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.     

Micromammals and the formation of the Name Chamber at Sterkfontein, South Africa

The depositional history of the Name Chamber at the Sterkfontein early hominid site is complex, as is the case with most such cavities. Unravelling this history may therefore benefit from the input of less usual lines of evidence to complement baseline geological investigations. In this case, micromammalian remains from the Western Talus of the Name Chamber provide tentative evidence for the depositional history of these deposits. Correlation of samples based on minimum numbers of individuals referred to genera occurring in one third or more of the samples suggests that a large proportion of the Western Talus material, particularly that from the area infiltrated by the Eastern Talus deposit, originated in the vicinity of squares P54, Q54 and Q55 in the main excavation, from a depth spanning the boundary between Acheulean and Oldowan levels in Member 5. Differences in general diversity between the samples from the main excavation and some from the Name Chamber support the proposal that surface sediments of the homogeneous deposits have been contaminated by material entering the cavern during the 1994 opening of the feeder shaft. Initial taphonomic analysis indicates that all samples, both the original and those from the Name Chamber, were accumulated by the same avian predator, that is, one or more of three owl species (barn owl Tyto alba, grass owl Tyto capensis and marsh owl Asio capensis).     

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.