A morphometric comparison of dissimilar early development in sibling species of Platynereis (Annelida,Polychaeta)

Summary Early development of Platynereis massiliensis was studied in serial sections of fixed embryos and in living or fixed embryos whose nuclei had been made visible with a fluorescent label. The unfertilized egg is an ellipsoid with three axes of differing length. The longest axis corresponds to the dorsoventral axis of the developing embryo. Egg volume is ten times that in the sibling species, P. dumerilii, mainly due to increased yolk content. The timing and spatial pattern of cleavage were observed from first cleavage to the 62-cell stage. Volumes of the blastomeres, their nuclei, their yolk-free cytoplasm and their yolk were determined from serial sections up to the 29-cell stage. In the P. massiliensis embryo, cell cycles are on average 3.7 times longer than in P. dumerilii; volume proportions among the blastomeres also differ and the macromeres containing the bulk of yolk are particularly large, but otherwise the cleavage patterns, differential segregation of yolk and yolk-free cytoplasm, and the histogenetic fates of the blastomeres are the same as in P. dumerilii. This equivalence of cell lineage and of cytoplasmic segregation mechanisms in both species, maintained in spite of the different appearance of the embryos, suggests functional importance of and selective constraint on these developmental features. The relatively accelerated divisions of the 2d cell line in P. massiliensis may be interpreted as the precocious development of cell lines which give rise to adult structures. Several structures, obviously functional in developing P. dumerilii, have lost their function in P. massiliensis: the egg contains few cortical granules, giving rise to only a moderate egg jelly layer in the zygote; prototroch cells develop cilia, but the heavy embryo is unable to swim; the larva develops three pairs of parapodia but, unlike the corresponding stage in P. dumerilii, is not capable of coordinate locomotion. This loss of motility is related to the brooding habit of the species developing inside the parental tube and is explained as the result of a switch from pelagic to benthic, protected reproduction in P. massiliensis. Offprint requests to: A.W.C. Dorresteijn     

A cross-diffusion model of forest boundary dynamics

A simple mathematical model of mono-species forest with two age classes which takes into account seed production and dispersal is presented in the paper. This reaction — diffusion type model is then reduced by means of an asymptotic procedure to a lower dimensional reaction — cross-diffusion model. The existence of standing and travelling wave front solutions corresponding to the forest boundary is shown for the later model. On the basis of the analysis, possible changes in forest boundary dynamics caused by antropogenic impacts are discussed.     

Existence and stability of periodic travelling wave solutions to Nagumo's nerve equation

Summary Nagumo's nerve conduction equation has a one-parameter family of spatially periodic travelling wave solutions. First, we prove the existence of these solutions by using a topological method. (There are some exceptional cases in which this method cannot be applied in showing the existence.) A periodic travelling wave solution corresponds to a closed orbit of a third-order dynamical system. The Poincaré index of the closed orbit is determined as a direct consequence of the proof of the existence. Second, we prove that the periodic travelling wave solution is unstable if the Poincaré index of the corresponding closed orbit is + 1. By using this result, together with the result of the author's previous paper, it is concluded that the slow periodic travelling wave solutions are always unstable. Third, we consider the stability of the fast periodic travelling wave solutions. We denote by L(c) the spatial period of the travelling wave solution with the propagation speed c. It is shown that the fast solution is unstable if its period is close to L_min, the minimum of L(c).     

What is hidden in the pannexin treasure trove: the sneak peek and the guesswork

Connexins had been considered to be the only class of the vertebrate proteins capable of gap junction formation; however, new candidates for this function with no homology to connexins, termed pannexins were discovered. So far three pannexins were described in rodent and human genomes: Panx1, Panx2 and Panx3. Expressions of pannexins can be detected in numerous brain structures, and now found both in neuronal and glial cells. Hypothetical roles of pannexins in the nervous system include participating in sensory processing, hippocampal plasticity, synchronization between hippocampus and cortex, and propagation of the calcium waves supported by glial cells, which help maintain and modulate neuronal metabolism. Pannexin also may participate in pathological reactions of the neural cells, including their damage after ischemia and subsequent cell death. Recent study revealed non-gap junction function of Panx1 hemichannels in erythrocytes, where they serve as the conduits for the ATP release in response to the osmotic stress. High-throughput studies produced some evidences of the pannexin involvement in the process of tumorigenesis. According to brain cancer gene expression database REMBRANDT, PANX2 expression levels can predict post diagnosis survival for patients with glial tumors. Further investigations are needed to verify or reject hypotheses listed.     

Solitonlike and nonsoliton modes of interaction of taxis waves (illustrated with an example of bacterial population waves)

It was shown earlier that during collisions bacterial population waves may either penetrate one another or stop. In this communication, the mechanism of these two interaction modes is considered in detail. It is shown on the basis of theoretical and experimental results that this interaction is a graphic example confirming one of the characteristic properties of waves in cross-diffusion systems.     

Intercellular calcium waves in primary cultured rat mesenteric smooth muscle cells are mediated by Connexin43

Abstract

Intercellular Ca^{2 +} wave propagation between vascular smooth muscle cells (SMCs) is associated with the propagation of contraction along the vessel. Here, we characterize the involvement of gap junctions (GJs) in Ca^{2 +} wave propagation between SMCs at the cellular level. Gap junctional communication was assessed by the propagation of intercellular Ca^{2 +} waves and the transfer of Lucifer Yellow in A7r5 cells, primary rat mesenteric SMCs (pSMCs), and 6B5N cells, a clone of A7r5 cells expressing higher connexin43 (Cx43) to Cx40 ratio. Mechanical stimulation induced an intracellular Ca^{2 +} wave in pSMC and 6B5N cells that propagated to neighboring cells, whereas Ca^{2 +} waves in A7r5 cells failed to progress to neighboring cells. We demonstrate that Cx43 forms the functional GJs that are involved in mediating intercellular Ca^{2 +} waves and that co-expression of Cx40 with Cx43, depending on their expression ratio, may interfere with Cx43 GJ formation, thus altering junctional communication.     

Influence of temperature on the infradian growth rhythm in Ulva lactuca (Chlorophyta)

The vegetative growth of Ulva lactuca was studied to determine if the growth rate of the alga is driven by infradian rhythmicity. The influence of temperature on the infradian rhythm of growth was also investigated. Discs of Ulva were grown in controlled laboratory conditions at different combinations of temperature (5, 10, 15, 20°С) and irradiance (40 and 60 μmol photons m^?2 s^?1) under 12 : 12 h light : dark cycles. The growth rates exhibited a rhythmic pattern with one major peak every 2 or 3 days. Growth at 5 or 10°С increased the prevalence of 3-day cycles and maintained U. lactuca in the vegetative growth stage. In contrast, growth at 15 or 20°С provoked a predominance of the 2-day cycle and induced reproduction. The 2- or 3-day cycles were combined in longer cycles having a period close to 6 days. We suppose that the 2-, 3- and 6-day rhythms of physiological processes are related to large-scale Rossby and Kelvin waves, which produce oscillations in the geomagnetic field and seawater temperature with the same periods. The predominance of 2-day or 3-day fluctuations of the geomagnetic field and temperature probably determine the prevalence of reproduction and vegetative growth, respectively, in Ulva.     

螺旋CT扫描及三维重建技术在股骨颈骨折分型及治疗中的应用

目的:探讨螺旋CT扫描及三维重建技术在股骨颈骨折分型及治疗中的应用价值。方法:选择2010年5月~2013年5月期间我院收治的股骨颈骨折患者237例为研究对象,根据患者扫描检查方式的不同将其分为对照组(112例)和观察组(125例),对照组患者行髋关节X线正位扫描,观察组行髋关节正位64排螺旋CT扫描,两组均根据扫描结果进行分型并制定相应的治疗方案,比较两组患者骨折内固定手术后2年的股骨头坏死率及骨折不愈合率。结果:两组行骨折内固定手术比例比较,差异无统计学意义(P0.05);术后2年,对照组股骨头坏死5例(22.73%),骨不连6例(27.27%);观察组股骨头坏死1例(3.70%),骨不连1例(3.70%),观察组患者股骨头坏死率及骨折不愈合率均显著低于对照组,差异均有统计学意义(P0.05)。结论:螺旋CT扫描及三维重建成像能够全面、准确显示股骨颈骨折的损伤情况,有助于骨折的正确分型和治疗方法的选择,改善预后。     

Effect of low-energy microwaves on DNA stability in solution

DNA isolated from liver of healthy and tumor-bearing (sarcoma 45) rats was irradiated in water-salt solution with weak microwaves (64.5 GHz, 50 μW/cm²). The heat stability of DNA increased with irradiation time (a raise of 1.5°C in T _m for “tumor” DNA after 90 min, without changes in ΔT), which may be associated with dehydration of the surrounding Na⁺ ions.     

Intra-annual genetic variation in the downstream larval drift of sutchi catfish (Pangasianodon hypophthalmus) in the Mekong river

Larvae of the sutchi catfish Pangasianodon hypophthalmus were collected during peak downstream drift in the Lower Mekong river on four occasions over an 8-week period during the 2003 spawning season, and genotyped using seven microsatellite loci. We provide evidence for several heterogeneous groups within and among the temporally discrete larval peak samples. Strong evidence for a significant deficit of heterozygotes was observed for each larval sample and the pooled sample, possibly due to population admixture. Although individual-based assignment tests suggested that each larval peak sample was admixed, significant but low genetic differentiation was observed among larval samples ( F _ST = 0.0052, P  < 0.01). The lack of significant relatedness confirms the multifamily composition of each larval group, excluding family bias to explain the observed genetic heterogeneity. Both the entire larval peak and each temporally separated larval peak originated from spawning groups with heterogeneous allelic composition involving several distinct spawning events. We propose three explanations to account for our findings: (1) the ecological match/mismatch hypothesis; (2) the genetic 'sweepstakes' selection hypothesis; and (3) life-history-specific characteristics of the spawning populations. Finally, an intra-annual shift in the contribution of the spawning populations to the larval drift was detected on successive occasions.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 719–728.