The independent evolution of two closely related satellite DNA elements in rats (Rattus).

We have identified and determined the sequence and organization of a new rat satellite DNA in Rattus rattus, the roof rat. This satellite DNA, which we call R. rattus satellite I', consists of tandem arrays of a 185 base pair (bp) repeat unit that we call a'. a' is 86% homologous to a 185 bp portion of the 370 bp repeat unit of the previously described rat satellite [Pech et al. (1979) Nucleic Acids Res. 7, 417-432] present in the common laboratory rat species, R. norvegicus. We can thereby distinguish two 185 bp portions of the satellite I 370 bp repeat unit: "a" (homologous to a') and "b". Satellite I has the structure (a,b)n, and satellite I' has the structure (a')n. Like a, a' is only about 60% homologous to b and fails to hybridize to b. Although R. norvegicus and R. rattus contain about the same total concentration of satellite sequences, R. norvegicus contains essentially only the a,b type (satellite I), whereas R. rattus contains a' type (satellite I') and lesser amounts of the a,b type (satellite I). The a,b type (satellite I) in R. rattus is very similar to that in R. norvegicus as judged both by hybridization and by the presence of all but one of the major restriction enzyme sites that characterize the R. norvegicus satellite I. In R. rattus the a' and a,b repeat units are not detectably present in the same tandem array. All of the sequence differences between a' (R. rattus) and a (R. norvegicus) can be accounted for by simple base substitutions, and the implication of this and other features of rat satellite DNA structure for satellite DNA evolution are discussed.     

Dating of divergences within the Rattus genus phylogeny using whole mitochondrial genomes

The timing and order of divergences within the genus Rattus have, to date, been quite speculative. In order to address these important issues we sequenced six new whole mitochondrial genomes from wild-caught specimens from four species, Rattus exulans, Rattus praetor, Rattus rattus and Rattus tanezumi. The only rat whole mitochondrial genomes available previously were all from Rattus norvegicus specimens. Our phylogenetic and dating analyses place the deepest divergence within Rattus at approximately 3.5 million years ago (Mya). This divergence separates the New Guinean endemic R. praetor lineage from the Asian lineages. Within the Asian/Island Southeast Asian clade R. norvegicus diverged earliest at approximately 2.9Mya. R. exulans and the ancestor of the sister species R. rattus and R. tanezumi subsequently diverged at approximately 2.2Mya, with R. rattus and R. tanezumi separating as recently as approximately 0.4Mya. Our results give both a better resolved species divergence order and diversification dates within Rattus than previous studies.     

Vocalizations of nine species of rat (Rattus; Muridae)

The sounds produced by seven species of Rattus native to Australia and the Black rat ( R. rattus ) and the Brown rat ( R. norvegicus ), were investigated in the laboratory. Both audible and ultrasonic sounds were recorded and the ontogeny of the different vocalizations investigated. All nine species had the same basic repertoire of seven more or less discrete calls. Some calls varied more between the different species than did others. Similarly there were species' differences in the ease with which some calls could be elicited. Two major continua were identified, one audible and one ultrasonic. An attempt was made to put the vocalizations recorded into an evolutionary perspective.     

Black rat (Rattus rattus) genomic variability characterized by chromosome painting

Black rats are of outstanding interest in parasitology and infective disease analysis. We used chromosome paints from both the mouse(Mus musculus) and the Norway rat(Rattus norvegicus) to characterize the genome of two Black rat subspecies from Italy. Both subspecies have two large metacentrics (n. 1, 4) not present in the Norway rat (2n = 42).Rattus rattus rattus has a diploid number of 2n = 38, whileRattus rattus frugivorous has two small metacentric “supernumerary” or B chromosomes for a diploid number of 2n = 38 + 2B. The 21 mouse paints gave 38 signals on theR. r. rattus karyotype and 39 signals in theR. r. frugivorous karyotype. The two metacentrics, not present inR. norvegicus, were hybridized by mouse 16/1/17 and mouse 4/10/15. These chromosomes are homologous to: RRA1 = RNO 5/7, and RRA4 = RNO 9/11 and not “4/7” and “11/12” as previously reported. Furthermore, the synteny of Chr 13 of theR. r. frugivorous withR. norvegicus Chr 16 and mouse Chrs 8/14 is not complete, because there is a small pericentromeric insertion of RNO Chr 18 (mouse Chr 18). If we consider only the two metacentrics, RRA1 and RRA4, the principal differences betweenR. norvegicus andR. rattus, then we can propose the derived synteny of 124 genes in the black rat. A comparison of the Z index between rats and mice shows an acceleration of genomic evolution among genus, species, and subspecies. The chromosomal differences betweenR. r. rattus xR. r. frugivorous suggest that they may be classified as different species because hybrids would produce 50% unbalanced gametes.     

八种大鼠染色体银染核仁组织者的比较研究

本文对我国大鼠属(Rattus)8种鼠类的银染核仁组织者(NORs)进行了比较研究,结果表明:8种大鼠银染核仁组织者(Ag-NORs)的数目和分布均存在一定的差异,它们的NORs都呈现比较显著的多态性,并观察到了Ag-NORs的联合现象和异形现象。此外,将其银染核型差异数量化,通过模糊聚类分析,得到8种大鼠的聚类分析分支图,并结合它们的地理分布等对其分类地位进行了讨论。     

Isolation and characterization of microsatellites in Rattus rattus

We isolated and characterized 10 microsatellite loci in the black rat Rattus rattus (Muridae, Rodentia), a widespread invasive species largely known to cause serious problems in agriculture and human health. Polymorphism was studied in two populations, one from Madagascar and one from Senegal. It ranged from three to 12 alleles in Madagascar, and from two to five alleles in Senegal. Together with the loci previously adapted from Rattus norvegicus, this set of markers should allow the conduct of thorough studies on the genetic structure of natural populations of R. rattus.     

Population distribution and zoonotic potential of gastrointestinal helminths of wild rats Rattus rattus and R. norvegicus from Jamaica

The population distribution and zoonotic potential of gastrointestinal helminths in a naturally infected population of wild rats (Rattus rattus and Rattus norvegicus) in Jamaica are described. One hundred and thirty (29.7%) of 437 rats captured in the study were infected: 104 (35%) of 297 R. rattus compared with 26 (18.6%) of 140 R. norvegicus. Nine species of gastrointestinal helminths were recovered: Raillietina sp. (0.2%), Trichuris sp. (0.2%), Rictularia sp. (0.7%), Syphacia obvelata (1.1%), Strongyloides ratti (1.4%), Hymenolepis diminuta (3.8%), Protospirura muricola (4.3%), Moniliformis moniliformis (11.2%), and Nippostrongylus brasiliensis (14.2%). In a logistic model, the single risk factor identified for both M. moniliformis and P. muricola was R. rattus, compared with R. norvegicus (OR = 8.369 and 9.714, respectively). In comparison, the risk factor predicted for infection with N. brasiliensis was the northeastern section of Jamaica (OR = 11.000) compared with western Jamaica. Rictularia sp. represents a new geographic distribution record for the Caribbean region. Hymenolepis diminuta, M. moniliformis, Raillietina sp., and Rictularia sp. are potentially zoonotic, but only human infection with H. diminuta has been previously reported in the Caribbean.     

Epizootiological and epidemiological study of hantavirus infection in Japan

Epizootiological surveys on hantavirus infections in rodents were carried out in various areas of Japan, including the four major islands of Hokkaido, Honshu, Shikoku, and Kyushu from 2000 to 2003. A total of 1,221 rodents and insectivores were captured. Seropositive animals were found in Apodemus (A.) speciosus (5/482, 1.0%), Rattus (R.) norvegicus (4/364, 1.1%), R. rattus (3/45, 6.7%), and Clethrionomys (C.) rufocanus (7/197, 3.6%). The partial S segment was amplified from one seropositive R. rattus captured at Hakodate. The nucleotide sequence showed 96% identity with the Seoul virus (SEOV) prototype strain SR-11. In addition, we conducted an epidemiological survey on human hantavirus infection in a high-risk population, the personnel of the Japan Ground Self-defense Force on Hokkaido. One out of 207 human blood samples was positive for anti-hantavirus antibody by IFA, ELISA, and WB analysis. The result of the serotype specific ELISA indicates that this individual acquired SEOV infection. This study indicates that A. speciosus, R. norvegicus, R. rattus, and C. rufocanus carry hantaviruses as the reservoir animals in Japan. Infected R. rattus and R. norvegicus in port areas could be the sources of human SEOV infection and a threat to travelers and individuals working in seaports.     

Comparative studies on release of enzymes from platelets during blood clotting in Rattus rattus flavitecus and Rattus norvegicus (author's transl)

Increase of lactate dehydrogenase (EC 1.1.1.28) and creatine kinase (EC 2.7.3.2) in serum and plasma level during blood clotting was compared in R. rattus flavitectus (black rat) and R. norvegicus (albino rat). Both the enzyme level increased by the release from platelets in process of clotting in rat as previously described (Emori T., Takahashi M. and Nagase S. (1978) Exp. Animals, 27, 167), but the change in black rat was very slight. Owing to search for the reason to prove the difference in this phenomenon, physiological and chemical properties of blood from both the animals were compared, and it was demonstrated that the content of plasma fibrinogen in black rat is higher than that in albino rat, while the platelet number contained in each ml of blood and the enzyme activities in each platelet are not different between them. The analysis of the membrane proteins from platelets of both the animals by SDS-polyacrylamide gel electrophoresis showed that the fractional value of glycoproteins was found to be different between them.     

Life history and pathogenesis of Gallegostrongylus australis (Nematoda: Angiostrongylidae) in muridae

Gallegostrongylus australis Spratt, Haycock & Walter, 2001 (Nematoda: Angiostrongylidae) developed in Deroceras panormitanum, Lehmannia nyctelia, L. flava and Milax gigates (Gastropoda). The first moult occurred at 18-19 days after infection (DAI) and the second moult at 28 DAI. Larvae were infective to experimental murid definitive hosts at 35 DAI. In experimentally infected Rattus fuscipes larvae moulted L3-4 at 3 DAI and L4-5 at 6-7 DAI. Patency in R.fuscipes, R. lutreolus, R. norvegicus and R. rattus occurred 27-64 DAI and duration varied from 7-392 days. Histopathological changes in the lungs of R. lutreolus and development of debilitating clinical signs, in contrast to R. fuscipes, suggests that the former host-parasite relationship may be the more recent one but other traits suggest the opposite. Patent infections were established in some wild R. rattus and some laboratory R. norvegicus but not in wild M. domesticus, laboratory M. musculus, rabbit, Oryctolagus cuniculus, and marsupial bandicoot, Isoodon macrourus.     

Prevalence and genetic properties of Salmonella enterica serovar typhimurium definitive phage type 104 isolated from Rattus norvegicus and Rattus rattus house rats in Yokohama City, Japan

Salmonella enterica serovar Typhimurium was isolated from the intestinal contents of Rattus rattus and Rattus norvegicus house rats captured at two buildings, designated buildings J and YS, in Yokohama City, Japan. From October 1997 to September 1998, 52 of 339 (15.3%) house rats were found to carry Salmonella serovar Typhimurium definitive phage type 104 (DT104). In building J, 26 of 161 (16.1%) house rats carried DT104 over the 1-year study period, compared to 26 of 178 (14.6%) rats in building YS. The isolation rates of DT104 from R. rattus and R. norvegicus were similar in the two buildings. Most DT104 strains from building J (24 of 26) showed resistance to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline and contained both the 1.0- and 1.2-kbp integrons, carrying genes pse1, pasppflo-like, aadA2, sulI, and tet(G). All DT104 strains from building YS were resistant to ampicillin and sulfisoxazole, and had the 1.2-kbp integron carrying pse1 and sulI. Cluster analysis of pulsed-field gel electrophoresis patterns of BlnI-digested DT104 DNAs showed that 22 of 26 DT104 strains from building J and 24 of 26 strains from building YS could be grouped into separate clusters each specific for the building origin. These results indicated that DT104 strains were prevalent in house rat colonies in each building and suggest that house rats may play an important role in the epidemiology of DT104.     

Similarity of giemsa banding patterns of chromosomes in several species of the Genus Rattus

Giemsa banding patterns of chromosomes in seven Rattus species were compared. Four species (R. rattus tanezumi, R. norvegicus, R. exulans and R. muelleri) had all 2n=42 and their karyotypes and banding patterns were similar, although slight differences were observed. Another subspecies (R. rattus rattus) and two other species (R. fuscipes and R. conatus) had fewer chromosomes than the above species by having large biarmed chromosomes developed probably by Robertsonian fusion. The origin of the arms of biarmed chromosomes was recognized by their characteristic banding patterns. The remaining species, R. sabanus, had a karyotype markedly different from the other species by having two small metacentrics although in the others their number was 7. Banding patterns of the chromosomes in this species, however, were also very similar to those of the other, and therefore the 7 small metacentrics seemed to have originated by pericentric inversion of small acrocentrics.Contribution No. 912 from the National Institute of Genetics, Japan. Supported by a grant-in-aid from the Ministry of Education of Japan, Nos. 90183, 90375 and 744002.     

Variation of C-bands in the chromosomes of several subspecies of Rattus rattus

All subspecies of black rats (Rattus rattus) used in the present study are characterized by having large and clear C-bands at the centromeric region. The appearance of the bands, however, is different in the subspecies. Chromosome pair No. 1 in Asian type black rats (2n=42), which are characterized by an acrocentric and subtelocentric polymorphism, showed C-band polymorphism. In Phillipine rats (R. rattus mindanensis) the pair was subtelocentric with C-bands, but in Malayan black rats (R. rattus diardii) it was usually acrocentric with C-bands. In Hong-Kong (R. rattus flavipectus) and Japanese black rats (R. rattus tanezumi) it was polymorphic with respect to the presence of acrocentrics with C-bands or subtelocentrics without C-bands. The other chromosomes pairs showed clear C-bands, but in Hong-Kong black rats the pairs No. 2 and 5 were polymorphic with and without C-bands. In Japanese black rats, 6 chromosome pairs (No. 3, 4, 7, 9, 11 and 13) were polymorphic in regard to presence and absence of C-bands, but the other 5 chromosome pairs (No. 2, 5, 6, 8 and 10) showed always absence of C-bands. Only pair No. 12 usually showed C-bands. C-bands in small metacentric pairs (No. 14 to 20) in Asian type black rats generally large in size, but those in the Oceanian (2n=38) and Ceylon type black rats (2n=40) were small. In the hybrids between Asian and Oceanian type rats, heteromorphic C-bands, one large and the other small, were observed. Based on the consideration of karyotype evolution in the black rats, the C-band is suggested to have a tendency toward the diminution as far as the related species are concerned.     

The spread of sequence variants in Rattus satellite DNAs

The genus Rattus has two related families of satellite DNA: Satellite I consists of tandem arrays of a 370 base pair repeat unit which is a dimer of two 185 base pair portions (a, b) which are about 60% homologous. Satellite I' consists of tandem arrays of a 185 base pair repeat unit (a') which is about 85% homologous to a and 60% homologous to b. R. norvegicus contains only satellite I but R. rattus contains both satellites I and I'. We examined certain aspects of satellite DNA evolution by comparing the spacing at which variant repeat units of each satellite have spread among non-variant repeat units in these two species. With but one exception, in R. rattus, 15 different variant repeat units have spread among non-variant repeat units of satellite I, with a spacing equal to the length of the (a,b) dimer. Similarly, fourteen different variant repeat units of the monomeric satellite I' have mixed among non-variant repeat units with a spacing equal to the length of the (a') monomer. These results suggest that a mechanism involving homologous interaction among satellite sequences could account for the spread of variant family members. We also found that a sequence variant present in certain portions of the dimeric repeat unit of satellite I is more efficiently amplified (or less efficiently corrected) than variants occurring in other regions. This was not true for the monomeric repeat unit of satellite I'.     

Seasonal studies on commensal rats and their ectoparasites in a rural area of Egypt: the relationship of ectoparasites to the species, locality, and relative abundance of the host.

The present study was carried out in 3 villages, namely Kafr Ayoub Soliman, Kafr Ibrahim El-Aidi, and El-Sa'adat, Sharqiya Governorate, Egypt. A total of 519 rats was collected from the 3 study sites: 46.6% Rattus rattus, and 53.4% Rattus norvegicus. A total of 20,643 ectoparasites was recovered from R. rattus: 33.3% mites, 33.8% fleas, and 32.9% lice. From R. norvegicus a total of 40,997 ectoparasites was recovered: 28.9% mites, 31% fleas, and 40.1% lice. Three common mite species were recovered from both rat hosts, i.e., Ornithonyssus bacoti, Radfordia ensifera, and Laelaps nuttalli. Three common flea species were also recovered from both rat hosts, i.e., Echidnophaga gallinacea, Leptopsylla segnis, and Xenopsylla cheopis. Polyplax spinulosa was the only dominant louse species that infested both rat hosts. Rats did not show a definite breeding season, and the seasonal rat indices were generally low in different study sites. There were no significant differences between the prevalence of each of mites, fleas, and lice in both rat species. The total general indices of mites and fleas, on the other hand, was significantly higher in R. norvegicus. The general index of X. cheopis was high and ranged between 5.9 in R. rattus and 14.5 in R. norvegicus. Season-related changes were observed in the general index of each of L. segnis infesting both rat species and R. ensifera and O. bacoti infesting R. norvegicus. The prevalence and general indices of some ectoparasites showed differences related to the locality of their rat hosts. Seasonal changes in the general indices of some ectoparasites paralleled seasonal changes in the relative abundance of their rat hosts.     

A mathematical epidemiological model of gram-negative Bartonella bacteria: does differential ectoparasite load fully explain the differences in infection prevalence of Rattus rattus and Rattus norvegicus?

We postulate that the large difference in infection prevalence, 24% versus 5%, in R. norvegicus and R. rattus, respectively, between these two co-occurring host species may be due to differences in ectoparasite and potential vector infestation rates. A compartmental model, representative of an infectious system containing these two Rattus species and two ectoparasite vectors, was constructed and the coefficients of the forces of infection determined mathematically. The maximum difference obtained by the model in the prevalence of Bartonella in the two Rattus species amounts to 4.6%, compared to the observed mean difference of 19%. Results suggest the observed higher Bartonella infection prevalence in Rattus norvegicus compared to Rattus rattus, cannot be explained solely by higher ectoparasite load. The model also highlights the need for more detailed biological research on Bartonella infections in Rattus and the importance of the flea vector in the spread of this disease.     

Detection of Streptobacillus spp. in feral rats by specific polymerase chain reaction

Streptobacillus moniliformis is an etiological agent of rat-bite fever and Haverhill fever in human infection. As the currently available methods for identifying the causative bacteria are not satisfactory, we attempted to establish them by PCR using newly designed primers for the 16S rRNA gene of S. moniliformis. We then determined the prevalence of Streptobacillus spp. in two species of feral rats that inhabit an urban region in Japan, because information on the prevalence of the bacteria in feral rats is obscure. The use of PCR with newly designed primers showed that an extremely high proportion of R. norvegicus harbored the bacteria (61/66, 92%), whereas the prevalence was only 58% in R. rattus (30/52). The nucleotide sequence analysis of the 16S rRNA gene of Streptobacillus spp. isolated from oral swabs of feral rats showed at least two different types of bacteria among isolates from R. norvegicus and R. rattus.     

Occurrence of Yersinia enterocolitica in house rats.

From July 1976 to May 1977, 270 rats (259 Rattus norvegicus and R. rattus) in Sapporo were examined for the presence of Yersinia enterocolitica in house rats. The organism was isolated in 55 rats (54 R. norvegicus and 1 R. rattus). Isolated strains were determined as O group (O)3, biovar 4; O4, biovar 1; O5A, biovar 1; and O6, biovar 1. The isolation of O3, biovar 4 strains from R. norvegicus is the first in the world, as far as we know. The organism was isolated from the duodenum in 3 rats, the jejunum in 7 rats, the ileum in 8 rats, the cecum in 34 rats, the colon in 23 rats, the rectum in 16 rats, and the mesenteric lymph nodes in 5 rats. The organism was not isolated from liver, spleen, and kidneys. Isolation of the organism from the mesenteric lymph nodes was made in 1 out of 2 O3-positive rats, 1 out of 7 O5A-positive ones, and 3 out of 29 O6-positive ones. A high agglutinin titer was recorded in the two O3-positive rats and in one O6-positive animal.     

Metabolism of fluoroacetate in the skink (Tiliqua rugosa) and the rat (Rattus norvegicus)

Administration of 100 mg sodium fluoroacetate (compound 1080) per kilogram body weight to T. rugosa resulted in a 3.4-fold increase in plasma citrate levels 48 h after dosing while administration of 3 mg sodium fluoroacetate per kilogram body weight to R. norvegicus produced a fivefold increase in plasma citrate levels within 4 h. Administration of 300 mg sodium fluoroacetate per kilogram body weight reduced the oxygen consumption of the skink by between 2.5 and 11% while in the rat, 2 mg sodium fluoroacetate per kilogram body weight reduced oxygen consumption by between 28 and 57%. Aconitate hydratase activity in extracts of liver acetone powders from T. rugosa was less inhibited by (-)erythrofluorocitrate (Ki: 0.065 mM) than that in extracts derived from R. norvegicus (Ki: 0.026 mM). The rate of defluorination of fluoroacetate in erythrocytes and in extracts of liver acetone powders of T. rugosa was 8- and 4.5-fold greater, respectively, than that found in similar preparations from R. norvegicus. A rapid rate of defluorination together with a low reliance on aerobic respiration favoured detoxification of fluoroacetate in T. rugosa rather than its conversion into fluorocitrate. Though defluorination in this species helped to minimize the immediate effects of fluoroacetate on aerobic respiration, it resulted in rapid depletion of liver glutathione levels.