process remain to be elucidated. To elucidate the pathological process of this disease development, we have produced transgenic mouse. The genes introduced are hMet30 gene carrying either its own promoter spanning either 0.6 kb or 6.0 kb (0.6-hMet30 and 6.0-hMet30) or mouse metallothionein promoter (Mt-hMet30), and human serum amyloid P component (hSAP) gene. From analyses of these transgenic mice we confirmed the amyloid deposition and its progression with aging in transgenic mice. The presence of mouse SAP (mSAP) together with hMet30 was shown by immunohistochemical analyses suggesting that the mSAP plays the same pathological role in the process of amyloid deposition as hSAP. Then, we found that the earliest age of amyloid deposition was at around 6 months. This result clearly suggests that the amyloid deposition itself starts later in life, and that several factors can affect this initiation of amyloid deposition. Other findings obtained from analyses on single or double (hMet30 × hSAP) transgenic mice are as follows: (1) the tetramers composed of mostly hMet30 are important for deposition as amyloid due to physico-chemical property of this molecule, (2) hSAP does not affect the initiation, progression and tissue distribution of amyloid deposition, (3) microenvironment in each tissue, such as blood flow and loose tissue structure, can affect greatly the amount of amyloid deposition, (4) purely environmental factor, for example living condition, can affect the amyloid deposition.

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The tremor rat is a mutant that exhibits absence-like seizure and spongiform degeneration in the central nervous system (CNS), as well as body tremor, curled whisker, waved hair, and dysgenesis of gonads in both sexes. The causative gene, tremor (tm) , has been mapped on rat chromosome 10q24 in the previous genetic and cytogenetic study. Here we describe the identification of the causative gene by means of the positional cloning approach as a review [Kitada et al, J. Neurochem. 74, 2512-2519 (2000) ] . To effectively identify the causative gene, a “genome-shift approach” between rats and mice was carried out by reciprocal use of microsatellite markers applicable to both species. As a result, a genomic deletion was found within the tm critical region. Sequencing of a constructed mouse BAC contig corresponding the deleted region uncovered three genes in the region: olfactory receptor gene, vanilloid receptor subtype I gene, and aspartoacylase gene. Olfactory receptors for odor molecules are exclusively expressed in olfactory sensory neuron, and vanilloid receptors characterized by their sensitivity to capsaicin are predominantly expressed in trigeminal and dorsal root ganglia. Although these genes were located in the deleted region in the tremor rat genome, it is unlikely that the lack of sensory receptors causes absence-like seizure and spongiform degeneration. On the other hand, aspartoacylase is an enzyme that hydrolyzes NAA into aspartate and acetic acid; its deficiency is known as Canavan disease. This disease is characterized by spongy degeneration in the white matter of the CNS, as seen in the tremor rat. Indeed, no enzyme activity was detected in the brain, and the concentration of its substrate NAA was, accordingly, increased in various regions in the CNS of the mutant rat, in correlation with the severity of the vacuole formation. Therefore, the tremor rat may be regarded as a suitable animal model of human Canavan disease. Interestingly, direct injection of NAA into normal rat cerebroventricle induced 4-10 Hz polyspikes or spike-wave-like complexes in cortical and hippocampal electroencephalogram (EEG), concomitantly with behavior characterized by sudden immobility and staring. These results suggested that accumulated NAA in the CNS would induce neuroexcitation and neurodegeneration directly or indirectly. Recently, a knock-out mouse for aspartoacylase gene was established, and it was reported that the mice develop both of spongiform degeneration and clonic seizure. Based on these results, we concluded that the accumulated NAA in the brain causes both of characteristic seizures and spongiform degeneration in the CNS.

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The strain of FGS/Nga mouse was reported to develop proteinuria and progressive glomerulosclerosis. It was established from cross between CBA/Nga and RFM/Nga mice in the Laboratory of Animal Genetics, Faculty of Agriculture, Nagoya University. We studied clinical parameters and the renal pathology of the strain. Proteinuria began to appear at the age of 2 months and increased thereafter. No hematuria was observed throughout the experiment. The level of serum creatinine increased at 6 months of age and some mice showed oliguria after 10 months.
By light microscopy, mild glomerular proliferation was observed within three months. Focal segmental glomerulosclerosis was observed 3 months after birth and the sclerotic changes increased by 6 months. The lesion progressed to the glomerular obsolescence in a year. Electron microscopic study revealed electron dense deposits (DD) in the mesangial area. The splitting of glomerular basement membrane was also observed. Studies using immunofluorescent microscopy revealed the deposition of IgG, IgA, IgM and C3 in the mesangial area. These data suggest that this strain of mouse provides us an useful tool (animal model) for studying mechanisms of human chronic glomerulopathy.

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Nihon rat is a novel rat model that was recently discovered from a colony of Sprague-Dawley strain to develop renal cancers in a hereditary manner. It has already been reported in this model that renal tubular adenomas were developed at 16 weeks of age. A peculiar feature is seen in the cell type consisting of these lesions where the clear cells predominate as found in human renal cancers. Southern blot, northern blot and SSCP analyses on TSC1, TSC2, VHL and c-Met, all of which are incriminated in hereditary renal cancers, revealed no mutation present in Nihon rats. When the kidneys were microscopically carefully examined from Week 0 age to characterize the onset of the renal lesions of Nihon rats, atypical renal tubules considered to be precancerous changes were present as early as 3 weeks of age, and the adenomas were found at 8 weeks of age. Transplacental administration of N-Ethyl-N-Nitrosourea to neonates resulted in accelerating the onset and increasing the number of tumors per rat. Thus, Nihon rat in which renal tumors as well as precancerous lesions are developed from very early age will serve as a useful rat model for research on renal cancers.

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G_M1-gangliosidosis is an inherited neurodegenerative disease caused by a deficiency of lysosomal acid β-galactosidase that catalyzes the terminal nonreducing β-galactosidic residue from a variety of glycoconjugates including ganglioside G_M1. We recently generated β-galactosidase knockout (β-Gal KO) mice and characterized them as an authentic model for G_M1-gangliosidosis. The β-Gal KO mice present progressive neurological manifestations, widespread cerebral lesions and massive storage of ganglioside G_M1 in brains. In this study, we introduced the human β-Gal transgene into β-Gal KO mice in order to rescue their G_M1-gangliosidosis phenotypes. The transgenic mice carrying the β-actin promoter/human β-Gal cDNA transgene and overexpressing human β-Gal were mated with the β-Gal KO mice to obtain F1 progeny. By intercrossing F1 mice, we obtained β-Gal KO mice with the human β-Gal transgene. These mice were phenotypically normal and expressed human β-galactosidase at high levels in all tissues examined. They showed no abnormalities in the pathological findings. In addition, we could not detect the excess storage of ganglioside G_M1 and asialo G_M1 in their brains. These results clearly demonstrate that the human β-galactosidase transgene is expressed in the β-Gal KO mice and the human enzyme can rescue the mouse G_M1-gangliosidosis.

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The present study examined the morphological differences between the homozygous db+/db+ and the heterozygous db+/+m mice in pancreas and muscle tissue.
Method: Every mouse was six weeks old and female. Pancreas tissue was stained by the aldehyde-fuchsin method of Gomori. The area of Langerhans islet and the number of beta cells secreting the insulin were measured. Muscle tissue (gastrocnemius) was stained by the succinic dehydrogenase method (SDH method) . The numbers and area of red and white muscle fiber were measured.
Result: Neither did the area of Langerhans islet nor the number of beta cells in Langerhans islet has a significant difference. The numbers of beta cells in Langerhans islet (/mm²) were significantly higher in the db+/+m mice than those of the db+/db+ mice (p<0.05) . The ratio of area and the number in red muscle fibers were significant high in db+/db+ mice compared with db+/+m mice (p<0.05) . There was no significant difference between mice respecting the size of red muscle fibers, however, the size of white muscle fiber was significantly larger in the db+/+m mice than that of the db+/db+ mice (p<0.05) .
Discussion: In order to select animals that are genetically abnormal for control group, we should consider the morphological differences.

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