Relation of spatial and temporal frequencies to vernier acuity

Vernier thresholds were measured with a pair of vertical sinusoidal gratings of one and a half cycles as targets. The amplitude was weighted by a one-dimensional Gaussian and contrast was set one log unit above contrast threshold. The vernier thresholds were estimated with the method of constant stimuli. Temporal frequency effects were introduced by movement of the vernier targets. It was found that vernier thresholds expressed in phase angle were unchanged in the effective range of spatial frequencies provided that the temporal frequency and the visibility were unchanged, and that thresholds deteriorated by increasing the temporal frequency. It is suggested that the detection of relative phase may be involved in the discrimination of vernier offsets and that it may be mediated by a sustained unit. Three possible types of mechanisms, edge-localization processes, orientation-selective units and phase-sensitive units, were considered in relation to vernier acuity.     

A comparison of vernier acuity for narrowband and broadband stimuli

This study investigates the influence of contrast and exposure duration on vernier acuity thresholds for abutting and separated narrowband stimuli, and asks whether these data can predict broadband vernier performance. Vernier thresholds were determined for sinusoidal grating stimuli at two spatial frequencies (1 and 8 c/deg) across a range of contrasts (0.05-0.8) and exposure durations (35-2100 ms). Performance was assessed for the abutting configuration, and when a gap equivalent to 0.5 to 1.5 times the spatial period of the grating was introduced between the upper and lower halves of the grating. Vernier thresholds were also determined for a square-wave stimulus as a function of contrast (0.06 to 0.78). Exposure duration was fixed at 2100 ms. In addition, thresholds were determined at the appropriate contrast levels for the fundamental frequency (1.8 c/deg) of the square-wave, and for a number of the harmonics (3F, 5F, 7F, 9F). Our results provide support for filter models of vernier acuity by showing that vernier performance for abutting and closely-separated broadband stimuli represents the envelope of vernier sensitivity of those spatial frequency mechanisms that are activated by the broadband stimulus. In the case of high frequency grating stimuli presented for long exposure durations, vernier performance can be invariant across much of the contrast range. Despite this, however, contrast independence is not exhibited for abutting broadband stimuli because, within the broadband stimuli, the contrast of the higher harmonic components never reaches a level to reveal this plateau.     

Short-term and long-term leptin exposure differentially affect human natural killer cell immune functions

Epidemiological studies have indicated that obesity is associated with a higher risk for certain cancers caused by elevated levels of adipocyte-derived hormones. Leptin, one such hormone produced by adipocytes, is a major regulator of metabolism and has also been shown to modulate immunity. However, its role in regulating human natural killer (NK) cell functions is largely unknown. Here, we show that the leptin receptor (Ob-R) is expressed on 5% of NK cells isolated from blood donors, as measured with flow cytometry, and expression of the signal-transducing long form of the leptin receptor Ob-Rb was confirmed with quantitative PCR. The Ob-R+ subpopulation displayed a lower expression of CD16, a cell surface receptor mediating antibody-dependent activation. Short-term stimulation with leptin increased IFNγ secretion, CD69 activation marker expression, and cytotoxic lysis of tumor cells; this was mediated by an improved conjugate forming between NK cells and tumor cells as well as higher expression of tumor necrosis factor-related apoptosis-inducing ligand. On the contrary, long-term incubation with leptin significantly impaired these NK cell immune functions and decreased cell proliferation. In addition, phosphorylation of Jak-2 after leptin stimulation was reduced in peripheral mononuclear blood cells from obese humans compared with normal-weight controls. NK cells represent an immune cell population that is crucial for an effective antitumor response. Here, we show that long-term exposure to leptin, similarly to the situation in obese individuals with elevated serum leptin levels, significantly impairs integral parts of NK cell immune functions, possibly linking leptin to increased cancer susceptibility in obesity.     

Gonadotropin exposure,salt storage and storage duration affect penetration of domestic cat oocytes by homologous spermatozoa

Salt-stored domestic cat oocytes are routinely used to study sperm function in domestic and nondomestic felids. Our objectives were to assess the effects of in vitro maturation (IVM), salt storage and storage duration on penetration of domestic cat oocytes by homologous spermatozoa. In Experiment 1, domestic cat spermatozoa were coincubated with fresh immature oocytes, salt-stored (2-3 weeks) immature oocytes, or salt-stored (2-3 weeks) IVM oocytes matured in Minimum Essential Medium containing 0.1IU FSH and 0.1IU LH/ml (IVM1) or 0.5IU FSH and 2.2IULH/ml (IVM2). In Experiment 2, all oocytes were matured (IVM2) and inseminated fresh or after salt storage for 2-3 weeks, 2-3 months or 9 months. In Experiment 1, penetration of the outer zona pellucida (OZP) was greater (P<0.05) in salt-stored IVM2 oocytes than in salt-stored immature oocytes, whereas penetration of salt-stored IVM1 oocytes was intermediate (P>0.05). In Experiment 2, penetration of the OZP and inner zona pellucida (IZP) was higher (P<0.05) in fresh IVM2 oocytes than in salt-stored oocytes, and a higher (P<0.05) proportion of oocytes had IZP sperm after 2-3 weeks of storage than after 2-3 months. Penetration of the perivitelline space was higher (P<0.05) in fresh IVM2 oocytes than in oocytes stored for 2-3 weeks or 2-3 months. These results suggest that oocyte penetration is improved by IVM, but is impaired by exposure to salt-storage solution and prolonged storage duration.     

EXO1 and MSH4 differentially affect crossing-over and segregation

The 5′-3′ exonuclease Exo1p from Saccharomyces cerevisiae is required for wild-type levels of meiotic crossing-over and normal meiotic chromosome segregation as is the meiosis-specific MutS homologue, Msh4p. Mutations in both genes reduce crossing-over by approximately two-fold, but Δmsh4 strains have significantly lower viability and a higher frequency of meiosis I non-disjunction. Epistasis analysis indicates a complex interaction between the two genes. Although crossing-over was not detectably lower in the double mutant, viability was significantly worse than either single mutant. Such a result suggests that the two genes are affecting meiotic viability by distinct mechanisms. We propose that Δexo1 affects chromosome segregation by reducing crossing-over, while Δmsh4 affects both the frequency and distribution of crossovers. Mutation in EXO1 reduces gene conversion frequencies significantly at some but not all loci, suggesting that other enzymes are also involved in DNA resection. We propose that Exo1p plays an early role in establishing some recombination intermediates by generating single-stranded tails. The role of Msh4p is suggested to be in determining whether some recombination intermediates are resolved as crossover events and in generating crossover interference. The synergistic effect of Δexo1Δmsh4 on spore viability suggests that the two genes have partially compensatory roles in a process affecting meiotic success. Received: 10 November 1999; in revised form: 14 January 2000 / Accepted: 14 January 2000     

Pressure overload and neurohumoral activation differentially affect the myocardial proteome

Treatment with monocrotaline causes pulmonary hypertension in rats. This results in severe pressure overload-induced hypertrophy of the right ventricles, whilst the normally loaded left ventricles do not hypertrophy. Both ventricles are affected by enhanced neuroendocrine stimulation in this model. We analyzed in this model load-induced and catecholamine-induced changes of right and left ventricular proteome by two-dimensional gel electrophoresis, tryptic in-gel digest, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. All analyzed animals showed right ventricular hypertrophy without signs of heart failure. Changes of 27 proteins in the right and 21 proteins in the left ventricular myocardium were found. Given the hemodynamic features of this animal model, proteome changes restricted to the right ventricle are caused by pressure overload. We describe for the first time a potentially novel pathway (BRAP2/BRCA1) that is involved in myocardial hypertrophy. Furthermore, we demonstrate that increased afterload-induced hypertrophy leads to striking changes in the energy metabolism with down-regulation of pyruvate dehydrogenase (subunit beta E1), isocitrate dehydrogenase, succinyl coenzyme A ligase, NADH dehydrogenase, ubiquinol-cytochrome C reductase, and propionyl coenzyme A carboxylase. These changes go in parallel with alterations of the thin filament proteome (troponin T, tropomyosin), probably associated with Ca(2+) sensitization of the myofilaments. In contrast, neurohumoral stimulation of the left ventricle increases the abundance of proteins relevant for energy metabolism. This study represents the first in-depth analysis of global proteome alterations in a controlled animal model of pressure overload-induced myocardial hypertrophy.     

Small heat shock proteins differentially affect Abeta aggregation and toxicity

beta-Amyloid (Abeta) is the primary protein component of senile plaques in Alzheimer's disease (AD) and has been implicated in neurotoxicity associated with the disease. Abeta aggregates readily in vitro and in vivo, and its toxicity has been linked to its aggregation state. Prevention of Abeta aggregation has been investigated as a means to prevent Abeta toxicity associated with AD. Recently we found that Hsp20 from Babesia bovis prevented both Abeta aggregation and toxicity [S. Lee, K. Carson, A. Rice-Ficht, T. Good, Hsp20, a novel alpha-crystallin, prevents Abeta fibril formation and toxicity, Protein Sci. 14 (2005) 593-601.]. In this work, we examined the mechanism of Hsp20 interaction with Abeta1-40 and compared its activity to that of other small heat shock proteins, carrot Hsp17.7 and human Hsp27. While all three small heat shock proteins were able to prevent Abeta aggregation, only Hsp20 was able to attenuate Abeta toxicity in cultured SH-SY5Y cells. Understanding the mechanism of the Hsp20-Abeta interaction may provide insights into the design of the next generation of Abeta aggregation and toxicity inhibitors.     

Oligomeric and fibrillar species of amyloid-beta peptides differentially affect neuronal viability

Genetic evidence predicts a causative role for amyloid-beta (A beta) in Alzheimer's disease. Recent debate has focused on whether fibrils (amyloid) or soluble oligomers of A beta are the active species that contribute to neurodegeneration and dementia. We developed two aggregation protocols for the consistent production of stable oligomeric or fibrillar preparations of A beta-(1-42). Here we report that oligomers inhibit neuronal viability 10-fold more than fibrils and approximately 40-fold more than unaggregated peptide, with oligomeric A beta-(1-42)-induced inhibition significant at 10 nm. Under A beta-(1-42) oligomer- and fibril-forming conditions, A beta-(1-40) remains predominantly as unassembled monomer and had significantly less effect on neuronal viability than preparations of A beta-(1-42). We applied the aggregation protocols developed for wild type A beta-(1-42) to A beta-(1-42) with the Dutch (E22Q) or Arctic (E22G) mutations. Oligomeric preparations of the mutations exhibited extensive protofibril and fibril formation, respectively, but were not consistently different from wild type A beta-(1-42) in terms of inhibition of neuronal viability. However, fibrillar preparations of the mutants appeared larger and induced significantly more inhibition of neuronal viability than wild type A beta-(1-42) fibril preparations. These data demonstrate that protocols developed to produce oligomeric and fibrillar A beta-(1-42) are useful in distinguishing the structural and functional differences between A beta-(1-42) and A beta-(1-40) and genetic mutations of A beta-(1-42).     

Numblike and Numb differentially affect p53 and Sonic Hedgehog signaling

Numb serves as a key regulator of Notch and Sonic Hedgehog signaling and also modulates p53 protein levels. Numblike is a highly conserved homolog to mammalian Numb, but considerably less is known about its function. To address the role of Numblike, we have generated a mouse embryonic stem (ES) cell line, Nbl^TetOn, in which expression of Numblike can be induced and analyzed the effect of activation of Numblike. Induction of Numblike, similar to Numb, reduced the amount of Notch receptor, whereas Numblike differed from Numb with regard to p53 and Shh signaling. In contrast to Numb, Numblike did not elevate the level of p53 protein and Numblike potentiated, rather than reduced, the immediate downstream response of Shh signaling. In keeping with a role for Numblike in potentiating Shh signaling, Shh and Numblike synergistically increased the proportion of ES cells expressing pluripotency markers. In conclusion, the data demonstrate that Numb and Numblike have evolved to acquire at least partially distinct functions.     

Hyperosmotic and isosmotic shrinkage differentially affect protein phosphorylation and ion transport

In the present work, we compared the outcome of hyperosmotic and isosmotic shrinkage on ion transport and protein phosphorylation in C11-MDCK cells resembling intercalated cells from collecting ducts and in vascular smooth muscle cells (VSMC) from the rat aorta. Hyperosmotic shrinkage was triggered by cell exposure to hypertonic medium, whereas isosmotic shrinkage was evoked by cell transfer from an hypoosmotic to an isosmotic environment. Despite a similar cell volume decrease of 40%-50%, the consequences of hyperosmotic and isosmotic shrinkage on cellular functions were sharply different. In C11-MDCK and VSMC, hyperosmotic shrinkage completely inhibited Na(+),K(+)-ATPase and Na(+),P(i) cotransport. In contrast, in both types of cells isosmotic shrinkage slightly increased rather than suppressed Na(+),K(+)-ATPase and did not change Na(+),P(i) cotransport. In C11-MDCK cells, phosphorylation of JNK1/2 and Erk1/2 mitogen-activated protein kinases was augmented in hyperosmotically shrunken cells by ～7- and 2-fold, respectively, but was not affected in cells subjected to isosmotic shrinkage. These results demonstrate that the data obtained in cells subjected to hyperosmotic shrinkage cannot be considered as sufficient proof implicating cell volume perturbations in the regulation of cellular functions under isosmotic conditions.     

Homologous and non-homologous recombination differentially affect DNA damage repair in mice

Ionizing radiation and interstrand DNA crosslinking compounds provide important treatments against cancer due to their extreme genotoxicity for proliferating cells. Both the efficacies of such treatments and the mutagenic potential of these agents are modulated by the ability of cells to repair the inflicted DNA damage. Here we demonstrate that homologous recombination-deficient mRAD54(-/-) mice are hypersensitive to ionizing radiation at the embryonic but, unexpectedly, not at the adult stage. However, at the adult stage mRAD54 deficiency dramatically aggravates the ionizing radiation sensitivity of severe combined immune deficiency (scid) mice that are impaired in DNA double-strand break repair through DNA end-joining. In contrast, regardless of developmental stage, mRAD54(-/-) mice are hypersensitive to the interstrand DNA crosslinking compound mitomycin C. These results demonstrate that the two major DNA double-strand break repair pathways in mammals have overlapping as well as specialized roles, and that the relative contribution of these pathways towards repair of ionizing radiation-induced DNA damage changes during development of the animal.     

Electric footshocks differentially affect plasma and spinal cord vasopressin and oxytocin levels

Rats exposed for three minutes to repeated electric footshocks showed an approximate 10-fold increase of basal plasma vasopressin (AVP) and oxytocin (OXT) levels. In contrast, spinal AVP and OXT contents measured in the same rats remained unchanged when compared to undisturbed controls. This observation suggests that spinal AVP and OXT do not play a major role in the short-term adaptation of the organism to stress.     

Age and sex differentially affect regional changes in one repetition maximum strength

To assess the influences of age and sex on regional changes in 1 repetition maximum (1RM) strength, 10 young men (20-30 years), 8 young women (20-30 years), 11 older men (65- 75 years), and 10 older women (65-75 years) were studied before and after a 24-week whole-body strength training program. Changes in 1RM strength were analyzed for each individual exercise, as well as by calculating a total body score (TBS), an upper body score (UBS), and a lower body score (LBS). The effect of age and sex on changes in 1RM strength was analyzed using a repeated measures analysis of variance. When changes in strength for individual exercises were analyzed, the chest press, lat pulldown, shoulder press, and triceps pushdown were affected by both age (p < 0.05) and sex (p < 0.05), while the biceps curls were only influenced by age (p < 0.05). For the lower body, the leg press changes in 1RM strength were influenced by age (p < 0.0001), while leg extension was influenced by sex (p < 0.05). Total body score, UBS, and LBS showed significant increases with 24 weeks of ST (p < 0.001, all). Changes in TBS and UBS were affected by age (p < 0.001, both) and sex (p < 0.05 and p < 0.001, respectively). Younger subjects showed a greater increase in strength than older subjects, and men showed a greater increase in strength compared with women. Changes in LBS were affected by age (p < 0.001), with younger subjects showing a greater increase in strength compared with the older subjects, but not by sex (p = 0.464). These data indicate that regional increases in strength are differentially affected by age and sex.     

Thyroid hormones differentially affect sarcoplasmic reticulum function in rat atria and ventricles

The present study was undertaken to compare the effects of hypothyroidism and hyperthyroidism on sarcoplasmic reticulum (SR) Ca²⁺-pump activity, together with assessment of the functional role of SR in providing activator Ca²⁺ under these altered thyroid states. In response to a shift from hypothyroid to hyperthyroid state, a 10 fold and 2 fold increase in SR Ca²⁺-pump activity in atria and ventricles, respectively, were observed. This was associated with the 8-9 fold increases in atrial contractility (+dT/dt) and relaxation (-dT/dt), but only with a 3-4 fold increase in their ventricular counterparts. Also, the recirculation fraction of activator Ca²⁺ (RFA) increased to a far greater extent in atria (4 fold) than in papillary muscles, and the relative increment in inhibition of developed tension by ryanodine became 3 times larger in atria than in papillary muscles. A positive force-frequency relationship (FFR) was observed in hypothyroid atria, whereas the hyperthyroid atria, hypothyroid and hyperthyroid papillary muscles showed a negative FFR. These results suggest the greater role of transsarcolemmal (SL) Ca²⁺ and smaller role of SR Ca²⁺ in activating contraction in hypothyroid atria compared to other preparations. Thyroid hormones decrease the contribution of SL and increase that of SR in providing activator Ca²⁺ to the greater extent in atria than in ventricles. This effect of thyroid hormones is based on larger stimulation of SR Ca²⁺-pump in atria compared to ventricles.     

Cocaine and methamphetamine differentially affect opioid peptide mRNA expression in the striatum

In general, administration of methamphetamine and cocaine alters preprodynorphin and preproenkephalin mRNA levels in striatum. However, no study has directly compared the effects of these stimulants on opioid peptides in striatum. This study used in situ hybridization to compare directly the effects of cocaine and methamphetamine on preprodynorphin and preproenkephalin mRNAs in distinct striatal regions. Male Sprague-Dawley rats received a single administration of 15 mg/kg methamphetamine or 30 mg/kg cocaine and were killed 30 min or 3 h later. Methamphetamine and cocaine differentially affected preprodynorphin mRNA in striatum after 3 h. Densitometric analysis of film autoradiograms revealed that cocaine, but not methamphetamine, significantly increased preprodynorphin. This effect was seen throughout rostral striatum and dorsally in caudal striatum. However, specific analysis of "patches" in which preprodynorphin expression is high revealed a significantly greater effect of methamphetamine versus cocaine. In contrast, both cocaine and methamphetamine had similar effects on preproenkephalin mRNA, decreasing levels after 30 min in rostral striatum and in the core of nucleus accumbens. These data suggest that methamphetamine and cocaine have distinct postsynaptic consequences on striatal neurons.     

Monensin and brefeldin A differentially affect the phosphorylation and sulfation of secretory proteins.

Chromogranin B and secretogranin II, two members of the granin family, are known to be post-translationally modified by the addition of O-linked carbohydrates to serine and/or threonine, phosphate to serine and threonine, and sulfate to carbohydrate and tyrosine residues. In the present study, chromogranin B and secretogranin II were used as model proteins to investigate in which subcompartment of the Golgi complex secretory proteins become phosphorylated. Monensin, a drug known to block the transport from the medial to the trans cisternae of the Golgi stack, inhibited the phosphorylation of the granins, indicating that this modification occurred distal to the medial Golgi. Monensin also blocked the addition of galactose to O-linked carbohydrates and the sulfation of the granins, confirming previous data that these modifications take place in the trans Golgi. To distinguish, within the trans Golgi, between the trans cisternae of the Golgi stack and the trans Golgi network, we made use of the previous observation that brefeldin A results in the redistribution to the endoplasmic reticulum of membrane-bound enzymes of the trans cisternae of the Golgi stack, but not of the trans Golgi network. Brefeldin A treatment abolished granin sulfation but resulted in the accumulation of phosphorylated and galactosylated granins. Differential effects of brefeldin A on membranes of the Golgi stack versus the trans Golgi network were also observed by immunofluorescence analysis of marker proteins specific for either compartment. Our results suggest that the phosphorylation of secretory proteins, like their galactosylation, largely occurs in the trans cisternae of the Golgi stack, whereas the sulfation of secretory proteins on both carbohydrate and tyrosine residues takes place selectively in the trans Golgi network.     

Culture conditions differentially affect the translation of individual Escherichia coli mRNAs.

Our aim is to investigate whether changes in growth conditions can differentially affect the initiation of translation from individual Escherichia coli mRNAs that are not subjected to specific translational control. As a model system, we have constructed a series of point-mutated lacZ genes which differ in their Shine-Dalgarno (SD) sequence, their initiator codon, or the secondary structure around these elements. Alterations in growth conditions produced large (up to 8-fold) changes in the relative expression from these genes, which, we argue, stem from changes in their relative efficiencies of translation initiation. In particular, compared to genes bearing mutations outside the SD or initiator codon, genes mutated in these elements experience a significant decrease in their expression when cells are grown in minimal rather than rich medium; at 42 degrees C rather than 37 degrees C; or under amino acid starvation. We discuss the mechanisms underlying these effects, and evocate their possible generality.     

Cryptic microsporidian parasites differentially affect invasive and native Artemia spp.

We investigated the host specificity of two cryptic microsporidian species (Anostracospora rigaudi and Enterocytospora artemiae) infecting invasive (Artemia franciscana) and native (Artemia parthenogenetica) hosts in sympatry. Anostracospora rigaudi was on average four times more prevalent in the native host, whereas E. artemiae was three times more prevalent in the invasive host. Infection with An. rigaudi strongly reduced female reproduction in both host species, whereas infection with E. artemiae had weaker effects on female reproduction. We contrasted microsporidian prevalence in native A. franciscana populations (New World) and in both invaded and non-invaded Artemia populations (Old World). At a community level, microsporidian prevalence was twice as high in native compared with invasive hosts, due to the contrasting host-specificity of An. rigaudi and E. artemiae. At a higher biogeographical level, microsporidian prevalence in A. franciscana did not differ between the invaded populations and the native populations used for the introduction. Although E. artemiae was the only species found both in New and Old World populations, no evidence of its co-introduction with the invasive host was found in our experimental and phylogeographic tests. These results suggest that the success of A. franciscana invasion is probably due to a lower susceptibility to virulent microsporidian parasites rather than to decreased microsporidian prevalence compared with A. parthenogenetica or to lower microsporidian virulence in introduced areas.