Is there a pilot in a pseudopod?

The concept of pilot pseudopodia is reconsidered 30 years after its inauguration (Gerisch, G., Hülser, D., Malchow, D., Wick, U., 1975. Cell communication by periodic cyclic-AMP pulses. Phil. Trans. R. Soc. Lond. B 272, 181-192). The original hypothesis stated that protruding pseudopodia serve as dynamic sensory organelles that aid a cell in perceiving variations of chemoattractant concentration and, consequently, in navigation during chemotaxis. This influential idea is reevaluated in the light of recent findings about the mechanisms governing chemotactic cell motility, morphology and dynamics of pseudopodia, and about molecular constituents and regulators of pseudopod extension and retraction. It is proposed that stimulation by a chemoattractant modulates speed of pseudopod protrusion and thereby increases cell elongation. Elongation further enhances chemotactic sensitivity of the cell to shallow chemoattractant gradients, reinforces cell polarization, and finally leads to suppression of lateral pseudopodia and continuation of cell migration in the gradient direction.     

What's in a name?

The names of organisms have major impacts on the geopolitical world. The current state of flux in the taxonomy of the genera Cryptosporidium and Giardia illustrates the effects that names can have on environmental and governmental policy. Taxonomy remains a vital science that is very much alive in the application of modern methods for describing morphologically cryptic species.     

What's in a centromere?

The complete sequence of rice centromere 8 reveals a small amount of centromere-specific satellite sequence in blocks interrupted by retrotransposons and other repetitive DNA, in an arrangement that is strikingly similar in overall size and content to other centromeres of multicellular eukaryotes.     

What's in a name?

Have you ever wondered why professionals have so many complicated names for things? Two reasons come to mind: efficient communication, but also 'show'. Connecting with a wider audience means learning to tread the fine line between perfect accuracy and being understood.     

Fluorescence in situ hybridization reveals a break in the α-satellite DNA of chromosome 1 in a family with a balanced whole-arm translocation

We have characterized a whole-arm translocation involving chromosomes 1 and 19 by traditional cytogenetic methods and fluorescence in situ hybridization with chromosome-specific -satellite and whole-chromosome painting probes, and different satellite III DNA probes. We have identified a break in the -satellite DNA region of chromosome 1, with division of this material into two a-satellite DNA blocks. This leaves one translocation chromosome with truncated -satellite DNA from chromosome 1 and the other trranslocation chromosome with all the -satellite DNA from chromosome 19 and truncated -satellite DNA from chromosome 1. We speculate whether the recombination event observed has taken place in tetraplex structures of satellite III DNA interspersed between -satellite DNA.     

Functional Traits in a Species-Rich Grassland and a Short-Term Change in Management: Is There a Competition-Colonization Trade-Off?

The species richness of grasslands generally cannot be fully restored after changes in management. Some species with small statures and basal leaf rosettes can be lost forever. The same species, however, seem to possess the traits necessary for successful re-colonization – they produce small, easily dispersable seeds, numerous seedlings and have lasting seed banks. We tested the hypothesis that plants in species-rich grasslands can be characterized by a negative correlation between their competitive ability and potential for generative regeneration, i.e. by a competition-colonization trade-off. An analysis of the traits of 95 grassland species supported this hypothesis. We then conducted a manipulative experiment in three different meadow communities in the Bílé Karpaty Mts. The experiment involved characterizing species traits during periods of different grassland management regimes in the years 1997–2000 and comparing these with the original management regime, which was restored between 2000 and 2003. We found out that the hypothesis only holds true for the pooled dataset for all three communities. When the individual meadow communities were analyzed separately, plant traits other than those responsible for the competition-colonization trade-off appear to be characteristic of responsive species, e.g. shoot lifespan or phenology. Our results imply that despite the general trade-offs found in large comparative studies, the plant response in a specific community is constrained by the local species pool.     

Generation and exploration of a dense genetic map in a region of a QTL affecting corpora lutea in a Meishan × Yorkshire cross

Previously genomic scans revealed quantitative trait loci (QTL) on porcine Chromosome 8 (SSC8) as significantly affecting the number of corpora lutea (CL) in swine. In one study, statistical evidence for the putative QTL was found in the chromosomal region defined by the microsatellites (MS) SW205, SW444, SW206, and SW29. A Yeast Artificial Chromosome library was screened by using the corresponding primers for clones containing these MS by PCR. From five positive YAC clones, 10 additional MS were isolated and mapped to SSC8 with the INRA-University of Minnesota porcine Radiation Hybrid (IMpRH) panel. The genetic map position of the QTL has been refined by addition of these 10 markers. The QTL evaluation included pedigrees of F₂-intercross Meishan × Yorkshire design, with phenotypic data of 108 F₂ female offspring and genotypic data for 29 MS markers on SSC8. The analysis was performed by using the least squares regression method. The calculated QTL effect for CL obtained by the multilocus least squares method showed a maximum test statistic (F value = 13.98) at position 99 cM between three MS derived from YACs containing SW205 and SW1843 spanning an interval of 7.1 cM. The point-wise (nominal) P-value was 5.21 × 10⁻⁶ corresponding to a genome-wide P-value of 0.009. The additive QTL effect explained 17.4% of the phenotypic variance. Received: 23 December 2000 / Accepted: 07 May 2001     

Dynamics of Breakdown in a Low-Pressure Argon–Mercury Mixture in a Long Discharge Tube

Breakdown dynamics in the course of glow discharge ignition in a long discharge tube (80 cm in length and 25 mm in diameter) filled with argon at a pressure of 3–4 Torr and mercury vapor at room temperature was studied experimentally. Rectangular voltage pulses with amplitudes from 1 to 2.5 kV were applied to the tube anode, the cathode being grounded. Complex electrical and optical measurements of the breakdown dynamics were carried out. Breakdown begins with a primary discharge between the anode and the tube wall. In this stage, a jump in the anode current and a sharp decrease in the anode voltage are observed and prebreakdown ionization wave arises near the anode. The cathode current appears only after the ionization wave reaches the cathode. The wave propagation velocity was measured at different points along the tube axis. The wave emission spectrum contains Hg, Ar, and Ar⁺ lines. The intensities of these lines measured at a fixed point exhibit very different time behaviors. The effect of the tube shielding on the breakdown characteristics was examined. It is found that, at a sufficiently narrow gap between the shield and the tube, this effect can be substantial.     

Is a genetic defect in Fkbp6 a common cause of azoospermia in humans?

FK506-binding protein 6 (Fkbp6) is a member of a gene family containing a prolyl isomerase/FK506-binding domain and tetratricopeptide protein-protein interaction domains. Recently, the targeted inactivation of Fkbp6 in mice has been observed to result in aspermic males and the absence of normal pachytene spermatocytes. The loss of Fkbp6 results in abnormal pairing and a misalignment of the homologous chromosomes, and in non-homologous partner switches and autosynapsis of the X chromosome cores in meiotic spermatocytes. In this study, we analyzed whether human FKBP6 gene defects might be associated with human azoospermia. We performed a mutation analysis in all the coding regions of the human FKBP6 gene in 19 patients with azoospermia resulting from meiotic arrest. The expression of the human FKBP6 gene was specific to the testis, and a novel polymorphism site, 245C → G (Y60X) could be found in exon 3. Our findings suggest that the human FKBP6 gene might be imprinted in the testis based on an analysis using two polymorphism sites. These authors equally contributed to this paper