The energetic cost of arousal from torpor in the marsupial Sminthopsis macroura : benefits of summer ambient temperature cycles

The costs of arousal from induced torpor were measured in the striped-faced dunnart (Sminthopsis macroura; ca. 25 g) under two experimental ambient temperature cycles. The sinusoidal-type temperature cycles were designed to evaluate the effects of passive, ambient temperature heating during arousal from torpor in these insectivorous marsupials. It was hypothesised that diel ambient temperature cycles may offer significant energy savings during arousal in animals that employ daily torpor in summer as a response to unpredictable food availability. The cost of arousal in animals in which passive, exogenous heating occurred was significantly lower than that in animals not exposed to an ambient temperature cycle. The total cost of all three phases of torpor (entry, maintenance and arousal) was almost halved when animals were exposed to an ambient heating cycle from 15 °C to 25 °C over a 24-h period. In all animals, irrespective of the experimental ambient temperature cycle employed, the minimum torpor body temperature was 17–18 °C. The body temperature (T_b) of animals exposed to exogenous heating increased from the torpor T_b minimum to a mean value of 22.59 °C before endogenous heat production commenced. This relatively small increase in T_b of ca. 5 °C through `free' passive heating was sufficient to account for the significant ca. three-fold decrease in the cost of arousal and may represent an important energetic aid to free-ranging animals. Accepted: 4 October 1998     

Analysis of superfamily specific profile-profile recognition accuracy

Background  

Annotation of sequences that share little similarity to sequences of known function remains a major obstacle in genome annotation. Some of the best methods of detecting remote relationships between protein sequences are based on matching sequence profiles. We analyse the superfamily specific performance of sequence profile-profile matching. Our benchmark consists of a set of 16 protein superfamilies that are highly diverse at the sequence level. We relate the performance to the number of sequences in the profiles, the profile diversity and the extent of structural conservation in the superfamily.     

H(2)O(2) inhibits alveolar epithelial wound repair in vitro by induction of apoptosis

Reactive oxygen species (ROS) are released into the alveolar space and contribute to alveolar epithelial damage in patients with acute lung injury. However, the role of ROS in alveolar repair is not known. We studied the effect of ROS in our in vitro wound healing model using either human A549 alveolar epithelial cells or primary distal lung epithelial cells. We found that H(2)O(2) inhibited alveolar epithelial repair in a concentration-dependent manner. At similar concentrations, H(2)O(2) also induced apoptosis, an effect seen particularly at the edge of the wound, leading us to hypothesize that apoptosis contributes to H(2)O(2)-induced inhibition of wound repair. To learn the role of apoptosis, we blocked caspases with the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp (zVAD). In the presence of H(2)O(2), zVAD inhibited apoptosis, particularly at the wound edge and, most importantly, maintained alveolar epithelial wound repair. In H(2)O(2)-exposed cells, zVAD also maintained cell viability as judged by improved cell spreading and/or migration at the wound edge and by a more normal mitochondrial potential difference compared with cells not treated with zVAD. In conclusion, H(2)O(2) inhibits alveolar epithelial wound repair in large part by induction of apoptosis. Inhibition of apoptosis can maintain wound repair and cell viability in the face of ROS. Inhibiting apoptosis may be a promising new approach to improve repair of the alveolar epithelium in patients with acute lung injury.     

Determinants of S. cerevisiae dynein localization and activation: implications for the mechanism of spindle positioning

BACKGROUND: During anaphase in budding yeast, dynein inserts the mitotic spindle across the neck between mother and daughter cells. The mechanism of dynein-dependent spindle positioning is thought to involve recruitment of dynein to the cell cortex followed by capture of astral microtubules (aMTs). RESULTS: We report the native-level localization of the dynein heavy chain and characterize the effects of mutations in dynein regulators on its intracellular distribution. Budding yeast dynein displays discontinuous localization along aMTs, with enrichment at the spindle pole body and aMT plus ends. Loss of Bik1p (CLIP-170), the cargo binding domain of Bik1p, or Pac1p (LIS1) resulted in diminished targeting of dynein to aMTs. By contrast, loss of dynactin or a mutation in the second P loop domain of dynein resulted in an accumulation of dynein on the plus ends of aMTs. Unexpectedly, loss of Num1p, a proposed dynein cortical anchor, also resulted in selective accumulation of dynein on the plus ends of anaphase aMTs. CONCLUSIONS: We propose that, rather than first being recruited to the cell cortex, dynein is delivered to the cortex on the plus ends of polymerizing aMTs. Dynein may then undergo Num1p-dependent activation and transfer to the region of cortical contact. Based on the similar effects of loss of Num1p and loss of dynactin on dynein localization, we suggest that Num1p might also enhance dynein motor activity or processivity, perhaps by clustering dynein motors.     

Surface-lining layer of airways in cystic fibrosis mice

Lung disease is the major cause of death in individuals suffering from cystic fibrosis (CF), with abnormal lung-lining fluids occurring as early as early infancy. However, the precise etiology of CF lung disease is still poorly understood. We investigated the structural components of the airway surface-lining layer in targeted Cftrtm1HGU/Cftrtm1HGU mutant mice and non-CF controls. Five lungs per animal group were fixed by intravascular triple perfusion. The ultrastructure of the surface-lining layer of large and small intrapulmonary conducting airways was systematically investigated according to a standard protocol in transmission and scanning electron micrographs. In both animal groups, the surface-lining layer consisted of an aqueous phase and an osmiophilic film of variable thickness at the air-fluid interface. The aqueous phase usually did extend <1 microm beyond the uppermost tips of the epithelial cells in both animal groups. The aqueous phase of the small airways was slightly more electron dense in Cftrtm1HGU/Cftrtm1HGU than in non-CF mice. Neither the ultrastructure of the surfactant film at the air-fluid interface nor the forms assumed by the osmiophilic structures associated with surfactant turnover in the aqueous layer differed significantly in Cftrtm1HGU/Cftrtm1HGU and non-CF mice. Hence, there were no signs of any ultrastructural abnormalities in the surface-lining layer of young adult Cftrtm1HGU/Cftrtm1HGU mice before infection with CF-related pathogens.     

Effects of helium/oxygen and temperature on aerobic metabolism in the marsupial sugar glider, Petaurus breviceps

Helox (79% helium and 21% oxygen) has often been used for thermobiological studies, primarily because helium is thought to be metabolically inert and to produce no adverse effects other than increasing heat loss. However, these assumptions have been questioned. As basal metabolic rate (BMR) represents maintenance energy requirements for vital body functions, potential physiological effects of helox should be reflected in changes of BMR. In this study, sugar gliders were subjected to both air and helox atmospheres over a wide range of T(a)'s, including the thermoneutral zone (TNZ), to determine (1) whether helox has any influence other than on heat loss and (2) the maximum heat production (HP(max)) and thermal limits of this species. Although thermal conductance in the TNZ increased in helox, BMR was similar in air and helox (0.55+/-0.07 and 0.57+/-0.06 mL g(-1) h(-1), respectively). The TNZ in helox, however, was shifted upwards by about 3 degrees C. Below the TNZ, sugar gliders were able to withstand an effective temperature of -24.7+/-7.3 degrees C with an HP(max) of 3.14+/-0.36 mL g(-1) h(-1). The low effective temperature tolerated by sugar gliders shows that they are competent thermoregulators despite their apparent lack of functional brown fat. Similarities of BMRs in air and helox suggest that the effect of helox is restricted to an increase of heat loss, and, consequently, helox represents a useful tool for thermal physiologists. Moreover, the lack of increase of BMR in helox despite an increase in thermal conductance of sugar gliders suggests that BMR is not a function of body surface.     

Diagnostic criteria for diabetes revisited: making use of combined criteria

Background  

Existing cut-offs for fasting plasma glucose (FPG) and post-load glucose (2hPG) criteria are not equivalent in the diagnosis of diabetes and glucose intolerance. Adjusting cut-offs of single measurements have not helped so we undertook this project to see if they could be complementary.     

Natural use of heterothermy by a small, tree-roosting bat during summer

Little is known about the use of heterothermy by wild bats during summer, especially for tree-roosting species. Because thermal conditions within tree roosts can fluctuate widely with ambient temperature, which affects thermoregulatory energy expenditure during diurnal roosting, we measured skin temperatures of free-ranging male Nyctophilus geoffroyi (8 g) to quantify the relation between summer torpor use and roost thermal conditions. Bats roosted under bark on the northern (sunny) side of trees and entered torpor every day, usually near sunrise. Bats exhibited two bouts of torpor on most days: the first occurred in the morning, was terminated by partially passive rewarming, and was followed by a period of normothermy during the warmest part of the day; a second torpor bout occurred in the late afternoon, with arousal near sunset. On the warmest days, bats had only a single, short morning bout. On the coolest days, bats remained torpid throughout the day, and one 2-d bout was observed. Thus, presumably owing to their poorly insulated roosts and the high energetic cost of normothermy at temperatures below 30 degrees C, the extent and timing of heterothermy was closely related to the cycle of diurnal temperatures. Our study indicates that torpor use is important for energy maintenance during summer diurnal roosting of N. geoffroyi and likely of other small, tree-roosting bats.     

Daily torpor and energetics in a tropical mammal, the northern blossom-bat Macroglossus minimus (Megachiroptera)

Little is known about torpor in the tropics or torpor in megachiropteran species. We investigated thermoregulation, energetics and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to test whether physiological variables may explain why its range is limited to tropical regions. Normothermic bats showed a large variation in body temperature (T _b) (33 to 37 °C) over a wide range of ambient temperatures (T _as) and a relatively low basal metabolic rate (1.29 ml O₂ g⁻¹h⁻¹). Bats entered torpor frequently in the laboratory at T _as between 14 and 25 °C. Entry into torpor always occurred when lights were switched on in the morning, independent of T _a. MRs during torpor were reduced to about 20–40% of normothermic bats and T _bs were regulated at a minimum of 23.1 ± 1.4 °C. The duration of torpor bouts increased with decreasing T _a in non-thermoregulating bats, but generally terminated after 8 h in thermoregulating torpid bats. Both the mean minimum T _b and MR of torpid M. minimus were higher than that predicted for a 16-g daily heterotherm and the T _b was also about 5 °C higher than that of the common blossom-bat Syconycteris australis, which has a more subtropical distribution. These observations suggest that variables associated with torpor are affected by T _a and that the restriction to tropical areas in M. minimus to some extent may be due to their ability to enter only very shallow daily torpor. Accepted: 22 September 1997     

Isolation and characterization of highly pathogenic avian influenza virus subtype H5N1 from donkeys

Background  

The highly pathogenic H5N1 is a major avian pathogen that crosses species barriers and seriously affects humans as well as some mammals. It mutates in an intensified manner and is considered a potential candidate for the possible next pandemic with all the catastrophic consequences.