The role of ``conservatism' in herring migrations

Herring (Clupea harengus) migrationstend to remain constant over periods of severalyears or even decades, despite environmentalvariation. When a migration pattern is changed,apparently in response to an environmentalstimulus, the change in migratory behaviorsometimes lasts longer than the environmentalstimulus itself. This paper reviews evidencethat the response of herring to environmentalchange is restrained by conservatism. Herringapparently develop certain migratory habitsduring the early stage of adult life and tendto adhere to these habits for life, even whenthe environment changes. Two elements ofconservatism are distinguished: the formationof habits within one generation, and thetransfer of habits between generations. Anumber of case studies on North Sea herring andNorwegian spring spawning herring are reviewedin order to find evidence for habit formationand tradition in the migrations of thesepopulations. By eliminating the possibilitythat homing to spawning, wintering and feedinggrounds is due to innate behavior orenvironmental constraints, it is shown that thereturn of these fish to the same areas eachyear is most likely a form of learned behavior.In many cases, new year-classes adopt the samemigration pattern as their predecessors, whichis explained by the social transfer of habitsfrom old herring to young ones. A change ofmigration pattern is usually initiated by arecruiting year-class that lacks the ``guidance'of older herring at the time it has to startits first migration. This may be the effect ofa special environmental condition that affectsthe distribution of the recruiting age groupmore than that of the adult stock component, andthereby results in a separation of the twostock components. After the recruitingyear-class has adopted the new migration route,it tends to repeat it in subsequent years. Thenew migration thus becomes habitual. Subsequentgenerations may copy the migration and continuethis behavior even after the originalenvironmental cause has disappeared.     

Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo

The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis.     

Immunohistochemical detection of factor XIII subunit a in histiocytes of human uterus

As spontaneous abortion is a frequent finding in females with Factor XIII (FXIII) deficiency it has been presumed that this clotting factor is essential to normal pregnancy. FXIII subunit a (FXIII A) has been demonstrated in the homogenate of human uterus, but no information on its cellular distribution has been published, so far. In the present study first FXIII A was detected in paraformaldehyde-fixed, paraffin-embedded sections of human uterus by immunoperoxidase technique. Cells containing FXIII A were localized between collagen fibrils stained by Picrosirius Red F3B in the connective tissue. To characterize them the immunofluorescent detection of FXIII A was combined by the visualization of different marker antigens of monocytes and macrophages recognized by Leu-M3, RFD7, anti-HLA-DR and DAKO-anti-macrophage monoclonal antibodies on frozen sections. The coexpression of FXIII A with monocyte and macrophage differentiation marker antigens clearly proves that cells containing FXIII A in the uterus are monocyte-derived tissue macrophages. The results well agree with our previous findings demonstrating FXIII A in human monocytes and different types of macrophages. On the basis of these results, the presence of FXIII A does not seem to be a specificity of the uterus but a characteristic of monocyte/macrophage cell line including tissue macrophages, in general.     

Activity dynamics and propagation of synchronous spiking in locally connected random networks

Random network models have been a popular tool for investigating cortical network dynamics. On the scale of roughly a cubic millimeter of cortex, containing about 100,000 neurons, cortical anatomy suggests a more realistic architecture. In this locally connected random network, the connection probability decreases in a Gaussian fashion with the distance between neurons. Here we present three main results from a simulation study of the activity dynamics in such networks. First, for a broad range of parameters these dynamics exhibit a stationary state of asynchronous network activity with irregular single-neuron spiking. This state can be used as a realistic model of ongoing network activity. Parametric dependence of this state and the nature of the network dynamics in other regimes are described. Second, a synchronous excitatory stimulus to a fraction of the neurons results in a strong activity response that easily dominates the network dynamics. And third, due to that activity response an embedding of a divergent-convergent feed-forward subnetwork (as in synfire chains) does not naturally lead to a stable propagation of synchronous activity in the subnetwork; this is in contrast to our earlier findings in isolated subnetworks of that type. Possible mechanisms for stabilizing the interplay of volleys of synchronous spikes and network dynamics by specific learning rules or generalizations of the subnetworks are discussed.     

An Appended Domain Results in an Unusual Architecture for Malaria Parasite Tryptophanyl-tRNA Synthetase

Specific activation of amino acids by aminoacyl-tRNA synthetases (aaRSs) is essential for maintaining fidelity during protein translation. Here, we present crystal structure of malaria parasite Plasmodium falciparum tryptophanyl-tRNA synthetase (Pf-WRS) catalytic domain (AAD) at 2.6 Å resolution in complex with L-tryptophan. Confocal microscopy-based localization data suggest cytoplasmic residency of this protein. Pf-WRS has an unusual N-terminal extension of AlaX-like domain (AXD) along with linker regions which together seem vital for enzymatic activity and tRNA binding. Pf-WRS is not proteolytically processed in the parasites and therefore AXD likely provides tRNA binding capability rather than editing activity. The N-terminal domain containing AXD and linker region is monomeric and would result in an unusual overall architecture for Pf-WRS where the dimeric catalytic domains have monomeric AXDs on either side. Our PDB-wide comparative analyses of 47 WRS crystal structures also provide new mechanistic insights into this enzyme family in context conserved KMSKS loop conformations.     

Raccoons (Procyon lotor) in Germany as potential reservoir species for Lyssaviruses

Raccoons can be found almost everywhere in Germany since their first successful introduction in 1934. Although the animal is a well-known reservoir species for rabies in the USA, during the last European fox rabies epizootic, only a few rabid raccoons were reported from Germany. In recent years, the raccoon population density has increased tremendously, especially in (semi) urban settings. Presently, Germany is free of terrestrial wildlife rabies. To assess the potential risk that the raccoon population in Germany could act as a reservoir species upon reemergence of rabies, the susceptibility of the local raccoon population was investigated. Wild-caught animals were inoculated with the most likely lyssavirus variants to infect the local population. It was shown that the raccoons were fully susceptible for a dog and raccoon rabies virus isolate. Also, five of six raccoons inoculated with a fox rabies virus isolate showed clinical signs. However, none of the raccoons infected with European Bat Lyssavirus type 1 succumbed to rabies; meanwhile, all these raccoons seroconverted. It is concluded that the highest risk for the raccoon population in Germany to become infected with lyssaviruses is through the importation of rabies infected dogs.