Improving the time efficiency of the Fourier synthesis method for slice selection in magnetic resonance imaging.

The design of slice selective pulses for magnetic resonance imaging can be cast as an optimal control problem. The Fourier synthesis method is an existing approach to solve these optimal control problems. In this method the gradient field as well as the excitation field are switched rapidly and their amplitudes are calculated based on a Fourier series expansion. Here, we provide a novel insight into the Fourier synthesis method via representing the Bloch equation in spherical coordinates. Based on the spherical Bloch equation, we propose an alternative sequence of pulses that can be used for slice selection which is more time efficient compared to the original method. Simulation results demonstrate that while the performance of both methods is approximately the same, the required time for the proposed sequence of pulses is half of the original sequence of pulses. Furthermore, the slice selectivity of both sequences of pulses changes with radio frequency field inhomogeneities in a similar way. We also introduce a measure, referred to as gradient complexity, to compare the performance of both sequences of pulses. This measure indicates that for a desired level of uniformity in the excited slice, the gradient complexity for the proposed sequence of pulses is less than the original sequence.

An ancient defense system eliminates unfit cells from developing tissues during cell competition.

Developing tissues that contain mutant or compromised cells present risks to animal health. Accordingly, the appearance of a population of suboptimal cells in a tissue elicits cellular interactions that prevent their contribution to the adult. Here we report that this quality control process, cell competition, uses specific components of the evolutionarily ancient and conserved innate immune system to eliminate Drosophila cells perceived as unfit. We find that Toll-related receptors (TRRs) and the cytokine Spätzle (Spz) lead to NFκB-dependent apoptosis. Diverse "loser" cells require different TRRs and NFκB factors and activate distinct pro-death genes, implying that the particular response is stipulated by the competitive context. Our findings demonstrate a functional repurposing of components of TRRs and NFκB signaling modules in the surveillance of cell fitness during development.

Automated differentiation of pre-diagnosis Huntington's disease from healthy control individuals based on quadratic discriminant analysis of the basal ganglia: the IMAGE-HD study.

We investigated two measures of neural integrity, T1-weighted volumetric measures and diffusion tensor imaging (DTI), and explored their combined potential to differentiate pre-diagnosis Huntington's disease (pre-HD) individuals from healthy controls. We applied quadratic discriminant analysis (QDA) to discriminate pre-HD individuals from controls and we utilised feature selection and dimension reduction to increase the robustness of the discrimination method. Thirty six symptomatic HD (symp-HD), 35 pre-HD, and 36 control individuals participated as part of the IMAGE-HD study and underwent T1-weighted MRI, and DTI using a Siemens 3 Tesla scanner. Volume and DTI measures [mean diffusivity (MD) and fractional anisotropy (FA)] were calculated for each group within five regions of interest (ROI; caudate, putamen, pallidum, accumbens and thalamus). QDA was then performed in a stepwise manner to differentiate pre-HD individuals from controls, based initially on unimodal analysis of motor or neurocognitive measures, or on volume, MD or FA measures from within the caudate, pallidum and putamen. We then tested for potential improvements to this model, by examining multi-modal MRI classifications (volume, FA and MD), and also included motor and neurocognitive measures, and additional brain regions (i.e., accumbens and thalamus). Volume, MD and FA differed across the three groups, with pre-HD characterised by significant volumetric reductions and increased FA within caudate, putamen and pallidum, relative to controls. The QDA results demonstrated that the differentiation of pre-HD from controls was highly accurate when both volumetric and diffusion data sets from basal ganglia (BG) regions were used. The highest discriminative accuracy however was achieved in a multi-modality approach and when including all available measures: motor and neurocognitive scores and multi-modal MRI measures from the BG, accumbens and thalamus. Our QDA findings provide evidence that combined multi-modal imaging measures can accurately classify individuals up to 15 years prior to onset when therapeutic intervention is likely to have maximal effects in slowing the trajectory of disease development.

Larval Schistosoma mansoni excretory-secretory glycoproteins (ESPs) bind to hemocytes of Biomphalaria glabrata (Gastropoda) via surface carbohydrate binding receptors.

Flow cytometric analysis of circulating blood cells (hemocytes) of Biomphalaria glabrata, molluscan intermediate host of Schistosoma mansoni, revealed the presence of 2 overlapping hemocyte subpopulations, designated R1 and R2. R1 hemocytes are characterized by their smaller size, reduced granularity, and the presence of the BGH1 surface epitope, whereas R2 cells are larger, more granulated, and generally lack the BGH1 cell marker. Both hemocyte subpopulations bound fluorescent dye (Oregon Green)-conjugated excretory-secretory glycoproteins (fESPs), although the specific fESP binding signal (geometric mean value), after correction for cellular autofluorescence, was greater in the R1 hemocyte subpopulation compared to that of the R2 subset. Partial inhibition of fESP binding to hemocytes consistently was achieved using various glycoconjugates (mucin, asialo-mucin, asialo-fetuin, heparin) and polysaccharides (fucoidan, dextran sulfate 8000), suggesting the involvement of hemocyte carbohydrate-binding receptors (CBRs) in reactions with ESP-associated glycans. Although sulfation of carbohydrate ligands contributed significantly to ESP blocking activity of some inhibitory polysaccharides and heparin, other sulfated proteoglycans (chondroitins A and B, heparan sulfate) were noninhibitory, indicating that charge alone was not solely responsible for the observed inhibition of hemocyte binding by fESPs. A similar blocking effect by desialylated glycoproteins (asialo-mucin, asialo-fetuin) further supports the contention that ESP-hemocyte interactions are mediated primarily through CBRs. The glycoconjugate inhibitors of ESP binding were only partially effective over a range of concentrations and their glycan moieties (oligosaccharides or long-chain polymers) comprised a diversity of major sugar groups, suggesting that hemocyte CBRs and S. mansoni larval ESPs likely represent a multiple receptor-ligand system. Previously reported findings of differential effects of ESPs on a variety of in vitro hemocyte functions are consistent with such a hypothesis.

Pattern- and growth-linked cell cycles in Drosophila development.

During Drosophila development the cell cycle is subject to diverse regulatory inputs. In embryos, cells divide in stereotypic patterns that correspond to the cell fate map. There is little cell growth during this period, and cell proliferation is regulated at G2/M transitions by patterned transcription of the Cdk1-activator, Cdc25/String. The string locus senses pattern information via a > 40 kb cis-regulatory region composed of many cell-type specific transcriptional enhancers. Later, in differentiated larval tissues, the cell cycle responds to nutrition via mechanisms that sense cellular growth. These larval cell cycles lack mitoses altogether, and are regulated at G/S transitions. Cells in developing imaginal discs exhibit a cycle that is regulated at both G1/S and G2/M transitions. G2/M progression in disc cells is regulated, as in the embryo, by string transcription and is thus influenced by the many transcription factors that interact with string's 'pattern-sensing' control region. G1/S progression in disc cells is controlled, at least in part, by factors that regulate cell growth such as Myc, Ras and phosphatidylinositol-3-kinase. Thus G1/S progression appears to be growth-coupled, much as in the larval endocycles. The dual control mechanism used by imaginal disc cells allows integration of diverse inputs which operate in both cell specification and cell metabolism.

The trouble with tribbles.

Cell division and cell movements must be coordinated during development. A novel inhibitor of cell division, Tribbles, has been identified that blocks mitosis at a critical point in Drosophila morphogenesis. The data support a role for Tribbles in promoting proteolytic degradation of String/Cdc25, a key regulator of mitosis.

Metallostars: high-nuclearity linearly developed nanostructures containing multiple cluster motifs.

Metallostars are complexes in which a single branching site bears a number of metallated arms. Although they are related to metallodendrimers, they have the advantage of being capable of extending in an unlimited sense; in contrast to metallodendrimers, steric interactions decrease with increasing generation number. In this paper a series of polyalkyne stars with four and six arms, based upon a single tetrahedral carbon core and a benzene core, respectively, are reported and their reactions with [Co2(CO)8] to give metallostars that contain multiple [C2Co2(CO)6] motifs are described.

Drosophila myc regulates cellular growth during development.

Transcription factors of the Myc proto-oncogene family promote cell division, but how they do this is poorly understood. Here we address the functions of Drosophila Myc (dMyc) during development. Using mosaic analysis in the fly wing, we show that loss of dMyc retards cellular growth (accumulation of cell mass) and reduces cell size, whereas dMyc overproduction increases growth rates and cell size. dMyc-induced growth promotes G1/S progression but fails to accelerate cell division because G2/M progression is independently controlled by Cdc25/String. We also show that the secreted signal Wingless patterns growth in the wing primordium by modulating dMyc expression. Our results indicate that dMyc links patterning signals to cell division by regulating primary targets involved in cellular growth and metabolism.

Cis-regulatory elements of the mitotic regulator, string/Cdc25.

Mitosis in most Drosophila cells is triggered by brief bursts of transcription of string (stg), a Cdc25-type phosphatase that activates the mitotic kinase, Cdk1 (Cdc2). To understand how string transcription is regulated, we analyzed the expression of string-lacZ reporter genes covering approximately 40 kb of the string locus. We also tested protein coding fragments of the string locus of 6 kb to 31.6 kb for their ability to complement loss of string function in embryos and imaginal discs. A plethora of cis-acting elements spread over >30 kb control string transcription in different cells and tissue types. Regulatory elements specific to subsets of epidermal cells, mesoderm, trachea and nurse cells were identified, but the majority of the string locus appears to be devoted to controlling cell proliferation during neurogenesis. Consistent with this, compact promotor-proximal sequences are sufficient for string function during imaginal disc growth, but additional distal elements are required for the development of neural structures in the eye, wing, leg and notum. We suggest that, during evolution, cell-type-specific control elements were acquired by a simple growth-regulated promoter as a means of coordinating cell division with developmental processes, particularly neurogenesis.

Coordination of growth and cell division in the Drosophila wing.

In most tissues, cell division is coordinated with increases in mass (i.e., growth). To understand this coordination, we altered rates of division in cell clones or compartments of the Drosophila wing and measured the effects on growth. Constitutive overproduction of the transcriptional regulator dE2F increased expression of the S- and M-phase initiators Cyclin E and String (Cdc25), thereby accelerating cell proliferation. Loss of dE2F or overproduction of its corepressor, RBF, retarded cell proliferation. These manipulations altered cell numbers over a 4- to 5-fold range but had little effect on clone or compartment sizes. Instead, changes in cell division rates were offset by changes in cell size. We infer that dE2F and RBF function specifically in cell cycle control, and that cell cycle acceleration is insufficient to stimulate growth. Variations in dE2F activity could be used to coordinate cell division with growth.

Wingless and Notch regulate cell-cycle arrest in the developing Drosophila wing.

In developing organs, the regulation of cell proliferation and patterning of cell fates is coordinated. How this coordination is achieved, however, is unknown. In the developing Drosophila wing, both cell proliferation and patterning require the secreted morphogen Wingless (Wg) at the dorsoventral compartment boundary. Late in wing development, Wg also induces a zone of non-proliferating cells at the dorsoventral boundary. This zone gives rise to sensory bristles of the adult wing margin. Here we investigate how Wg coordinates the cell cycle with patterning by studying the regulation of this growth arrest. We show that Wg, in conjunction with Notch, induces arrest in both the G1 and G2 phases of the cell cycle in separate subdomains of the zone of non-proliferating cells. Wg induces G2 arrest in two subdomains by inducing the proneural genes achaete and scute, which downregulate the mitosis-inducing phosphatase String (Cdc25). Notch activity creates a third domain by preventing arrest at G2 in wg-expressing cells, resulting in their arrest in G1.

Uncoupling growth from the cell cycle.

How does a Drosophila wing grow to the appropriate size and shape? Although a collaboration of cell division with the patterning of cell fates seems obvious, almost nothing is known about how these two processes are coordinated during development. A recent paper finds that blocking cell division uncouples cell growth from the cell division cycle, displaying remarkable flexibility in the ability of the wing primordia to achieve the right proportions with fewer than normal cells.

The homeobox gene cut interacts genetically with the homeotic genes proboscipedia and Antennapedia.

The cut locus (ct) codes for a homeodomain protein (Cut) and controls the identity of a subset of cells in the peripheral nervous system in Drosophila. During a screen to identify ct-interacting genes, we observed that flies containing a hypomorphic ct mutation and a heterozygous deletion of the Antennapedia complex exhibit a transformation of mouthparts into leg and antennal structures similar to that seen in homozygous proboscipedia (pb) mutants. The same phenotype is produced with all heterozygous pb alleles tested and is fully penetrant in two different ct mutant backgrounds. We show that this phenotype is accompanied by pronounced changes in the expression patterns of both ct and pb in labial discs. Furthermore, a significant proportion of ct mutant flies that are heterozygous for certain Antennapedia (Antp) alleles have thoracic defects that mimic loss-of-function Antp phenotypes, and ectopic expression of Cut in antennal discs results in ectopic Antp expression and a dominant Antp-like phenotype. Our results implicate ct in the regulation of expression and/or function of two homeotic genes and document a new role of ct in the control of segmental identity.

Phenoloxidase activity in the reproductive system of Biomphalaria glabrata: role in egg production and effect of schistosome infection.

Infection by larval trematodes often causes a cessation of egg production in its molluscan intermediate host and is referred to as parasitic castration. Because phenoloxidase (PO) has been shown to be involved in egg formation in other invertebrate species, we investigated the role of PO in normal egg production in the snail, Biomphalaria glabrata, and the effects of Schistosoma mansoni infection on the PO pathway in this snail. Our data showed that PO activity in the albumen gland (AG) is initially expressed when snails reach a size of approximately 8 mm in shell diameter and continues to increase as snails grow, indicating a developmental link between snail size and AG PO expression. Egglaying was also shown to be coincidental with the onset of PO expression in the AG, thereby supporting a direct association between PO activity and egg production. In addition, exposure of snails to diethyldithiocarbamate (DDC), a PO inhibitor, affected normal in vivo egg production, as evidenced by a significant decrease in the numbers of eggs laid in DDC-treated groups compared to nontreated groups. Normal resumption of egg-laying activity in treated snails following withdrawal of the drug indicated that inhibition was reversible. Taken together, the results of our developmental and DDC-exposure studies provide strong support for a crucial role of PO in normal egg production in this animal. Finally, AG PO activities of infected and uninfected control snails were measured over the course of S. mansoni infection. Our results showed that both total and specific enzyme activities in the AG of infected snails were significantly decreased at 28 and 33 days postinfection (PI) when compared to those of control snails. Results of subsequent experiments assessing the effects of larval infection on L-tyrosine (PO substrate) levels in AG and ovotestis revealed a significant increase in the levels of this compound in both organs over the course of infection. It is concluded that AG PO activity is functionally linked to egg formation in normal snails and that a strong association exists between parasite-mediated decrease in AG PO activity and parasitic castration. However, from the data presented, a direct causal relationship linking infection, decreased PO, and castration has yet to be established.

Ectopic expression of wingless in imaginal discs interferes with decapentaplegic expression and alters cell determination.

We have expressed the segment polarity gene wingless (wg) ectopically in imaginal discs to examine its regulation of both ventral patterning and transdetermination. By experimentally manipulating the amount of Wg protein, we show that different thresholds of Wg activity elicit different outcomes, which are mediated by regulation of decapentaplegic (dpp) expression and result in alterations in the expression of homeotic genes. A high level of Wg activity leads to loss of all dorsal pattern elements and the formation of a complete complement of ventral pattern elements on the dorsal side of legs, and is correlated with repression of dpp expression. wg expression in dorsal cells of each disc also leads to dose-dependent transdetermination in those cells in homologous discs such as the labial, antennal and leg, but not in cells of dorsally located discs. When dpp expression is repressed by high levels of Wg, transdetermination does not occur, confirming that dpp participates with wg to induce transdetermination. These and other experiments suggest that dorsal expression of wg alters disc patterning and disc cell determination by modulating the expression of dpp. The dose-dependent effects of wg on dpp expression, ventralization of dorsal cells and transdetermination support a model in which wg functions as a morphogen in imaginal discs.

Analysis of lectin- and snail plasma-binding glycopeptides associated with the tegumental surface of the primary sporocysts of Schistosoma mansoni.

Carbohydrates associated with the tegumental surface of Schistosoma mansoni primary sporocyst may serve as potential receptors for mediating recognition by the internal defence system of the molluscan host, Biomphalaria glabrata. Therefore, a combination of SDS-PAGE and lectin probe analyses were carried out on biotin-labelled tegumental glycopeptides as a first step to defining the carbohydrates expressed at the sporocyst surface. The majority of surface polypeptides, ranging in relative molecular masses from 27 to 113 kDa, reacted with horseradish peroxidase-labelled Canavalia ensiformis (Con A), Erythrina corallodendron (ECA), Glycine max (SBA) and Triticum vulgaris (WGA) lectins indicating that most, if not all, tegumental proteins are glycosylated. However, differences in the binding of some lectins to individual glycopeptides suggest a degree of heterogeneity in the structure/composition of sugar moieties comprising these surface glycoconjugates. This notion is supported by the finding that the fucose-specific Tetragonolobus purpureas (TPA) lectin only reacted with approximately 50% of glycopeptides identified at the tegumental surface. Experiments employing biotin-labelled plasma (cell-free haemolymph) from S. mansoni-susceptible and -resistant B. glabrata snails as probes, further demonstrated that many of the identified surface glycoproteins also serve as plasma-binding sites for both snail strains. Binding interactions between plasma and sporocyst surface glycoproteins appeared to be, at least in part, mediated by carbohydrates since periodate treatment of sporocyst proteins or pre-incubation of plasma with the glycoproteins, fetuin or mucin, resulted in a decrease in plasma reactivity to blotted larval proteins.

Timing of ovulation after gonadotrophin induction and its importance to successful intrauterine insemination in the tiger (Panthera tigris).

The ovarian response to equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG), the effect of timing of ovulation relative to hCG injection and the use of laparoscopic intrauterine artificial insemination (AI) were examined in two subspecies of tiger (Panthera tigris). Adult female tigers were subjected to the same eCG/hCG treatment followed by laparoscopy under xylazine/diazapam/ketamine HCl anaesthesia at 39-42 h (Group I, n = 9), 46-49 h (Group II, n = 5) or 51-55 h (Group III, n = 5) after hCG. Six of these females, observed to be postovulatory at the time of laparoscopy (Group II, n = 3; Group III, n = 3), were subjected to intrauterine AI. The number of preovulatory follicles observed on the ovaries of Group I females was twofold greater (P < 0.05) than the number observed on ovaries of females in Group II and III. Fewer (P < 0.05) corpora lutea were observed on ovaries of Group I females (1.3 +/- 0.6) compared with the number of corpora lutea in Group II and III (combined average, 7.8 +/- 0.8 corpora lutea per female). Only one of ten females in Groups II and III failed to ovulate by the time of laparoscopy. Four Group I females never ovulated, based on a laparoscopic re-evaluation 4 weeks later. One female inseminated 46 h after hCG (Group II) became pregnant and delivered a healthy cub after a normal gestation. There were no apparent differences between subspecies in response to the same ovulation induction protocol. Results demonstrate the importance of the relationship between exogenous gonadotrophin treatment and onset of anaesthesia for laparoscopic examination and AI in tigers. Data clearly indicate that anaesthesia/laparoscopy conducted too early (39-42 h after hCG) compromises the number of females and proportion of follicles ovulating. In contrast, ovulation success is high if anaesthesia/laparoscopy is performed after this time, and intrauterine insemination can result in healthy young.

Genome resource banking for species conservation: selection of sperm donors.

The systematic banking of genome resources using cryopreserved germ plasm offers the opportunity to further conservation strategies of endangered species by assisting in the effective genetic management of captive populations. Cryopreserved germ plasm will allow indefinite preservation of the presently available gene diversity represented in either captive or wild populations. If properly utilized, genome resource banks have the potential to decelerate the loss of gene and allelic diversity in captive populations through reintroducing "original" genetic material through time to counter genetic drift. However, in order for any genome resource bank to be effective, strategies need to be developed to identify genetically valuable individuals to bank which will represent optimal gene diversity of the specific population. Four selection strategies were evaluated to identify individual donors from four North American captive populations representing differently structured pedigrees. The strategies consisted of selecting: (1) all males in the population ("All Male Bank"); (2) only living founders and early generation descendents ("Founder Method Bank," FMB); (3) males remaining after culling to minimize mean kinship ("Culled Male Bank 1"); and (4) males remaining after culling to minimize mean kinship, with the males reduced to the number in the FMB ("Culled Male Bank 2"). The effectiveness of each strategy was based on the comparison of genetic variation metrics in each bank with the genetic variation in the present living managed population. Although maximal retention of allelic diversity was achieved by banking genes from all living animals, nearly optimal retention of allelic and gene diversity was obtained by utilizing the selection strategy based on minimizing mean kinships. As a consequence, properly designed and utilized, genome resource banks can become effective tools for preserving gene diversity in future generations of living populations.

Seasonal effects on seminal and endocrine traits in the captive snow leopard (Panthera uncia).

The annual reproductive cycle of the male snow leopard (Panthera uncia) was characterized by evaluating seminal and endocrine traits monthly. Testicular volume was greatest (P < 0.05) during the winter months when the quality of ejaculate was optimal. Ejaculate volume, total sperm concentration ml-1, motile sperm concentration per ejaculate, sperm morphology and sperm motility index were lowest during the summer and autumn months compared with the winter and spring. Peripheral LH, FSH and testosterone concentrations were also lowest during the summer months, increasing during the autumn just before the increase in semen quality, and were maximal during the winter months. There was a direct relationship (P < 0.01) between: (1) testosterone and testicular volume, total sperm concentration ml-1, motile sperm concentration per ejaculate and ejaculate volume, and (2) LH and testicular volume and motile sperm concentration per ejaculate. In summary, although spermatozoa were recovered throughout the year, optimal gamete quality was observed during the winter and spring. Although previous studies in felids have demonstrated seasonal effects on either seminal or endocrine traits, this is the first study to demonstrate a distinct effect of season on both pituitary and testicular function.

Oocyte recovery and maturation in the American black bear (Ursus americanus): a model for endangered ursids.

A study was conducted to determine if meiotic maturation could be induced in ovarian oocytes of the American black bear (Ursus americanus), a model for gamete "rescue" techniques for endangered ursids. Ovaries obtained from 48 black bears yielded 2,403 oocytes (51.1 +/- 4.9/female), of which 777 (32.3%) were morphologically classified as excellent quality. More total oocytes were recovered from donors that were anestrous compared to luteal/pregnant (P < 0.05) at the time of ovarian excision. Delaying the recovery of oocytes from antral follicles within excised ovaries from 12-24 hr to 25-36 hr had no effect (P > 0.05) on the overall number of high quality oocytes recovered or subsequent maturational ability. The highest incidence of metaphase II was reached between 48 and 60 hr of in vitro incubation. Donor status (anestrous vs. luteal/pregnant) had no influence on the oocyte maturation rate by 24 or 48 hr, but by 60 hr, more (P < 0.05) oocytes recovered from anestrous females (43.9%) had achieved metaphase II compared to luteal/pregnant counterparts (23.1%). In preliminary trials involving endangered ursids, 54 ovarian oocytes were recovered from three aged sun bears (Helarctos malayanus), of which 72.2% were excellent quality and 15.4% matured in vitro to metaphase II. Similarly, 119 antral oocytes were recovered from two aged sloth bears (Melursus ursinus), of which 41.2% were excellent and 17.5% matured in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)