Effect of Mitochondrial Inhibitors On Metaphase-Telophase Progression and Nuclear Membrane Formation In Chinese Hamster Cells

Chinese hamster Don cells in log-phase were exposed to Colcemid during the G₂ period with and without a combination of divalent cation chelators and mitochondrial inhibitors. Isolated metaphase cells were incubated as follows: (i) without Colcemid but with other agents and the progression was monitored from metaphase (M) to telophase (Tel) and to cell division; (ii) with Colcemid and other agents and the rate of micronuclei formation in the absence of anaphase was studied. Both EDTA and EGTA accelerated the progression from M to Tel, but did not affect the overall rate of cell division. Chloramphenicol (CAP), an inhibitor of mitochondrial protein synthesis, blocked the effect of the chelators and also retarded the progression. an inhibitor of mitochondrial respiration, Antimycin A (AA), also retarded the progression in the absence of the chelators and prevented the promoting effect of the chelators. A stimulator of ATPase for ATP breakdown. 2,4-dinitrophenol (DNP), accelerated the M to Tel progression. Chloramphenicol (CAP) and AA, as well as DNP, appeared to have little effect on the formation of micronuclei in the presence of Colcemid. EGTA, which affects cell surface Ca²⁺, stimulated the formation of micronuclei. This study indicates that Ca²⁺ ions and mitochondrial function are involved in the regulation of a certain segment of mitosis beyond metaphase, with Ca²⁺ sequestration in the mitochondria and chelation of Ca²⁺ by EGTA as dominant factors.     

The analysis of intron data and their use in the detection of short signals

Summary In order to examine whether certain short DNA sequences (putative splice signals) occurred in a certain region of an intron more often than would be expected by chance, intron data were examined to see what structure they took. There were significant departures from equal nucleotide frequency, and successive nucleotides clearly did not occur independently in the rat and mouse introns examined. The nonindependence was mainly due to a CG shortage and a less marked TA shortage. However the pairwise frequencies explained almost all the variability in triplet frequencies in the data and so the data could be approximately modeled by using nucleotide frequencies conditional on what the previous nucleotide was. Some coding DNA was also examined and the pairs in second and third positions, and third and first positions in a codon, showed similar departures from independence to those of the intron data. Using the probability model derived for intron data, expected frequencies of putative signals were derived and compared with the observed frequencies.Some of the work for this paper was done while the author was at the Department of Applied Statistics, University of Reading, England     

Sperm-epithelium relationships in relation to the time of insemination in little brown bats (Myotis lucifugus)

Copulation lasted for up to 46 min in little brown bats. Spermatozoa were stored in both the uterus and the utero-tubal junction, although intimate relationships between spermatozoa and the epithelium were particularly evident in the utero-tubal junction, and were established at the beginning of the period of sperm storage. Polymorphonuclear leucocytes were present in all uteri irrespective of whether or not they had been inseminated but were not generally present in the utero-tubal junction or oviduct. Engulfment of spermatozoa by the epithelial cells of the utero-tubal junction and by polymorphonuclear leucocytes in the uterine glands was evident soon after copulation. It is suggested that this may effect the removal of defective spermatozoa and allow luminal spermatozoa access to the spatially restricted storage sites. Uninseminated female bats attempted to elicit copulation from torpid males, and were also observed adjacent to copulating pairs. Female bats also uttered copulation calls.     

Selection effects in a model of two intermigrating colonies of finite size

A model of two intermigrating colonies of finite size, in which the fitnesses of the different genotypes vary between the colonies, is considered. It is found that substantial increases in genetic variability occur in colonies with small amounts of heterozygote superiority if a small amount of migration (e.g., one migrant gene per generation) is allowed. Large increases in variability are also found to be maintained if two colonies, in which selection acts in opposite directions in them, intermigrate. The maximum effect is when the migration rate is very small (e.g., one migrant gene every two or three generations). A maximum value of the heterozygosity at a small value of the migration rate also occurs when there is heterozygote disadvantage in each of the two colonies.