Northward displacement of optimal climate conditions for ecotypes of Eriophorum vaginatum L. across a latitudinal gradient in Alaska

Plants are often genetically specialized as ecotypes attuned to local environmental conditions. When conditions change, the optimal environment may be physically displaced from the local population, unless dispersal or in situ evolution keep pace, resulting in a phenomenon called adaptational lag. Using a 30‐year‐old reciprocal transplant study across a 475 km latitudinal gradient, we tested the adaptational lag hypothesis by measuring both short‐term (tiller population growth rates) and long‐term (17‐year survival) fitness components of Eriophorum vaginatum ecotypes in Alaska, where climate change may have already displaced the optimum. Analyzing the transplant study as a climate transfer experiment, we showed that the climate optimum for plant performance was displaced ca. 140 km north of home sites, although plants were not generally declining in size at home sites. Adaptational lag is expected to be widespread globally for long‐lived, ecotypically specialized plants, with disruptive consequences for communities and ecosystems.     

CD4+CD8+ T cells represent a significant portion of the anti-HIV T cell response to acute HIV infection

Previous studies have revealed that HIV-infected individuals possess circulating CD4(+)CD8(+) double-positive (DP) T cells specific for HIV Ags. In the present study, we analyzed the proliferation and functional profile of circulating DP T cells from 30 acutely HIV-infected individuals and 10 chronically HIV-infected viral controllers. The acutely infected group had DP T cells that showed more proliferative capability and multifunctionality than did both their CD4(+) and CD8(+) T cells. DP T cells were found to exhibit greater proliferation and higher multifunctionality compared with CD4 T cells in the viral controller group. The DP T cell response represented 16% of the total anti-HIV proliferative response and >70% of the anti-HIV multifunctional response in the acutely infected subjects. Proliferating DP T cells of the acutely infected subjects responded to all HIV Ag pools with equal magnitude. Conversely, the multifunctional response was focused on the pool representing Nef, Rev, Tat, VPR, and VPU. Meanwhile, the controllers' DP T cells focused on Gag and the Nef, Rev, Tat, VPR, and VPU pool for both their proliferative and multifunctional responses. Finally, we show that the presence of proliferating DP T cells following all HIV Ag stimulations is well correlated with proliferating CD4 T cells whereas multifunctionality appears to be largely independent of multifunctionality in other T cell compartments. Therefore, DP T cells represent a highly reactive cell population during acute HIV infection, which responds independently from the traditional T cell compartments.     

Cloning and analysis of sooty mangabey alternative coreceptors that support simian immunodeficiency virus SIVsmm entry independently of CCR5

Natural host sooty mangabeys (SM) infected with simian immunodeficiency virus SIVsmm do not develop AIDS despite high viremia. SM and other natural hosts express very low levels of CCR5 on CD4(+) T cells, and we recently showed that SIVsmm infection and robust replication occur in vivo in SM genetically lacking CCR5, indicating the use of additional entry pathways. SIVsmm uses several alternative coreceptors of human origin in vitro, but which molecules of SM origin support entry is unknown. We cloned a panel of putative coreceptors from SM and tested their ability to mediate infection, in conjunction with smCD4, by pseudotypes carrying Envs from multiple SIVsmm subtypes. smCXCR6 supported efficient infection by all SIVsmm isolates with entry levels comparable to those for smCCR5, and smGPR15 enabled entry by all isolates at modest levels. smGPR1 and smAPJ supported low and variable entry, whereas smCCR2b, smCCR3, smCCR4, smCCR8, and smCXCR4 were not used by most isolates. In contrast, SIVsmm from rare infected SM with profound CD4(+) T cell loss, previously reported to have expanded use of human coreceptors, including CXCR4, used smCXCR4, smCXCR6, and smCCR5 efficiently and also exhibited robust entry through smCCR3, smCCR8, smGPR1, smGPR15, and smAPJ. Entry was similar with both known alleles of smCD4. These alternative coreceptors, particularly smCXCR6 and smGPR15, may support virus replication in SM that have restricted CCR5 expression as well as SM genetically lacking CCR5. Defining expression of these molecules on SM CD4(+) subsets may delineate distinct natural host target cell populations capable of supporting SIVsmm replication without CD4(+) T cell loss.     

LXRα is uniquely required for maximal reverse cholesterol transport and atheroprotection in ApoE-deficient mice

The liver X receptor (LXR) signaling pathway is an important modulator of atherosclerosis, but the relative importance of the two LXRs in atheroprotection is incompletely understood. We show here that LXRα, the dominant LXR isotype expressed in liver, plays a particularly important role in whole-body sterol homeostasis. In the context of the ApoE(-/-) background, deletion of LXRα, but not LXRβ, led to prominent increases in atherosclerosis and peripheral cholesterol accumulation. However, combined loss of LXRα and LXRβ on the ApoE(-/-) background led to an even more severe cholesterol accumulation phenotype compared to LXRα(-/-)ApoE(-/-) mice, indicating that LXRβ does contribute to reverse cholesterol transport (RCT) but that this contribution is quantitatively less important than that of LXRα. Unexpectedly, macrophages did not appear to underlie the differential phenotype of LXRα(-/-)ApoE(-/-) and LXRβ(-/-)ApoE(-/-) mice, as in vitro assays revealed no difference in the efficiency of cholesterol efflux from isolated macrophages. By contrast, in vivo assays of RCT using exogenously labeled macrophages revealed a marked defect in fecal sterol efflux in LXRα(-/-)ApoE(-/-) mice. Mechanistically, this defect was linked to a specific requirement for LXRα(-/-) in the expression of hepatic LXR target genes involved in sterol transport and metabolism. These studies reveal a previously unrecognized requirement for hepatic LXRα for optimal reverse cholesterol transport in mice.     

Functional Consequences of Sulfhydryl Modification of the γ-Aminobutyric Acid Transporter 1 at a Single Solvent-Exposed Cysteine Residue

The aims of this study were to optimize the experimental conditions for labeling extracellularly oriented, solvent-exposed cysteine residues of ??-aminobutyric acid transporter 1 (GAT1) with the membrane-impermeant sulfhydryl reagent [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET) and to characterize the functional and pharmacological consequences of labeling on transporter steady-state and presteady-state kinetic properties. We expressed human GAT1 in Xenopus laevis oocytes and used radiotracer and electrophysiological methods to assay transporter function before and after sulfhydryl modification with MTSET. In the presence of NaCl, transporter exposure to MTSET (1?C2.5?mM for 5?C20?min) led to partial inhibition of GAT1-mediated transport, and this loss of function was completely reversed by the reducing reagent dithiothreitol. MTSET treatment had no functional effect on the mutant GAT1 C74A, whereas the membrane-permeant reagents N-ethylmaleimide and tetramethylrhodamine-6-maleimide inhibited GABA transport mediated by GAT1 C74A. Ion replacement experiments indicated that MTSET labeling of GAT1 could be driven to completion when valproate replaced chloride in the labeling buffer, suggesting that valproate induces a GAT1 conformation that significantly increases C74 accessibility to the extracellular fluid. Following partial inhibition by MTSET, there was a proportional reduction in both the presteady-state and steady-state macroscopic signals, and the functional and pharmacological properties of the remaining signals were indistinguishable from those of unlabeled GAT1. Therefore, covalent modification of GAT1 at C74 results in completely nonfunctional as well as electrically silent transporters.     

Embryonic diapause in the elasmobranchs

Embryonic diapause is a temporary suspension of development at any stage of embryogenesis, which prolongs the gestation period, allowing parturition to occur in conditions that are more suitable for newborns. This reproductive trait is widespread among all vertebrates, including elasmobranchs. Although it has only been confirmed in two elasmobranchs (Rhizoprionodon taylori and Dasyatis say), evidence indicates that at least 14 species of rays and two sharks undergo diapause, suggesting that this form of reproduction exists within a wide range of elasmobranch reproductive modes, including lecithotrophs and matrotrophs. Where it has been studied, embryogenesis is arrested at the blastodisc stage and preserved in the uterus for periods from four to 10?months. There are still many questions that remain unanswered concerning the knowledge on the biology of most diapausing species but it is clear that species benefit differently from this reproductive trait. As in other vertebrates, it is likely that environmental cues and hormones (especially progesterone and prolactin) are involved in the control of diapause in elasmobranchs, however rigorous testing of current hypothesis remains to be carried out.     

Design and synthesis of 6,6-fused heterocyclic amides as raf kinase inhibitors

Compounds belonging to several scaffolds-quinazolines, quinolines and quinoxalines-were designed and synthesized as Raf kinase inhibitors. Scaffolds were assessed for in vitro Braf(V600E) inhibition, and overall kinase selectivity. Pharmacokinetic parameters for one of the scaffolds were also determined.     

Rac signaling in breast cancer: a tale of GEFs and GAPs

Rac GTPases, small G-proteins widely implicated in tumorigenesis and metastasis, transduce signals from tyrosine-kinase, G-protein-coupled receptors (GPCRs), and integrins, and control a number of essential cellular functions including motility, adhesion, and proliferation. Deregulation of Rac signaling in cancer is generally a consequence of enhanced upstream inputs from tyrosine-kinase receptors, PI3K or Guanine nucleotide Exchange Factors (GEFs), or reduced Rac inactivation by GTPase Activating Proteins (GAPs). In breast cancer cells Rac1 is a downstream effector of ErbB receptors and mediates migratory responses by ErbB1/EGFR ligands such as EGF or TGFα and ErbB3 ligands such as heregulins. Recent advances in the field led to the identification of the Rac-GEF P-Rex1 as an essential mediator of Rac1 responses in breast cancer cells. P-Rex1 is activated by the PI3K product PIP3 and Gβγ subunits, and integrates signals from ErbB receptors and GPCRs. Most notably, P-Rex1 is highly overexpressed in human luminal breast tumors, particularly those expressing ErbB2 and estrogen receptor (ER). The P-Rex1/Rac signaling pathway may represent an attractive target for breast cancer therapy.