Satoshi Nakanishi

A set of highly informative rat simple sequence length polymorphism (SSLP) markers and genetically defined rat strains

BackgroundThe National Bio Resource Project for the Rat in Japan (NBRP-Rat) is focusing on collecting, preserving and distributing various rat strains, including spontaneous mutant, transgenic, congenic, and recombinant inbred (RI) strains. To evaluate their value as models of human diseases, we are characterizing them using 109 phenotypic parameters, such as clinical measurements, internal anatomy, metabolic parameters, and behavioral tests, as part of the Rat Phenome Project. Here, we report on a set of 357 simple sequence length polymorphism (SSLP) markers and 122 rat strains, which were genotyped by the marker set.ResultsThe SSLP markers were selected according to their distribution patterns throughout the whole rat genome with an average spacing of 7.59 Mb. The average number of informative markers between all possible pairs of strains was 259 (72.5% of 357 markers), showing their high degree of polymorphism. From the genetic profile of these rat inbred strains, we constructed a rat family tree to clarify their genetic background.ConclusionThese highly informative SSLP markers as well as genetically and phenotypically defined rat strains are useful for designing experiments for quantitative trait loci (QTL) analysis and to choose strategies for developing new genetic resources. The data and resources are freely available at the NBRP-Rat web site [1].

Evaluation of the general suitability of the rat for the micronucleus assay: the effect of cyclophosphamide in 14 strains

To evaluate the general suitability of the rat for the micronucleus assay, we conducted the assay in males of 14 different strains, 13 inbred (ACI, BN, BUF, COP, DRH, F344, IS, LEW, RCS, SHR, WAG, WKYO, WTC) and 1 outbred (SD), using cyclophosphamide as the test chemical. Cyclophosphamide at 0 (vehicle), 5, 10, or 20mg/kg per day was administered orally twice, 24h apart, to five rats per dosage group. Bone marrow and peripheral blood were collected 24h after the second treatment. All 14 strains showed a positive response to cyclophosphamide, with slight differences in sensitivity. We concluded that the rat is suitable for the micronucleus assay regardless of strain.

Origins of Albino and Hooded Rats: Implications from Molecular Genetic Analysis across Modern Laboratory Rat Strains

Albino and hooded (or piebald) rats are one of the most frequently used laboratory animals for the past 150 years. Despite this fact, the origin of the albino mutation as well as the genetic basis of the hooded phenotype remained unclear. Recently, the albino mutation has been identified as the Arg299His missense mutation in the Tyrosinase gene and the hooded (H) locus has been mapped to the ∼460-kb region in which only the Kit gene exists. Here, we surveyed 172 laboratory rat strains for the albino mutation and the hooded (h) mutation that we identified by positional cloning approach to investigate possible genetic roots and relationships of albino and hooded rats. All of 117 existing laboratory albino rats shared the same albino missense mutation, indicating they had only one single ancestor. Genetic fine mapping followed by de novo sequencing of BAC inserts covering the H locus revealed that an endogenous retrovirus (ERV) element was inserted into the first intron of the Kit gene where the hooded allele maps. A solitary long terminal repeat (LTR) was found at the same position to the ERV insertion in another allele of the H locus, which causes the so called Irish (hi) phenotype. The ERV and the solitary LTR insertions were completely associated with the hooded and Irish coat patterns, respectively, across all colored rat strains examined. Interestingly, all 117 albino rat strains shared the ERV insertion without any exception, which strongly suggests that the albino mutation had originally occurred in hooded rats.

A novel middle-wavelength opsin (M-opsin) null-mutation in the retinal cone dysfunction rat

The disease-causing gene which underlies a naturally occurring X-linked mutant cone dysfunction Sprague-Dawley rat model was investigated. Full-field electroretinogram (ERG) and simple sequence length polymorphism analyses were applied to 441-second filial generation rats that were derived from crossing a mutant rat and a Brown-Norway rat. After identifying a mutation mapping within the telomeric region of chromosome X, a candidate gene related to retinal cone function in this region was further screened using real-time PCR, immunohistochemistry and histological methods. The results showed that a G-to-T substitution at the splice acceptor site of intron 4 was present in the opsin 1, medium-wave sensitive (Opn1mw) gene, thereby causing down-regulated transcription and translation. These changes were consistent with abnormities seen in the ERG response. However, there was no significant histological change in the mutant rat retina. Therefore, we infer from this that the causative gene for the mutation is Opn1mw and consequently term this a middle-wavelength opsin cone dysfunction (MCD) rat model. The deficiency in vision of the MCD rat is similar to the color vision defects that occur in humans with a color vision defect but without recessive retinal degeneration. This rat model may be useful for understanding the mechanism that is responsible for color vision and for developing clinical therapies for several retinal dystrophies caused by cone opsin deficiencies.

Functional polymorphisms in inbred rat strains and their allele frequencies in commercially available outbred stocks

Polymorphisms that have been proven to influence gene functions are called functional polymorphisms. It is significant to know the distribution of functional polymorphisms in the rat, widely used in animal models for human diseases. In this study, we assessed 16 functional polymorphisms consisting of 3 coat color and 13 disease-associated genes in 136 rat strains, as a part of the genetic profiling program of the National Bio Resource Project for the Rat (NBRP-Rat). Polymorphisms of Cdkn1a, Fcgr3, Grp10, Lss, and Fdft1, which were proven to function in prostate tumorigenesis, glomerulonephritis, hyperphagia, and cholesterol biosynthesis, were shared among various inbred strains. These findings indicated that most rat strains harbored the disease-associated alleles and suggested that many unidentified functional polymorphisms might exist in inbred rat strains. The functional polymorphisms shared in inbred strains were also observed within outbred stocks available commercially. Therefore, this implies that experimental plans based on either rat inbred strains or outbred stocks need to be carefully designed with a full understanding of the genetic characteristics of the animals. To select the most suitable strains for experiments, the NBRP-Rat will periodically improve and update the genetic profiles of rat strains.

Slc:Wistar outbred rats show close genetic similarity with F344 inbred rats

Although Slc:Wistar rats are used widely in biomedical research as outbred rats, close similarities in growth curves, survival rates, and immunological and biochemical phenotypes have been reported between Slc:Wistar and F344 inbred rats. We reported previously that nine genetic variations that were fixed in Slc:Wistar rats had identical genotypes in F344 rats. Here, we examined the genetic characteristics of Slc:Wistar rats using 27 simple-sequence length polymorphism (SSLP) markers and compared them with other Wistar stocks available in Japan and with some F344 strains. Among 27 SSLP loci, 23 (85%) were fixed in the Slc:Wistar rats, which was the highest among the other Wistar stocks. The 23 fixed loci shared identical genotypes with corresponding loci in F344 rats. Further, the predominant allele types in the unfixed loci had allele frequencies as high as 80%, and these alleles were identical in the F344 rats. When the nine genetic variations reported previously are added, a total of 32 (89%) out of the 36 loci examined were fixed and identical in the Slc:Wistar and F344 rat genomes. These findings indicate the low genetic variation in Slc:Wistar rats and the high genetic similarity between the Slc:Wistar and F344 inbred rats. This study demonstrates the importance of characterizing outbred rats and the need to pay ample attention to the genetic characteristics the Slc:Wistar rats for their proper use.

Rat polyomavirus 2 infection in a colony of X-linked severe combined immunodeficiency rats in Japan

Polyomaviruses (PyVs) infect a wide range of animals and provoke wasting diseases, particularly in immunosuppressed hosts. Recently, a novel Rattus norvegicus polyomavirus 2 (RatPyV2) has been identified in a colony of X-linked severe combined immunodeficiency (X-SCID) rats in the United States. Here, we describe the first report of the RatPyV2 infection in an X-SCID rat colony in Japan. The affected rats exhibited adult-onset wasting. Histologically, we observed large basophilic intranuclear inclusion bodies within the hyperplastic or dysplastic epithelial cells in the salivary glands, Harderian glands, extraorbital lacrimal glands, and in respiratory and reproductive tissues. Among these organs, the parotid salivary, Harderian, and extraorbital lacrimal glands were most obviously affected. In particular, the parotid salivary glands were the most severely and diffusely affected and atrophic lesions were prominent even at 1 month of age, which suggested that the parotid salivary glands would be highly susceptible to RatPyV2 in X-SCID rats. RatPyV2 inclusion bodies were also detected in the tail of the epididymis and deferent duct. Such reproductive lesions developed significantly in the later stage of breeding age, and therefore may be associated with the reduced fecundity observed in the infected X-SCID rats. We also established a simple, rapid, and non-invasive diagnostic method based on the Amp-FTA method, using buccal swabs for the detection of RatPyV2 in immunodeficient rats. Our findings contribute to the early detection and diagnosis of RatPyV2 infections.

Genetic profiling of two phenotypically distinct outbred rats derived from a colony of the Zucker fatty rats maintained at Tokyo Medical University

The Zucker fatty (ZF) rat is an outbred rat and a well-known model of obesity without diabetes, harboring a missense mutation (fatty, abbreviated as fa) in the leptin receptor gene (Lepr). Slc:Zucker (Slc:ZF) outbred rats exhibit obesity while Hos:ZFDM-Leprfa (Hos:ZFDM) outbred rats exhibit obesity and type 2 diabetes. Both outbred rats have been derived from an outbred ZF rat colony maintained at Tokyo Medical University. So far, genetic profiles of these outbred rats remain unknown. Here, we applied a simple genotyping method using Ampdirect reagents and FTA cards (Amp-FTA) in combination with simple sequence length polymorphisms (SSLP) markers to determine genetic profiles of Slc:ZF and Hos:ZFDM rats. Among 27 SSLP marker loci, 24 loci (89%) were fixed for specific allele at each locus in Slc:ZF rats and 26 loci (96%) were fixed in Hos:ZFDM rats, respectively. This indicates the low genetic heterogeneity in both colonies of outbred rats. Nine loci (33%) showed different alleles between the two outbred rats, suggesting considerably different genetic profiles between the two outbred rats in spite of the same origin. Additional analysis using 72 SSLP markers further supported these results and clarified the profiles in detail. This study revealed that genetic profiles of the Slc:ZF and Hos:ZFDM outbred rats are different for about 30% of the SSLP marker loci, which is the underlying basis for the phenotypic difference between the two outbred rats.