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Biomedical subjects

G Breckon

Publications and source records attributed to G Breckon.

30 records · Page 2Linked to original sources
PubMed1985

Photoperiodic control of meiosis in the male Syrian hamster (Mesocricetus auratus).

Male Syrian hamsters exposed to short photoperiods of 6 h light/day (6L:18D) show regression of the testes within 12 weeks. Chromosome preparations of the meiotic stages (pachytene, metaphase I (MI) and metaphase II (MII)), testicular weights relative to body weights, sperm counts, seminiferous tubule diameter and histological appearance were examined at intervals during regression and subsequent recovery in a long photoperiod (14L:10D). The fall of testicular weight was associated with the decrease in tubule diameter. Spermatogenesis and sperm count were reduced rapidly and finally ceased after 10 weeks in short days. The numbers of MI and MII cells relative to 100 pachytene cells progressively decreased during the short-day treatment, although the ratio of MI:MII stayed constant whenever there was meiotic activity (except in the first week of the recovery phase). This suggests that an increasing proportion of pachytene cells did not progress to MI with increased time in short days, but cells which did reach MI progressed to MII in the same proportions as in the control testes. Meiosis ceased after 10 weeks in short days. Recovery in the long days was marked by a peak in the number of MI and MII cells/100 pachytene cells soon after the return to long days. This preceded the return (to control values) of the sperm count by 10 weeks. Initial recovery in the first 3 weeks was very rapid in all the determined values.

Animals↗
PubMed1983

Synaptonemal complexes as indicators of induced structural change in chromosomes after irradiation of spermatogonia.

The incidence of multivalent formation has been compared in primary spermatocytes at pachytene, using synaptonemal complex preparations and at diakinesis/metaphase, using air-dried preparations, from testes of Syrian hamsters several weeks after exposure to an acute dose of X-rays. The pachytene preparations revealed nearly twice the number of multivalents found at diakinesis/metaphase I, and showed the ability to reveal types of structural alteration undetectable in conventional air-dried techniques.

Animals↗
PubMed1982

Early-replication DNA patterns in a derivative chromosome in a Syrian hamster with only 42 chromosomes.

From crosses within a 2n=43 line of Syrian hamsters (Mesocricetus auratus) lacking one derivative (der 11) of an 11;20 reciprocal translocation we have obtained homozygotes with only 42 chromosomes. These animals are homozygous deficient (nullisomic) for the centromere and short arm of chromosome 11 and for the bulk of the long arm of chromosome 20. -During cytogenetic studies, we investigated the frequency patterns of early-replicating bands in the surviving derivative (der 20) at two cytologically defined sub-phases of S using short-term fibroblast cultures. These patterns were compared with those observed in the component, untranslocated arms in normal 2n=44 cells at the same two sub-phases. -Very close agreement was found, indicating that neither the nullisomy, nor the new arm combination has interfered detectably with the pattern or programme of early band replication.

Aneuploidy↗
PubMed1982

Homozygous deficiency: Syrian hamsters with only 42 chromosomes.

By crossing individuals of a line of Syrian hamsters (1SH), 2n = 43, which lack one derivative chromosome (der 11) of a reciprocal translocation T(11;20), two homozygous deficient males were obtained. These animals have only 52 chromosomes and completely lack the centromere and short arm of chromosome 11 and most of the long arm of chromosome 20. Phenotypically and anatomically these animals are apparently normal. Meiosis in both animals was regular with 21 bivalents, and mature sperm were produced. One of the animals sired two litters when mated to normal females. Detailed cytogenetic studies gave no evidence of mosaicism, and the kinetic behaviour of blood and skin cells in short-term culture was identical to control (2n = 44) cells. The detailed kinetics of DNA synthesis of fibroblasts in vitro did not differ from those of normal cells. The missing material, which constitutes about 2.5% of the total chromosome length, synthesizes DNA late, replicating bands being absent until the last sub-phase (Sk5) of the hamster S phase.

Animals↗
PubMed1982

A modified hypotonic treatment for increasing the frequency and quality of meiotic metaphases from spermatocytes of the Syrian hamster.

A modified hypotonic treatment for the spermatocytes of the Syrian hamster (Mesocricetus auratus) has been developed using a micro-osmometer to determine optimum conditions for the frequency and quality of Metaphase I and II figures. A suspension of germinal cells from the tubules is made in 3.2% sodium citrate solution and allowed to stand for 5 minutes. Water is then added until the concentration of the sodium citrate is reduced to 1.4%. This is followed after 15 minutes by fixation and air drying. The number and quality of the metaphase figures is enhanced considerably by this technique. A comparison is made of blood, plasma and testicular osmolality in several animal species and corresponding values for various solutions used for cytogenetic techniques.

Animals↗
PubMed1981

Differential effects of sulphur mustard on S-phase cells of primary fibroblast cultures from Syrian hamsters.

Sulphur mustard (SM) (5 x 10(-8) M) given to primary Syrian hamster fibroblasts growing short-term in vitro produces a very sharp peak of chromatid aberrations 12-16 h after treatment. The composition of this peak has been investigated in relation to the cell cycle using the facility to divide S-phase into 5 cytologically defined sub-phases on the basis of replication band patterns following bromodeoxyuridine incorporation. It is shown that: (1) Considerable delay and perturbation of the cycle is present. (2) A major contribution to the aberration peak comes from pre-S cells, and the highest aberration frequencies are observed in such cells. (3) The bulk of the contribution from S-cells comes from the last subphase, SkV. (4) The majority of early S cells (sub-phases SkI-IV) fail to reach division within 36 h. Of the total S-cells scored, 54% are non-SkV in controls but only 14% after SM. (5) Aberrations are localized to late-replicating regions in SkV but are random in pre-S. (6) No measurable perturbation of replication programme was found in chromosome arms synthesizing in late SkV after SM. (7) The rapid fall in aberration frequency at later sampling times is consistent with a quick and efficient repair of DNA lesions which is known to occur after SM alkylation. The preferential loss of early S cells seems most likely to result from selective lethality, though differential delay and perturbation may make a contribution. It is interesting to note that the subphases missing are just those where the euchromatin replicates (early replicating R and G bands). The late-replicating chromatin, some of which is known to be dispensable in Syrian hamster, is confined to SkV, the sub-phase which appears to survive this dose of SM.

Alkylating Agents↗
PubMed1980

Tolerance of autosomal imbalance by the Syrian hamster (Mesocricetus auratus).

Cytogenetic and transmission data are given for a number of radiation-induced and spontaneous chromosomal changes which show that the Syrian hamster (Mesocricetus auratus) can tolerate a considerable amount of autosomal imbalance without phenotypic effect. It is suggested that the reason for this may lie in the very large amount of late-replicating chromatin present in this species.

Animals↗
PubMed1979

Routine chromosome screening in Syrian hamsters (Mesocricetus auratus) using orbital sinus blood.

Blood from the posterior orbital sinus of Syrian hamsters, obtained under halothane anaesthesia, can be cultured to give large numbers of metaphase chromosome spreads for analysis. The procedure has been used for rapid routine screening of the karyotypes of all offspring in a breeding colony where translocations are present. Results can be obtained within 3 days of collecting the blood sample.

Anesthesia, Inhalation↗
PubMedDate not supplied

Control of haemoglobin switching by a developmental clock?

The pattern of haemoglobin production changes at the embryonic, fetal and postnatal stages of human development, reflecting the expression of different globin genes in both the alpha-like and beta-like gene clusters. Recent studies have identified alterations in the state of DNA methylation and sensitivity to nuclease digestion associated with developmental expression of the globin genes in red blood cell precursors, but the mechanism initiating these changes remains unknown. Despite the screening of large numbers of blood samples from newborn infants, no mutants have been found which affect the timing of these changes (with one possible exception involving a chromosomal translocation), thus necessitating alternative approaches to analysing the cellular basis for the timing of haemoglobin switching. Although many mechanisms are possible, the initiation of the switch from fetal to adult haemoglobin could be regulated essentially either by a developmental clock inherent to haematopoietic stem cells or by an inductive environment, and in an attempt to distinguish between these possibilities, we have transplanted sheep fetal haematopoietic tissue into adult animals. Although previous experiments of this type produced conflicting results, the accumulated results presented here demonstrate that the pattern of haemoglobin production after transplantation is determined largely by the gestational age of the fetal donor cells.

Animals↗