Relationship of size at return with environmental variation,hatchery production,and productivity of wild pink salmon in Prince William Sound,Alaska: does size matter?

Pink salmon (Oncorhynchus gorbuscha) returning to Prince William Sound (PWS), Alaska, have increased to historically high levels of abundance in recent years, but average body size at return has declined. We examined how body size at return of PWS pink salmon was related to 10 biophysical factors, including the scale of hatchery production. We also examined the effect of body size at return on productivity of wild pink salmon in PWS. For the 1975–1999 brood years, we found that an index of total abundance of pink salmon in the Gulf of Alaska and sea surface temperature during the year of return best explained the variation in pink salmon body size over time. Body size at return was significantly correlated with productivity of wild pink salmon. We used stepwise-regression to fit a generalized linear version of the Ricker spawner-recruit model to determine if body size would explain significant variation in wild-stock productivity in context with other environmental variation, including hatchery production. The results indicate that variability in wild-stock productivity is primarily driven by density-independent factors in the marine environment, but that body size of wild spawners also significantly affects productivity of wild PWS pink salmon. We conclude that the success of large-scale enhancement increasing the total run in PWS may have contributed to the decline in body size because of density-dependent growth in the Gulf of Alaska. We used a simulation model to estimate the impact of hatchery-induced changes in adult body size on wild-stock production in PWS. We estimated an annual wild-stock yield loss of 1.03 million pink salmon, less than 5% of the annual hatchery return of 24.2 million adult pink salmon for brood years 1990–1999.     

MHC-I-restricted presentation of HIV-1 virion antigens without viral replication

Dendritic cells and macrophages can process extracellular antigens for presentation by MHC-I molecules. This exogenous pathway may have a crucial role in the activation of CD8+ cytotoxic T lymphocytes during human viral infections. We show here that HIV-1 epitopes derived from incoming virions are presented through the exogenous MHC-I pathway in primary human dendritic cells, and to a lower extent in macrophages, leading to cytotoxic T-lymphocyte activation in the absence of viral protein synthesis. Exogenous antigen presentation required adequate virus-receptor interactions and fusion of viral and cellular membranes. These results provide new insights into how anti-HIV cytotoxic T lymphocytes can be activated and have implications for anti-HIV vaccine design.     

Social stimuli, testosterone, and aggression in gull chicks: support for the challenge hypothesis

We tested the challenge hypothesis for the hormonal regulation of aggression in chicks of the black-headed gull, Larus ridibundus. Chicks of this species are highly aggressive toward conspecifics, but never to peers that hatched from the same clutch (modal clutch size is three). Therefore, in the first experiment small families were housed together in large groups (challenged condition) and compared to families kept isolated (nonchallenged condition). As expected, in the challenged condition during the initial stage of territory establishment basal levels of testosterone (T) were clearly higher than those in the nonchallenged condition. In the second experiment we tested the effect of a short social challenge on short-term T-fluctuations. The design was based on an earlier experiment, showing that after temporary T-treatment chicks become very sensitive to social challenges while having low basal T-levels. We now show that these social challenges induce brief elevations in plasma T-levels. These peaks are similar to those in previously untreated chicks but untreated chicks do not respond with aggression to a challenge. Therefore, we conclude that the initial exposure to elevated T-levels increases the sensitivity to brief changes in T induced by social challenges. In this way exposure to T, that may be detrimental for development, is minimized while birds remain able to defend territories. This is the first report showing that the challenge hypothesis as established for adult birds, is also applicable for aggressive behavior in young birds outside the sexual context. Furthermore we suggest that a phase of priming with T is necessary to obtain the high behavioral responsiveness to a challenge.     

Lack of an immune response against the tetracycline-dependent transactivator correlates with long-term doxycycline-regulated transgene expression in nonhuman primates after intramuscular injection of recombinant adeno-associated virus

We previously documented persistent regulation of erythropoietin (Epo) secretion in mice after a single intramuscular (i.m.) injection of a recombinant adeno-associated virus (rAAV) vector harboring both the tetracycline-dependent transactivator (rtTA) and the Epo cDNA (D. Bohl, A. Salvetti, P. Moullier, and J. M. Heard, Blood 92:1512-1517, 1998). Using the same vector harboring the cynomolgus macaque Epo cDNA instead, the present study evaluated the ability of the tetracycline-regulatable (tetR) system to establish long-term transgene regulation in nonhuman primates. The vector was administered i.m., after which 5-day induction pulses were performed monthly for up to 13 months by using doxycycline (DOX), a tetracycline analog. We show that initial inductions were successful in all individuals and that there was a tight regulation and a rapid deinduction pattern upon DOX withdrawal. For one macaque, regulation of Epo secretion was maintained during the entire experimental period; for the five remaining macaques, secreted Epo became indistinguishable from endogenous Epo upon repeated DOX inductions. We investigated the mechanism involved and showed that, except in the animal in which secretion persisted, delayed humoral and cellular immune responses were directed against the rtTA transactivator protein associated with the reduction of vector DNA in transduced muscles. This study provides some evidence that, when the immune system is not mobilized against the rtTA transactivator, the tetR-regulatable system is able to support long-term transgene regulation in the context of an rAAV in nonhuman primates. In addition, our results suggest potential improvements for vector design.     

Ectopic expression of active processed form of atrial natriuretic peptide in skeletal myoblasts

Atrial natriuretic peptide (ANP) is a cardiac hormone that elicits a profound diuresis, natriuresis, and hypotension. As a preliminary study toward ANP gene therapy of cardiovascular disorders, we have cloned a cDNA for mouse preproANP and carried out expression studies in muscle cells. The expression cassette, which was flanked by ITRs from AAV-2, consisted of HCMV IE enhancer/promoter, preproANP gene, and polyadenylation signal from bovine growth hormone. We transfected this expression vector into primary skeletal myoblasts and examined the following points: (1) secretion of immunoreactive ANP, (2) biological activity, and (3) nature of secreted ANP(s). The conditioned media from cells transfected with ANP vector had significantly higher levels of irANP in comparison to mock control. The secreted irANP had biological activity as confirmed by the elevated level of intracellular cGMP in human umbilical vein endothelial cells. Reverse-phase HPLC analysis showed that the processed form of ANP was the predominant form. These results demonstrate that preproANP gene could be ectopically expressed and correctly processed in skeletal myoblasts, which has implications for development of muscle-based ANP gene therapy.     

Fumonisin B1-induced cell death in arabidopsis protoplasts requires jasmonate-, ethylene-, and salicylate-dependent signaling pathways

We have established an Arabidopsis protoplast model system to study plant cell death signaling. The fungal toxin fumonisin B1 (FB1) induces apoptosis-like programmed cell death (PCD) in wild-type protoplasts. FB1, however, only marginally affects the viability of protoplasts isolated from transgenic NahG plants, in which salicylic acid (SA) is metabolically degraded; from pad4-1 mutant plants, in which an SA amplification mechanism is thought to be impaired; or from jar1-1 or etr1-1 mutant plants, which are insensitive to jasmonate (JA) or ethylene (ET), respectively. FB1 susceptibility of wild-type protoplasts decreases in the dark, as does the cellular content of phenylalanine ammonia-lyase, a light-inducible enzyme involved in SA biosynthesis. Interestingly, however, FB1-induced PCD does not require the SA signal transmitter NPR1, given that npr1-1 protoplasts display wild-type FB1 susceptibility. Arabidopsis cpr1-1, cpr6-1, and acd2-2 protoplasts, in which the SA signaling pathway is constitutively activated, exhibit increased susceptibility to FB1. The cpr6-1 and acd2-2 mutants also constitutively express the JA and ET signaling pathways, but only the acd2-2 protoplasts undergo PCD in the absence of FB1. These results demonstrate that FB1 killing of Arabidopsis is light dependent and requires SA-, JA-, and ET-mediated signaling pathways as well as one or more unidentified factors activated by FB1 and the acd2-2 mutation.     

ATP-dependent substrate occlusion by the human erythrocyte sugar transporter

Human erythrocyte sugar transport presents a functional complexity that is not explained by existing models for carrier-mediated transport. It has been suggested that net sugar uptake is the sum of three serial processes: sugar translocation, sugar interaction with an intracellular binding complex, and the release from this complex into bulk cytosol. The present study was carried out to identify the erythrocyte sugar binding complex, to determine whether sugar binding occurs inside or outside the cell, and to determine whether this binding complex is affected by cytosolic ATP or transporter quaternary structure. Sugar binding assays using cells and membrane protein fractions indicate that sugar binding to erythrocytes is quantitatively accounted for by sugar binding to the hexose transport protein, GluT1. Kinetic analysis of net sugar fluxes indicates that GluT1 sugar binding sites are cytoplasmic. Intracellular ATP increases GluT1 sugar binding capacity from 1 to 2 mol of 3-O-methylglucose/mol GluT1 and inhibits the release of bound sugar into cytosol. Reductant-mediated, tetrameric GluT1 dissociation into dimeric GluT1 is associated with the loss of ATP and 3-O-methylglucose binding. We propose that sugar uptake involves GluT1-mediated, extracellular sugar translocation into an ATP-dependent cage formed by GluT1 cytoplasmic domains. Caged or occluded sugar has three possible fates: (1) transport out of the cell (substrate cycling); (2) interaction with sugar binding sites within the cage, or (3) release into bulk cytosol. We show how this hypothesis can account for the complexity of erythrocyte sugar transport and its regulation by cytoplasmic ATP.     

Distinct trafficking pathways mediate Nef-induced and clathrin-dependent major histocompatibility complex class I down-regulation

The human immunodeficiency virus type 1 Nef protein alters the post-Golgi stages of major histocompatibility complex class I (MHC-I) biogenesis. Presumed mechanisms involve the disclosure of a cryptic tyrosine-based sorting signal (YSQA) located in the cytoplasmic tail of HLA-A and -B heavy chains. We changed this signal for a prototypic sorting motif (YSQI or YSQL). Modified HLA-A2 molecules, termed A2-endo, displayed constitutively low surface levels and accumulated in a region close to or within the Golgi apparatus, a behavior reminiscent of wild-type HLA-A2 in Nef-expressing cells. However, several lines of evidence indicate that the action of prototypic signals on MHC-I trafficking differs from that of Nef. Internalization of surface A2-endo was more rapid and was associated with efficient recycling to the surface. A transdominant-negative mutant of dynamin-1 inhibited A2-endo constitutive internalization and Nef-induced CD4 down-regulation, whereas it did not affect the activity of Nef on MHC-I. Moreover, trafficking of A2-endo was still affected by the viral protein, indicating additive effects of prototypic signals and Nef. Therefore, distinct trafficking pathways regulate clathrin-dependent and Nef-induced MHC-I modulation.