Distribution and prevalence of Sin Nombre hantavirus in rodent species in eastern New Mexico

Orthohantaviruses are diverse zoonotic RNA viruses. Small mammals, such as mice and rats are common chronic, asymptomatic hosts that transmit the virus through their feces and urine. In North America, hantavirus infection primarily causes hantavirus cardiopulmonary syndrome (HCPS), which has a mortality rate of nearly 36%. In the United States of America, New Mexico (NM) is leading the nation in the number of HCPS-reported cases (N = 129). However, no reported cases of HCPS have occurred within eastern NM. In this study, we assessed the prevalence of Sin Nombre virus (SNV) in rodent assemblages across eastern NM, using RT-qPCR. We screened for potential rodent hosts in the region, as well as identified areas that may pose significant infection risk to humans. We captured and collected blood and lung tissues from 738 rodents belonging to 23 species. 167 individuals from 16 different species were positive for SNV RNA by RT-qPCR, including 6 species unreported in the literature: Onychomys leucogaster (Northern grasshopper mouse), Dipodomys merriami (Merriam's kangaroo rat), Dipodomys ordii (Ord's kangaroo rat), Dipodomys spectabilis (Banner-tailed kangaroo rat), Perognathus flavus (Silky pocket mouse), and Chaetodipus hispidus (Hispid pocket mouse). The infection rates did not differ between sexes or rodent families (i.e., Cricetidae vs. Heteromyidae). Generalized linear model showed that disturbed habitat types positively influenced the prevalence of SNV at sites of survey. Overall, the results of this study indicate that many rodent species in east New Mexico have the potential to maintain SNV in the environment, but further research is needed to assess species specific infectivity mechanisms and potential risk to humans.

Ecological factors shaping ectoparasite communities on heteromyid rodents at Médanos de Samalayuca

Rodent ectoparasites are vectors for important pathogens of wildlife, domestic animals, and even zoonosis. Nevertheless, distribution patterns of ectoparasites are not fully understood; habitat, season, and host species are important predictors of distribution and prevalence. Heteromyid rodents are considered important reservoirs of diseases, given the presence of different ectoparasites and pathogens in them, and they offer the opportunity to learn about the ecology of parasites. The aim of the present work was to survey ectoparasites associated with heteromyid rodents near a National Protected Area in Chihuahua Mexico, south of the USA-Mexico border, and asses the effects of ecological factors (season, vegetation type, host species, and host body condition) on parasite infestation. We sampled five different locations from January 2018 to July 2022; 845 heteromyid rodents were examined and 49 fleas and 33 ticks were collected. Ectoparasites belonged to the Siphonaptera and Ixodida orders, including three families Ixodidae (Riphicephalus sanguineus), Pulicidae (Pulex irritans), and Ctenophthalmidae (Meringins altipecten, M. dipodomys). Five species of host rodents were captured, Dipodomys merriami, D. ordii, Chaetodipus eremicus, C. hispidus, and C. intermedius, but the last two species did not present any ectoparasites. Dipodomys merriami presented the highest flea and tick prevalence followed by D. ordii. We found parasitic partnerships between heteromyids according to ecological factors. The infestation in C. eremicus was related to body condition, vegetation type, and sex; in D. merriami, it was related to vegetation type and season, while D. ordii did not present a clear pattern of infestation. Our results suggest that the infestation patterns of heteromyid rodents in desert habitats are species dependent.

The earliest dipodomyine heteromyid in North America and the phylogenetic relationships of geomorph rodents

Dipodomyine heteromyids (kangaroo rats and mice) are a diverse group of arid-adapted ricochetal rodents of North America. Here, a new genus and species of a large dipodomyine is reported from early Miocene-aged deposits of the John Day Formation in Oregon that represents the earliest record of the subfamily. The taxon is known from a single specimen consisting of a nearly complete skull, dentary, partial pes, and caudal vertebra. The specimen is characterized by a mosaic of ancestral and highly derived cranial features of heteromyids. Specifically, the dental morphology and some cranial characteristics are similar to early heteromyids, but other aspects of morphology, including the exceptionally inflated auditory bullae, are more similar to known dipodomyines. This specimen was included in a phylogenetic analysis comprising 96 characters and the broadest sampling of living and extinct geomorph rodents of any morphological phylogenetic analysis to date. Results support the monophyly of crown-group Heteromyidae exclusive of Geomyidae and place the new taxon within Dipodomyinae. The new heteromyid is the largest known member of the family. Analyses suggest that large body size evolved several times within Heteromyidae. Overall, the morphology of the new heteromyid supports a mosaic evolution of the open-habitat adaptations that characterize kangaroo rats and mice, with the inflation of the auditory bulla appearing early in the group, and bipedality/ricochetal locomotion appearing later. We hypothesize that cooling and drying conditions in the late Oligocene and early Miocene favored adaptations for life in more open habitats, resulting in increased locomotor specialization in this lineage over time from a terrestrial ancestor.

Immunohistochemistry of kangaroo rat hindlimb muscles

Kangaroo rats (Dipodomys spp.) use specialized bipedal hopping like that of kangaroos. In contrast to kangaroos that have elastic tendons capable of storing energy, kangaroo rats have inelastic tendons that are unable to store large amounts of energy. Thus, the musculature of the ankle joint provides the greatest power contribution to kangaroo rat hopping. Skeletal muscle can be characterized by several fiber types, including slow twitch (Type I) and fast twitch (Type II) fibers. Fast fibers are found in higher concentration in muscles that perform quick, dynamic movements, whereas slow fibers are found in higher proportion in muscles that perform slow, endurant movements. Using fiber type specific antibodies, we identified four pure (Types I, IIA, IIB, and IIX) and two hybrid (Types I/IIA and IIA/IIX) fiber types in six hindlimb muscles from three kangaroo rats (Dipodomys merriami) to investigate the relationship between fiber composition and hindlimb muscle function. Hindlimb muscles (except soleus) were dominated by Type IIB fibers, which were largest in cross-sectional area, and are known to be best suited for rapid and explosive movements. Oxidative Type IIA and Type IIX fibers were found at moderate concentrations and likely function in maintaining continual saltatory locomotion. Thus, kangaroo rats can use these two fiber type populations as "gears" for both endurant and explosive behaviors.

Estimation of the force-velocity properties of individual muscles from measurement of the combined plantarflexor properties

The force-velocity (F-V) properties of isolated muscles or muscle fibers have been well studied in humans and other animals. However, determining properties of individual muscles in vivo remains a challenge because muscles usually function within a synergistic group. Modeling has been used to estimate the properties of an individual muscle from the experimental measurement of the muscle group properties. While this approach can be valuable, the models and the associated predictions are difficult to validate. In this study, we measured the in situ F-V properties of the maximally activated kangaroo rat plantarflexor group and used two different assumptions and associated models to estimate the properties of the individual plantarflexors. The first model (Mdl1) assumed that the percent contributions of individual muscles to group force and power were based upon the muscles' cross-sectional area and were constant across the different isotonic loads applied to the muscle group. The second model (Mdl2) assumed that the F-V properties of the fibers within each muscle were identical, but because of differences in muscle architecture, the muscles' contributions to the group properties changed with isotonic load. We compared the two model predictions with independent estimates of the muscles' contributions based upon sonomicrometry measurements of muscle length. We found that predictions from Mdl2 were not significantly different from sonomicrometry-based estimates while those from Mdl1 were significantly different. The results of this study show that incorporating appropriate fiber properties and muscle architecture is necessary to parse the individual muscles' contributions to the group F-V properties.

Individual kinetochore-fibers locally dissipate force to maintain robust mammalian spindle structure

At cell division, the mammalian kinetochore binds many spindle microtubules that make up the kinetochore-fiber. To segregate chromosomes, the kinetochore-fiber must be dynamic and generate and respond to force. Yet, how it remodels under force remains poorly understood. Kinetochore-fibers cannot be reconstituted in vitro, and exerting controlled forces in vivo remains challenging. Here, we use microneedles to pull on mammalian kinetochore-fibers and probe how sustained force regulates their dynamics and structure. We show that force lengthens kinetochore-fibers by persistently favoring plus-end polymerization, not by increasing polymerization rate. We demonstrate that force suppresses depolymerization at both plus and minus ends, rather than sliding microtubules within the kinetochore-fiber. Finally, we observe that kinetochore-fibers break but do not detach from kinetochores or poles. Together, this work suggests an engineering principle for spindle structural homeostasis: different physical mechanisms of local force dissipation by the k-fiber limit force transmission to preserve robust spindle structure. These findings may inform how other dynamic, force-generating cellular machines achieve mechanical robustness.

Derivation of soil-screening thresholds to protect the chisel-toothed kangaroo rat from uranium mine waste in northern Arizona

Chemical data from soil and weathered waste material samples collected from five uranium mines north of the Grand Canyon (three reclaimed, one mined but not reclaimed, and one never mined) were used in a screening-level risk analysis for the Arizona chisel-toothed kangaroo rat (Dipodomys microps leucotis); risks from radiation exposure were not evaluated. Dietary toxicity reference values were used to estimate soil-screening thresholds presenting risk to kangaroo rats. Sensitivity analyses indicated that body weight critically affected outcomes of exposed-dose calculations; juvenile kangaroo rats were more sensitive to the inorganic constituent toxicities than adult kangaroo rats. Species-specific soil-screening thresholds were derived for arsenic (137 mg/kg), cadmium (16 mg/kg), copper (1,461 mg/kg), lead (1,143 mg/kg), nickel (771 mg/kg), thallium (1.3 mg/kg), uranium (1,513 mg/kg), and zinc (731 mg/kg) using toxicity reference values that incorporate expected chronic field exposures. Inorganic contaminants in soils within and near the mine areas generally posed minimal risk to kangaroo rats. Most exceedances of soil thresholds were for arsenic and thallium and were associated with weathered mine wastes.

Mitochondrial cristae revealed with focused light

Because of the diffraction resolution barrier, optical microscopes have so far failed in visualizing the mitochondrial cristae, that is, the folds of the inner membrane of this 200 to 400 nm diameter sized tubular organelle. Realizing a approximately 30 nm isotropic subdiffraction resolution in isoSTED fluorescence nanoscopy, we have visualized these essential structures in the mitochondria of intact cells. We find a pronounced heterogeneity in the cristae arrangements even within individual mitochondrial tubules.

Assessment of mercury concentrations in small mammals collected near Las Vegas, Nevada, USA

Mercury concentrations in liver and hair tissue were determined for five species of small mammals captured near Las Vegas, Nevada, USA. These data were then used to evaluate the suitability of using hair as a noninvasive technique for determining body burdens of mercury. A total of 104 small mammals were captured and analyzed; four main species were examined and included: Dipodomys merriami, Chaetodipus penicillatus, Peromyscus eremicus, and Neotoma lepida. Mean mercury concentrations were highest in N. lepida, followed by D. merriami, C. penicillatus, and P. eremicus respectively. Positive associations were found between hair and liver taken from D. merriami (r = 0.647) and C. penicillatus (r = 0.533) indicating that hair may be a suitable indicator of body burdens in these two species.

Phosphoinositide 3-Kinase Is Required for Intracellular Listeria monocytogenes Actin-based Motility and Filopod Formation

Motile nonmuscle cells concentrate phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) in areas of new actin filament assembly. There is great interest in assessing the in vivo functional significance of these phosphoinositides, and we have used Listeria monocytogenes to explore the contribution of PtdIns(3,4,5)P3 and PtdIns(4,5)P2 to its actin-based motility. In Listeria-infected PtK2 cells Akt-pleckstrin homology (PH)-green fluorescent protein (GFP) and phospholipase C delta (PLC delta)-PH-GFP both first concentrate at the front of motile Listeria, subsequently surrounding the bacterium and then concentrating in the actin filament tail. Surprisingly, Listeria ActA mutant strains lacking the putative phosphoinositide binding site are also able to concentrate these probes. Reduction of available PtdIns(3,4,5)P3 by expression of Akt-PH-GFP and available PtdIns(4,5)P2 by expression of PLC delta-PH-GFP both significantly slow Listeria actin-based movement. Treatment of cells with the PI 3-kinase inhibitor, LY294002, dissociates Akt-PH but not PLC delta-PH, from the bacterial surface and cell membranes, and results in near complete inhibition of Listeria actin-based motility and filopod formation. Removal of LY294002 results in rapid and full recovery of Akt-PH localization, Listeria actin-based motility, and filopod formation. These findings suggest that PtdIns(4,5)P2 is concentrated at the surface of Listeria and serves as the substrate for PtdIns(3,4,5)P3 production, indicating a central role for PI 3-kinases in Listeria intracellular actin-based motility and filopod formation.

Cache Decision Making: The Effects of Competition on Cache Decisions in Merriam's Kangaroo Rat (Dipodomys merriami)

Caching food is an economic, decision-making process that requires animals to take many factors into account, including the risk of pilferage. However, little is known about how food-storing animals determine the risk of pilferage. In this study, the authors examined the effect of a dominant competitor species on the caching and behavior of Merriam's kangaroo rat (Dipodomys merriami). The authors found that, as with conspecific competitors, kangaroo rats did not alter caching in response to the mere presence of a heterospecific competitor, but moved caches to an unpreferred area when the competitor's presence was paired with pilferage. These data suggest that Merriam's kangaroo rat assesses pilfer risk from actual pilferage by a competitor and adaptively alters cache strategy to minimize future risk.

Detection of non-Brownian diffusion in the cell membrane in single molecule tracking

Molecules undergo non-Brownian diffusion in the plasma membrane, but the mechanism behind this anomalous diffusion is controversial. To characterize the anomalous diffusion in the complex system of the plasma membrane and to understand its underlying mechanism, single-molecule/particle methods that allow researchers to avoid ensemble averaging have turned out to be highly effective. However, the intrinsic problems of time-averaging (resolution) and the frequency of the observations have not been explored. These would not matter for the observations of simple Brownian particles, but they do strongly affect the observation of molecules undergoing anomalous diffusion. We examined these effects on the apparent motion of molecules undergoing simple, totally confined, or hop diffusion, using Monte Carlo simulations of particles undergoing short-term confined diffusion within a compartment and long-term hop diffusion between these compartments, explicitly including the effects of time-averaging during a single frame of the camera (exposure time) and the frequency of observations (frame rate). The intricate relationships of these time-related experimental parameters with the intrinsic diffusion parameters have been clarified, which indicated that by systematically varying the frame time and rate, the anomalous diffusion can be clearly detected and characterized. Based on these results, single-particle tracking of transferrin receptor in the plasma membrane of live PtK2 cells were carried out, varying the frame time between 0.025 and 33 ms (0.03-40 kHz), which revealed the hop diffusion of the receptor between 47-nm (average) compartments with an average residency time of 1.7 ms, with the aid of single fluorescent-molecule video imaging.

Hesseltin A, a Novel Antiviral Metabolite from Penicillium hesseltinei

[structure: see text] Hesseltin A 1, a novel compound of mixed polyketide-terpenoid origins was isolated from the filamentous fungus Penicillium hesseltinei. The structure and stereochemistry were determined from extensive one- and two-dimensional NMR and mass spectral data.

Membrane organization and function of M1 and M23 isoforms of aquaporin-4 in epithelial cells

Aquaporin-4 (AQP4) water channels exist as heterotetramers of M1 and M23 splice variants and appear to be present in orthogonal arrays of intramembraneous particles (OAPs) visualized by freeze-fracture microscopy. We report that AQP4 forms OAPs in rat gastric parietal cells but not in parietal cells from the mouse or kangaroo rat. Furthermore, the organization of principal cell OAPs in Brattleboro rat kidney is perturbed by vasopressin (arginine vasopressin). Membranes of LLC-PK1cells expressing M23-AQP4 showed large, abundant OAPs, but none were detectable in cells expressing M1-AQP4. Measurements of osmotic swelling of transfected LLC-PK1cells using videomicroscopy, gave osmotic water permeability coefficient ( Pf) values (in cm/s) of 0.018 (M1-AQP4), 0.019 (M23-AQP4), and 0.003 (control). Quantitative immunoblot and immunofluorescence showed an eightfold greater expression of M1- over M23-AQP4 in the cell lines, suggesting that single-channel pf(cm3/s) is much greater for the M23 variant. Somatic fusion of M1- and M23-AQP4 cells ( Pf= 0.028 cm/s) yielded OAPs that were fewer and smaller than in M23 cells alone, and M1-to-M23 expression ratios (∼1:4) normalized to AQP4 in M1 or M23 cells indicated a reduced single-channel pffor the M23 variant. Expression of an M23-AQP4-Ser111Emutant produced ∼1.5-fold greater single-channel pfand OAPs that were up to 2.5-fold larger than wild-type M23-AQP4 OAPs, suggesting that a putative PKA phosphorylation site Ser111is involved in OAP formation. We conclude that the higher-order organization of AQP4 in OAPs increases single-channel osmotic water permeability by one order of magnitude and that differential cellular expression levels of the two isoforms could regulate this organization.

Partitioning of aquaporin-4 water channel mRNA and protein in gastric glands

Immunolocalization studies in proximal, middle, and distal stomach indicated that aquaporin-4 (AQP4) protein is localized only in parietal cells located in the middle or deep regions of the gastric glands. In studies using in situ hybridization, AQP4 mRNA failed to localize in parietal cells but was identified in neighboring mucosal cells that were triangular in shape and smaller than parietal cells in size, and in columnar cells at the base of the gastric gland. This spatial separation of mRNA and protein was also observed in other species and with other kind of mRNA/protein. In neonatal and adolescent rats, the appearance of morphologically mature parietal cells was preceded by identification of mRNA-bearing triangular cells. Cells harboring both protein and mRNA were observed in postnatal rats and in the pyloric region of the glandular stomach, during induced hypergastrinaemia. The results suggest that such cells represent a transition between those that bear only mRNA and those that are terminally differentiated, expressing proteins that are related to acid secretion.

Both alpha and beta isoforms of mammalian DNA topoisomerase II associate with chromosomes in mitosis

Two isoforms of DNA topoisomerase II, alpha and beta, coded by separate genes, are expressed in actively cycling vertebrate cells. Some previous studies have suggested that only topoisomerase II alpha remains associated with chromosomes at mitosis. Here, the distributions of topoisomerase II alpha and beta in mitosis were studied by subcellular fractionation and by immunolocalization. Both isoforms of topoisomerase II were found to remain associated with mitotic chromatin. Topoisomerase II alpha was distributed along chromosome arms throughout mitosis and was highly concentrated at centromeres until mid-anaphase, particularly in some cell types. Topoisomerase II beta showed weak concentration at centromeres in early mitosis in some cell types and was distributed along chromosome arms at every stage of mitosis through telophase. These studies suggest that in most cells both the major topoisomerase II isoforms may play roles in chromatin remodeling during M phase.

A fluorescent resonant energy transfer-based biosensor reveals transient and regional myosin light chain kinase activation in lamella and cleavage furrows

Approaches with high spatial and temporal resolution are required to understand the regulation of nonmuscle myosin II in vivo. Using fluorescence resonance energy transfer we have produced a novel biosensor allowing simultaneous determination of myosin light chain kinase (MLCK) localization and its [Ca2+]4/calmodulin-binding state in living cells. We observe transient recruitment of diffuse MLCK to stress fibers and its in situ activation before contraction. MLCK is highly active in the lamella of migrating cells, but not at the retracting tail. This unexpected result highlights a potential role for MLCK-mediated myosin contractility in the lamella as a driving force for migration. During cytokinesis, MLCK was enriched at the spindle equator during late metaphase, and was maximally activated just before cleavage furrow constriction. As furrow contraction was completed, active MLCK was redistributed to the poles of the daughter cells. These results show MLCK is a myosin regulator in the lamella and contractile ring, and pinpoints sites where myosin function may be mediated by other kinases.

HOXC13 is involved in the regulation of human hair keratin gene expression

At present, HOXC13 is the only member of the HOX multigene family that produces a fragile hair phenotype when mutated or overexpressed in mice. To determine whether hair keratin genes are targets for this transcription factor, we analyzed the HOXC13 responsiveness of human hair keratin genes, whose expression matched that of nuclear HOXC13, immunologically revealed in cells of the lower hair-forming compartment of the human anagen hair follicle. We show that HOXC13, but not a homeobox-deleted HOXC13, strongly activated the promoters of the genes, with the respective proximal promoter regions being sufficient for optimal activation. The hair keratin promoters contained numerous putative Hox binding core motifs TAAT, TTAT, and TTAC. Electrophoretic mobility shift assays revealed that HOXC13 bound exclusively to distinct TAAT and TTAT core motifs that were clearly concentrated in the proximal promoter regions. A comparison of the sequences flanking HOXC13 binding and nonbinding core motifs, respectively, allowed the deduction of an extended 8-bp HOXC13 consensus binding sequence TT(A/T)ATNPuPu. Thus, the DNA binding conditions for HOXC13 were distinct from those of other members of the paralogous group 13, i.e. murine Hoxb13 and HOXd13, for which previous investigations yielded the consensus binding sequence TTTA(T/C)NPuPu. Collectively, our data speak for a direct involvement of HOXC13 in the control of hair keratin expression during early trichocyte differentiation.

Use of fluorescently labelled deoxyribonuclease I to spatially measure G-actin levels in migrating and non-migrating cells

Lamellipodium protrusion is linked to actin filament disassembly in migrating fibroblasts [Cramer, 1999: Curr. Biol. 9:1095-1105]. To further study this relationship, we have identified a method to specifically and sensitively detect G-actin in distinct spatial locations in motile cells using deoxyribonuclease I (DNase I). Although DNase I can bind both G- and F-actin in vitro [Mannherz et al., 1980: Eur. J. Biochem. 95:377-385], when cells were fixed in formaldehyde and permeabilized in detergent, fluorescently-labelled DNase I specifically stained G-actin and not F-actin. 92-98% of actin molecules were stably retained in cells during fixation and permeabilization. Further, increasing or decreasing cellular G-actin concentration by treating live cells with latrunculin-A or jasplakinolide, respectively, caused a respective increase and decrease in DNase I cell-staining intensity as expected. These changes in DNase I fluorescence intensity accurately reflected increases and decreases in cellular G-actin concentration independently measured in lysates prepared from drug-treated live cells (regression coefficient = 0.98). This shows that DNase I cell-staining is very sensitive using this method. Applying this method, we found that the ratio of G-/F-actin is lower in both the lamellipodium and in a broad band immediately behind the lamellipodium in migrating compared to non-migrating fibroblasts. Thus, we predict that protrusion of the lamellipodium in migrating fibroblasts requires tight coupling to filament disassembly at least in part because G-actin is relatively limited within and behind the lamellipodium. This is the first report to directly demonstrate high sensitivity of cell-staining for any G-actin probe and this, together with the ready commercial accessibility of fluorescently-labelled DNase I, make it a simple, convenient, and sensitive tool for cell-staining of G-actin.

Urea excretion in white rats and kangaroo rats as influenced by excitement and by diet

Reprinted from The American Journal of Physiology, Vol. 181, No.1, April, 1955.

Dolastatin 11, a marine depsipeptide, arrests cells at cytokinesis and induces hyperpolymerization of purified actin

The successful synthesis of dolastatin 11, a depsipeptide originally isolated from the mollusk Dolabella auricularia, permitted us to study its effects on cells. The compound arrested cells at cytokinesis by causing a rapid and massive rearrangement of the cellular actin filament network. In a dose-and time-dependent manner, F-actin was rearranged into aggregates, and subsequently the cells displayed dramatic cytoplasmic retraction. The effects of dolastatin 11 were most similar to those of the sponge-derived depsipeptide jasplakinolide, but dolastatin 11 was about 3-fold more cytotoxic than jasplakinolide in the cells studied. Like jasplakinolide, dolastatin 11 induced the hyperassembly of purified actin into filaments of apparently normal morphology. Dolastatin 11 was qualitatively more active than jasplakinolide and, in a quantitative assay we developed, dolastatin 11 was twice as active as jasplakinolide and 4-fold more active than phalloidin. However, in contrast to jasplakinolide and phalloidin, dolastatin 11 did not inhibit the binding of a fluorescent phalloidin derivative to actin polymer nor was it able to displace the phalloidin derivative from polymer. Thus, despite its structural similarity to other agents that induce actin assembly (all are peptides or depsipeptides), dolastatin 11 may interact with actin polymers at a distinct drug binding site.

Residues in the 1A rod domain segment and the linker L2 are required for stabilizing the A11 molecular alignment mode in keratin intermediate filaments

Both analyses of x-ray diffraction patterns of well oriented specimens of trichocyte keratin intermediate filaments (IF) and in vitro cross-linking experiments on several types of IF have documented that there are three modes of alignment of pairs of antiparallel molecules in all IF: A11, A22 and A12, based on which parts of the major rod domain segments are overlapped. Here we have examined which residues may be important for stabilizing the A11 mode. Using the K5/K14 system, we have made point mutations of charged residues along the chains and examined the propensities of equimolar mixtures of wild type and mutant chains to reassemble using as criteria: the formation (or not) of IF in vitro or in vivo; and stabilities of one- and two-molecule assemblies. We identified that the conserved residue Arg10 of the 1A rod domain, and the conserved residues Glu4 and Glu6 of the linker L2, were essential for stability. Additionally, conserved residues Lys31 of 1A and Asp1 of 2A and non-conserved residues Asp/Asn9 of 1A, Asp/Asn3 of 2A, and Asp7 of L2 are important for stability. Notably, these groups of residues lie close to each other when two antiparallel molecules are aligned in the A11 mode, and are located toward the ends of the overlap region. Although other sets of residues might theoretically also contribute, we conclude that these residues in particular engage in favorable intermolecular ionic and/or H-bonding interactions and thereby may play a role in stabilizing the A11 mode of alignment in keratin IF.

Single amino acid (arginine) deprivation: rapid and selective death of cultured transformed and malignant cells

The effects of arginine deprivation (-Arg) has been examined in 26 cell lines. Less than 10% of those with transformed or malignant phenotype survived for > 5 days, and many died more rapidly, notably leukaemic cells. Bivariate flow cytometry confirmed that vulnerable cell lines failed to move out of cell cycle into a quiescent state (G0), but reinitiated DNA synthesis. Many cells remained in S-phase, and/or had difficulty progressing through to G2 and M. Two tumour lines proved relatively 'resistant', A549 and MCF7. Although considerable cell loss occurred initially, both lines showed a 'cell cycle freeze', in which cells survived for > 10 days. These cells recovered their proliferative activity in +Arg medium, but behaved in the same manner to a second -Arg episode as they did to the first episode. In contrast, normal cells entered G0 and survived in -Arg medium for several weeks, with the majority of cells recovering with predictable kinetics in +Arg medium. In general, cells from a wide range of tumours and established lines die quickly in vitro following -Arg treatment, because of defective cell cycle checkpoint stringency, the efficacy of the treatment being most clearly demonstrated in co-cultures in which only the normal cells survived. The findings demonstrate a potentially simple, effective and non-genotoxic strategy for the treatment of a wide range of cancers.

Regional regulation of microtubule dynamics in polarized, motile cells

Microtubules are known to be required for locomotion of mammalian cells, and recent experiments demonstrate that suppression of microtubule dynamic turnover reduces the rate of cell motility and induces wandering of growth cones [Liao et al., 1995: J Cell Sci. 108:3473-3483; Tanaka et al., 1995: J Cell Biol. 128:139-155]. To determine how microtubule dynamic instability behavior contributes to directed cell locomotion, the behavior of individual microtubules has been directly observed and quantified at leading and lateral edges of hepatocyte growth factor-treated motile cells. Microtubules extended into newly formed protrusions at the leading edge; these "pioneer" microtubules [Waterman-Storer and Salmon, 1997: J Cell Biol. 139:417-434] showed persistent growth when compared with microtubules in non-leading, lateral edges. The percentage of total observation time spent in the growth phase was 68.2% at the leading edge compared with 32.0% in non-leading edges, and net microtubule elongation was observed in lamellipodia at the leading edge. The frequency of catastrophe transitions was threefold greater and the average number of transitions/microtubule/min was twofold greater in non-leading edges, as compared with the leading edge. These observations demonstrate that pioneer microtubules that enter newly formed lamellipodia at the leading edge of motile cells are characterized by persistent growth excursions, and directly demonstrate that the frequency of catastrophe transitions can be regionally regulated in polarized motile cells. The data indicate that region specific differences in the organization and dynamics of actin filaments may regulate microtubule dynamic instability behavior in vivo.

Subcellular phototoxicity of 5-aminolaevulinic acid (ALA)

BACKGROUND AND OBJECTIVE

5-aminolaevulinic acid (ALA) is a new, promising photosensitizer for PDT of cancer. Subcellular toxicity induced by ALA and light exposure in single cells was studied to elucidate the mechanism of cell damage.

STUDY DESIGN/MATERIALS AND METHODS

CPAE, PTK2, and rat neonatal myocardial cells treated with ALA were examined for localization using fluorescence microscopy and for subcellular phototoxicity using 630 nm laser microbeam irradiation of specific subcellular regions.

RESULTS

In CPAE and PTK2 cells, a large amount of fluorescence was detected in the peri-nuclear cytoplasm. In rat neonatal myocardial cells, the sensitizer selectively localized in the large mitochondria. In both cell types, there was little phototoxicity when the peripheral cytoplasmic region was exposed, as compared to considerable phototoxicity with exposure of either the perinuclear or nuclear regions.

CONCLUSION

Both the CPAE and PTK2 cells demonstrated that the nucleus followed by the perinuclear cytoplasm are the most sensitive cell areas with no sensitivity in the peripheral cytoplasm.

Molecular dissection of zyxin function reveals its involvement in cell motility

Spatially controlled actin filament assembly is critical for numerous processes, including the vectorial cell migration required for wound healing, cell- mediated immunity, and embryogenesis. One protein implicated in the regulation of actin assembly is zyxin, a protein concentrated at sites where the fast growing ends of actin filaments are enriched. To evaluate the role of zyxin in vivo, we developed a specific peptide inhibitor of zyxin function that blocks its interaction with alpha-actinin and displaces it from its normal subcellular location. Mislocalization of zyxin perturbs cell migration and spreading, and affects the behavior of the cell edge, a structure maintained by assembly of actin at sites proximal to the plasma membrane. These results support a role for zyxin in cell motility, and demonstrate that the correct positioning of zyxin within the cell is critical for its physiological function. Interestingly, the mislocalization of zyxin in the peptide-injected cells is accompanied by disturbances in the distribution of Ena/VASP family members, proteins that have a well-established role in promoting actin assembly. In concert with previous work, our findings suggest that zyxin promotes the spatially restricted assembly of protein complexes necessary for cell motility.

Chmadrin: a novel Ki-67 antigen-related perichromosomal protein possibly implicated in higher order chromatin structure

A novel perichromosomal protein, which we have named chmadrin, was identified from rat kangaroo PtK2 cells. The deduced amino acid sequence revealed structural homologies in several limited regions to the Ki-67 antigen (pKi-67). The subcellular localization of chmadrin was found to be similar to that of pKi-67 throughout the cell cycle, that is, predominantly nucleolar during interphase and perichromosomal in the mitotic phase. In addition, a certain population of the protein was found to be localized in heterochromatic foci in interphase nuclei. Transient expression analysis of the truncated proteins corresponding to the conserved regions clearly demonstrated the structural basis for the characteristic cellular localization. Residues 494–778, which show extensive similarity to the corresponding region of pKi-67, were efficiently targeted to nucleoli, whereas a repetitive structure found at the C-terminal portion, whose similarity to pKi-67 is weak, was localized precisely to mitotic chromosomes. The C-terminal portion was designated the ‘LR domain’ since several LR (leucine and arginine) pairs commonly appear in chmadrin and pKi-67. When overproduced in the interphase nuclei, the LR domain induced the formation of aberrant heterochromatin as a structural constituent. These are the first empirical data suggesting the involvement of perichromosomal proteins in the organization of chromatin structure.

Temporal and spatial control of cyclin B1 destruction in metaphase

The proteolysis of key regulatory proteins is thought to control progress through mitosis. Here we analyse cyclin B1 degradation in real time and find that it begins as soon as the last chromosome aligns on the metaphase plate, just after the spindle-assembly checkpoint is inactivated. At this point, cyclin B1 staining disappears from the spindle poles and from the chromosomes. Cyclin B1 destruction can subsequently be inactivated throughout metaphase if the spindle checkpoint is reimposed, and this correlates with the reappearance of cyclin B1 on the spindle poles and the chromosomes. These results provide a temporal and spatial link between the spindle-assembly checkpoint and ubiquitin-mediated proteolysis.

Characterization of the p22 subunit of dynactin reveals the localization of cytoplasmic dynein and dynactin to the midbody of dividing cells

Dynactin, a multisubunit complex that binds to the microtubule motor cytoplasmic dynein, may provide a link between dynein and its cargo. Many subunits of dynactin have been characterized, elucidating the multifunctional nature of this complex. Using a dynein affinity column, p22, the smallest dynactin subunit, was isolated and microsequenced. The peptide sequences were used to clone a full-length human cDNA. Database searches with the predicted amino acid sequence of p22 indicate that this polypeptide is novel. We have characterized p22 as an integral component of dynactin by biochemical and immunocytochemical methods. Affinity chromatography experiments indicate that p22 binds directly to the p150(Glued) subunit of dynactin. Immunocytochemistry with antibodies to p22 demonstrates that this polypeptide localizes to punctate cytoplasmic structures and to the centrosome during interphase, and to kinetochores and to spindle poles throughout mitosis. Antibodies to p22, as well as to other dynactin subunits, also revealed a novel localization for dynactin to the cleavage furrow and to the midbodies of dividing cells; cytoplasmic dynein was also localized to these structures. We therefore propose that dynein/dynactin complexes may have a novel function during cytokinesis.

Entry into mitosis in vertebrate somatic cells is guarded by a chromosome damage checkpoint that reverses the cell cycle when triggered during early but not late prophase

When vertebrate somatic cells are selectively irradiated in the nucleus during late prophase (<30 min before nuclear envelope breakdown) they progress normally through mitosis even if they contain broken chromosomes. However, if early prophase nuclei are similarly irradiated, chromosome condensation is reversed and the cells return to interphase. Thus, the G2 checkpoint that prevents entry into mitosis in response to nuclear damage ceases to function in late prophase. If one nucleus in a cell containing two early prophase nuclei is selectively irradiated, both return to interphase, and prophase cells that have been induced to returned to interphase retain a normal cytoplasmic microtubule complex. Thus, damage to an early prophase nucleus is converted into a signal that not only reverses the nuclear events of prophase, but this signal also enters the cytoplasm where it inhibits e.g., centrosome maturation and the formation of asters. Immunofluorescent analyses reveal that the irradiation-induced reversion of prophase is correlated with the dephosphorylation of histone H1, histone H3, and the MPM2 epitopes. Together, these data reveal that a checkpoint control exists in early but not late prophase in vertebrate cells that, when triggered, reverses the cell cycle by apparently downregulating existing cyclin-dependent kinase (CDK1) activity.

Genome composition in Venezuelan spiny-rats of the genus Proechimys(Rodentia, Echimyidae). I. Genome size, C-heterochromatin and repetitive DNAs in situ hybridization patterns

The genome sizes of the Venezuelan spiny-rats Proechimys guairae guairae (2n = 48) and P. trinitatis (2n = 62) were evaluated and proved to be 12.5 +/- 0.5 pg and 12.6 +/- 0.3 pg respectively, the highest so far recorded among mammals; also the C-heterochromatin (32.7%, Coefficient of Variation [CV] 3.8 and 35.8%, CV 4.4) and GC (44.2%, CV 2.7 and 43.6%, CV 2.9) contents are very high. Highly repetitive (rep) DNAs were isolated from restriction enzyme digested genomic DNAs of both species. The intra- and inter-specific chromosomal allocations of these rep DNAs were analyzed by direct and cross-hybridizations. Results show that the two genomes harbour several rep DNA families which show both species-specificity and interspecific relatedness in their in situ hybridization patterns. The rep DNA families show an equilocal distribution at both the pericentromeric areas of all chromosomes and in the whole arms of two pairs of the uniarmed group, suggesting co-evolution of the rep DNAs. P. g. guairae BamHI digested DNA, when cloned and sequenced, proved to consist of a long "composite" unit (1,239 bp) containing two copies of each of 75-bp and 110-bp internal subrepeats. Karyotype restructuring between P. g. guairae and P. trinitatis, mainly due to Robertsonian changes, was accompanied by slight intra- and intergenomic movements of the putative satellite DNA families within stable genome sizes and C-heterochromatin contents. We discuss the findings obtained in Proechimys in the light of those regarding the kangaroo rat, the pocket gopher and the house mouse; they support the idea that karyotype restructuring could be the expression of molecular driven events of rep DNA amplification and homogenisation through non-homologous chromosomes.

Microtubule release from the centrosome

Although microtubules (MTs) are generally thought to originate at the centrosome, a number of cell types have significant populations of MTs with no apparent centrosomal connection. The origin of these noncentrosomal MTs has been unclear. We applied kinetic analysis of MT formation in vivo to establish their mode of origin. Time-lapse fluorescence microscopy demonstrated that noncentrosomal MTs in cultured epithelial cells arise primarily by constitutive nucleation at, and release from, the centrosome. After release, MTs moved away from the centrosome and tended to depolymerize. Laser-marking experiments demonstrated that released MTs moved individually with their plus ends leading, suggesting that they were transported by minus end-directed motors. Released MTs were dynamic. The laser marking experiments demonstrated that plus ends of released MTs grew, paused, or shortened while the minus ends were stable or shortened. Microtubule release may serve two kinds of cellular function. Release and transport could generate the noncentrosomal MT arrays observed in epithelial cells, neurons, and other asymmetric, differentiated cells. Release would also contribute to polymer turnover by exposing MT minus ends, thereby providing additional sites for loss of subunits. The noncentrosomal population of MTs may reflect a steady-state of centrosomal nucleation, release, and dynamics.

Mitosis in vertebrate somatic cells with two spindles: implications for the metaphase/anaphase transition checkpoint and cleavage

During mitosis an inhibitory activity associated with unattached kinetochores prevents PtK1 cells from entering anaphase until all kinetochores become attached to the spindle. To gain a better understanding of how unattached kinetochores block the metaphase/anaphase transition we followed mitosis in PtK1 cells containing two independent spindles in a common cytoplasm. We found that unattached kinetochores on one spindle did not block anaphase onset in a neighboring mature metaphase spindle 20 microm away that lacked unattached kinetochores. As in cells containing a single spindle, anaphase onset occurred in the mature spindles x = 24 min after the last kinetochore attached regardless of whether the adjacent immature spindle contained one or more unattached kinetochores. These findings reveal that the inhibitory activity associated with an unattached kinetochore is functionally limited to the vicinity of the spindle containing the unattached kinetochore. We also found that once a mature spindle entered anaphase the neighboring spindle also entered anaphase x = 9 min later regardless of whether it contained monooriented chromosomes. Thus, anaphase onset in the mature spindle catalyzes a "start anaphase" reaction that spreads globally throughout the cytoplasm and overrides the inhibitory signal produced by unattached kinetochores in an adjacent spindle. Finally, we found that cleavage furrows often formed between the two independent spindles. This reveals that the presence of chromosomes and/or a spindle between two centrosomes is not a prerequisite for cleavage in vertebrate somatic cells.

Kangaroo rats exhibit spongiform degeneration of the central auditory system similar to that found in gerbils

Kangaroo rats develop spongiform degeneration of the central auditory system similar to that seen in the gerbil. Light microscopic and transmission electron microscopic study of the cochlear nucleus and auditory nerve root (ANR) of Dipodomys deserti and D. merriami show that spongiform lesions develop in dendrites and oligodendrocytes of the cochlear nucleus and in oligodendrocytes of the ANR that are morphologically indistinguishable from those extensively described in the Mongolian gerbil, Meriones unguiculatus. As in Mongolian gerbils, the spongiform degeneration in Dipodomys were much more numerous in animals continually exposed to modest levels of low-frequency noise (< 75 dB SPL). The kangaroo rats with extensive spongiform degeneration also show slightly, but significantly, elevated auditory brainstem evoked response (ABR) thresholds to low-frequency stimuli, a result also found in Mongolian gerbils. These results suggest that the elevated ABR thresholds may be the result of spongiform degeneration. Because low-frequency noise-induced spongiform degeneration has now been shown in the cochlear nucleus of animals from separate families of Rodentia (Heteromyidae and Muridae), the possibility should be investigated that similar noise-induced degenerative changes occur in the central auditory system of other mammals with good low-frequency hearing.

Hemorrhagic gastritis in free-living rodents in Idaho

Between February 1992 and March 1994, four species of rodent from the Snake River Birds of Prey Area near Boise, Idaho (USA) were necropsied. Hemorrhagic gastritis was observed in 16 of 131 Townsend's ground squirrels (Spermophilus townsendii), one of 11 Ord's kangaroo rats (Dipodomys ordii) and the one Great Basin pocket mouse (Perognathus parvus) evaluated. No lesions were observed in 14 white-footed deer mice (Peromyscus maniculatus). Tissue from one Townsend's ground squirrel was negative for Helicobacter sp.-like bacteria.

Gastric trichobezoar in a banner-tailed kangaroo rat (Dipodomys spectabilis)

A male, wild-caught kangaroo rat developed anorexia and wasting. The animal was euthanized and a gastric trichobezoar found at necropsy. The paucity of information regarding the clinical medicine of this species is a hindrance to those charged with the care of kangaroo rats. Gastric trichobezoar should be considered as a differential diagnosis in cases of anorexia in kangaroo rats.

A hyperphosphorylated form of the large subunit of RNA polymerase II is associated with splicing complexes and the nuclear matrix

A hyperphosphorylated form of the largest subunit of RNA polymerase II (pol IIo) is associated with the pre-mRNA splicing process. Pol IIo was detected in association with a subset of small nuclear ribonucleoprotein particle and Ser-Arg protein splicing factors and also with pre-mRNA splicing complexes assembled in vitro. A subpopulation of pol IIo was localized to nuclear "speckle" domains enriched in splicing factors, indicating that it may also be associated with RNA processing in vivo. Moreover, pol IIo was retained in a similar pattern following in situ extraction of cells and was quantitatively recovered in the nuclear matrix fraction. The results implicate nuclear matrix-associated hyperphosphorylated pol IIo as a possible link in the coordination of transcription and splicing processes.

Kangaroo rat bone compared to white rat bone after short-term disuse and exercise

Kangaroo rats (Dipodomys ordii) were used to study the effects of confinement on mechanical properties of bone with a long range objective of proposing an alternative to the white rat model for the study of disuse osteoporosis. Kangaroo rats exhibit bipedal locomotion, which subjects their limbs to substantial accelerative forces in addition to the normal stress of weight bearing. We subjected groups of kangaroo rats and white rats (Rattus norvegicus) to one of two confinement treatments or to an exercise regime; animals were exercised at a rate calculated to replicate their (respective) daily exercise patterns. White laboratory rats were used as the comparison because they are currently the accepted model used in the study of disuse osteoporosis. After 6 weeks of treatment, rats were killed and the long bones of their hind limbs were tested mechanically and examined for histomorphometric changes. We found that kangaroo rats held in confinement had less ash content in their hind limbs than exercised kangaroo rats. In general, treated kangaroo rats showed morphometric and mechanical bone deterioration compared to controls and exercised kangaroo rats appeared to have slightly "stronger" bones than confined animals. White rats exhibited no significant differences between treatments. These preliminary results suggest that kangaroo rats may be an effective model in the study of disuse osteoporosis.

Ixodes (Ixodes) jellisoni and I. (I.) neotomae (Acari:Ixodidae): descriptions of the immature stages from California

Nymphal and larval stages of Ixodes (Ixodes) jellisoni Cooley & Kohls and I. (I.) neotomae Cooley are described for the first time. These 2 tick species occur only in the western United States, predominantly in California. The primary host for I. jellisoni is the California kangaroo rat, Dipodomys californicus (Merriam); that for I. neotomae is the dusky-footed woodrat, Neotoma fuscipes Baird. The etiologic agent of Lyme disease Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt & Brenner has recently been isolated from both tick species, and I. neotomae was proven a competent enzootic vector of the Lyme disease spirochete.

[The genotoxic effect of ciprofloxacin on cultured cells from the kangaroo rat kidney and on skin fibroblasts from the Indian muntjac]

The genotoxicity of an antibiotic ciprofloxacin (CF) in doses of 10, 25, 50 and 100 mkg/ml under its short-term (6-48 h) and long-term (15-30 days) action on sublines of Rat kangaroo kidney, NBL-3-11, and Indian muntjak skin fibroblasts has been studied. The emergence of genotoxic effect depends on the dose and time of ciprofloxacin action on both the sublines, but the degree of this effect does not depend on these parameters directly. Ciprofloxacin exerts no influence on cell distribution for chromosome number in subline NBL-3-11, and increases heterogeneity of this parameter in the subline of Indian muntjac skin fibroblasts in 30 days after its addition in doses of 25 and 50 mkg/ml. The degree of increase of chromosomal aberrations in the subline of Indian muntjak skin fibroblasts was in average 1.5 times more than in NBL-3-11 in all examined variants compared to the control. The minimum antibiotic dose that induced chromosomal aberrations was 25 mkg/ml in the subline of NBL-3-11 under a short-term action and 50 mkg/ml under a long-term action. For the subline of Indian muntjac skin fibroblasts the minimum inducing dose was 50 mkg/ml irrespective of the duration of action, except the case of 15 days, when the number of dicentrics increased still at 25 mkg/ml. In both sublines with the duration of ciprofloxacin action within 6-24 h the replacement of chromatid aberrations by chromosomal aberrations occurred. Under a long-term ciprofloxan action differences in types of chromosomal aberrations were discovered: for subline NBL-3-11 these were mainly chromosomal breaks; in the case of muntjac cells both chromosomal breaks and dicentrics (telomeric associations) occurred. The preferential involvement of some chromosomes in dicentric formation was observed. In cells of the muntjac subline, unlike NBL-3-11, the sensitivity of individual chromosomes to ciprofloxacin-induced breaks differed from that to spontaneous breaks. In both the sublines ciprofloxacin induces chromosomal breaks mainly in definite regions of chromosomes. Possible reasons of differences between the examined sublines towards the character of chromosomal instability are discussed in addition to the role of dicentrics as a proposed adaptation of cells to unfavourable factors of the environment.

Mos oncogene product associates with kinetochores in mammalian somatic cells and disrupts mitotic progression

The mos protooncogene has opposing effects on cell cycle progression. It is required for reinitiation of meiotic maturation and for meiotic progression through metaphase II, yet it is an active component of cytostatic factor. mos is a potent oncogene in fibroblasts, but high levels of expression are lethal. The lethality of mos gene expression in mammalian cells could be a consequence of a blockage induced by its cytostatic factor-related activity, which may appear at high dosage in mitotic cells. We have directly tested whether expression of the Mos protein can block mitosis in mammalian cells by microinjecting a fusion protein between Escherichia coli maltose-binding protein and Xenopus c-Mos into PtK1 epithelial cells and analyzing the cells by video time-lapse and immunofluorescence microscopy. Time-course analyses showed that Mos blocked mitosis by preventing progression to a normal metaphase. Chromosomes frequently failed to attain a bipolar orientation and were found near one pole. Injection of a kinase-deficient mutant Mos had no effect on mitosis, indicating that the blockage of mitotic progression required Mos kinase activity. Antitubulin immunostaining of cells blocked by Mos showed that microtubules were present but that spindle morphology was abnormal. Immunostaining for the Mos fusion protein showed that both wild-type and kinase mutant proteins localized at the kinetochores. Our results suggest that mitotic blockage by Mos may result from an action of the Mos kinase on the kinetochores, thus increasing chromosome instability and preventing normal congression.

Cytolocation of prosome antigens on intermediate filament subnetworks of cytokeratin, vimentin and desmin type

Analysis by double-label indirect immunofluorescence of PtK1 and HeLa cells had previously demonstrated that prosome* antigens form networks that superimpose on those of the intermediate filaments of the cytokeratin type. We show here that in PtK1 cells various prosomal antigens also reside to a variable extent on intermediate filaments subnetworks of the vimentin type. In proliferating human fibroblasts the prosome and vimentin networks were found to coincide, while in proliferating myoblasts of the C2.7 mouse myogenic cell line the prosomal antigens seem to superimpose on the intermediate filaments of the desmin type. Thus, the prosomes, which are RNP particles of variable composition and subcomplexes of untranslated mRNP, and carry a multicatalytic proteinase activity, seem to co-localize with the specific kind of cytoplasmic intermediate filament in relation to the cell type. These results, which generalize the previous data, are discussed in view of possible role(s) for prosomes in mRNA metabolism and/or intermediate filaments remodelling.

Cell cycle progression and chromosome segregation in mammalian cells cultured in the presence of the topoisomerase II inhibitors ICRF-187 [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane; ADR-529] and ICRF-159 (Razoxane)

Certain bis(2,6-dioxopiperazine) derivatives, which include ICRF-187 [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl]propane; ADR-529) and its racemic compound ICRF 159 (Razoxane), have been investigated as antineoplastic agents. In addition, ICRF-187 is currently under intense study as an agent to ameliorate the cardiac toxicity of anthracycline therapy. These agents have recently been identified as inhibitors of topoisomerase II. We studied the effects of ICRF-187 and ICRF-159 on the progression of cultured epithelial cells through M phase. Beginning approximately 1.5 h after drug addition, chromosome condensation was significantly inhibited. Cells entered and progressed through M phase at near normal rates, but the lack of complete chromosome separation during anaphase resulted in catastrophic effects on normal chromosome distribution. Immunolabeling with Crest autoimmune sera, which recognizes centromere proteins, and with MPM-2 monoclonal antibody, which recognizes mitotic phosphoproteins, indicated that the centromeres of the chromosomes assembled a normal metaphase array in the presence of ICRF-187 and ICRF-159. Centromere separation in anaphase was initiated normally but was not completed because the chromatid arms failed to disengage from each other. Massive chromosome bridges were formed, and the chromatin mass became trapped in the cleavage furrow leading to its unequal distribution to the daughter cells. In many cases, all the chromatin was pushed into one of the two dividing cells. It is likely that previous studies, based on flow cytometry, indicating that bis(2,6-dioxypiperazine) derivatives cause an accumulation of cells with a 4N DNA content, reflect the incomplete segregation of chromosomes in mitosis rather than a block in G2 of the cell cycle as had been proposed.

Running springs: speed and animal size

Trotting and hopping animals use muscles, tendons and ligaments to store and return elastic energy as they bounce along the ground. We examine how the musculoskeletal spring system operates at different speeds and in animals of different sizes. We model trotting and hopping as a simple spring-mass system which consists of a leg spring and a mass. We find that the stiffness of the leg spring (k(leg)) is nearly independent of speed in dogs, goats, horses and red kangaroos. As these animals trot or hop faster, the leg spring sweeps a greater angle during the stance phase, and the vertical excursion of the center of mass during the ground contact phase decreases. The combination of these changes to the spring system causes animals to bounce off the ground more quickly at higher speeds. Analysis of a wide size range of animals (0.1-140 kg) at equivalent speeds reveals that larger animals have stiffer leg springs (k(leg) [symbol: see text] M0.67, where M is body mass), but that the angle swept by the leg spring is nearly independent of body mass. As a result, the resonant period of vertical vibration of the spring-mass system is longer in larger animals. The length of time that the feet are in contact with the ground increases with body mass in nearly the same way as the resonant period of vertical vibration.

The RNA polymerase I-specific transcription initiation factor UBF is associated with transcriptionally active and inactive ribosomal genes

We have characterized an anti-NOR (nucleolar organizer region) serum (P419) from a patient with rheumatoid arthritis and show that it contains antibodies directed against the RNA polymerase I-specific transcription initiation factor UBF. This serum reacts with UBF from a variety of vertebrate cells as revealed both by immunoblotting and by indirect immunofluorescence. We have used the P419 serum to study the intracellular localization of this transcription factor at the light and electron microscopic level. In interphase cells, UBF exhibits a pronounced punctate pattern and is found to be associated with necklace-like structures, which appear to reflect the transcriptionally active state of the nucleolus. Inhibition of rRNA synthetic activity caused either by nutritional starvation or by actinomycin D treatment resulted in a marked decrease in the number and in a significant increase in the size of UBF-positive granules. Under all experimental conditions applied, UBF was exclusively found within the nucleolus and was not released into the nucleoplasm or cytoplasm. During mitosis, UBF was found to be concentrated at the chromosomal NOR indicating that a significant quantity, if not all, of this factor remains bound to the ribosomal transcription units. From this we conclude that UBF is associated both with transcriptionally active and inactive rRNA genes and, therefore, changes in the intracellular localization of UBF are very likely not involved in rDNA transcription regulation.

A nuclear localization signal within HIV-1 matrix protein that governs infection of non-dividing cells

Permissiveness of the host cell to productive infection by oncoretroviruses is cell-cycle dependent, and nuclear localization of viral nucleoprotein preintegration complexes will occur only after cells have passed through mitosis. In contrast, establishment of an integrated provirus after infection by the lentivirus HIV-1 is independent of host cell proliferation. The ability of HIV-1 to replicate in non-dividing cells is partly accounted for by the karyophilic properties of the viral preintegration complex which, after virus infection, is actively transported to the host cell nucleus. Here we report that the gag matrix protein of HIV-1 contains a nuclear localization sequence which, when conjugated to a heterologous protein, directs its nuclear import. In addition, HIV-1 mutants containing amino-acid substitutions in this nuclear localization signal integrate and replicate within dividing but not growth-arrested cells, and thus display a phenotype more representative of an oncoretrovirus.