Influence of thyroid hormones on satellite association in man and the origin of chromosome abnormalities

Variation in pattern and frequency of acrocentric association in normal and trisomy-21 individuals

Chromosomally normal and trisomy-21 individuals were studied for the ability of their nucleolus-organising chromosomes to form satellite associations in G-banded lymphocyte metaphases. Two types of parameter, absolute association frequency and relative association frequency, were used. There was no significant difference between females and males or between Caucasoids and Mongoloids for either type of association parameter in the controls, nor was there significant correlation between age (17-40 years) and either type of parameter in the controls. The pattern of two chromosome associations is accounted for by two related models in both normal and trisomic individuals. These models imply that there is an extensive polymorphism for associating ability and that this ability may be zero in individual chromosomes. Homologous do not associate preferentially with each other. The absolute frequency of acrocentric association is lower in trisomy 21 individuals than disomic controls, but the relative involvement of chromosome 21 (after correction for the trisomic state) is higher than in the controls.

Age-related influence of piracetam on mitotic index and number of silver-stained nucleolus organizer regions

Mitotic indices and the number of silver-positive nucleolus organizer regions (AgNORs) were scored in phytohemagglutinin-stimulated cultures of peripheral lymphocytes from two age groups of females (mean = 23.1 and 84.0 yr, respectively) under the influence of Piracetam (2-oxo-pyrrolidine-1-acetamid; Nootropil, Reg. No. 17051) and in simultaneously set up control cultures without Piracetam addition. Piracetam concentrations of 10, 14 and 16 mg/ml culture medium produced a highly significant, decreasing effect on both parameters tested, without an age-related difference. Lower Piracetam concentrations (2 and 4 mg/ml culture medium) showed a depressant effect on some of the cultures only; but, on average, there was a rather equal, significant, dose-dependent, linear decrease of the mitotic indices of both age groups, whereas the suppressive effect on the number of AgNORs was significant in cultures from the young females only.

Chromosomal aberrations, sister-chromatid exchanges, cell-cycle kinetics and satellite associations in human lymphocyte cultures exposed to vanadium pentoxide

Treatment of human lymphocytes with vanadium pentoxide (V2O5) was not found to increase the frequency of structural chromosomal aberrations (CA) and sister-chromatid exchanges (SCE). However, V2O5 significantly increased polyploid cell frequency; also, the mitotic index (MI) was significantly decreased, and the average generation time (AGT) was significantly increased. Finally, the frequency of cells with satellite associations (SA), the frequency of SA per cell, and the frequency of chromosomes associated increased in treated cultures.

On the possible effects of homeostatic shifts in human embryonic development

Possible etiological factors of congenital malformations as well as of human trisomies are considered in the framework of the repressor hypothesis. In this approach gene expression is envisaged from the point of view of the functional variations of the total activation energy for normal gene expression in homeostatic equilibrium. We restrict our attention to variations of the total activation energy under the effect of temperature gradients. We discuss the evidence that hyperthermia may be an etiological factor for trisomies in humans.

High degree of satellite association and decreased nucleolar organizer activity in cystic fibrosis subjects

The effect of colchicine at concentrations of 0.25 X 10(-6) M, 1.0 X 10(-6) M, and 2.0 X 10(-6) M on the degree of satellite association (SA) was estimated in phytohemagglutinin-stimulated lymphocytes of individuals in the following groups: cystic fibrosis (CF) children, obligatory CF heterozygotes, control children, and control adults. In all four groups increasing colchicine concentration caused a higher degree of SA. The degree of SA differed between the two control age groups (children vs adults) only at the lowest concentration. CF patients had a significantly higher degree of SA than CF heterozygotes and than control individuals at all colchicine concentrations; CF heterozygotes had a significantly higher degree of SA than control adults at the low and intermediate concentrations. There was a strong interaction between genotype and colchicine concentration: the differences between the CF patients and the control individuals were most distinct at the intermediate concentration and between the carriers and the control individuals at the low colchicine concentration. Colchicine had no effect on the activity of the nucleolar organizer regions (NORs), as measured by the frequency of the silver-stained NORs (AgNORs), while the frequency of AgNORs in CF patients was significantly lower as compared to control individuals. Yet, the increase in the degree of SA caused by the CF mutant allele involved specifically the satellited chromosomes carrying active NORs.

Preferential association of nucleolar organizing human chromosomes as revealed by silver staining technique at mitosis

The frequency of different types of satellite associations of nucleolar organizing human chromosomes (i.e. acrocentric chromosomes; 13, 14, 15, 21, and 22) is reported using 10 normal individuals by Ag-staining technique. The preferential involvement of acrocentric chromosomes in satellite association is suggested. Only acrocentric chromosomes with active NORs (i.e. Ag-stained) were found in association while unstained (inactive NORs) chromosomes were never seen in satellite association. In general as number of NORs expression increase, the frequency of association per cell was also increased. A possible mechanism and the clinical consequences of such an unusual phenophenon is described.

Effect of hormone treatment on spontaneous and radiation-induced chromosomal breakage in normal and dwarf mice

Treatment of dwarf mice with growth hormone, insulin and testosterone had no effect on the spontaneous frequencies of micronuclei (MN) in bone-marrow cells, whereas thyroxine decreased these frequencies. The induction of MN by X-rays and mitomycin C was significantly lower in dwarf mice than in normal mice. Treatment with thyroxine plus growth hormone restored normal radiosensitivity in dwarfs.

Correlations between relatives for acrocentric association frequency

Acrocentric association was investigated in peripheral blood lymphocytes of twins (10 female monozygotic and 11 females dizygotic pairs), newborns and both parents (30 families), and spouses (51 pairs). Seventy two hour cultures were G-banded and scored for both absolute and relative acrocentric association frequency, except in the case of the spouse pairs where only the absolute frequency was measured. Both relative and absolute parameters of acrocentric association show positive correlations between relatives with the values being highest and most consistent in monozygotic twins, intermediate in parent and offspring, and most variable in dizygotic twins. Husband and wife pairs from our family collections show a positive correlation for the absolute parameter but not for relative parameters. The environmental factors responsible have not been identified. A rough estimate of broad sense heritability (0.81) has been made for the relative parameters. It probably contains a large component due to genetic dominance. Heritability of the absolute parameters is probably lower than for the relative parameters though estimation of its value is complicated by inconsistent results. A model is proposed to account for the variation in satellite association frequency which contains two elements: (i) The genotype determines the ratio of one chromosome type to another in the population of associated chromosomes (ii) All other environmental factors influence the absolute frequency of association without altering this basic ratio.

Association frequency and silver staining of nucleolus organizing regions in hyperthyroid patients

The intensity of the silver staining of nucleolus organizing regions (NORs) and the frequency of chromosomal associations were studied before and after antithyroid treatment in seven and eight hyperthyroid patients, respectively. For one patient, the NOR staining was significantly more intense after treatment, while for another the opposite result was found. A higher stainability of chromosome 22 was observed after treatment in six of seven patients. The difference was significant for the group of patients considered as a whole but only for one patient considered separately. Chromosome 22 also showed an increased association frequency. Fro one patient, the number of large associations and the total number of associating chromosomes was also significantly increased after treatment. A decrease of associating chromosomes 14 and 21 such as was reported by Nilsson et al, (1975) after antithyroid treatment could not be found in our sample. The possible reason for this difference are discussed.