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Nitric oxide is involved in growth regulation and re-orientation of pollen tubes
Full text linkNitric oxide (NO) controls diverse functions in many cells and organs of animals. It is also produced in plants and has a variety of effects, but little is known about their underlying mechanisms. In the present study, we have discovered a role for NO in the regulation of pollen tube growth, a fast tip-growing cellular system. Pollen tubes must be precisely oriented inside the anatomically complex female ovary in order to deliver sperm. We hypothesized that NO could play a role in this guidance and tested this hypothesis by challenging the growth of pollen tubes with an external NO point source. When a critical concentration was sensed, the growth rate was reduced and the growth axis underwent a subsequent sharp reorientation, after which normal growth was attained. This response was abrogated in the presence of the NO scavenger CPTIO and affected by drugs interfering in the cGMP signaling pathway. The sensitivity threshold of the response was significantly augmented by sildenafil citrate (SC), an inhibitor of cGMP-specific phosphodiesterases in animals. NO distribution inside pollen tubes was investigated using DAF2-DA and was shown to occur mostly in peroxisomes. Peroxisomes are normally excluded from the tip of pollen tubes and little if any NO is found in the cytosol of that region. Our data indicate that the rate and orientation of pollen tube growth is regulated by NO levels at the pollen tube tip and suggest that this NO function is mediated by cGMP
Transcriptional profiling of arabidopsis tissues reveals the Unique Characteristics of the pollen transcriptome
Full text linkPollen tubes are a good model for the study of cell growth and morphogenesis because of their extreme elongation without cell division. Yet, knowledge about the genetic basis of pollen germination and tube growth is still lagging behind advances in pollen physiology and biochemistry. In an effort to reduce this gap, we have developed a new method to obtain highly purified, hydrated pollen grains of Arabidopsis through flowcytometric sorting, and we used GeneChips (Affymetrix, Santa Clara, CA; representing approximately 8,200 genes) to compare the transcriptional profile of sorted pollen with those of four vegetative tissues (seedlings, leaves, roots, and siliques). We present a new graphical tool allowing genomic scale visualization of the unique transcriptional profile of pollen. The 1,584 genes expressed in pollen showed a 90% overlap with genes expressed in these vegetative tissues, whereas one-third of the genes constitutively expressed in the vegetative tissues were not expressed in pollen. Among the 469 genes enriched in pollen, 162 were selectively expressed, and most of these had not been associated previously with pollen. Their functional classification reveals several new candidate genes, mainly in the categories of signal transduction and cell wall biosynthesis and regulation. Thus, the results presented improve our knowledge of the molecular mechanisms underlying pollen germination and tube growth and provide new directions for deciphering their genetic basis. Because pollen expresses about one-third of the number of genes expressed on average in other organs, it may constitute an ideal system to study fundamental mechanisms of cell biology and, by omission, of cell division
Regulatory T cells selectively express toll-like receptors and are activated by lipopolysaccharide
Full text linkRegulatory CD4 T cells (Treg) control inflammatory reactions to commensal bacteria and opportunist pathogens. Activation of Treg functions during these processes might be mediated by host-derived proinflammatory molecules or directly by bacterial products. We tested the hypothesis that engagement of germline-encoded receptors expressed by Treg participate in the triggering of their function. We report that the subset of CD4 cells known to exert regulatory functions in vivo (CD45RB(low) CD25(+)) selectively express Toll-like receptors (TLR)-4, -5, -7, and -8. Exposure of CD4(+) CD25(+) cells to the TLR-4 ligand lipopolysaccharide (LPS) induces up-regulation of several activation markers and enhances their survival/proliferation. This proliferative response does not require antigen-presenting cells and is augmented by T cell receptor triggering and interleukin 2 stimulation. Most importantly, LPS treatment increases CD4(+) CD25(+) cell suppressor efficiency by 10-fold and reveals suppressive activity in the CD4(+) CD45RB(low) CD25(-) subset that when tested ex-vivo, scores negative. Moreover, LPS-activated Treg efficiently control naive CD4 T cell-dependent wasting disease. These findings provide the first evidence that Treg respond directly to proinflammatory bacterial products, a mechanism that likely contributes to the control of inflammatory response
Muller’s ratchet and the pattern of variation at a neutral locus
Full text linkFor access the publication please visit the following link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1462134/The levels and patterns of variation at a neutral locus are analyzed in a haploid asexual population Undergoing accumulation of deleterious mutations due to Muller's ratchet. We find that the movement Of Muller's ratchet can be associated with a considerable reduction in genetic diversity below classical neutral expectation. The extent to which variability is reduced is a function Of the deleterious initiation rate, the fitness effects of the Imitations, and the population size. Approximate analytical expressions for the expected genetic diversity are compared with simulation results under two different models of deleterious imitations: a model where all deleterious imitations have equal effects and a model where there are two classes of deleterious imitations. We also find that Muller's ratchet can produce a considerable distortion in the neutral frequency spectrum toward an excess of rare variants
The nodulin VfENOD18 is an ATP-binding protein in infected cells of Vicia faba L. nodules
No full textRecently we described the novel nodulin gene VfENOD18, whose corresponding transcripts were restricted to the nitrogen-fixing zone III of broad bean root nodules. To characterize VfENOD18 on the protein level, polyclonal antibodies were generated using the purified recombinant VfENOD18 protein produced in Escherichia coli by employing the pMAL-c expression system. These antibodies recognized immunoreactive proteins isolated from indeterminate nodules of different leguminous plants, but also from non-symbiotic tissues of Glycine max and from tissues of Arabidopsis thaliana and Zea mays. Using immunogold labelling the nodulin VfENOD18 was localized to the cytoplasm of infected cells in the nitrogen-fixing zone of broad bean nodules. Due to the homology of the VfENOD18 sequence to that of the ATP-binding protein MJ0577 from the hyperthermophile Methanococcus jannaschii the recombinant VfENOD18 protein was tested for ATP-binding. Using the biotin photoaffinity ATP analogue 8N3ATP[gamma]biotin it could be demonstrated that VfENOD18 is an ATP-binding protein. PCR experiments revealed that the amino acid sequences of the putative C-terminal ATP-binding sites of the VfENOD 18 homologues from Lens culinaris, Vicia hirsuta, Vicia sativa and Vicia villosa were conserved. We propose that VfENOD18 is a member of a novel family of ATP-binding proteins in plants
Arrested B Lymphopoiesis and Persistence of Activated B Cells in Adult Interleukin 7
Full text linkThis deposit is composed by a publication in which the IGC' authors have had the role of collaboration (it's a collaboration publication). This type of deposit in ARCA is in restrictedAccess (it can't be in open access to the public), and could only be accessed by two ways: either by requesting a legal copy to the author (the email contact present in this deposit) or by visiting the following link:
https://f1000.com/prime/1003667Interleukin 7 is a crucial factor for the development of murine T and B lymphocytes. We now
report that, in the absence of interleukin 7, B lymphocyte production takes place exclusively
during fetal and perinatal life, ceasing after 7 wk of age. In peripheral organs, however, the pool
of B lymphocytes is stable throughout adult life and consists only of cells that belong to the B1
and marginal zone (MZ) compartments. This is accompanied by a 50-fold increase in the frequency
of immunoglobulin (Ig)M- and IgG-secreting cells, and the concentration of serum
immunoglobulins is increased three- to fivefold. Both the MZ phenotype and the increase in
serum IgM are T cell independent. These findings reveal a previously undescribed pathway of
B lymphopoiesis that is active in early life and is interleukin 7 independent. This pathway generates
B1 cells and a normal sized MZ B lymphocyte compartment
Growing pollen tubes possess a constitutive alkaline band in the clear zone and a growth-dependent acidic tip
Full text linkUsing both the proton selective vibrating electrode to probe the extracellular currents and ratio-metric wide-field fluorescence microscopy with the indicator 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (Hf) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 mu M or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth