Effects of TPA on mitosis of V79 Chinese hamster cells. Reduced precision of chromosome distribution and modification of entrance into and exit out of mitosis.

Protein kinase C (PKC) was activated in V79 Chinese hamster cells with 10 nM 12-O-tetradecanoylphorbol-13-acetate (TPA). Within 30 min soluble activity decreased concomitant with a 10-fold increase of particulate activity. The latter was still elevated after 3 h but was back to control levels after 24 h of treatment; by then soluble activity was lost. The frequency of mitotic cells with signs of abnormal spindle function increased within 15 min and reached a plateau after 45-60 min which lasted throughout the 4 h treatment. The c-mitotic effect was delayed and significantly lower when 10 nM TPA was combined with 50 microM of the protein kinase inhibitor H7. The frequency of disturbed mitotic cells decreased after 24 h of treatment but remained significantly higher than in non-treated cells. Change of medium and addition of new TPA caused a slight but significant further increase. It is suggested that PKC takes part in eliciting the c-mitotic effect of TPA. However, the sustained effect coincident with down-regulation points to significant alterations of the level or the activity of an as yet unidentified ultimate elicitor. TPA also caused a transient block in the G2 phase which was ameliorated by H7 and which could not be detected at all in TPA-pretreated cells (24 h) given new TPA. This suggests that PKC takes part in eliciting the G2/M block as well but the mechanism is different from the one(s) behind the c-mitotic effect. V79 cells were found to exit from mitosis in the presence of 0.2 microgram/ml of colcemid but TPA-pretreated cells showed a decreased exit rate. There was no sign of hampered exit among cells going into mitosis soon after the G2 block was reversed, which implies that the spontaneous reversal of the block does not involve rapid down-regulation of PKC.

Sex-chromosome segregation in inbred Drosophila melanogaster XXY females. I. Influence of closely related Y chromosome derivatives.

In tests of XXYder hybrids from two inbred lines of Drosophila melanogaster, a non-random distribution of various Yder chromosomes was found at regular X disjunction. This non-random Yder distribution was dependent on differences within the proximal X chromosome region (forked--centromere) of these particular lines, with a limited influence of the Yder,s. The Yder,s (originating from BsYy+ chromosome) showed a large influence on both level and brood pattern of secondary non-disjunction. There was no correlation between secondary non-disjunction and non-random Yder distribution, indicating different mechanisms. Cytological examination of the five Yder chromosomes disclosed no relation between the composition or configuration of the Yder,s and the observed distribution effects. Various parts of the present results show inconsistencies with either of the two existing segregation models (Grell, Novitski), suggesting that the mechanistic understanding of the meiotic process requires additional assumptions and/or alternatives.

Recombination in the region between the marker forked and the centromere in inbred Drosophila melanogaster XX and XXY females.

Recombination in the proximal X chromosome interval (forked-centromere) has been studied in hybrids from two inbred lines of Drosophila melanogaster. Attached Ysy+ arms or the proximal region of the Dp (1:1) scV1y+ were used as markers of the centromere. A derived Y chromosome (BsYK) induced a reduction of the recombination frequency in only one of five comparative experiments of XXBsYK and XX females. In two of the tests there was a higher frequency of recombination in the presence of the BsYK. This is not consistent with a competitive preexchange XX and XY association, which according to a generally accepted idea should result in an inevitable decrease in recombination. This is considered as further evidence for non-random Y distribution at regular X disjunction being determined after exchange.