Genetic studies of the Syrian hamster

A new mutant allele of the Syrian hamster is described. It is inherited as an autosomal recessive and is probably an homologue of the gene for brown pigment, a mutational step which is known to occur in a number of rodent species. In animals homozygous for the mutant allele, all the normal black eumelanin is changed to brown. The new coat colour engendered in this manner is described in detail. The brown allele has been tested for linkage against the genes cream and ruby-eye but the results were negative.     

Genetic studies of the Syrian hamster

A new mutant gene,anophthalmic white, is described for the Syrian hamster. The gene is inherited as a dominant to normal and, when homozygous, produces a characteristic syndrome of achromia and anophthalmia or microphthalmia. The heterozygote possesses white belly fur (instead of cream), a fine sprinkling of white hairs in the adult coat and a diminution of eye pigmentation. An occasional heterozygote may possess a small patch of unpigmented fur on the head or body. The new mutant does not appear to be linked with the gene forcream coat colour nor that forpiebald spotting. The significance of homologous mutants, with the above syndrome, in the mouse and hamster is briefly discussed.     

Heterogeneity of constitutive heterochromatin in somatic Syrian hamster chromosomes.

Syrian hamster constitutive heterochromatin was analyzed for C-band distribution and for BrU late-replication pattern. Characteristic for this species is relatively large amounts of sex-chromosome and autosomal heterochromatin. The distribution of constitutive heterochromatin was determined. The long term of the X chromosome, the whole Y, the short arms of 8 autosomal pairs, the long arm of the smallest metacentric pair, and the centromeric regions of 12 pairs stained intensely dark on C-band preparations. In contrast to the heterochromatin in the centromeric regions, the autosomal short-arm heterochromatin has an increased susceptibility to the denaturation process, as indicated by prolonged exposure to NaOH or Ba(OH)2. Such further exposure to denaturing agents results in an intense dark stain only on the sex-chromosome heterochromatin and centromeric regions of the autosomes. The BrdU late-replication pattern demonstrated that the late-replicating regions correspond to C-bands. Centromeric regions replicate late in the S phase; however, no centromeric region is among the latest replicating segments of the complement. Centromeric and noncentromeric heterochromatin are two distinct categories of constitutive heterochromatin.     

Cytogenetic analysis of Q-banded pronuclear chromosomes in fertilized Syrian hamster eggs

The frequency and type of chromosome abnormalities were analyzed in 917 female pronuclei in Syrian hamster eggs fertilized by human sperm. Analysis at this stage allows detection of errors which have occurred during meiosis I and II. The chromosomes were Q-banded to identify individual chromosomes and detect subtle alterations. Thirty-three (3.6%) of the hamster egg complements were abnormal: 19 (2.1%) were hypohaploid, seven (0.76%) were hyperhaploid, two (0.2%) had double aneuploidy, and five (0.5%) had a structural chromosome abnormality. Since there were significantly more hypohaploid than hyperhaploid complements, a conservative estimate of aneuploidy can be derived by doubling the frequency of hyperhaploid complements. Thus a minimal estimate of aneuploidy (single, 1.5%, and double, 0.2%) is 1.7% and a minimal estimate of the total frequency of abnormalities is 2.2%. All chromosome groups were represented among the aneuploid complements suggesting that all chromosomes are susceptible to non-disjunction.     

High-resolution mapping of interstitial telomeric repeats in Syrian hamster metaphase chromosomes

Karyotype analysis of the Syrian hamster (Mesocricetus auratus) was performed after DAPI-banding of metaphase chromosomes obtained from cultivated skin fibroblasts of a newborn animal. Fluorescence in situ hybridization with telomeric FITC-conjugated peptide nucleic acid probe was applied to map interstitial blocks of (TTAGGG)(n) repeats. Strong fluorescence in situ hybridization signals corresponded to interstitial telomeric repeats in pericentromeric chromatin bands of chromosomes 2, 4, 14, 20, and X. High-resolution DAPI-banding allowed specifying the arrangement of bands in the pericentromeric regions of these chromosomes.     

Growth in the myopathic Syrian hamster (Cricetus auratus)

The objective was to assess the effect of the hereditary myopathic disease (muscular dystrophy) on 4 growth parameters: body-weight, head-body length, skull weight and cranial length in the Syrian hamster over a 4-13 month period. A control colony of 34 males and 32 females was compared to a muscular dystrophy colony consisting of 37 males and 27 females. The monthly means of the 4 growth parameters were computed and full data were used for computations of analysis of variance with regression of each group, sex and growth parameter. Intersex and intergroup comparisons of the same parameters were made using analysis of covariance. In the controls, the male bodies were heavier and longer than the female bodies; males grew over the total period. In dystrophic hamsters, males were heavier than females, but females were longer. In both control and dystrophic hamsters, female skulls were longer and heavier. In all parameters the means of the control colony were greater than those of the dystrophic colony relative to age. The disease factor in the muscular dystrophy colony adversely influenced all 4 growth parameters.     

Effect of Hoechst 33258 on Chinese hamster chromosomes

Cells of the Chinese hamster strain C-125 were treated for different time intervals with H 33258, a bibenzimidazole derivative. The same compound was used to stain fixed cells of the same strain. — H 33258 induced in cells in culture specific areas of reduced spiralization on the metaphase chromosomes of some cells. These probably correspond to DNA segments rich in A-T bases interspersed along the chromosomes. Probably H 33258 acts during S period of cell cycle. — The banding obtained by staining with H 33258 is similar to that induced by quinacrine dihydrochloride but shows a better resolution.     

Chromosome replication in fibroblasts of the Syrian hamster (Mesocricetus auratus)

The BrdU/Hoechst 33258/Giemsa method for sub-dividing S-phase in asynchronous cell populations has been re-evaluated and modified to give better definition and more even distribution of sub-phases. A reference pattern of early-relicating euchromatic bands is given for all chromosomes at Sk2 in primary cultures of skin fibroblasts. The overall band patterns at each sub-phase have allowed more objective definitions of early and late replication for these cells, and show that in both classes of chromatin light G-bands preceed dark G-bands. Asynchrony between homologous bands is observed at all stages of S, albeit with a variable frequency. The observed in vitro replication patterns and programme for the chromosomes of skin fibroblasts does not appear to be affected by the age or sex of the source.     

Genetic studies of the Syrian hamster. X. Rex.

The rex mutant has its most obvious effect on coat structure but it also reduces 21-day body weight by about 14 per cent. There is no apparent effect on viability nor on the fecundity of the more robust rex females. Extensive tests for linkage with the genes b, Ba, cd, Ds, e l, Lg, ru, Sa and Wh have proved to be negative. A less extensive test with s was also negative.     

Cytological sub-division of S-phase in the Syrian hamster (Mesocricetus auratus)

Using BrdU/Hoechst 33258/Giemsa methods for detecting replicating chromosome bands, a method is described by which the DNA synthesis phase may be sub-divided on the basis of distinctive patterns displayed by certain chromosomes. — Applied to asynchronous populations successively sampled through one cell cycle, cells in S can be unscrambled and replaced in their correct time sequence. — This helps to overcome the sampling-time variable inherent in such populations, and allows a clearer picture of the progression of events both qualitatively and quantitatively.     

Biochemical and cytological studies of bleomycin actions on chromatin and chromosomes

Interaction of bleomycin with nuclei isolated from a variety of mammalian cells resulted in the release of nucleosomes. When isolated mononucleosomes (core plus linker) were re-treated with bleomycin, no further degradation of DNA occurred. The results suggest that the bleomycin cleavage sites in chromatin are present only in the linker region and that there are probably only one or two cleavage sites per linker. The repeat lengths of nucleosomal DNA released by bleomycin from nuclei of different species are different; this variability is considered to reflect the length of the linker. Incorporation of BrdU into DNA did not alter the bleomycin action on nucleosomes. When mitotic cells were held at metaphase for a prolonged period, bleomycin caused a gradual disintegration of chromosomes, although the bleomycin cleavage sites in metaphase chromosomes were found to be the same as those in interphase nuclei.     

Age-related changes of the ultrastructure in the cardiomyopathic hamster (UM-X7.1 Syrian hamster) parathyroid gland

We qualitatively and quantitatively investigated parathyroid glands of the UM-X7.1 cardiomyopathic hamster at 1, 2, 6 and 12 months of age to compare them with those of the normal hamster. We found that at 1 month of age in the UM-X7.1 hamster, the Golgi apparatus, lipid droplets and secretory granules decreased. There were no significant differences between the UM-X7.1 hamster and the control hamster at 2 months of age. At 6 months of age, the Golgi apparatus, rER and the secretory granules significantly increased in the UM-X7.1 hamster. At 12 months of age, the Golgi apparatus and lysosomes increased, while the secretory granules decreased. Ultrastructurally, we consider that in the UM-X7.1 hamster, the synthesis and release of the parathyroid at 6 months of age may be activated by an excessive amount of circulating catecholamine, and the functional activity of the parathyroid glands at 12 months of age may be depressed by the increased plasma calcium level. These findings suggest that the activities of the synthesis and release of the parathyroid hormone were the highest at 6 months of age in the UM-X7.1 hamster.     

Variation in the growth of the preweaning Syrian hamster (Cricetus auratus)

An assessment of the growth rate spectrum based on a longitudinal weight study of golden hamsters was undertaken over the preweaning period. The period covered 23 days with data probes at 24-hourly intervals and encompassed 16 litters providing a birth number of 120 young and a weaning survival number of 82. Subsequent analysis directed initially at the pooled or averaged data showed sex differences with males gaining weight faster than females. Further analysis showed the total period to have three definitive break-points and therefore four phases of growth activity. The segmented linear regression line calculations showed that the phasic duration of males in the second and third phases were two days later than the females. Following data-analysis adjustments and taken into account aberrations of the sample, final indications pointed to the preweaning hamster growth spectrum as quadrophasic, exhibiting a stable first phase, a second and third phase terminating earlier in females and a final weaning weight being heavier in males. The growth curves demonstrated a 'U' shaped outline and formed an integral part of hamster preweaning precocity.     

Flow microfluorometric analysis of isolated Chinese hamster chromosomes

Isolated Chinese hamster chromosomes were analysed by flow microfluorometry after staining with ethidium bromide. Peaks corresponding to the expected DNA content of each of the autosomes were observed. Examination of chromosomes partially fractionated by zonal centrifugation on sucrose gradients verified the identity of the chromosomes in the various peaks of the whole karyotype. The significance of these observations to karyotype analysis is discussed.