Persistence of Mhc heterozygosity in homozygous clonal killifish,Rivulus marmoratus: implications for the origin of hermaphroditism

The mangrove killifish Rivulus marmoratus, a neotropical fish in the order Cyprinodontiformes, is the only known obligatorily selfing, synchronous hermaphroditic vertebrate. To shed light on its population structure and the origin of hermaphroditism, major histocompatibility complex (Mhc) class I genes of the killifish from seven different localities in Florida, Belize, and the Bahamas were cloned and sequenced. Thirteen loci and their alleles were identified and classified into eight groups. The loci apparently arose approximately 20 million years ago (MYA) by gene duplications from a single common progenitor in the ancestors of R. marmoratus and its closest relatives. Distinct loci were found to be restricted to different populations and different individuals in the same population. Up to 44% of the fish were heterozygotes at Mhc loci, as compared to near homozygosity at non-Mhc loci. Large genetic distances between some of the Mhc alleles revealed the presence of ancestral allelic lineages. Computer simulation designed to explain these findings indicated that selfing is incomplete in R. marmoratus populations, that Mhc allelic lineages must have diverged before the onset of selfing, and that the hermaphroditism arose in a population containing multiple ancestral Mhc lineages. A model is proposed in which hermaphroditism arose stage-wise by mutations, each of which spread through the entire population and was fixed independently in the emerging clones.     

Enhancing the proteolytic maturation of human immunodeficiency virus type 1 envelope glycoproteins

In virus-infected cells, the envelope glycoprotein (Env) precursor, gp160, of human immunodeficiency virus type 1 is cleaved by cellular proteases into a fusion-competent gp120-gp41 heterodimer in which the two subunits are noncovalently associated. However, cleavage can be inefficient when recombinant Env is expressed at high levels, either as a full-length gp160 or as a soluble gp140 truncated immediately N-terminal to the transmembrane domain. We have explored several methods for obtaining fully cleaved Env for use as a vaccine antigen. We tested whether purified Env could be enzymatically digested with purified protease in vitro. Plasmin efficiently cleaved the Env precursor but also cut at a second site in gp120, most probably the V3 loop. In contrast, a soluble form of furin was specific for the gp120-gp41 cleavage site but cleaved inefficiently. Coexpression of Env with the full-length or soluble form of furin enhanced Env cleavage but also reduced Env expression. When the Env cleavage site (REKR) was mutated in order to see if its use by cellular proteases could be enhanced, several mutants were found to be processed more efficiently than the wild-type protein. The optimal cleavage site sequences were RRRRRR, RRRRKR, and RRRKKR. These mutations did not significantly alter the capacity of the Env protein to mediate fusion, so they have not radically perturbed Env structure. Furthermore, unlike that of wild-type Env, expression of the cleavage site mutants was not significantly reduced by furin coexpression. Coexpression of Env cleavage site mutants and furin is therefore a useful method for obtaining high-level expression of processed Env.     

Critical role of chromium (Cr)-DNA interactions in the formation of Cr-induced polymerase arresting lesions

The genotoxicity associated with the metabolic reduction of hexavalent chromium [Cr(VI)] is complex and can impede DNA polymerase-mediated replication in vitro. The exact biochemical nature of Cr-induced polymerase arresting lesions (PALs) is not understood, but is believed to involve the formation of Cr-DNA interstrand cross-links (ICLs). The aim of this investigation was to determine the dependence of direct Cr-DNA interactions on the development of PALs in DNA treated with trivalent Cr [Cr(III)] or with Cr(VI) in the presence of ascorbic acid (Asc), a major intracellular reductant, using an in vitro, acellular system. The formation of Cr-DNA adducts, ICLs, and PALs was maximal at Asc:Cr(VI) molar ratios of 0.5-2, but gradually decreased at higher ratios. EDTA, a Cr(III) chelator, significantly decreased Cr-DNA binding and ICL and PAL formation. Co-treatment of DNA with Cr(VI)/Asc and mannitol, a Cr(V) chelator, selectively inhibited the formation of mono/bifunctional DNA adducts and PALs produced by Cr(VI) reduction, but had no effect on Cr(III)-DNA binding or Cr(III)-induced polymerase arrest. Blocking Cr-DNA phosphate interaction by preincubation of DNA with MgCl(2) abrogated DNA binding and ICL and PAL production. DNA strand breaks and abasic sites may lead to the in vitro arrest of DNA polymerases; however, we failed to detect significant increases in the frequency of these lesions following Cr(VI)/Asc treatment. These data indicate that the bifunctional adduction of Cr to DNA phosphates (ICLs) constitutes a major PAL. Furthermore, the generation of DNA strand breaks and abasic sites by Cr(VI) reduction is insufficient to explain PALs observed in vitro.     

Isomerization and oxidation of vitamin a in cone-dominant retinas: a novel pathway for visual-pigment regeneration in daylight

The first step toward light perception is 11-cis to all-trans photoisomerization of the retinaldehyde chromophore in a rod or cone opsin-pigment molecule. Light sensitivity of the opsin pigment is restored through a multistep pathway called the visual cycle, which effects all-trans to 11-cis re-isomerization of the retinoid chromophore. The maximum throughput of the known visual cycle, however, is too slow to explain sustained photosensitivity in bright light. Here, we demonstrate three novel enzymatic activities in cone-dominant ground-squirrel and chicken retinas: an all-trans-retinol isomerase, an 11-cis-retinyl-ester synthase, and an 11-cis-retinol dehydrogenase. Together these activities comprise a novel pathway that regenerates opsin photopigments at a rate 20-fold faster than the known visual cycle. We suggest that this pathway is responsible for sustained daylight vision in vertebrates.     

Exploring human interaction and diet effects on the behavior of dogs in a public animal shelter

This study examined the effects of 2 manipulations-a brief, regular period of human contact and diet-on the behavior of dogs confined in a public animal shelter. A behavioral battery designed to assess reactions to novel situations, and a test of responsiveness to an unfamiliar human were administered both prior to (pretest) and immediately following (posttest) the 8-week intervention period. Overall, the regular periods of increased human contact together with a diet that contained augmented levels of digestible protein, fat, calories, and animal-derived ingredients reduced signs of behavioral reactivity from pretest to posttest. In some cases, the comparison diet appeared more effective, but only for dogs receiving minimal human interaction. The results indicate that a combination of human interaction and high quality diet may positively affect the behavior of dogs in animal shelters.     

Inhibition of arginine gingipains (RgpB and HRgpA) with benzamidine inhibitors: zinc increases inhibitory potency

We assayed several benzamidine derivatives for inhibition potency with HRgpA and RgpB gingipains, enzymes which are involved in the pathogenesis of gingivitis and periodontal disease. The benzamidine derivatives proved to be effective inhibitors of HRgpA and RgpB, with the best inhibitor being a bis-benzamidine with a urea linker (Ki=30 microM). The inhibition potency was increased 2-3 fold in the presence of low concentrations of zinc with the benzamidines containing a urea moiety linking the two aromatic rings. We propose an inhibition model involving a tetrahedral zinc atom coordinated with the active site Cys and His of gingipain and the urea linker in the benzamidine inhibitor. In summary, we have discovered a new series of effective inhibitors for the gingipains and found a novel way to increase inhibitor potency with the HRgpA and RgpB gingipains using zinc.     

A structure-activity study of spermicidal and anti-HIV properties of hydroxylated cationic surfactants

The syntheses of 2-hydroxy-N-(2-hydroxyethyl)-N,N-dimethylhexadecan-1-aminium chloride [1(16)Cl] and iodide [1(16)I], 2-hydroxy-N,N,N-trimethylhexadecan-1-aminium chloride (6), N-(2-hydroxyethyl)-N,N-dimethylhexadecan-1-aminium chloride (8), N,N-bis(2-hydroxyethyl)-N-methylhexadecan-1-aminium chloride (11), and 2-hydroxy-N-(2-hydroxyethyl)-N,N-dimethyl-4-oxahexadecan-1-aminium chloride (14) are reported along with the critical micelle concentrations (cmcs), as measured by conductivity at 25 degrees C, of 1(16)Cl, 1(16)I, 6, 8, 11, and N,N,N-trimethylhexadecan-1-aminium chloride (12). All compounds display spermicidal and virucidal activity. A plot of minimum effective concentration (MEC) in the Sander-Cramer spermicidal assay and cmc shows that 1(16)Cl and 6 have the best spermicidal activity and highest cmcs. Compounds 8, 11, and 1(16)Cl are the most active at 0.05 mg mL(-1) against cell-free and cell-associated virus. In conclusion, 1(16)Cl shows the best combination of dual activity against sperm and HIV; it is a promising candidate for further preclinical studies as a topical, contraceptive microbicide.     

The effect of heavy- vs. light-load jump squats on the development of strength, power, and speed

The purpose of this investigation was to examine the effect of an 8-week training program with heavy- vs. light-load jump squats on various physical performance measures and electromyography (EMG). Twenty-six athletic men with varying levels of resistance training experience performed sessions of jump squats with either 30% (JS30, n = 9) or 80% (JS80, n = 10) of their one repetition maximum in the squat (1RM) or served as a control (C, n = 7). An agility test, 20-m sprint, and jump squats with 30% (30J), 55% (55J), and 80% (80J) of their 1RM were performed before and after training. Peak force, peak velocity (PV), peak power (PP), jump height, and average EMG (concentric phase) were calculated for the jumps. There were significant increases in PP and PV in the 30J, 55J, and 80J for the JS30 group (p 相似文献   

An analysis of turbulent shear stresses in leakage flow through a bileaflet mechanical prostheses

In this work, estimates of turbulence were made from pulsatile flow laser Doppler velocimetry measurements using traditional phase averaging and averaging after the removal of cyclic variation. These estimates were compared with estimates obtained from steady leakage flow LDV measurements and an analytical method. The results of these studies indicate that leakage jets which are free and planar in shape may be more unstable than other leakage jets, and that cyclic variation does not cause a gross overestimation of the Reynolds stresses at large distances from the leakage jet orifice.     

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,4,7,8-pentachlorodibenzofuran reduces growth and disrupts reproductive parameters in female rats

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PCDF) are widespread environmental pollutants. TCDD is well known for its adverse effects on female reproduction when administered acutely to immature or adult rats. It is also known that fetal/neonatal exposure to this compound alters reproductive parameters. It is unknown whether exposure to PCDF causes similar adverse effects in offspring. The objectives of the study were to investigate the effects of in utero and lactational (IUL) exposure to TCDD and PCDF on subsequent growth, estrous cycles, and ovulation. Additionally a gonadotropin-primed immature rat model was used to investigate possible direct effects on the ovary after IUL exposure to TCDD (2.5 microg/kg) by evaluating 1) ovarian morphometrics and 2) serum estradiol concentrations. Body weights were reduced in animals with IUL exposure to TCDD and PCDF relative to those in controls at 10 days of age (P < 0.05 for each), and this difference was maintained until termination of the experiment at 125-165 days of age (P < 0.05). Exposure to TCDD or PCDF also disrupted regular estrous cycles and inhibited ovulation rate. On Day 23 (before eCG stimulation), ovaries from animals exposed to TCDD contained the same number of primordial, primary, secondary, preantral, and antral follicles as ovaries from control animals. On Day 25 (48 h after eCG stimulation), ovaries from TCDD-exposed rats had significantly fewer large preovulatory follicles when compared with ovaries from controls. The numbers of smaller follicles (both antral and small antral) were not different. Serum estradiol was significantly lower in TCDD-exposed animals 48 h after eCG stimulation.