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PubMed2001

Cytochrome b sequences reveal Acomys minous (Rodentia, Muridae) paraphyly and answer the question about the ancestral karyotype of Acomys dimidiatus.

Sequences of the cytochrome b (cyt b) mitochondrial gene show that the spiny mouse Acomys from Crete, known as the endemic species A. minous, is composed of two distinct maternal lineages ("A" and "B"). Group "A" sequences cluster with A. nesiotes (Cyprus) and group "B" sequences cluster with A. cilicicus (Turkey), which is evidence of paraphyly of A. minous in regard to these two species. From cyt b sequences, the three taxa are very closely related to A. cahirinus (Egypt): the maximum divergence found among these sequences is 1.6%, which is equivalent to the intraspecific diversity observed in other Acomys species. Paleozoology evidenced that man unintentionally introduced Acomys into Crete and Cyprus during antiquity. The divergence time between Acomys cyt b sequences found in Crete was estimated at 0.4 Myr, which means that the diversity observed did not appear after the introduction but reflects a much more ancient polymorphism. Cytochrome b phylogeny and cytogenetic data together comprise evidence that, within the species A. dimidiatus (Saudi Arabia, Israel, Egypt), it is the karyotypic form with 36 chromosomes that derives from the form with 38 chromosomes, due to a single acrocentric fusion.

Animals↗
PubMed2001

Molecular phylogeny of the genus Oryzomys (Rodentia: Sigmodontinae) based on cytochrome b DNA sequences.

The genus Oryzomys comprises 40 species arranged in several species groups. To test the monophyly of three Oryzomys species groups ("capito," nitidus, and subflavus), we analyzed, by distance, parsimony, and maximum-likelihood (ML), 801 bp of the mitochondrial gene cytochrome b. Our results did not sustain the monophyly of Oryzomys nor of the nitidus and subflavus species groups. Within the "capito" species group, O. perenensis appeared as a valid species, as a sister branch of the clade formed by O. megacephalus and O. laticeps. Within the nitidius species group, only the association between O. nitidus and O. lamia was well supported. The subflavus species group split into two clades: one with O. subflavus karyomorphotypes and another grouping O. angouya with species of different genera in the parsimony, distance, and ML trees.

Animals↗
PubMed1989

Inter- and intra-individual chromosome variability in Thamnomys (Grammomys) gazellae (Rodentia, Muridae) B-chromosomes and structural heteromorphisms.

The present paper reports intra- and inter-individual variability related to the occurrence of numerous B-chromosomes in Thamnomys (Grammomys) gazellae, a species of African Climber rat belonging to the 'dolichurus' group. The frequency of B-chromosomes in somatic and spermatogonial metaphases is investigated, together with their behaviour during meiosis. Moreover, G-banding makes it possible to identify a structural polymorphism resulting from a pericentric inversion in a large chromosome (no. 6). The distribution of the constitutive heterochromatin has been assessed by C-banding. The nucleolus organizer regions (NOR's) were located by means of silver staining in four chromosomal pairs (nos. 1, 2, 4, and 6). The karyotype of T. (G.) gazellae is compared with that of other taxa of the dolichurus group, particularly the Somaliland population which also exhibits the occurrence of B-chromosomes. The origin and significance of B-chromosomes is discussed.

Animals↗
PubMed1990

Synergistic action of white spotting genes in the Syrian hamster (Rodentia, Cricetidae).

The phenotypic interaction of three mutant genes Ba, Ds and Wh are quantitatively analysed for proportion of white areas in the coat. Each of the genes individually induces a characteristic amount of white spotting which is synergistically enhanced in combination. So much so, that the genotypes Ba+Ds+Wh+ has an almost or completely white coat.

Analysis of Variance↗
PubMed1988

Evidence for eight tandem and five centric fusions in the evolution of the karyotype of Aethomys namaquensis A. Smith (Rodentia: Muridae).

G- and C-banded chromosomes of Aethomys namaquensis (2n = 24), A. chrysophilus (2n = 44), and Praomys coucha (2n = 36) are compared and contrasted with published material on Australian Muridae and North American Sigmodontidae. Direction and types of chromosomal rearrangements are established using cladistic methodology. An acrocentric morphology for chromosomes 5, 14, 15 and 20 (numbering system from Peromyscus) are proposed as primitive for the common ancestor of the Muridae and Sigmodontidae rodent lineages. Reduced diploid number of Aethomys namaquensis is derived by eight tandem and five centric fusions since divergence from the common ancestor with A. chrysophilus. The two species of Aethomys share one derived metacentric chromosome that distinguishes them from Praomys. Praomys has unique chromosomes which can be derived from the proposed primitive condition by five centric fusions and five pericentric inversions. It is concluded that karyotypic orthoselection for tandem and centric fusions is best explained by cellular or biochemical mechanisms rather than variation in population characteristics.

Animals↗
PubMed1977

Polymorphism of the X-chromosome, Y-chromosome and autosomes in the Australian hopping mice, Notomys alexis, N. cervinus and N. fuscus (rodentia, muridae).

All three species of Notomys so far studied possess a diploid number of 48. Many elements in the karyotype of N. alexis are polymorphic due to variation in heterochromatin, but the variation is most marked in autosomal pair 1, which occurs in at least four forms, the X-chromosome, which occurs in three forms, and the Y-chromosome which occurs in many forms. N. cervinus is unique in the genus in possessing an entirely biarmed karyotype due mainly to the addition of heterochromatic short arms. The X-chromosome of N. cervinus occurs in three forms and the Y-chromosome in two forms. The karyotype of N. fuscus is mainly telocentric although two autosomal pairs are polymorphic due to pericentric inversions. The X- and Y-chromosomes both occur in two forms in N. fuscus. Chromosome measurements and C-banding show that most of the variation in the size and morphology of the sex-pair both within and between species is due to variation in constitutive heterochromatin.

Animals↗
PubMed1984

Characterisation of a very complex constitutive heterochromatin in two Gerbillus species (Rodentia).

A large amount of heterochromatin is observed in two species of the genus Gerbillus, G. nigeriae and G. hesperinus. The C-band material represents about one-half of the total karyotype length in the former species, and about one-third in the latter. Several banding techniques and various 5-bromodeoxyuridine (BrdU) treatments were used to characterise these heterochromatic segments. After applying the R-banding technique, three different staining responses of the heterochromatin can be distinguished. In G. nigeriae, strongly stained segments (R-band positive) appear in most chromosomes and, in particular, constitute the short arms of all the larger chromosomes. Palely staining heterochromatic segments (R-band negative) are less abundant in G. nigeriae but predominate in G. hesperinus. In addition, in both species an intermediate staining of heterochromatin is observed near the centromere or in the heterochromatic short arms of some acrocentric and small submetacentric chromosomes. Very short BrdU treatment during the end of the last cell cycle results in asymmetrical staining of chromatids in heterochromatic segments after applying the acridine orange or FPG (fluorescence plus Giemsa) technique. The alternating location of strongly staining segments in one or the other chromatid simulates sister chromatid exchanges ("pseudo-SCE"). This pattern persists after longer BrdU treatment during different stages of the last cell cycle and is independent of the R-staining properties of the heterochromatin. The lateral asymmetric appearance of the large heterochromatic segments in Gerbillus is interpreted as reflecting an uneven distribution of adenine and thymidine between the two strands of DNA.

Animals↗
PubMed1988

Simple GATCA repeats characterize the X chromosomal heterochromatin of Microtus agrestis, European field vole (Rodentia, Cricetidae).

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have identified two prominent satellite bands of 2.0 and 2.8 kb in length after HaeIII and HinfI restriction enzyme digestion of genomic DNA, respectively. These satellites are located on the heterochromatic long arm of the X chromosome as shown using Microtus x mouse somatic cell hybrids. By in-gel hybridization with oligonucleotide probes, the organization of the two satellites was studied: among the many copies of the simple tandem tetranucleotide repeat GATA are interspersed rare single GACA tetramers. One of the satellites also harbours related GGAT simple tandem repeats. In situ hybridizations with plasmid-carried or oligonucleotide GATCA probes show clustered silver grains on the long and short arm of the X chromosome. Interspersion of differently organized (GATA)n elements is also demonstrable in the autosomal complement and on the Y chromosome. These results are discussed in the context of the evolution of vertebrate sex chromosomes in relation to heterochromatin and simple repetitive DNA sequences.

Animals↗
PubMed1977

Genome analysis of Peromyscus (Rodentia, Cricetidae) VII. Localization of satellite DNA sequences and cytoplasmic poly(A) RNA sequences of P. eremicus on metaphase chromosomes.

A satellite DNA fraction from P. eremicus, having a buoyant density of 1.705 g/ml in neutral CsCl density gradients, was isolated. In situ hybridization experiments, using 3H-RNA complementary to this DNA fraction indicated that the short (heterochromatic) arms of most of the autosomes contained this sequence. Conversely, in situ hybridization using 3H-complementary DNA (cDNA) synthesized from the cytoplasmic poly (A) RNA of P. eremicus (comprising a substantial fraction of total messenger RNA) showed that the number of silver grains in the long arms (euchromatin) was significantly higher than that in the short arms. The X chromosomes showed a distinct localization pattern of both sequences.

Animals↗
PubMed1992

Nucleotide sequence and genomic organization of a tandem satellite array from the rock vole Microtus chrotorrhinus (Rodentia).

A tandem satellite array (herein named MSAT-160) has been isolated and characterized from the rodent Microtus chrotorrhinus. Sequence data from 15 partial or complete monomers revealed a repeat unit length of 160 bp. This unit length was apparently derived from two shorter sub-motifs, one a tetramer (GAAA), the other a hexamer (CTTTCT), through polymerase slippage and mutation. Collectively, perfect or imperfect variants of these two motifs comprise nearly 60% of the component. Southern blot analyses of genomic DNA digested with 14 different restriction endonucleases indicated that most enzymes yielded either classical type A or type B restriction patterns, while RsaI yielded a pattern that combined features of both the A and B types, and BamHI appeared to lack sites altogether in MSAT-160. An examination of restriction patterns from 16 individuals with three enzymes failed to identify intraspecific variation, while a related study compared 11 species and documented interspecific distinctiveness (Modi, submitted). Fluorescence in situ hybridization indicated that the satellite DNA was located at the centromeres of several autosomes and at sex chromosome heterochromatin.

Animals↗
PubMed1984

An estimation of the degree of the genetic divergence of sibling species Microtus arvalis and Microtus subarvalis (Rodentia) based on electrophoretic analysis.

The electrophoretic mobilities of 52 enzymes and proteins were used as measures of the genetic similarity between the sibling species Microtus arvalis and M. subarvalis. The two vole species differed in the electrophoretic mobilities of seven (glucose-6-phosphate dehydrogenase, adenylate kinase, diaphorase, lactate dehydrogenase-A, alpha-galactosidase, 6-phosphogluconate dehydrogenase, and hemoglobin) of these markers. This allowed us to accept the seven markers assayed as species-specific markers. Based on the frequency distribution of the genes at the polymorphic loci of M. arvalis and M. subarvalis, the degree of their genetic similarity was estimated as 0.312 and the genetic distance as 1.164 by Nei's formula. The estimates for genetic similarity were close to those obtained for species recognized as distinct.

Animals↗
PubMed1985

Identification of crystalline allantoin in the urine of African Cricetidae (Rodentia) and its role in their water economy.

All eleven cricetid species, examined in this investigation, produced an off-white crystalline precipitate in their urine when deprived of water, whereas not one murid examined did so. This crystalline compound was identified as allantoin, a common end product of purine catabolism. The quantity found in the solid precipitate alone accounted for 47% of the total nitrogen excreted and was approximately 14 times greater than the predicted quantity of allantoin from purine degradation. It appears that there is a shift in nitrogen excretion from urea to allantoin in the Cricetidae. Water-deprived cricetids had higher urine osmolalities, urea concentrations and lower daily percentage body water turnovers than the murids. This can be explained by the substantial water savings associated with excreting solid allantoin. The discrepancy in the mode of nitrogen excretion between the two families inhabiting the Namib Desert can be attributed to their different evolutionary histories, the Cricetidae being pre-adapted for survival in deserts.

Adaptation, Physiological↗
PubMed1995

Loss of telomeric sites in the chromosomes of Mus musculus domesticus (Rodentia: Muridae) during Robertsonian rearrangements.

Mouse chromosomes possessing multiple Robertsonian rearrangements (Rb chromosomes) have been examined using fluorescence in situ hybridization with the telomeric consensus sequence (TTAGGG)n. No hybridization signals were detected at the primary constriction of Rb chromosomes. This observation leads us to conclude that the formation of Rb chromosomes in the mouse is invariably associated with the loss of telomeric regions. More significantly, a further alteration in regions flanking the primary constrictions was observed after hybridizing with a minor satellite DNA probe to Rb chromosomes. It seems likely that the breakpoints required for a Robertsonian process do not include telomeric sites exclusively but extend to the adjacent pericentromeric regions of the original acrocentric chromosomes. In contrast to previous reports, these observations demonstrate the elimination of substantial amounts of chromosomal DNA during the formation of mouse Rb chromosomes.

Animals↗
PubMed1995

Interferon-gamma levels during the course of Trypanosoma cruzi infection of Calomys callosus (Rodentia-Cricetidae) and Swiss mice.

Serum levels of interferon-gamma (IFN-gamma) were evaluated in Calomys callosus and Swiss mice during the course of infection by four strains of Trypanosoma cruzi. All strains stimulated the production of this interleukine; however, the timing of its onset and permanence varied among strains and between the two animal models. When chronically infected animals with no detectable serum IFN-gamma were challenged with the homologous strain, they produced quantities comparable with those obtained during the acute phase of infection. In C. callosus there was a correlation between H2O2 liberation by peritoneal macrophages and serum IFN-gamma levels, whereas no such correlation was found in mice. C. callosus had a higher capacity to heal histopathological lesions, whereas lesions in mice were progressive. The results obtained suggest that C. callosus develops well-adapted immune mechanisms that may be important for its role as a reservoir of T. cruzi.

Animals↗
PubMed1990

Hantavirus strains isolated from rodentia and insectivora in rural China differentiated by polymerase chain reaction assay.

Polymerase chain reaction (PCR) assay and other techniques were applied to differentiate Hantavirus strains isolated from different animal hosts and geographic regions in China. Two groups of related strains, Hantaan and Seoul, have been classified by cross-neutralization, radioimmunoprecipitation (RIP), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assays. The molecular weights of glycoprotein 1 (G1) of Hantaan and Seoul viruses were 72k and 80k, whereas those of the nucleocapsid (N) and glycoprotein 2 (G2) remained the same, respectively. The PCR assay was used to differentiate these isolates using synthetic oligonucleotide primers selected from various regions of the M genome of 76118 and R22 strains. 76118-specific primers amplified only the RNAs extracted from Hantaan strains while R22-specific primers, the RNAs from Seoul strains. The PCR results for classification are consistent with those obtained by cross-neutralization, RIP and SDS-PAGE assays.

Animals↗