Characterization of 5' truncated transposed copies of the I factor in Drosophila melanogaster.

I factors in Drosophila melanogaster are transposable elements structurally related to Mammalian LINEs. Their transposition is activated at high frequencies during I-R hybrid dysgenesis and is associated with the production of mutations of various sorts. Very few of these mutations have been studied at the molecular level; those reported so far result either from chromosomal rearrangements or from insertions of complete I factors. We have analysed three I-R induced yellow mutations and have found that one of them is due to the insertion of an I element very similar to the complete I factor, whereas the other two are due to insertions of I elements that are truncated at their 5' ends; one of them exhibits an unusual 3' end. We discuss possible mechanisms of production of such modified I elements.     

CENTROSOMES AND MICROTUBULES DURING MEIOSIS IN THE MUSHROOM BOLETUS RUBINELLUS

The double centrosome in the basidium of Boletus rubinellus has been observed in three planes with the electron microscope at interphase preceding nuclear fusion, at prophase I, and at interphase I. It is composed of two components connected by a band-shaped middle part. At anaphase I a single, enlarged centrosome is found at the spindle pole, which is attached to the cell membrane. Microtubules mainly oriented parallel to the longitudinal axis of the basidium are present at prefusion, prophase I and interphase I. Cytoplasmic microtubules are absent when the spindle is present. The relationship of the centrosome in B. rubinellus to that in other organisms and the role of the cytoplasmic microtubules are discussed.     

The sex-specific impact of systolic hypertension and systolic blood pressure on arterial-ventricular coupling at rest and during exercise

In healthy subjects the arterial system and the left ventricle (LV) are tightly coupled at rest to optimize cardiac performance. Systolic hypertension (SH) is a major risk factor for heart failure and is associated with structural and functional alterations in the arteries and the LV. The effects of SH and resting systolic blood pressure (SBP) on arterial-ventricular coupling (E(a)I/E(LV)I) at rest, at peak exercise, and during recovery are not well described. We noninvasively characterized E(a)I/E(LV)I as end-systolic volume index/stroke volume index in subjects who were normotensive (NT, n = 203) or had SH (brachial SBP > or =140 mmHg, n = 79). Cardiac volumes were measured at rest and throughout exhaustive upright cycle exercise with gated blood pool scans. E(a)I/E(LV)I reserve was calculated by subtracting peak from resting E(a)I/E(LV)I. At rest, E(a)I/E(LV)I did not differ between SH and NT men but was 23% (P = 0.001) lower in SH vs. NT women. E(a)I/E(LV)I did not differ between SH and NT men or women at peak exercise or during recovery. Nevertheless, E(a)I/E(LV)I reserve was 61% (P < 0.001) lower in SH vs. NT women. Similarly, resting SBP (as a continuous variable) was not associated with E(a)I/E(LV)I in men (beta = -0.12, P = 0.17) but was inversely associated with E(a)I/E(LV)I in women (beta = -0.47, P < 0.001). SH and a higher resting brachial SBP are associated with a lower E(a)I/E(LV)I at rest in women but not in men, and SH women have an attenuated E(a)I/E(LV)I reserve. Whether a smaller E(a)I/E(LV)I reserve leads to functional limitations warrants further examination.     

Ultrastructure of meiosis in the hollyhock rust fungus,Puccinia malvacearum II. Metaphase I—Telophase I

Summary The three-dimensional structure of the spindle pole body (SPB) and meiotic spindle during early metaphase I through telophase I inPuccinia malvacearum is analyzed ultrastructurally from serial sections. During early metaphase I the spindle rotates from the perpendicular to a position oblique to the longitudinal axis and parallel to the sagittal plane of the cell. Tubular cisternae are present within the spindle at this stage. The half middle piece (MP) subtends a collateral disc (co-disc) which is inserted eccentrically within each SPB. The SPB, co-disc and half MP at opposite poles are in mirror image. During the transition from early metaphase I to full metaphase I, the spindle orients parallel to the lateral wall of the promycelium and the half MPs are lost. The co-discs partially detach from each discoid SPB and maintain this relation until the end of interphase I. Co-discs become further differentiated as they attach to the subtending sheath-like extension of the nuclear envelope previously occupied by the half MPs. Microvesicles within the nucleoplasm are specific to mid metaphase I. A metaphase plate is absent. The 14 bivalents, which are directly connected to each polar SPB by 2 to 3 kinetochore MTs, are spread over nearly the entire length of the central spindle. The first anaphasic movement involves asynchronous shortening of the kinetochore MTs while the second consists of extensive pole-to-pole elongation. Astral MTs first appear at early metaphase I and become most numerous at anaphase I. An intact nuclear envelope constricts against the central spindle at either end of the interzonal region. Concurrently, centripetal growth of the nuclear envelope under each SPB results in their gradual externalization by the end of telophase I. The sibling nuclei are cut off by constriction of the nuclear envelope at either end of the interzonal region. These meiotic stages inP. malvacearum are compared with those in other basidiomycetes and ascomycetes.     

Photocycle and photoreversal of photoactive yellow protein at alkaline pH: kinetics, intermediates, and equilibria

Since the habitat of Halorhodospira halophila is distinctly alkaline, we investigated the kinetics and intermediates of the photocycle and photoreversal of the photoreceptor photoactive yellow protein (PYP) from pH 8 to 11. SVD analysis of the transient absorption time traces in a broad wavelength range (330-510 nm) shows the presence of three spectrally distinct species (I1, I1', and I2') at pH 10. The spectrum of I1' was obtained in two different ways. The maximal absorption is at 425 nm. I1' probably has a deprotonated chromophore and may be regarded as the alkaline form of I2'. At pH 10, the I1 intermediate decays in approximately 330 micros in part to I1' before I1 and I1' decay further to I2' in approximately 1 ms. From the rise of I2' (approximately 1 ms) to the end of the photocycle, the three intermediates (I1, I1', and I2') remain in equilibrium and decay together to P in approximately 830 ms. Assuming that the spectra of I1, I1', and I2' are pH-independent, their time courses were determined. On the millisecond to second time scale, they are in a pH-dependent equilibrium with a pKa of approximately 9.9. With an increase in pH, the I1 and I1' populations increase at the expense of the amount of I2'. The apparent rate constant for the recovery of P slows with an increase in pH with a pKa of approximately 9.7. The equal pH dependence of this rate and the equilibrium concentrations follows, if we assume that the equilibration rates between the intermediates are much faster than the recovery rate and that the recovery occurs from I2'. The pKa of approximately 9.9 is assigned to the deprotonation of the phenol of the surface-exposed chromophore in the I1'-I2' equilibrium. The I1-I1' equilibrium is pH-independent. Photoreversal experiments at pH 10 with the second flash at 355 nm indicate the presence of only one I2-like intermediate, which we assign on the basis of its lambda(max) value to I2'. After the rapid unresolved photoisomerization to I2'(trans), the reversal pathway back to P involves two sequential steps (60 micros and 3 ms). The amplitude spectra show that I1'(trans) and I1(trans) intermediates participate in this reversal.     

Direct binding of peptide to empty MHC class I molecules on intact cells and in vitro

MHC class I molecules devoid of peptide are expressed on the cell surface of the mouse mutant lymphoma cell line RMA-S upon culture at reduced temperature. Empty class I molecules are thermolabile at the cell surface and in detergent lysates, but can be stabilized by the addition of presentable peptide; peptide binding appears to be a rapid process. Furthermore, class I molecules on the surface of RMA-S (H-2b haplotype) cells cultured at 26 degrees C can efficiently and specifically bind iodinated peptide presented by H-2Kb. Binding of iodinated peptide is also observed at a lower level for nonmutant cells (RMA) cultured at 26 degrees C. These experiments underscore the role for peptide in maintenance of the structure of class I molecules and, more importantly, provide two assay systems to study the interactions of peptides with MHC class I molecules independent of the availability of T cells that recognize a particular peptide-MHC class I complex.     

Mutants of human insulin-like growth factor I with reduced affinity for the type 1 insulin-like growth factor receptor

Four mutants of human insulin-like growth factor I (hIGF I) have been purified from the conditioned media of yeast transformed with an expression vector containing a synthetic gene for hIGF I altered by site-directed mutagenesis. hIGF I has the sequence Phe-23-Tyr-24-Phe-25 which is homologous to a region in the B-chain of insulin. [Phe23,Phe24,Tyr25]IGF I, in which the sequence is altered to exactly correspond to the homologous sequence in insulin, is equipotent to hIGF I at the types 1 and 2 IGF and insulin receptors. [Leu24]IGF I and [Ser24]IGF I have 32- and 16-fold less affinity than hIGF I at the human placental type 1 IGF receptor, respectively. These peptides are 10- and 2-fold less potent at the placental insulin receptor, respectively. [Leu24]IGF I and [Ser24]IGF I have similarly reduced affinities for the type 1 IGF receptor of rat A10 and mouse L cells. Thus, the importance of the interaction of residue 24 with the receptor is conserved in several species. In three cell-based assays, [Leu24]IGF I and [Ser24]IGF I are full agonists with reduced efficacy compared to hIGF I. Desoctapeptide [Leu24]IGF I, in which the loss of aromaticity at position 24 is combined with the deletion of the carboxyl-terminal D region of hIGF I, has 3-fold lower affinity than [Leu24]IGF I for the type 1 receptor and 2-fold higher affinity for the insulin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on triploid Allium triquetrum

This work describes the relationship between the univalents seen at metaphase I and the distribution of dyads at anaphase I in the pollen mother cells of triploid Allium triquetrum. The orientation of the centromeres within the trivalents and bivalents at metaphase I towards the two poles of the pollen mother cells is random. The distribution of polar univalents towards the two poles at metaphase I is also random, as is the distribution of dyads at anaphase I in low univalent frequency collections. However, in a high univalent frequency collection, the distribution of dyads at anaphase I is non-random. There is an excess of cells with the most equal dyad distribution (13–14) and a paucity of cells with a 12–15 distribution. In low univalent frequency collections, the equatorial univalents are believed to remain in the equatorial region during anaphase I and are seen as laggards at late anaphase I. The remaining chromosomes move according to the metaphase I orientation of their centromeres to give a random distribution of dyads at anaphase I. In high univalent frequency collections it is argued that the non-random dyad distribution seen at anaphase I is the result of non-random movement of some of the equatorial univalents away from the equatorial region during anaphase I. The remaining equatorial univalents remain in the equatorial region and are seen as laggards at late anaphase I.     

Transient sampling of aggregation‐prone conformations causes pathogenic instability of a parkinsonian mutant of DJ‐1 at physiological temperature

Various missense mutations in the cytoprotective protein DJ‐1 cause rare forms of inherited parkinsonism. One mutation, M26I, diminishes DJ‐1 protein levels in the cell but does not result in large changes in the three‐dimensional structure or thermal stability of the protein. Therefore, the molecular defect that results in loss of M26I DJ‐1 protective function is unclear. Using NMR spectroscopy near physiological temperature, we found that the picosecond–nanosecond dynamics of wild‐type and M26I DJ‐1 are similar. In contrast, elevated amide hydrogen/deuterium exchange rates indicate that M26I DJ‐1 is more flexible than the wild‐type protein on longer timescales and that hydrophobic regions of M26I DJ‐1 are transiently exposed to solvent. Tryptophan fluorescence spectroscopy and thiol crosslinking analyzed by mass spectrometry also demonstrate that M26I DJ‐1 samples conformations that differ from the wild‐type protein at 37°C. These transiently sampled conformations are unstable and cause M26I DJ‐1 to aggregate in vitro at physiological temperature but not at lower temperatures. M26I DJ‐1 aggregation is correlated with pathogenicity, as the structurally similar but non‐pathogenic M26L mutation does not aggregate at 37°C. The onset of dynamically driven M26I DJ‐1 instability at physiological temperature resolves conflicting literature reports about the behavior of this disease‐associated mutant and illustrates the pitfalls of characterizing proteins exclusively at room temperature or below, as key aspects of their behavior may not be apparent.     

Sequence non-specific double-strand breaks and interhomolog interactions prior to double-strand break formation at a meiotic recombination hot spot in yeast.

The HIS4LEU2 meiotic recombination hot spot specifies two double-strand break (DSB) sites, I and II. Results presented demonstrate that DSBs at site I occur at many positions throughout a region of approximately 150 bp; we infer that breaks occur in a sequence non-specific fashion. Single-strand nicks at sites I and II are not detectable. Analysis of the effects of a 36 bp linker insertion at site I reveals the existence of communication along and between homologs prior to DSB formation. In cis, the insertion allele causes an increase in DSBs at site I but a decrease in DSBs at site II. In trans, two effects are observed. One effect likely reflects very early pre-DSB interhomolog interactions; the second is suggestive of a later, more intimate interaction in which sites I and II on the two homologs all compete for DSBs. The existence of interhomolog interactions in early meiotic prophase can explain how the sites of crossovers come to lie between the homolog axes at pachytene.     

Modification of excitation energy distribution to photosystem I by protein phosphorylation and cation depletion during thylakoid biogenesis in wheat

The effects of protein phosphorylation and cation depletion on the electron transport rate and fluorescence emission characteristics of photosystem I at two stages of chloroplast development in light-grown wheat leaves are examined. The light-harvesting chlorophyll a/b protein complex associated with photosystem I (LHC I) was absent from the thylakoids at the early stage of development, but that associated with photosystem II (LHC II) was present. Protein phosphorylation produced an increase in the light-limited rate of photosystem I electron transport at the early stage of development when chlorophyll b was preferentially excited, indicating that LHC I is not required for transfer of excitation energy from phosphorylated LHC II to the core complex of photosystem I. However, no enhancement of photosystem I fluorescence at 77 K was observed at this stage of development, demonstrating that a strict relationship between excitation energy density in photosystem I pigment matrices and the long-wavelength fluorescence emission from photosystem I at 77 K does not exist. Depletion of Mg²⁺ from the thylakoids produced a stimulation of photosystem I electron transport at both stages of development, but a large enhancement of the photosystem I fluorescence emission was observed only in the thylakoids containing LHC I. It is suggested that the enhancement of PS I electron transport by Mg²⁺-depletion and phosphorylation of LHC II is associated with an enhancement of fluorescence at 77 K from LHC I and not from the core complex of PS I.     

Distribution and dispersal of desert mistletoe is scale-dependent, hierarchically nested

Spatial patterns are important to many ecological processes, and scale is a critical component of both patterns and processes. I examined the pattern and scale of the spatial distribution of infection of host plants by the desert mistletoe, Phoradendron californicum, in a landscape that spans several square kilometers. I also studied the relationship between mistletoe infection and seed dispersal. I found elevated seed rain in areas with a high prevalence of mistletoes and I found that a greater proportion of trees receive seeds than are infected, suggesting that mistletoes will be aggregated in space. Using nested analysis of variance and variograms, I found that mistletoe infections were distributed in hierarchical patches. Mistletoes were aggregated within trees and mistletoe prevalence was correlated at scales of <1500 m, and at scales >4000 m. Patterns at the largest scales were correlated with elevation: sites at higher elevations showed reduced mistletoe infection compared to those at lower elevations. I propose that at small scales, mistletoe distributions are primarily the result of aggregation of seed-dispersing birds, and that the elevational effect could reflect the recent colonization of higher elevations by the mistletoes' mesquite hosts or the limits of the mistletoes' physiological tolerance to freezing-induced cavitation.     

Structure and genomic organization of I elements involved in I-R hybrid dysgenesis in Drosophila melanogaster.

I-R hybrid dysgenesis in D. melanogaster is controlled by transposable elements known as I factors which terminate at their 3' ends by an A-rich sequence. Inducer strains contain active I factors. Both reactive and inducer stocks possess defective I elements. We have cloned various I elements from both categories of strains. The I elements having recently transposed in inducer strains have a structure closely related to that of active I factors. However we have isolated one such I element that is truncated at its 5' end. The I elements common to reactive and inducer strains are affected by various rearrangements and many point mutations. They do not appear to be simple derivatives of complete I factors.     

How does visual thinking work in the mind of a person with autism? A personal account

My mind is similar to an Internet search engine that searches for photographs. I use language to narrate the photo-realistic pictures that pop up in my imagination. When I design equipment for the cattle industry, I can test run it in my imagination similar to a virtual reality computer program. All my thinking is associative and not linear. To form concepts, I sort pictures into categories similar to computer files. To form the concept of orange, I see many different orange objects, such as oranges, pumpkins, orange juice and marmalade. I have observed that there are three different specialized autistic/Asperger cognitive types. They are: (i) visual thinkers such as I who are often poor at algebra, (ii) pattern thinkers such as Daniel Tammet who excel in math and music but may have problems with reading or writing composition, and (iii) verbal specialists who are good at talking and writing but they lack visual skills.     

X-ray structure of the cyclomaltohexaicosaose triiodide inclusion complex provides a model for amylose-iodine at atomic resolution

Cyclomaltohexaicosaose (CA26) is folded into two 1(2)/(3) turns long V-helices that are oriented antiparallel. Crystals of complexes of CA26 with NH(4)I(3) and Ba(I(3))(2) are brown and X-ray analyses show that I(3)(-) units are located in the approximately 5 A wide central channels of the V-helices. In the complex with NH(4)I(3), two CA26 molecules are stacked to form 2 x 1(2)/(3) turns long channels harbouring 3 I(3)(-) at 3.66-3.85 A inter I(3)(-) distance (shorter than van der Waals distance, 4.3 A), whereas in the Ba(I(3))(2) complex, CA26 are not stacked and only one I(3)(-) each fills the V-helices. Glucose...I contacts are formed with C5-H, C3-H, C6-H and (at the ends of the V-helices) with O6 in (+) gauche orientation. By contrast, O2, O3, O4 and O6 in the preferred (-) gauche orientation do not interact with I because these distances are >/=4.01 A and exceed the van der Waals I...O sum of radii by about 0.5 A except for one O2...I distance of 3.68 A near the end of one V-helix. Raman spectra indicate that the complexes share the presence of I(3)(-) with blue amylose-iodine.     

New insight for fluoroquinophenoxazine derivatives as possibly new potent topoisomerase I inhibitor

Fluoroquinolones, represented by ciproxacin and norfloxacin, are well-known clinical antimicrobial agents, and their phenyl ring expanded quinophenoxazines are reported as possible antitumor active compounds. These quinophenoxazines are known to inhibit DNA topoisomerase II essential for cell replication cycle. But there were no reports for topoisomerase I inhibition study for these compounds. In this report, we have prepared a few quinophenoxazine analogues and tested their topoisomerases I and II inhibitory activities and cytotoxicity. From the result, we found that quinophenoxazine analogues possessed strong topoisomerase I inhibitory capacity as well as topoisomerase II inhibition. Among the compounds prepared, A-62176 analogues showed strong topoisomerases I and II inhibitory activities. Interestingly, compound 8 missing the 3-aminopyrrolidine moiety at C2 position has similar potent inhibitory capacity against topoisomerases I and II at higher concentrations (20 and 10 microM, respectively). But compound 8 inhibited topoisomerase I function more selectively at lower concentration, 2 microM. Our observation might strongly implicate that fluoroquinophenoxazines can be developed as efficient topoisomerase I inhibitor with the elaborate modification.     

Intergeneric coaggregation of strains isolated from phenol-degrading aerobic granules

This work aims at exploring the intergeneric coaggregation of the pairs of strains, Acinetobacter calcoaceticus I6 and Bacillus thuringiensis I2 or Candida tropicalis I9 (with GenBank accession numbers EU250016, EU036759, and DQ515822) isolated from phenol-degrading aerobic granules. The I2 and I6 are functionally similar stains, while the I6 and I9 are functionally dissimilar strains. The lectin-saccharide interaction controlled the coaggregation of both the I2+I6 and I6+I9 pairs, with the protein adhesin being associated with the strain I6, and the complementary galactosamine-like or fucose-like sugar receptor with the strain I2 or I9, respectively. The rod-like I2 cells bridged the clusters of I2 or I6 cells to form aggregates, while the small I6 cells attached on and modified the surface of I9 to form aggregates.     

Meiotic stage-dependent induction of chromosome aberrations in Chinese hamster primary oocytes exposed to topoisomerase II inhibitor etoposide

To investigate the chromosomal effects of topoisomerase II (topo-II)-interactive drugs on mammalian primary oocytes, female Chinese hamsters were treated with etoposide (VP-16) at various intervals pre- and post-human chorionic gonadotropin (hCG) injections. Chromosome analysis of oocytes at metaphase II (M II) showed that treatment with VP-16 at 50h pre-hCG had no effect, but the treatments between 24h pre-hCG and 2h post-hCG often caused structural chromosome aberrations. Although treatment at 4h post-hCG had no effect, subsequent treatments at 6 and 8h post-hCG produced a significant increase in structural chromosome aberrations. No effect was found following treatment at 10h post-hCG. The incidence of aneuploidy following exposure to VP-16 was also dependent on the time of hCG injection. Taking the time course of meiotic progression in primary oocytes following hCG injection and pharmacokinetics of VP-16 into consideration, it is likely that meiotic stages from late dictyate to diakinesis are highly sensitive to VP-16, while stages at dictyate and from metaphase I (M I) to telophase I (telo I) are relatively insensitive to the drug. Moreover, the effect of VP-16 on structural chromosome aberrations and aneuploidy was dose-dependent.Chromosome analysis at M I detected a frequent occurrence of structural chromosome aberrations in treated oocytes. This suggests that structural aberrations may be caused by disruption of cleavable complexes during chromosome condensation. Detection of chromosome bridges during anaphase I/telophase I (ana I/telo I) may support the hypothesis that induction of aneuploidy by VP-16 is due to failure in decatenation of recombinant homologous chromosomes.     

Global change,biodiversity, and ecosystem services: What can we learn from studies of pollination?

The study of global environmental change and its effect on biodiversity and ecosystem function is at an exciting crossroads, at which ideas developed largely through theory and small-scale experiments are now being tested with ecosystem services as they are delivered to people in real-world landscapes. Pollinators and pollination are emerging as a model system for exploring these questions, which inherently required working large spatio-temporal scales. In this Invited View, I discuss current questions that are at the leading edge of this research. I first point out some surprising knowledge gaps in our understanding of pollinators’ response to global change. I then outline several ways in which current understanding of the biodiversity-ecosystem functioning relationship might be transformed by studies conducted at large spatio-temporal scales. Specifically, I propose two hypotheses that relate to the number of species required to saturate ecosystem function, and to the mechanisms through which biodiversity stabilizes ecosystem function over space or time.