Three-dimensional structure of clathrin cages in ice.

We have collected tilt series of electron micrographs from unstained clathrin cages embedded in vitreous ice. From these micrographs we have generated three-dimensional reconstructions of individual hexagonal barrels, which show details of the internal structure. Four types of preparation have been examined: (i) coated vesicles; (ii) cages reassembled from clathrin heavy and light chains; (iii) reassembled cages treated with elastase to remove the light chains; and (iv) reassembled cages treated with trypsin to remove the light chains and the terminal domains of the clathrin heavy chains. In the intact and elastase-treated cages, the clathrin extends from the vertices into the interior of the polyhedron and forms an inner shell of material. Limited digestion with trypsin removes the inner shell, which indicates that this material corresponds to the terminal domains of the clathrin heavy chains.     

Comparison of age-related peripheral nerve changes in mice housed in either plastic cages with sawdust-covered solid flooring or wire-mesh-floor cages.

A comparative histologic survey was conducted on the dorsal root, sciatic, tibial and medial plantar nerves of 90- and 110-week-old B6C3F1 female mice reared in either solid-floor cages covered in sawdust or wire-mesh-floor cages. Age-related peripheral nerve lesions, characterized by axonal degeneration and remyelination, were present in all nerves surveyed, and were especially prominent in the sciatic and medial plantar nerves at 110 weeks of age but, there were no differences associated with the type of cage floor in clinical signs, grasping power of the fore- and hind-limbs, motor nerve conduction velocity or histopathologic findings at these ages.     

The effects of intracage ventilation on microenvironmental conditions in filter-top cages.

Filter-top cages, while effective in reducing cross contamination by particulate material including microbes, can also cause accumulation of the waste gases carbon dioxide and ammonia as well as increased intracage relative humidity. A prototype system which provided each cage with 23 air changes per hour through a nozzle inserted in the filter lid was evaluated. The ventilated cageing system was effective in reducing intracage carbon dioxide, ammonia and relative humidity levels. Mean weekly carbon dioxide levels were 2900 ppm lower, ammonia levels 240 ppm lower and intracage relative humidity levels 8% lower in the ventilated cages than in unventilated controls.     

Endocytosis: an assembly protein for clathrin cages.

The protein AP180 is known to have clathrin-assembly activity in vitro. AP180 has now been found to be crucial for synaptic vesicle endocytosis and the maintenance of a uniform-size vesicle population in vivo. These results significantly advance our understanding of clathrin-mediated endocytosis in the synapse and elsewhere.     

Microclimate in two types of rat cages

The microclimate in two types of rat cages (a Makrolon type IV with a solid floor and a stainless steel cage with a wire mesh floor (five rats per cage)) placed in the same macro-environment was compared. The temperature, relative humidity and ammonia concentration in the cages were measured twice a day for 8 days. The cages were cleaned every 4 days. The greatest difference between the cage types was in the ammonia build-up. In Makrolon cages the ammonia concentration never reached 5 ppm, whereas in steel cages it showed a constant increase and already exceeded the threshold limit for man (25 ppm for 8 h per day) on the third day after cleaning.     

Self-assembly of minimal COPII cages

The small G-protein Sar1 and the cytosolic complexes Sec23/24 and Sec13/31 associate sequentially on endoplasmic reticulum membranes to form a protein coat named COPII, which drives the formation of transport vesicles. Using dynamic light scattering, we show that Sec23/24 and Sec13/31 can self-assemble in a stoichiometric manner in solution to form particles with hydrodynamic radii in the range of 40–60 nm. Self-assembly is favoured by lowering the pH, the ionic strength and/or the temperature. Electron microscopy reveals the formation of spherical particles 60–120 nm in diameter with a tight, rough mesh on their surfaces. We suggest that these stuctures, which represent a minimal COPII cage, mimic the molecular organization of the membrane-associated COPII coat.     

Carbon dioxide concentrations in unventilated IVC cages

The use of individually ventilated cage (IVC) systems has become more common worldwide. The various systems are becoming more and more sealed in order to protect the animals against infections and the staff against allergens; which, however, may lead to problematic CO2 concentrations, if the cages are left unventilated. In this study it is shown that, depending on how tight the cage is and the number of animals housed in each cage, CO2 inside the cage within 2 h will increase to levels of between 2 and 8%.     

Enzymatic dissociation of clathrin cages in a two-stage process

Uncoating ATPase catalyzes the ATP-dependent dissociation of clathrin from coated vesicles and empty cages. Following an uncoating reaction, clathrin triskelions are released intact, in a stoichiometric complex with bound uncoating protein. This overall uncoating process was dissected into two partial reactions. In the first, ATP hydrolysis drives the transient displacement of a portion of a triskelion from a cage. Uncoating protein then captures the displaced triskelion, in the second stage, by binding to a newly exposed site on clathrin that had previously been buried in the cage lattice. Triskelion-uncoating protein complexes are released when all points of attachment of the triskelion to the cage have been severed. The uncoating protein interacts with a distinct site on clathrin for each of these reactions.     

Estimation of effective generation interval in Drosophila population cages

An approximation method for calculating the effective generation interval in populations with overlapping generations was presented and illustrated with Drosophila melanogaster data where a sustained heterosis (or pseudo-overdominance) was observed for sex-linked genes balanced by an inversion. An equilibrium frequeney was established in replicated 2-bottle population eages which was different for males and females. The fitnesses of the genotypes were thus estimable and the expected gene frequencies with diserete generations were calculated. The effective generation interval was estimated by fitting the observed frequencies to those expected by minimizing the lack of fit chisquare. The best fit resulted if the interval was allowed to increase as the population approached a stable age distribution. The best estimate indicated that there was an average interval of 14.75 days per generation in the first 5 generations and 16.25 days thereafter. This estimate is particular to 2-bottle eages; as the number of bottles increases the expected generation interval is also expected to inerease.Journal Paper Number 79-5-211 of the University of Kentucky Agricultural Experiment Station, and Journal Paper Number 7942 of the Purdue University Agricultural Experiment Station.     

No overall benefit of predator exclosure cages for the endangered St. Helena Plover Charadrius sanctaehelenae

Predator exclosure cages are designed to increase the clutch survival of ground‐nesting birds. Predator exclosures provided for the endangered St. Helena Plover Charadrius sanctaehelenae, however, did not result in differences in clutch survival between protected and control nests and may have resulted in elevated adult mortality. Exclosures did not exclude all cats, the dominant nest predator, and it is likely that cats caused the adult mortalities observed close to the exclosures. A population model indicates that even if predator exclosures had excluded all cats, the benefits of increased clutch survival would have been more than negated by the estimated decrease in adult survival. The overall effect of predator exclosures needs to be clarified for other species, taking into consideration annual productivity and adult survival, to understand the circumstances in which predator exclosures are beneficial.