A skeletochronological study of growth,longevity, and age at sexual maturity in a population of<Emphasis Type="Italic">Rana latastei</Emphasis> (Amphibia,Anura)

Longevity and age at sexual maturity in an Italian population ofRana latastei were studied by skeletochronology performed on the phalanges. Frogs collected in 1998 and 1999 by drift fences and pitfall traps were marked by toe-clipping. After marking, individuals were released and the cut phalanges were processed for skeletochronological analysis. The maximum age so far recorded was 3 years in males and 4 years in females. The smallest male and female that were sexually mature on the basis of histological analysis of the gonads were 36 and 35 mm snout vent length (SVL), respectively. In both sexes, most individuals were estimated to breed shortly after emergence from their first overwintering. Among the European Brown Frogs,Rana latastei appears to be one of the shortest-lived and one of the first to reach sexual maturity.     

Role of the carboxy terminus of Escherichia coli FtsA in self-interaction and cell division

The role of the carboxy terminus of the Escherichia coli cell division protein FtsA in bacterial division has been studied by making a series of short sequential deletions spanning from residue 394 to 420. Deletions as short as 5 residues destroy the biological function of the protein. Residue W415 is essential for the localization of the protein into septal rings. Overexpression of the ftsA alleles harboring these deletions caused a coiled cell phenotype previously described for another carboxy-terminal mutation (Gayda et al., J. Bacteriol. 174:5362-5370, 1992), suggesting that an interaction of FtsA with itself might play a role in its function. The existence of such an interaction was demonstrated using the yeast two-hybrid system and a protein overlay assay. Even these short deletions are sufficient for impairing the interaction of the truncated FtsA forms with the wild-type protein in the yeast two-hybrid system. The existence of additional interactions between FtsA molecules, involving other domains, can be postulated from the interaction properties shown by the FtsA deletion mutant forms, because although unable to interact with the wild-type and with FtsADelta1, they can interact with themselves and cross-interact with each other. The secondary structures of an extensive deletion, FtsADelta27, and the wild-type protein are indistinguishable when analyzed by Fourier transform infrared spectroscopy, and moreover, FtsADelta27 retains the ability to bind ATP. These results indicate that deletion of the carboxy-terminal 27 residues does not alter substantially the structure of the protein and suggest that the loss of biological function of the carboxy-terminal deletion mutants might be related to the modification of their interacting properties.     

Genetic and morphological heterogeneity in small rodent whipworms in southwestern Europe: characterization of Trichuris muris and description of Trichuris arvicolae n. sp. (Nematoda: Trichuridae)

Genetic and morphological variability of whipworms Trichuris Roederer, 1761 (Nematoda: Trichuridae), parasites of small rodents in southwestern Europe, was studied. Isozyme patterns of natural populations of nematodes parasitizing rodent species of the Muridae (Apodemus sylvaticus, Apodemus flavicollis, Mus musculus) and Arvicolidae (Clethrionomys glareolus, Microtus agrestis, Microtus arvalis) were analyzed at 6 putative loci. Two diagnostic loci were found in T. muris from Muridae and from Arvicolidae. Thus, the existence of 2 species of Trichuris restricted to different host families was indicated. They included Trichuris muris Schrank, 1788, originally described as being from mice, and Trichuris arvicolae n. sp., parasitizing the above species of Arvicolidae. The morphological variability of both species was compared. Although ranges of all morphological characters of the new species overlapped with those of T. muris, stepwise discriminant analysis yielded a 100% accurate classification of females when using vagina length and egg size. Males of T. muris and T. arvicolae cannot be separated entirely. A set of 6 variables yielded 95.7% discrimination; the most discriminating variables were spicule size and body width.     

Amphotericin B inhibits the generation of the scrapie isoform of the prion protein in infected cultures

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic, or genetic in origin. Although some doubts about the nature of the responsible agent of these diseases remain, it is clear that a protein called PrP(Sc) plays a central role. PrP(Sc) is a conformational variant of PrP(C), the normal host protein. Polyene antibiotics such as amphotericin B have been shown to delay the accumulation of PrP(Sc) and to increase the incubation time of the disease after experimental transmission in laboratory animals. Unlike for Congo red and sulfated polyanions, no effect of amphotericin B has been observed in infected cultures. We show here for the first time that amphotericin B can inhibit PrP(Sc) generation in scrapie-infected GT1-7 and N2a cells. Its activity seems to be related to a modification of the properties of detergent-resistant microdomains. These results provide new insights into the mechanism of action of amphotericin B and confirm the usefulness of infected cultures in the therapeutic research of transmissible spongiform encephalopathies.     

Calcium Dependence of Synaptic Vesicle Recycling Before and After Synaptogenesis

Abstract: Using an immunocytochemical assay to monitor synaptic vesicle exocytosis/endocytosis independently of neurotransmitter release, we have investigated some aspects of vesicle recycling in hippocampal neurons at different developmental stages. A calcium- and depolarization-dependent exocytotic/endocytotic recycling of synaptic vesicles was found to take place in neurons already before the formation of synaptic contacts. The analysis of synaptic vesicle recycling at different calcium concentrations revealed the presence of two release components: the first one activated by low calcium concentrations and sustaining vesicle recycling before synaptogenesis, and a second one activated by high calcium concentrations, which is specifically turned on after the establishment of synaptic contacts. These data suggest that formation of synapses correlates with the activation of a putative low-affinity calcium sensor, which allows synaptic vesicle exocytosis to be triggered and turned off over extremely short time scales, in response to large increases in the level of intracellular calcium.     

Dissecting the mechanism of torso receptor activation

Regulated activation of receptor tyrosine kinases depends both on the presence of the receptors at the cell surface and on the availability of their ligands. In Drosophila the torso (tor) tyrosine kinase receptor is distributed along the surface of the embryo but it is only activated at the poles by a diffusible extracellular ligand generated at each pole which is trapped by the receptor, thereby impeding further diffusion. However, it is not well understood how this signal is generated, although it is known to depend on the activity of many genes such as torso-like (tsl) and trunk (trk). To further investigate the mechanism involved in the local activation of the tor receptor we have altered the normal expression of the tsl protein by generating females in which the tsl gene is expressed in the oocyte under the control of the tor promoter rather than in the ovarian follicle cells. Analysis of the phenotypes generated by this hybrid gene and its interactions with mutations in other genes in the pathway has enabled us to further dissect the mechanism of tor receptor activation and to define more precisely the role of the different genes acting in this process.