Morphology and cross-linkage of stereocilia in the guinea-pig labyrinth examined without the use of osmium as a fixative

Summary Hair cells of the guinea-pig cochlea and vestibular system were prepared for electron-microscopic examination by fixing in glutaraldehyde without the use of osmium. An extensive array of cross-links was seen between the apical ends of the stereocilia, by both scanning and transmission electron microscopy. Some cross-links ran laterally between stereocilia of the same row. Others ran laterally between the stereocilia of the different rows, holding the tips of the shorter stereocilia in towards the longer stereocilia of the next row. In addition, each tip on the shorter stereocilia gave rise to a single, upwards pointing link, which ran upwards to join the adjacent taller stereocilium of the next row. We suggest that distortion of this link might be involved in the mechanics or even the membrane biophysics of sensory transduction.With this method of preservation, all the apical surface membranes of the hair cells appeared rough, and contained dense granules. The roughness was greatest in the parts of the stereocilia to which the cross-links were attached. The mitochondrial and synaptic membranes of the hair cells appeared normal.     

OBSERVATIONS ON SYNAPTONEMAL COMPLEXES IN PREMEIOTIC INTERPHASE OF WHEAT

Synaptonemal complexes (SCs) were found in stage 3, premeiotic (S phase) pollen mother cell (PMC) nuclei of wheat which were labeled with ³H-thymidine. Three nucleoli are present in PMC nuclei at the beginning of stage 3, premeiotic interphase (S3). During S3, nucleoli move toward the nuclear envelope and fuse to form one nucleolus near the end of the stage. PMC nuclei labeled with ³H-thymidine were serially sectioned to show that more than one nucleolus was present and that SCs were also present in these DNA synthetic nuclei. Entire S3 PMC nuclei were serially sectioned to show the presence of SCs and all three nucleoli. Entire leptotene nuclei were also serially sectioned and segments of SCs were found. It is concluded that the association of homologous chromosomes in S3 of wheat is an early step in SC formation which proceeds through leptotene and is completed in zygotene and pachytene. Thus there is evidence that the continuum of chromosome pairing in wheat starts much earlier than was once thought.     

Paired development of hair cells in neuromasts of the teleost lateral line.

Lateral line neuromasts of the bullseye Parapriacanthus ransonetti and the cardinal fish Apogon cyanosoma were examined by scanning electron microscopy. Neuromasts showed large numbers of degenerating hair cells and immature hair cells, suggesting a high degree of hair cell turnover. New hair cells were mainly produced in pairs (fewer than 5% appear singly), the two cells of a pair having opposite but parallel orientations of their mechanosensitive axes. It is suggested that each pair results, directly or indirectly, from a single mitosis. The results further suggest that the axis of mitosis is one of the factors which determine the direction of the hair cell axis of mechanosensitivity.     

Predicting shifts in parasite distribution with climate change: a multitrophic level approach

Climate change likely will lead to increasingly favourable environmental conditions for many parasites. However, predictions regarding parasitism's impacts often fail to account for the likely variability in host distribution and how this may alter parasite occurrence. Here, we investigate potential distributional shifts in the meningeal worm, Parelaphostrongylosis tenuis, a protostrongylid nematode commonly found in white‐tailed deer in North America, whose life cycle also involves a free‐living stage and a gastropod intermediate host. We modelled the distribution of the hosts and free‐living larva as a complete assemblage to assess whether a complex trophic system will lead to an overall increase in parasite distribution with climate change, or whether divergent environmental niches may promote an ecological mismatch. Using an ensemble approach to climate modelling under two different carbon emission scenarios, we show that whereas the overall trend is for an increase in niche breadth for each species, mismatches arise in habitat suitability of the free‐living larva vs. the definitive and intermediate hosts. By incorporating these projected mismatches into a combined model, we project a shift in parasite distribution accounting for all steps in the transmission cycle, and identify that overall habitat suitability of the parasite will decline in the Great Plains and southeastern USA, but will increase in the Boreal Forest ecoregion, particularly in Alberta. These results have important implications for wildlife conservation and management due to the known pathogenicity of parelaphostrongylosis to alternate hosts including moose, caribou and elk. Our results suggest that disease risk forecasts which fail to consider biotic interactions may be overly simplistic, and that accounting for each of the parasite's life stages is key to refining predicted responses to climate change.     

Evidence for interplay between genes and maternal stress in utero: monoamine oxidase A polymorphism moderates effects of life events during pregnancy on infant negative emotionality at 5 weeks

The low activity variant of the monoamine oxidase A (MAOA) functional promoter polymorphism, MAOA‐LPR, in interaction with adverse environments (G × E) is associated with child and adult antisocial behaviour disorders. MAOA is expressed during foetal development so in utero G × E may influence early neurodevelopment. We tested the hypothesis that MAOA G × E during pregnancy predicts infant negative emotionality soon after birth. In an epidemiological longitudinal study starting in pregnancy, using a two stage stratified design, we ascertained MAOA‐LPR status (low vs. high activity variants) from the saliva of 209 infants (104 boys and 105 girls), and examined predictions to observed infant negative emotionality at 5 weeks post‐partum from life events during pregnancy. In analyses weighted to provide estimates for the general population, and including possible confounders for life events, there was an MAOA status by life events interaction (P = 0.017). There was also an interaction between MAOA status and neighbourhood deprivation (P = 0.028). Both interactions arose from a greater effect of increasing life events on negative emotionality in the MAOA‐LPR low activity, compared with MAOA‐LPR high activity infants. The study provides the first evidence of moderation by MAOA‐LPR of the effect of the social environment in pregnancy on negative emotionality in infancy, an early risk for the development of child and adult antisocial behaviour disorders .     

Mitochondrial DNA and microsatellite loci data supporting a management plan for a critically endangered lizard from Brazil

Endemic and endangered species are highly vulnerable to habitat perturbations and may be subject to variations in their population size. Management plan for these species is crucial to avoid population decline, loss of genetic variability, inbreeding and ultimately extinction. The sand lizard, Liolaemus lutzae, is endemic to a habitat of sandy coastal plain (restinga). Its geographical distribution extends for only 200 km stretch of the coast of Rio de Janeiro state, Brazil, one of South America’s most densely populated regions. Extensive development and degradation of the beaches where the species inhabits, have led to the species becoming critically endangered. We used mitochondrial DNA sequences and microsatellite loci to resolve patterns of population connectivity and genetic variation within the species in order to provide a platform for a species management plan. Our results indicate the existence of three main populations, separated from each other by the Guanabara Bay and by the Arraial do Cabo Peninsula. The low microsatellite genetic variation and heterozygosity witnessed in each of the three populations, together with high levels of inbreeding and low effective population sizes suggest that the species is in urgent need of intensive management. Based on the results of this study we propose strong measures to protect existing restinga fragments and the implementation of programmes of captive breeding and reintroduction of individuals from the heavily threatened regions to protected refugia. Such measures may be the only way of ensuring the continuity of the species.     

A role for oxalic acid generation in ozone‐induced signallization in Arabidopis cells

Ozone (O₃) is an air pollutant with an impact increasingly important in our industrialized world. It affects human health and productivity in various crops. We provide the evidences that treatment of Arabidopsis thaliana with O₃ results in ascorbate‐derived oxalic acid production. Using cultured cells of A. thaliana as a model, here we further showed that oxalic acid induces activation of anion channels that trigger depolarization of the cell, increase in cytosolic Ca²⁺ concentration, generation of reactive oxygen species and cell death. We confirmed that O₃ reacts with ascorbate in the culture, thus resulting in production of oxalic acid and this could be part of the O₃‐induced signalling pathways that trigger programmed cell death.