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New families of site-specific repetitive DNA sequences that comprise constitutive heterochromatin of the Syrian hamster (Mesocricetus auratus, Cricetinae, Rodentia).

We molecularly cloned new families of site-specific repetitive DNA sequences from BglII- and EcoRI-digested genomic DNA of the Syrian hamster (Mesocricetus auratus, Cricetrinae, Rodentia) and characterized them by chromosome in situ hybridization and filter hybridization. They were classified into six different types of repetitive DNA sequence families according to chromosomal distribution and genome organization. The hybridization patterns of the sequences were consistent with the distribution of C-positive bands and/or Hoechst-stained heterochromatin. The centromeric major satellite DNA and sex chromosome-specific and telomeric region-specific repetitive sequences were conserved in the same genus (Mesocricetus) but divergent in different genera. The chromosome-2-specific sequence was conserved in two genera, Mesocricetus and Cricetulus, and a low copy number of repetitive sequences on the heterochromatic chromosome arms were conserved in the subfamily Cricetinae but not in the subfamily Calomyscinae. By contrast, the other type of repetitive sequences on the heterochromatic chromosome arms, which had sequence similarities to a LINE sequence of rodents, was conserved through the three subfamilies, Cricetinae, Calomyscinae and Murinae. The nucleotide divergence of the repetitive sequences of heterochromatin was well correlated with the phylogenetic relationships of the Cricetinae species, and each sequence has been independently amplified and diverged in the same genome.

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Molecular phylogeny of the Cricetinae subfamily based on the mitochondrial cytochrome b and 12S rRNA genes and the nuclear vWF gene.

Despite some popularity of hamsters as pets and laboratory animals there is no reliable phylogeny of the subfamily Cricetinae available so far. Contradicting views exist not only about the actual number of species but also concerning the validity of several genera. We used partial DNA sequences of two mitochondrial (cytochrome b, 12S rRNA) and one partial nuclear gene (von Willebrand Factor exon 28) to provide a first gene tree of the Cricetinae based on 15 taxa comprising six genera. According to our data, Palaearctic hamsters fall into three distinct phylogenetic groups: Phodopus, Mesocricetus, and Cricetus-related species which evolved during the late Miocene about 7-12MY ago. Surprisingly, the genus Phodopus, which was previously thought to have appeared during the Pleistocene, forms the oldest clade. The largest number of extant hamster genera is found in a group of Cricetus-related hamsters. The genus Cricetulus itself proved to be not truly monophyletic with Cricetulus migratorius appearing more closely related to Tscherskia, Cricetus, and Allocricetulus. We propose to place the species within a new monotypic genus. Molecular clock calculations are not always in line with the dating of fossil records. DNA based divergence time estimates as well as taxonomic relationships demand a reevaluation of morphological characters previously used to identify fossils and extant hamsters.

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Goblet cell mucins of four genera of the subfamily Cricetinae with reference to the protective activity against Strongyloides venezuelensis.

Goblet and mast cell responses in the jejunum of four genera, Mesocricetus auratus (Syrian hamster), Phodopus campbelli, Cricetulus griseus (Chinese hamster), and Tscherskia triton, belonging to the subfamily Cricetinae, were examined after infection with Strongyloides venezuelensis. Parasite eggs became detectable in faeces of all four genera on Day 7. Faecal egg count peaked around Day 8 in C. griseus and T. triton and around Day 14 in M. auratus and P. campbelli. In M. auratus and P. campbelli, faecal egg production persisted over 40 days, whereas that in C. griseus and T. triton rapidly terminated within 14 days. In all four genera examined, goblet cell hyperplasia and mastocytosis were observed at the time of expulsion of S. venezuelensis. However, in the comparative study of all four genera, neither the degree of goblet or mast cell hyperplasia nor the phenotype of mast cells correlated to the rapidity of the expulsion of S. venezuelensis. On the other hand, the rapidity of expulsion closely correlated with the degree of sulphation of goblet cell mucins because two genera, C. griseus and T. triton, having highly sulphated goblet cell mucins showed faster expulsion of S. venezuelensis than the other two genera, P. campbelli and M. auratus, having less sulphated mucins. These results suggest that physicochemical nature of mucins is critical for the expulsion of S. venezuelensis from the subfamily Cricetinae.

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Chromosomal homoeologies in hamster species of the genus Phodopus (Rodentia, Cricetinae).

The karyotypes of the two hamster species Phodopus sungorus and P. roborovskii were analyzed with several banding techniques and compared. The homoeologies found between all chromosomes led to the proposal of the most likely common ancestral karyotype of these two species. The differences in the karyotypes were found to be a result of seven independent centric fusions, three inversions, and one possible telomeric fusion, as well as changes in the quantity and DNA-base pair composition of the constitutive heterochromatin.

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[Heterochromatin of the rat-like hamster Tscherskia triton de Winton (Rodentia, Cricetinae), II].

Differential staining of rat-like hamster chromosomes revealed: 1) C- and G-banding of chromosomes depending upon the Giemsa solvent (distilled H2O and phosphate buffer correspondingly) in case of ordinary staining; 2) dependence of C-banding pattern on the C-method; 3) different resistance of C-bands to trypsin action; 4) dependence of Q-bands on the fluorochroms employed (A, 33258 H, AO), the second non-fluorescent (A, 33258 H) near-centrometric heterochromatic region is brilliantly fluorescing when AO is employed; 5) heterogeneity of C-, G- and Q-bands, i.e. similarly stained region, may differ in their structural-functional peculiarities.

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The bushlike radiation of muroid rodents is exemplified by the molecular phylogeny of the LCAT nuclear gene.

Phylogenetic relationships among 40 extant species of rodents, with an emphasis on the taxonomic sampling of Muridae and Dipodidae, were studied using sequences of the nuclear protein-coding gene LCAT (lecithin cholesterol acyl transferase). Analysis of 804 bp from the exonic regions of LCAT confirmed many traditional groupings in and around Muridae. A strong support was found for the families Muridae (represented by 29 species) and Dipodidae (5 species). Compared with Sciuridae, Gliridae, and Caviomorpha, the Dipodidae family appeared the closest relative of Muridae, confirming the suprafamilial Myodonta concept. Within the speciose family Muridae, the first branching leads to the fossorial Spalacinae and semifossorial Rhyzomyinae. The remaining components of Muridae appear as a polytomy from which are issued Sigmodontinae, Calomyscinae, Arvicolinae, Cricetinae, Mystromyinae, Nesomyinae, and some Dendromurinae (Steatomys and Dendromus). This phylogeny is interpreted as the result of a bushlike radiation at the end of the early Miocene, leading to emergence of most living subfamilies. The separation between three additional taxa, Murinae, Gerbillinae, and "Acomyinae" (which comprises the genera Acomys, Deomys, Uranomys, and Lophuromys), has occurred more recently from a common ancestor issued from the main basal radiation. As previously shown by other molecular studies, the vlei rats, Otomyinae, are nested within Old World Murinae. In the same way, the zokors, Myospalacinae, appear strongly nested within the hamsters, Cricetinae. Finally, we propose a sister group relationship between Malagasy Nesomyinae and south African Mystromyinae.

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The phylogenetic position of the zokors (Myospalacinae) and comments on the families of muroids (Rodentia).

Recent molecular studies have concluded that the genus Myospalax evolved from within the rodent subfamily Cricetinae. This conclusion was tested using the complete sequences from the mitochondrial 12S rRNA and cytochrome b genes. Based on our analyses, Myospalax appears to be sister to a clade containing the subfamilies Spalacinae and Rhizomyinae, and all three of these lineages appear to be basal to the superfamily Muroidea. Based on the position of these three lineages, we suggest that they be placed in a distinct family, the Spalacidae, rather than subsumed as subfamilies in the family Muridae. Finally, our analyses suggest that the earlier placement of Myospalax as a member of the Cricetinae is the result of a single misidentified specimen, which was not a Myospalax.

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