Induction Of Premature Chromosome Condensation Research Articles

Fusion between interphase and mitotic plant protoplasts: Induction of premature chromosome condensation

Morphological changes in interphase nuclei were cytologically studied in heterophasic dinucleate cells formed by the fusion of mitotic and interphase plant protoplasts. Mitotic protoplasts were isolated from a partially synchronized suspension culture of wheat ( Triticum monococcum). The mitotic cells were accumulated by colchicine after release of hydroxyurea block. Treatment of protoplast populations with polyethylene glycol-dimethyl sulphoxide solution resulted in metaphase-interphase fusion. Three hours after fusion, the appearance of chromosomes with single chromatid as well as of fragmented, pulverized chromatin in heterophasic cells indicated the induction of premature chromosome condensation (PCC) in somatic wheat cells. Condensation in interphase nuclei of mitotically inactive rice protoplasts was also detected after fusion with mitotic wheat protoplasts.

Control of chromosome condensation in the sea urchin egg

Ammonia-activated sea urchin eggs are capable of inducing premature chromosome condensation (PCC) in fertilizing sperm nuclei introduced during the period of maternal pronuclear chromosome condensation. Activated nucleated and enucleated egg halves (merogons) are also capable of inducing PCC during this period. However, the lifetime of the PCC-inducing activity in the enucleated merogons is 5–10 times shorter than in corresponding nucleated merogons, whether they are prepared by density gradient centrifugation or manual bisection. Transcription of maternal nuclear or cytoplasmic genomes or of the sperm nuclear genomes is not required for the induction of PCC. PCC induction becomes independent of protein synthesis in late S or early G2 of the activated egg cycle. These results suggest that the only genetic contribution required to initiate the first chromosome condensation is the translation of stored maternal mRNA prior to G2. However, some maternal pronuclear component, possibly the chromosomes themselves, is responsible for stabilizing the chromosome condensing environment.

Chromosome Condensation and Radiation-induced G2Arrest Studied by the Induction of Premature Chromosome Condensation Following Cell Fusion

When mitotic and interphase cells are fused together, the chromosomes of the interphase cell sometimes condense prematurely. The phenomenon of premature chromosome condensation (PCC) was utilized in investigating the problem of whether the chromosomes of cells suffering a radiation-induced G2 delay are capable of condensation. Colcemide-arrested mitotic cells were fused with synchronized G2 cells, and with irradiated cells suffering a G2 delay. The frequency of PCC in mitotic X G2 binucleate cells was determined. This was compared to the PCC frequency in an unirradiated synchronized population rich in G2 cells after fusion with mitotic cells. Flash-labelling with 3HTdR and autoradiography allowed us to eliminate S-phase cells. The frequency of G2 PCCs was not significantly different for the irradiated G2-delayed or unirradiated cells. From these results we conclude that the chromosomes of cells suffering a G2 arrest are capable of condensation, although the involvement of the condensation process in radiation-induced G2 delay cannot be ruled out.

Induction of premature chromosome condensation in CHO cells fused with polyethylene glycol

Premature chromosome condensation (PCC) was induced in either suspension or monolayer cultures of Chinese hamster ovary (CHO) cells using the chemical fusogen polyethylene glycol (PEG) or PEG with dimethyl sulfoxide (DMSO). For metaphase-interphase fusions in suspension, the incidence of PCC was comparable to that obtained with UV-inactivated Sendai virus fusion. For monolayer fusions, the incidence of PCC increased gradually after a short exposure to PEG or PEG + DMSO to a maximum at about 10–14 h. Hence, both metaphase-interphase fusions and mitotic asynchrony in multinucleated cells were responsible for the induction of PCC. These results illustrated that no viral components were required for PCC formation.

Prematurely condensed chromosomes of dividing and non-dividing cells in aging human cell cultures

Chromosomes of dividing and non-dividing aging cells were examined by fusing senescent WI38 cells with mitotic HeLa cells to induce premature chromosome condensation (PCC). Exposure of the WI38 cells to 3H-thymidine 48 h prior to fusion allowed autoradiographic identification of cells that did not synthesize DNA (non-dividing cells). Ninety-six percent of the non-dividing cells, diploid or tetraploid, induced into PCC had single chromatids and were therefore blocked in the G1 phase of the cell cycle. Anomalous centromeric pairing of chromatids was noted in the remaining 4% of the non-dividing cells. Typical G2 configurations (double chromatids) were observed only among labeled (dividing) cells. The efficiency of PCC induction was independent of culture age. In addition, the efficiency of PCC induction was independent of phase in the cell cycle, as shown by comparison of observed frequencies with expected frequencies.

Premature chromosome condensation I. Visualization of X-ray-induced chromosome damage in interphase cells

A new method is described to visualize chromosome damage in interphase cells immediately after exposure to mutagenic agents. This method involves the fusion of treated interphase cells with untreated mitotic cells which results in the induction of premature chromosome condensation (PCC). Chinese hamster ovary (CHO) cells were treated with X-rays and chromosome aberrations were scored in G2-PCC and the mitotic chromosomes. The incidence of aberrations was significantly higher in PCC than that observed in the mitotic chromosomes of the treated cells. Post-irradiation incubation for I h before fusion allowed the repair of some of the chromosome damage. Data are also presented which indicate that the extent of radiation damage visualized in PCC is inversely proportional to the degree of chromosome condensation. These results indicate that the PCC method has a greater senstivity in the detection of induced chromosome damage than the standard method of scoring metaphase chromosomes.

Mammalian cell fusion. IV. Regulation of chromosome formation from interphase nuclei by various chemical compounds.

AbstractHybrid HeLa cells formed by the fusion of mitotic with interphase cells have been used as a test system to study the effects of various positively and negatively charged compounds on the induction of premature chromosome condensation (PCC) of the interphase nuclei. Among the various positively charged compounds tested, spermine, putrescine and Mg++ were specific in promoting the PCC induction while spermidine was unique in inhibiting this event. All the negatively charged compounds including estradiol‐17β were uniformly inhibitory. The inhibitory effect of estradiol was reversed by putrescine. The inhibition of PCC induction by estradiol seems to be due to its binding to interphase chromatin rather than to the PCC inducers. The differences between the polyamines in their effects on the PCC inducing system has been explained on the basis of their abilities to bind stereospecifically with chromatin.

Mammalian cell fusion: induction of premature chromosome condensation in interphase nuclei.

Further evidence is put forward for the inducibility of chromosome condensation, particularly its consequences in interphase cells that are not ready for mitosis.