The Yeast Dynactin Complex Is Involved in Partitioning the Mitotic Spindle between Mother and Daughter Cells during Anaphase B

Although vertebrate cytoplasmic dynein can move to the minus ends of microtubules in vitro, its ability to translocate purified vesicles on microtubules depends on the presence of an accessory complex known as dynactin. We have cloned and characterized a novel gene, NIP100, which encodes the yeast homologue of the vertebrate dynactin complex protein p150^glued. Like strains lacking the cytoplasmic dynein heavy chain Dyn1p or the centractin homologue Act5p, nip100Δ strains are viable but undergo a significant number of failed mitoses in which the mitotic spindle does not properly partition into the daughter cell. Analysis of spindle dynamics by time-lapse digital microscopy indicates that the precise role of Nip100p during anaphase is to promote the translocation of the partially elongated mitotic spindle through the bud neck. Consistent with the presence of a true dynactin complex in yeast, Nip100p exists in a stable complex with Act5p as well as Jnm1p, another protein required for proper spindle partitioning during anaphase. Moreover, genetic depletion experiments indicate that the binding of Nip100p to Act5p is dependent on the presence of Jnm1p. Finally, we find that a fusion of Nip100p to the green fluorescent protein localizes to the spindle poles throughout the cell cycle. Taken together, these results suggest that the yeast dynactin complex and cytoplasmic dynein together define a physiological pathway that is responsible for spindle translocation late in anaphase.     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption     

Dietary fats,selected body temperature and tissue fatty acid composition of agamid lizards (Amphibolurus nuchalis)

The composition of tissue and membrane fatty acids in ectothermic vertebrates is influenced by both temperature acclimation and diets. If such change in body lipid composition and thermal physiology were linked, a diet-induced change in body lipid composition should result in a change in thermal physiology. We therefore investigated whether the selected body temperature of the agamid lizardAmphibolurus nuchalis (body mass 20 g) is influenced by the lipid composition of dietary fatty acids and whether diet-induced changes in thermal physiology are correlated with changes in body lipid composition. The selected body temperature in two groups of lizards was indistinguishable before dietary treatments. The selected body temperature in lizards after 3 weeks on a diet rich in saturated fatty acids rose by 2.1 °C (photophase) and 3.3 °C (scotophase), whereas the body temperature of lizards on a diet rich in unsaturated fatty acids fell by 1.5 °C (photophase) and 2.0 °C (scotophase). Significant diet-induced differences were observed in the fatty acid composition of depot fat, liver and muscle. These observations suggest that dietary lipids may influence selection of body temperature in ectotherms via alterations of body lipid composition.Abbreviations bm body mass - FA fatty acid(s) - MUFA monounsaturated fatty acids - PUFA polyunsaturated fatty acids - SFA saturated fatty acids - T _a air temperature - T _b body temperature - UFA unsaturated fatty acids     

Evolution of base composition in the insulin and insulin-like growth factor genes

The genomes of homeothermic (warm-blooded) vertebrates are mosaic interspersions of homogeneously GC-rich and GC-poor regions (isochores). Evolution of genome compartmentalization and GC-rich isochores is hypothesized to reflect either selective advantages of an elevated GC content or chromosome location and mutational pressure associated with the timing of DNA replication in germ cells. To address the present controversy regarding the origins and maintenance of isochores in homeothermic vertebrates, newly obtained as well as published nucleotide sequences of the insulin and insulin-like growth factor (IGF) genes, members of a well-characterized gene family believed to have evolved by repeated duplication and divergence, were utilized to examine the evolution of base composition in nonconstrained (flanking) and weakly constrained (introns and fourfold degenerate sites) regions. A phylogeny derived from amino acid sequences supports a common evolutionary history for the insulin/IGF family genes. In cold- blooded vertebrates, insulin and the IGFs were similar in base composition. In contrast, insulin and IGF-II demonstrate dramatic increases in GC richness in mammals, but no such trend occurred in IGF- I. Base composition of the coding portions of the insulin and IGF genes across vertebrates correlated (r = 0.90) with that of the introns and flanking regions. The GC content of homologous introns differed dramatically between insulin/IGF-II and IGF-I genes in mammals but was similar to the GC level of noncoding regions in neighboring genes. Our findings suggest that the base composition of introns and flanking regions is determined by chromosomal location and the mutational pressure of the isochore in which the sequences are embedded. An elevated GC content at codon third positions in the insulin and the IGF genes may reflect selective constraints on the usage of synonymous codons.      

Torpor, thermal biology, and energetics in Australian long-eared bats (Nyctophilus)

Previous studies have suggested that Australian long-eared bats (Nyctophilus) differ from northern-hemisphere bats with respect to their thermal physiology and patterns of torpor. To determine whether this is a general trait of Australian bats, we characterised the temporal organisation of torpor and quantified metabolic rates and body temperatures of normothermic and torpid Australian bats (Nyctophilus geoffroyi, 7 g and N. gouldi, 10 g) over a range of air temperatures and in different seasons. The basal metabolic rate of normothermic bats was 1.36 ± 0.17 ml g⁻¹ h⁻¹ (N. geoffroyi) and 1.22 ± 0.13 ml g⁻¹ h⁻¹ (N. gouldi), about 65% of that predicted by allometric equations, and the corresponding body temperature was about 36 °C. Below an air temperature of about 25 °C bats usually remained normothermic for only brief periods and typically entered torpor. Arousal from torpor usually occurred shortly after the beginning of the dark phase and torpor re-entry occurred almost always during the dark phase after normothermic periods of only 111 ± 48 min (N. geoffroyi) and 115 ± 66 min (N. gouldi). At air temperatures below 10 °C, bats remained torpid for more than 1 day. Bats that were measured overnight had steady-state torpor metabolic rates representing only 2.7% (N. geoffroyi) and 4.2% (N. gouldi) of the basal metabolic rate, and their body temperatures fell to minima of 1.4 and 2.3 °C, respectively. In contrast, bats measured entirely during the day, as in previous studies, had torpor metabolic rates that were up to ten times higher than those measured overnight. The steady-state torpor metabolic rate of thermoconforming torpid bats showed an exponential relationship with body temperature (r ² = 0.94), suggesting that temperature effects are important for reduction of metabolic rate below basal levels. However, the 75% reduction of metabolic rate between basal metabolic rate and torpor metabolic rate at a body temperature of 29.3 °C suggests that metabolic inhibition also plays an important role. Torpor metabolic rate showed little or no seasonal change. Our study suggests that Australian Nyctophilus bats have a low basal metabolic rate and that their patterns of torpor are similar to those measured in bats from the northern hemisphere. The low basal metabolic rate and the high proclivity of these bats for using torpor suggest that they are constrained by limited energy availability and that heterothermy plays a key role in their natural biology. Accepted: 22 November 1999     

Phylogenetic analyses reveal deeply divergent species lineages in the genus Sphaerobolus (Phallales: Basidiomycota)

Phylogenetic analyses of 27 artillery fungus (Sphaerobolus sp.) isolates were conducted to identify species boundaries in the genus Sphaerobolus. Multiple gene genealogies inferred from maximum likelihood, Bayesian, and maximum-parsimony analyses of sequence data from individual loci (mtSSU, ITS, EF 1-alpha, and LSU) and a combined dataset (mtSSU, ITS, and EF 1-alpha) concordantly indicate the existence of three deeply divergent lineages in the genus Sphaerobolus, each representing a phylogenetic species. These three phylogenetic species correspond to two known species: Sphaerobolus iowensis and Sphaerobolus stellatus, and a newly discovered species. Suprageneric phylogenetic analyses of the mtSSU and LSU datasets containing representatives of related genera of the gomphoid-phalloid clade of Homobasidiomycetes suggested that the undescribed taxon likely is more closely related to S. stellatus than to S. iowensis.     

Localisation of the Vacuolar Proton Pump (V-H+-ATPase) and Carbonic Anhydrase II in the Human Eccrine Sweat Gland

The localisation of the vacuolar proton pump (V-H+ -ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+ -ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+ -ATPase and CAII in the secretory coil clear cells suggests that the formation of HCO3- and H+ by carbonic anhydrase II and the transport of H+ by V-H+ -ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption.     

Collagen types XII and XIV are present in basement membrane zones during human embryonic development

The collagens constitute a large group of proteins in the extracellular matrix that can be divided into several distinct families. Collagen types XII and XIV belong to a subgroup of non-fibrillar-collagens termed (fibril-associated collagens with interrupted triple-helices) (FACIT) and may be involved in basement membrane regulation providing specific molecular bridges between fibrils and other matrix components. However, the tissue distribution of the two proteins during human embryogenesis is still unclear. As a first step toward the elucidation of their possible cell biological functions, we compared the distribution of the two collagens during human organogenesis at the light microscopical level. We detected specific differences between the expression patterns of the two molecules, which may be related to their respective function within the basement membrane zones during human embryonic development. For example, in the developing intestine, collagen type-XII was present in the basement membrane zones of epithelia and endothelia. However, collagen type-XIV was restricted to the mesothelial basement membrane zones. We conclude that both collagens might well be able to serve different functions during human embryonic development although their structures are highly similar.