The influence of pre- and post-ovulatory insemination on sperm distribution in the oviduct,accessory sperm to the zona pellucida,fertilisation rate and embryo development in sows

The aim of present study was to investigate the influence of pre-compared with post-ovulatory insemination, on the distribution of spermatozoa in the oviduct, the accessory sperm counts on the zona pellucida and early embryonic development. Thirty-six crossbred multiparous sows (Swedish Landrace x Swedish Yorkshire) were artificially inseminated once either at 20-15 h before (group AIB) or at 15-20 h after (group AIA) ovulation by using a pooled semen of two boars. Thereafter, they were randomly allocated to one of five groups: slaughter at 5-6h after AI (group I-AIB), at 20-25 h after ovulation (groups II-AIB and II-AIA), at 70 h after ovulation (groups III-AIB and III-AIA), on day 11 (groups IV-AIB and IV-AIA, first day of standing oestrus=day 1) and on day 19 (groups V-AIB and V-AIA).The plasma levels of oestradiol-17beta and progesterone differed significantly (P相似文献   

Antizyme-dependent and -independent mechanisms are responsible for increased spermidine transport in amino acid-restricted human cancer cells

Amino acid deprivation can inhibit tumour cell proliferation. Since polyamines are required for cell growth, we hypothesised that their regulatory pathways can respond to amino acid restriction. We report here that exposure of human colon adenocarcinoma Caco-2 cells to a medium restricted for a single amino acid, but not for D-glucose, activates spermidine transport. The increase was rapid and seemed transient with a maximum 4-6 hr after amino acid removal. Kinetics showed that the maximal velocity of transport was solely increased in L-methionine- or L-leucine-deprived cells, indicating increased number of transporters. The intracellular level of complex of ornithine decarboxylase (ODC) with antizyme, a negative regulator of polyamine transport, was decreased by 16-29% in amino acid-deprived cells. However, exposure to limited amounts of amino acid increased transport without altering the ODC-antizyme complex level. We propose that antizyme-independent mechanisms, sensitive to the amino acid concentration, also participate to the control of spermidine transport.     

Dynamics and efficiency in vivo of UGA-directed selenocysteine insertion at the ribosome

The kinetics and efficiency of decoding of the UGA of a bacterial selenoprotein mRNA with selenocysteine has been studied in vivo. A gst-lacZ fusion, with the fdhF SECIS element ligated between the two fusion partners, gave an efficiency of read-through of 4-5%; overproduction of the selenocysteine insertion machinery increased it to 7-10%. This low efficiency is caused by termination at the UGA and not by translational barriers at the SECIS. When the selenocysteine UGA codon was replaced by UCA, and tRNASec with anticodon UGA was allowed to compete with seryl-tRNASer1 for this codon, selenocysteine was found in 7% of the protein produced. When a non-cognate SelB-tRNASec complex competed with EF-Tu for a sense codon, no effects were seen, whereas a non-cognate SelB-tRNASec competing with EF-Tu-mediated Su7-tRNA nonsense suppression of UGA interfered strongly with suppression. The induction kinetics of beta-galactosidase synthesis from fdhF'-'lacZ gene fusions in the absence or presence of SelB and/or the SECIS element, showed that there was a translational pause in the fusion containing the SECIS when SelB was present. The results show that decoding of UGA is an inefficient process and that using the third dimension of the mRNA to accommodate an additional amino acid is accompanied by considerable quantitative and kinetic costs.     

SDR and MDR: completed genome sequences show these protein families to be large, of old origin, and of complex nature

X-linked adrenoleukodystrophy is a demyelinating disorder of the central nervous system with an impaired very long chain fatty acid metabolism. The adrenoleukodystrophy gene encodes a peroxisomal membrane protein that is part of a family of related ATP-binding transporters including the adrenoleukodystrophy-related protein. The adrenoleukodystrophy protein and adrenoleukodystrophy-related protein show 66% identity and have a mirror expression in most mouse tissues. We show that retroviral-mediated adrenoleukodystrophy-related gene transfer corrects very long chain fatty acid accumulation in adrenoleukodystrophy fibroblasts, irrespective of the presence or absence of adrenoleukodystrophy protein. Pharmacological approaches aiming at overexpressing the adrenoleukodystrophy-related gene in the central nervous system of adrenoleukodystrophy patients might thus offer new therapeutic leads.     

Crystal structure analysis of a pentameric fungal and an icosahedral plant lumazine synthase reveals the structural basis for differences in assembly

Lumazine synthase catalyzes the penultimate step in the synthesis of riboflavin in plants, fungi, and microorganisms. The enzyme displays two quaternary structures, the pentameric forms in yeast and fungi and the 60-meric icosahedral capsids in plants and bacteria. To elucidate the structural features that might be responsible for differences in assembly, we have determined the crystal structures of lumazine synthase, complexed with the inhibitor 5-nitroso-6-ribitylamino-2,4-pyrimidinedione, from spinach and the fungus Magnaporthe grisea to 3.3 and 3.1 A resolution, respectively. The overall structure of the subunit and the mode of inhibitor binding are very similar in these enzyme species. The core of the subunit consists of a four-stranded parallel beta-sheet sandwiched between two helices on one side and three helices on the other. The packing of the five subunits in the pentameric M. grisea lumazine synthase is very similar to the packing in the pentameric substructures in the icosahedral capsid of the plant enzyme. Two structural features can be correlated to the differences in assembly. In the plant enzyme, the N-terminal beta-strand interacts with the beta-sheet of the adjacent subunit, thus extending the sheet from four to five strands. In fungal lumazine synthase, an insertion of two residues after strand beta1 results in a completely different orientation of this part of the polypeptide chain and this conformational difference prevents proper packing of the subunits at the trimer interface in the icosahedron. In the spinach enzyme, the beta-hairpin connecting helices alpha4 and alpha5 participates in the packing at the trimer interface of the icosahedron. Another insertion of two residues at this position of the polypeptide chain in the fungal enzyme disrupts the hydrogen bonding in the hairpin, and the resulting change in conformation of this loop also interferes with proper intrasubunit contacts at the trimer interface.     

Physiologically structured models – from versatile technique to ecological theory

A ubiquitous feature of natural communities is the variation in size that can be observed between organisms, a variation that to a substantial degree is intraspecific. Size variation within species by necessity implies that ecological interactions vary both in intensity and type over the life cycle of an individual. Physiologically structured population models (PSPMs) constitute a modelling approach especially designed to analyse these size‐dependent interactions as they explicitly link individual level processes such as consumption and growth to population dynamics. We discuss two cases where PSPMs have been used to analyse the dynamics of size‐structured populations. In the first case, a model of a size‐structured consumer population feeding on a non‐structured prey was successful in predicting both qualitative (mechanisms) and quantitative (individual growth, survival, cycle amplitude) aspects of the population dynamics of a planktivorous fish population. We conclude that single generation cycles as a result of intercohort competition is a general outcome of size‐structured consumer–resource interactions. In the second case, involving both cohort competition and cannibalism, we show that PSPMs may predict double asymptotic growth trajectories with individuals ending up as giants. These growth trajectories, which have also been observed in field data, could not be predicted from individual level information, but are emergent properties of the population feedback on individual processes. In contrast to the size‐structured consumer–resource model, the dynamics in this case cannot be reduced to simpler lumped stage‐based models, but can only be analysed within the domain of PSPMs. Parameter values used in PSPMs adhere to the individual level and are derived independently from the system at focus, whereas model predictions involve both population level processes and individual level processes under conditions of population feedback. This leads to an increased ability to test model predictions but also to a larger set of variables that is predicted at both the individual and population level. The results turn out to be relatively robust to specific model assumptions and thus render a higher degree of generality than purely individual‐based models. At the same time, PSPMs offer a much higher degree of realism, precision and testing ability than lumped stage‐based or non‐structured models. The results of our analyses so far suggest that also in more complex species configurations only a limited set of mechanisms determines the dynamics of PSPMs. We therefore conclude that there is a high potential for developing an individual‐based, size‐dependent community theory using PSPMs.     

The spoU gene of Escherichia coli, the fourth gene of the spoT operon, is essential for tRNA (Gm18) 2'-O-methyltransferase activity.

We have evidence that the open reading frame previously denoted spoU is necessary for tRNA (Gm18) 2'-O-methyltransferase activity. The spoU gene is located in the gmk-rpoZ-spoT-spoU-recG operon at 82 minutes on the Escherichia coli chromosome. The deduced amino acid sequence of spoU shows strong similarities to previously characterized 2'-O-methyltransferases. Comparison of the nucleoside modification pattern of hydrolyzed tRNA, 16S rRNA and 23S rRNA from wild-type and spoU null mutants showed that the modified nucleoside 2'-O-methylguanosine (Gm), present in a subset of E. coli tRNAs at residue 18, is completely absent in the spoU mutant, suggesting that spoU encodes tRNA (Gm18) 2'-O-methyltransferase. Nucleoside modification of 16S and 23S rRNA was unaffected in the spoU mutant. Insertions in the downstream recG gene did not affect RNA modification. Absence of Gm18 in tRNA does not influence growth rate under the tested conditions and does not interfere with activity of the SupF amber suppressor, a suppressor tRNA that normally has the Gm18 modification. We suggest that the spoU gene be renamed trmH (tRNA methylation).     

A novel ribosome-associated protein is important for efficient translation in Escherichia coli.

Previously, we showed that strains which have been deleted for the 21K gene (hereafter called yfjA), of the trmD operon, encoding a 21-kDa protein (21K protein) have an approximately fivefold-reduced growth rate in rich medium. Here we show that such mutants show an up to sevenfold reduced growth rate in minimal medium, a twofold-lower cell yield-to-carbon source concentration ratio, and a reduced polypeptide chain growth rate of beta-galactosidase. Suppressor mutations that increased the growth rate and translational efficiency of a delta yfjA mutant were localized to the 3' part of rpsM, encoding ribosomal protein S13. The 21K protein was shown to have affinity for free 30S ribosomal subunits but not for 70S ribosomes. Further, the 21K protein seems to contain a KH domain and a KOW motif, both suggested to be involved in binding of RNA. These findings suggest that the 21K protein is essential for a proper function of the ribosome and is involved in the maturation of the ribosomal 30S subunits or in translation initiation.