Dynamic G- and R-banding of human chromosomes for electron microscopy

Synchronized human lymphocytes were exposed to 5-bromo-2-deoxyuridine (BrdUrd) for incorporation in either G-or R-bands. The substituted bands were revealed by monoclonal anti-BrdUrd antibodies disclosed with either gold-labeled antibodies or with the protein A-gold complex. Sharp G-or R-banding, specific for electron microscopy (EM), was obtained. These banding patterns, referred to as GB-AAu (G-bands by BrdUrd using Antibodies and gold [Au]) and RB-AAu (R-bands by BrdUrd using Antibodies and gold [Au]), resemble dynamic band patterns (GBG and RBG) much more than they do morphologic band patterns (GTG and RHG). The G- and R- band patterns allow accurate chromosome identification and karyotyping. An actual karyotype of human GB-AAu-banded chromosomes at the 750 band level, photographed in the EM, is presented. The method produces excellent band separation and band contrast. Variations in band staining intensities were noted and correlated with BrdUrd enrichment. The C-band regions were positively stained after GB-AAu banding while they were negatively stained after RB-AAu banding. Telomeres appeared heterogeneous after GB-AAu banding suggesting that part of the telomeric bands might be late replicating.     

Seasonal activity patterns of female polar bears (Ursus maritimus) in the Canadian Arctic as revealed by satellite telemetry

We examined seasonal variations in activity level and mobility of female polar bears inhabiting the Canadian Arctic archipelago. The sea-ice habitat consisted primarily of landfast, multi-year ice except from July through October when loose pack-ice predominated. The proportion of the day during which bears were active, and the distance travelled, were documented for 18 bears during 20 months with the aid of satellite telemetry. A peak of activity and mobility occurred in May-July regardless of the reproductive status of tracked bears. The period of elevated activity coincided with a period when seals were especially vulnerable to bear predation. Winter months were characterized by low activity levels and mobility, a response probably related to a reduced access to seals and to inclement weather. During the period preceding den entry (May through September), pregnant females tended to be more mobile in May-June, and less active in August September, compared to non-pregnant, solitary females. Early den entry by pregnant females and facultative use of dens by other members of the population are viewed as a means to conserve energy for individuals with adequate fat reserves but experiencing conditions unfavourable for hunting seals. We conclude that seasonal variations in activity and mobility of polar bears seem closely linked to the temporal dynamics of bear-seal interactions.     

A novel POU domain protein which binds to the T-cell receptor beta enhancer.

POU domain proteins have been implicated in the regulation of a number of lineage-specific genes. Among the first POU domain proteins described were the immunoglobulin octamer-binding proteins Oct-1 and Oct-2. It was therefore of special interest when we identified a novel lymphoid POU domain protein in Southwestern (DNA-protein) screens of T-cell lambda gt11 libraries. This novel POU protein, TCF beta 1, binds in a sequence-specific manner to a critical motif in the T-cell receptor (TCR) beta enhancer. Sequence analysis revealed that TCF beta 1 represents a new class of POU domain proteins which are distantly related to other POU proteins. TCF beta 1 is encoded by multiple exons whose organization is distinct from that of other POU domain proteins. The expression of TCF beta 1 in a tissue-restricted manner and its ability to bind to multiple motifs in the TCR beta enhancer support a role in regulating TCR beta gene expression. The expression of TCF beta 1 in both B and T cells and the ability of recombinant TCF beta 1 to bind octamer and octamer-related motifs suggest that TCF beta 1 has additional roles in lymphoid cell function. The ability of TCF beta 1 to transactivate in a sequence-specific manner is consistent with a role for regulating lymphoid gene expression.     

Activation-induced T-cell death is cell cycle dependent and regulated by cyclin B.

Developing thymocytes and some T-cell hybridomas undergo activation-dependent programmed cell death. Although recent studies have identified some critical regulators in programmed cell death, the role of cell cycle regulation in activation-induced cell death in T cells has not been addressed. We demonstrate that synchronized T-cell hybridomas, irrespective of the point in the cell cycle at which they are activated, stop cycling shortly after they reach G2/M. These cells exhibit the diagnostic characteristics of apoptotic cell death. Although p34cdc2 levels are not perturbed after activation of synchronously cycling T cells, cyclin B- and p34cdc2-associated histone H1 kinase activity is persistently elevated. This activation-dependent induction of H1 kinase activity in T cells is associated with a decrease in the phosphotyrosine content of p34cdc2. We also demonstrate that transient inappropriate coexpression of cyclin B with p34cdc2 induces DNA fragmentation in a heterologous cell type. Finally, in T cells, cyclin B-specific antisense oligonucleotides suppress activation-induced cell death but not cell death induced by exposure to dexamethasone. We therefore conclude that a persistent elevation of the level of cyclin B kinase is required for activation-induced programmed T-cell death.     

Habitat selection as a hierarchy: the spatial scales of winter foraging by muskoxen

We studied the winter resource selection of muskoxen Ovibos moschatus in the High Arctic using a nested hierarchy of spatial scales 1) population range, 2) travel routes, 3) feeding sites (l e clusters of feeding craters), 4) feeding craters, and 5) diet (I e plant species) We found that, generally, patterns of selection remained consistent across all levels At successively smaller scales, muskoxen selected for higher graminoid abundance and particularly for thinner, softer snow cover, although we did not reject the hypothesis of random travel route selection Muskoxen uncovered forages from beneath the snow cover, by cratering, near the flonstic and nival extremes of availability Selection was consistently biased toward use of water sedge, Carex aquatilis As scale changed, however, muskoxen showed reversals of preference for some other forage species Diet was dominated by C aquatilis and cotton sedge, Eriophorum angustifolium , species characteristic of lowland meadows During spring melt, muskoxen moved to snow-free uplands to feed Dietary quality, as revealed by fecal nitrogen, increased at this time The consistency of the results across scales implied that these local levels of habitat selection occurred within one scaling domain     

Scent-marking in free-ranging coyotes, Canis latrans

From November 1977 to March 1978 we recorded the scent-marking behaviour of free-ranging coyotes in southern Québec. Fourteen animals were marked by foot-pad ablation, which made it possible to recognize individuals' tracks in the snow and therefore to relate scent-marking with social organization. We observed 949 scent-marks. The identity of the animals was known for 50% of the tracking distances. Animals living in territorial groups (pairs and pairs with juveniles) marked more than twice as much as solitary non-territorial individuals. In addition the former used stronger forms of marking significantly more often than the latter.     

Use of DNA fingerprinting to determine parentage in muskrats (Ondatra zibethicus).

The detection of high levels of genetic variability by DNA fingerprinting probes has allowed researchers to accurately assess relatedness. Multiple-mating strategies are characteristic of the mating systems of small mammals. As such, techniques that provide an accurate indication of how individuals are related genetically is of great importance to assess the mating system of a species. In this study, we applied the DNA fingerprinting technique to captive and wild muskrats (Ondatra zibethicus) to determine its usefulness for parentage analysis in wild populations. We found that DNA digested with the restriction enzyme Hae III and probed with Jeffrey's minisatellite 33. 15 identified a large amount of polymorphism in both groups of muskrats. The DNA fingerprinting technique correctly assessed parentage within the captive group. In the wild population, paternity was assigned between two adult males based on diagnostic fragments and similarity of banding patterns. The likelihood that paternity could be misassigned to a full sibling was high in this free-ranging population. However, because natal dispersal in muskrats is male biased, it is unlikely that two brothers would associate with the same female.     

Leishmania major LmACR2 is a pentavalent antimony reductase that confers sensitivity to the drug pentostam

Arsenicals and antimonials are first line drugs for the treatment of trypanosomal and leishmanial diseases. To create the active form of the drug, Sb(V) must be reduced to Sb(III). Because arsenic and antimony are related metalloids, and arsenical resistant Leishmania strains are frequently cross-resistant to antimonials, we considered the possibility that Sb(V) is reduced by a leishmanial As(V) reductase. The sequence for the arsenate reductase of Saccharomyces cerevisiae, ScAcr2p, was used to clone the gene for a homologue, LmACR2, from Leishmania major. LmACR2 was able to complement the arsenate-sensitive phenotype of an arsC deletion strain of Escherichia coli or an ScACR2 deletion strain of Saccharomyces cerevisiae. Transfection of Leishmania infantum with LmACR2 augmented Pentostam sensitivity in intracellular amastigotes. LmACR2 was purified and shown to reduce both As(V) and Sb(V). This is the first report of an enzyme that confers Pentostam sensitivity in intracellular amastigotes of Leishmania. We propose that LmACR2 is responsible for reduction of the pentavalent antimony in Pentostam to the active trivalent form of the drug in Leishmania.