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At least 217 records · Page 12Linked to original sources
PubMed2004

Are the dot-like chromosomes in Trinomys iheringi (Rodentia, Echimyidae) B chromosomes?

In this article we review the existing cytogenetic information on the polymorphic dot-like chromosomes in Trinomys iheringi, the only species in the family Echimyidae harboring them, and provide new data on the frequency, banding properties, meiotic behavior and DNA composition of these minute chromosomes. Since no individuals lacking these chromosomes have hitherto been found, one of the main properties of B chromosomes, i.e. dispensability, has not yet been tested, so that some reasonable doubt might exist on whether they are true B chromosomes. The dot-like chromosomes were also present in the twelve new individuals analyzed, showed intraindividual variation in number, most likely due to mitotic instability during development, failed to show C-bands, showed late-replication, paired among them in meiosis, but not with the large chromosomes, and appeared to be mainly composed of telomeric DNA. These results suggest that these dot-like chromosomes might actually be mitotically unstable micro B chromosomes showing very high frequency in the natural populations thus far analyzed. But, to be confident of this conclusion, individuals lacking the dot-like chromosomes should actively be searched in future research to test their dispensability.

Animals↗
PubMed1979

New karyotypes and somatic and germ-cell banding in Akodon arviculoides (Rodentia, Cricetidae).

Chromosomal polymorphism resulting from three autosomal pericentric inversions and a complex rearrangement involving the largest chromosome of the complement (pair 1) in Akodon arviculoides (2n= 14, 15) is reported. G- and C-banding patterns in somatic and meiotic cells allowed the precise identification of all chromosomes and rearrangements. In meiosis of male specimens with 2n = 15, a large trivalent reflecting the complex rearrangement in autosomal pair 1 was observed. Two possible explanations for it are discussed. G- and C-bands in diplotene cells in heterozygotes for the inversions showed different configurations depending on the pairing in the inverted segments. Chiasma frequency data fro three specimens are analyzed.

Animals↗
PubMed1980

Mastomys (=Praomys) natalensis is not a Rattus (Mammalia: Rodentia): karyological evidence.

Certain past studies have suggested that the taxa Mastomys (= Praomys) and Rattus were closely allied phyletically. We here present detailed (C- and G-banding and NOR's) comparisons of the karyotypes of M. natalensis (2n = 36) and R. norvegicus (2n = 42). A standardized G-banded karyotype of M. natalensis is also presented. About 45% of the G-banded karyotype of M. natalensis is homologous with that of R, norvegicus. Autosomal constitutive heterochromatin is nearly equivalent in the two species; the X and Y chromosomes of M. natalensis, however, have exceptionally large heterochromatic segments. Both species possess three pairs of NOR's, but adjacent G-banded regions are homologous for only one of these. Primarily on the basis of overall G-band homology, we regard the two taxa as only distantly related.

Animals↗
PubMed1994

Geographical variation of heterochromatin in Ctenomys flamarioni (Rodentia-Octodontidae) and its cytogenetic relationships with other species of the genus.

The first karyotype analysis of Ctenomys flamarioni, based on a sample of 46 specimens collected along the geographical range of this species, is reported. All specimens exhibited a diploid number of 48 but varied in autosomal arm number from a low of 50 to a high of 78. The amount of constitutive heterochromatin also varied with the species' geographical distribution. Comparison of G-band patterns showed a strong relationship between the karyotype of this species and those belonging to the Argentinian mendocinus group.

Animals↗
PubMed1996

The chromosomes of Nectomys (Rodentia, Cricetidae) with 2n = 52, 2n = 56, and interspecific hybrids (2n = 54)

Karyologic comparisons of Nectomys with 2n = 52 and 2n = 56, captured in different regions of Brazil, revealed the existence of two presumptive tandem fusions. These differences proved to represent drastic reproductive barriers between these two karyologic groups, based on an analysis of spermatogenesis in captive-bred hybrids (2n = 54). In these hybrid specimens, cytologic and histologic analyses indicated severe meiotic arrest and the presence of two trivalents in the first meiotic division, in which 26 elements were frequently observed. These findings and the sterility of crosses between F1 males and females as well as backcrosses indicated that Nectomys populations with 2n = 52 and 2n = 56 should be considered different species and that the present taxonomic arrangement of this genus must be reviewed.

Animals↗
PubMed1997

Genome composition in Venezuelan spiny-rats of the genus Proechimys(Rodentia, Echimyidae). I. Genome size, C-heterochromatin and repetitive DNAs in situ hybridization patterns.

The genome sizes of the Venezuelan spiny-rats Proechimys guairae guairae (2n = 48) and P. trinitatis (2n = 62) were evaluated and proved to be 12.5 +/- 0.5 pg and 12.6 +/- 0.3 pg respectively, the highest so far recorded among mammals; also the C-heterochromatin (32.7%, Coefficient of Variation [CV] 3.8 and 35.8%, CV 4.4) and GC (44.2%, CV 2.7 and 43.6%, CV 2.9) contents are very high. Highly repetitive (rep) DNAs were isolated from restriction enzyme digested genomic DNAs of both species. The intra- and inter-specific chromosomal allocations of these rep DNAs were analyzed by direct and cross-hybridizations. Results show that the two genomes harbour several rep DNA families which show both species-specificity and interspecific relatedness in their in situ hybridization patterns. The rep DNA families show an equilocal distribution at both the pericentromeric areas of all chromosomes and in the whole arms of two pairs of the uniarmed group, suggesting co-evolution of the rep DNAs. P. g. guairae BamHI digested DNA, when cloned and sequenced, proved to consist of a long "composite" unit (1,239 bp) containing two copies of each of 75-bp and 110-bp internal subrepeats. Karyotype restructuring between P. g. guairae and P. trinitatis, mainly due to Robertsonian changes, was accompanied by slight intra- and intergenomic movements of the putative satellite DNA families within stable genome sizes and C-heterochromatin contents. We discuss the findings obtained in Proechimys in the light of those regarding the kangaroo rat, the pocket gopher and the house mouse; they support the idea that karyotype restructuring could be the expression of molecular driven events of rep DNA amplification and homogenisation through non-homologous chromosomes.

Animals↗
PubMed2001

Olfactory cues accelerate reentrainment following phase shifts and entrain free-running rhythms in female Octodon degus (Rodentia).

Social interactions between conspecifics is a type of nonphotic zeitgeber common to several species. In the diurnal rodent Octodon degus, social interactions enhance reentrainment after phase shifts and can act as a weak zeitgeber. Olfactory stimuli appear necessary for these effects since bulbectomy eliminates socially enhanced reentrainment. In Experiment 1, the authors examined whether stimulation of the main olfactory system was sufficient to enhance reentrainment after 6-h phase advances and delays in the adult female O. degus. When test animals received conspecific odor cues during reentrainment, they entrained 39% faster after phase advances (p < 0.05) and 33% faster after phase delays (p < 0.001) than when they did not receive odor cues. Thus, olfactory cues from distant female donors were sufficient to enhance rates of entrainment in female O. degus and provided results equivalent to earlier studies with donors and shifters housed in the cages together. In Experiment 2, the authors examined whether discrete 3-h and 1-h daily pulses of airborne odors from a group of 5 entrained female degus would be sufficient to produce entrainment of wheel-running activity in adult female conspecifics. During the period of exposure to 3-h pulses, 50% (4/8) of the subjects temporarily entrained to a 24-h cycle, while 12.5% (1/8) of the subjects fully entrained. Exposure to 1-h pulses allowed 37.5% (3/8) of the subjects to temporarily entrain and 12.5% (1/8) of the subjects to fully entrain. Duration of entrained episodes was positively correlated with psi, daily onset of activity with respect to the timing of odor exposure (Pearson r = 0.731; p < 0.05), such that animals with the entraining odor pulse beginning during subjective day (psi = 7.8 h, CT 7.8 +/- 1.4) had longer periods of entrainment (22.2 +/- 5.6 days) than animals with the entraining pulse occurring during subjective night (psi = -4.6 h; CT 19.4 +/- 0.9; 5.6 +/- 0.9 days; p < 0.001). In addition, for each animal, the combined duration of all episodes of 24-h entrainment correlated with increased period length (tau) of free-running rhythms (Pearson r = 0.733; p < 0.05). Thus, daily discrete pulses of odors with durations of either 1 or 3 h from female conspecifics were sufficient to produce both temporary and full entrainment to a 24-h cycle in the majority of female O. degus, and the likelihood of long periods of entrainment correlated with long taus and coordination of the odor pulse with mid subjective day.

Animals↗
PubMed1980

Akodon molinae (Rodentia Cricetidae), a new laboratory animal: breeding, management and reproductive performance.

Akodon molinae, a vole mouse widely distributed in central Argentina, shows remarkable chromosome polymorphisms. It is one of the natural reservoirs of the aetiologic agent of haemorrhagic fever, and a laboratory colony could be of great help in investigating this disease. Pregnancy lasted 23 (range 21-25) days. Litters of 4-5 young were born to monogamous breeding pairs about every 30 days, with weaning at 26 days post partum. The sex ratio at birth was 505 males to 500 females: at weaning it was 460 to 440. Sexual maturity was attained at about 16 weeks of age in males and 12-20 weeks in females. Akodon molinae is easy to handle, but fighting and killing or neglect of young are problems.

Animals↗
PubMed1999

Superovulation in vesper mice, Calomys laucha--an important biomedical model for hantavirus and arenavirus (Rodentia-Sigmodontinae).

Sigmodontine rodents are poorly studied and have not received much attention as a reproductive model. Renewed interest in the South American rodents has been stimulated by their link to endemic diseases that are transmitted to man. Calomys laucha acts as a reservoir of two dangerous viruses: an arenavirus named 'Junin virus', the aetiological agent of Argentinian haemorrhagic fever, and the hantavirus, both of which constitute serious sanitary problems. The aim of this study was to establish suitable conditions to superovulate the vesper mouse, Calomys laucha. We examined the hormonal doses, the time interval between hormones, the time-course of ovulation, and the effect of female age on the response to exogenous hormone administration. Female mice were injected with 5-5, 8-8 or 12-15 IU of PMSG/hCG, 48 h apart, at different age intervals (from 30 to > 120 days old). The best superovulation rate was obtained with 8-8 IU PMSG/hCG. Ovulation started about 10 h post-hCG and was completed during the next 4-5 h, and was achieved irrespectively from the oestrus cycle stage. The number of oocytes was influenced by the age of the females. The youngest females had only a superovulatory response. Females older than 61 days showed both ovulatory and superovulatory responses, although 91-120-day-old females had a high ovulatory response. Most of the oocytes (96.5%) recovered were morphologically normal. The genus Calomys constitutes a reproductive model completely different from conventional laboratory rodents.

Aging↗
PubMed1979

Microtus oeconomus (Rodentia), a useful mammal for studying the induction of sex-chromosome nondisjunction and diploid gametes in male germ cells.

Preliminary data indicate that chemicals can also increase the frequency of sex-chromosome nondisjunction. Positive results--which certainly need further confirmation--have been obtained for MMS, p-fluorophenylalanine, vincristine, procarbazine, carbendazim, and bleomycin. Nocodazole, benomyl, colcemic, 6-mercaptopurine, and halothane were all negative at the concentrations tested. For the induction of diploid spermatids positive results were only obtained for MMS and parafluorophenylalanine. In view of the results obtained, the Microtus system is considered a very useful tool for analyzing factors contributing to the high frequency of aneuploidy and triploidy among abortuses and of aneuploidy in liveborn infants of men. A method is described for the detection of sex-chromosome nondisjunction and diploid spermatids in male germ cells of the field vole Microtus oeconomus. The method is based on the unique distribution pattern of heterochromatin in Microtus cells, which makes it possible to identify X and Y chromosomes in early spermatids with a simple C-banding procedure. Slide preparation is easy. Scoring of early spermatids for extra sex-chromosomes is simple and 2000-4000 cells per hour can be examined. With the Microtus system it has now been demonstrated that radiation of spermatocyte stages with doses of 50, 100 and 200 R results in a higher frequency of sex chromosome nondisjunction and of diploid gametes. Both types of aberrant gametes can be produced during the first and second meiotic division.

Animals↗
PubMed2005

Fatal placental subinvolution in a captive capybara (Hydrochaeris hydrochaeris, Order Rodentia).

An adult, captive-born female capybara died of systemic thrombosis and hemoperitoneum associated with placental subinvolution. Grossly, the uterus was enlarged, segmentally thickened, and associated with a large blood clot in the abdominal cavity. There was hemometra and a large ovoid mass in each uterine horn weakly adhered to the endometrium, and the right uterine horn wall had a small perforation over the mass. The mesometrial veins were markedly dilated due to thrombosis and occasionally perforated. Histologically, the uterine masses consisted of partly necrotic placental and subplacental tissue. The uterine wall surrounding the masses had full-thickness coagulative necrosis of the myometrium and diffuse endometrial ulceration with abundant syncytiotrophoblast-like cells within capillaries. Vascular lesions in the uterus and mesometrium consisted of mural invasion by cytotrophoblast and syncytiotrophoblast-like cells, thrombosis, fibrinoid necrosis, and/or heterophilic vasculitis. This is the first report of placental subinvolution in capybaras or any rodent species, to the authors' knowledge.

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