First microwave-assisted synthesis of an electron-rich phosphane and its coordination chemistry with platinum(II) and palladium(II)

The P-O ligand 3-(di(2-methoxyphenyl)phosphanyl)propionic acid (HL) was synthesized by a microwave-assisted reaction of a secondary phosphane. The coordination of HL to Pt^II yielded the neutral mononuclear complex trans-[PtCl(κ²-P,O-L)(κ-P-HL)] (1), while the reaction of PdClMe(η⁴-COD) (COD = 1,4-cyclooctadiene) with HL in the presence of NEt₃ gave the anionic Pd^II compound of the formula (HNEt₃)[PdClMe(κ²-P,O-L)] (2). Upon crystallization of the latter compound the neutral chloride-bridged dimetallic compound cis-[Pd(μ-Cl)Me(HL)]₂ (3) was obtained. HL, 1 and 3·CH₂Cl₂ have been characterized by single crystal X-ray structure analyses.     

Ubiquilin-1 is a molecular chaperone for the amyloid precursor protein

Alzheimer disease (AD) is associated with extracellular deposition of proteolytic fragments of amyloid precursor protein (APP). Although mutations in APP and proteases that mediate its processing are known to result in familial, early onset forms of AD, the mechanisms underlying the more common sporadic, yet genetically complex forms of the disease are still unclear. Four single-nucleotide polymorphisms within the ubiquilin-1 gene have been shown to be genetically associated with AD, implicating its gene product in the pathogenesis of late onset AD. However, genetic linkage between ubiquilin-1 and AD has not been confirmed in studies examining different populations. Here we show that regardless of genotype, ubiquilin-1 protein levels are significantly decreased in late onset AD patient brains, suggesting that diminished ubiquilin function may be a common denominator in AD progression. Our interrogation of putative ubiquilin-1 activities based on sequence similarities to proteins involved in cellular quality control showed that ubiquilin-1 can be biochemically defined as a bona fide molecular chaperone and that this activity is capable of preventing the aggregation of amyloid precursor protein both in vitro and in live neurons. Furthermore, we show that reduced activity of ubiquilin-1 results in augmented production of pathogenic amyloid precursor protein fragments as well as increased neuronal death. Our results support the notion that ubiquilin-1 chaperone activity is necessary to regulate the production of APP and its fragments and that diminished ubiquilin-1 levels may contribute to AD pathogenesis.     

Tracking climate impacts on the migratory monarch butterfly

Understanding the impacts of climate on migratory species is complicated by the fact that these species travel through several climates that may be changing in diverse ways throughout their complete migratory cycle. Most studies are not designed to tease out the direct and indirect effects of climate at various stages along the migration route. We assess the impacts of spring and summer climate conditions on breeding monarch butterflies, a species that completes its annual migration cycle over several generations. No single, broad‐scale climate metric can explain summer breeding phenology or the substantial year‐to‐year fluctuations observed in population abundances. As such, we built a Poisson regression model to help explain annual arrival times and abundances in the Midwestern United States. We incorporated the climate conditions experienced both during a spring migration/breeding phase in Texas as well as during subsequent arrival and breeding during the main recruitment period in Ohio. Using data from a state‐wide butterfly monitoring network in Ohio, our results suggest that climate acts in conflicting ways during the spring and summer seasons. High spring precipitation in Texas is associated with the largest annual population growth in Ohio and the earliest arrival to the summer breeding ground, as are intermediate spring temperatures in Texas. On the other hand, the timing of monarch arrivals to the summer breeding grounds is not affected by climate conditions within Ohio. Once in Ohio for summer breeding, precipitation has minimal impacts on overall abundances, whereas warmer summer temperatures are generally associated with the highest expected abundances, yet this effect is mitigated by the average seasonal temperature of each location in that the warmest sites receive no benefit of above average summer temperatures. Our results highlight the complex relationship between climate and performance for a migrating species and suggest that attempts to understand how monarchs will be affected by future climate conditions will be challenging.     

B lymphocyte compartments in the human splenic red pulp: capillary sheaths and periarteriolar regions

The microvasculature of human spleens is still incompletely understood. Two enigmatic types of red pulp microvessels, penicillar arterioles and sheathed capillaries, have already been described in the nineteenth century without gaining much attention afterwards. We performed a detailed analysis of sheathed capillaries to clarify the cellular composition of their sheaths by immunohistological double-staining experiments. Capillary sheaths comprise three different cell types, namely specialized cuboidal CD271⁺⁺ inner sheath cells surrounded by CD271^? macrophages and accumulations of B lymphocytes. The CD271⁺⁺ inner sheath cells express the chemokine CXCL13 in a unique single dot pattern. Sheath-associated B lymphocytes consist of IgM⁺, IgD⁺⁺, and of “switched” cells. T lymphocytes do not accumulate in pericapillary sheaths. The predominant sheath-associated macrophage population is CD163^?CD68⁺ and thus differs from the majority of red pulp macrophages. The sheath-associated macrophages strongly express CD169 only in perifollicular sheaths, but not in sheaths located deeper in the red pulp. IgM⁺, IgD⁺⁺, and “switched” B cells are also closely associated with red pulp arterioles characterized by the expression of smooth muscle actin in muscle cells and in branched periarteriolar stromal cells. Capillary sheaths are observed in a post-arteriolar position and appear to be of limited length. We suggest to change the term “Vagina periarteriolaris makrophagocytica” of the international histological and embryological terminologies to “Vagina pericapillaris.”     

Mechanical biochemistry of proteins one molecule at a time

The activity of proteins and their complexes often involves the conversion of chemical energy (stored or supplied) into mechanical work through conformational changes. Mechanical forces are also crucial for the regulation of the structure and function of cells and tissues. Thus, the shape of eukaryotic cells (and by extension, that of the multicellular organisms they form) is the result of cycles of mechanosensing, mechanotransduction, and mechanoresponse. Recently developed single-molecule atomic force microscopy techniques can be used to manipulate single molecules, both in real time and under physiological conditions, and are ideally suited to directly quantify the forces involved in both intra- and intermolecular protein interactions. In combination with molecular biology and computer simulations, these techniques have been applied to characterize the unfolding and refolding reactions in a variety of proteins. Single-molecule mechanical techniques are providing fundamental information on the structure and function of proteins and are becoming an indispensable tool to understand how these molecules fold and work.     

Point mutations alter the mechanical stability of immunoglobulin modules

Immunoglobulin-like modules are common components of proteins that play mechanical roles in cells such as muscle elasticity and cell adhesion. Mutations in these proteins may affect their mechanical stability and thus may compromise their function. Using single molecule atomic force microscopy (AFM) and protein engineering, we demonstrate that point mutations in two beta-strands of an immunoglobulin module in human cardiac titin alter the mechanical stability of the protein, resulting in mechanical phenotypes. Our results demonstrate a previously unrecognized class of phenotypes that may be common in cell adhesion and muscle proteins.     

Phenotypic differences between red pulp capillary and sinusoidal endothelia help localizing the open splenic circulation in humans

The distribution of capillaries, sinuses and larger vessels was investigated by immunohistology in paraffin sections of 12 adult human spleens using a panel of antibodies. Double staining for CD34 and CD141 (thrombomodulin) revealed that capillary endothelia in the cords of the splenic red pulp and at the surface of follicles were CD34⁺CD141⁻, while red pulp sinus endothelia had the phenotype CD34⁻CD141⁺. Only in the direct vicinity of splenic follicles did sinus endothelial cells exhibit both antigens. Thus, splenic sinuses do not replace conventional capillaries, but exist in addition to such vessels. The endothelium in arterioles, venules and larger arteries and veins was uniformly CD34⁺CD141⁺. Anti-CD34 and anti-CD141 both additionally reacted with different types of splenic stromal cells. Differential staining of capillaries and sinuses may permit a three-dimensional reconstruction of serial sections to unequivocally delineate the “open” and “closed” splenic circulation in humans.     

Targeting Viral Antigens to CD11c on Dendritic Cells Induces Retrovirus-Specific T Cell Responses

Dendritic cells (DC) represent the most potent antigen presenting cells and induce efficient cytotoxic T lymphocyte (CTL) responses against viral infections. Targeting antigens (Ag) to receptors on DCs is a promising strategy to enhance antitumor and antiviral immune responses induced by DCs. Here, we investigated the potential of CD11c-specific single-chain fragments (scFv) fused to an immunodominant peptide of Friend retrovirus for induction of virus-specific T cell responses by DCs. In vitro CD11c-specific scFv selectively targeted viral antigens to DCs and thereby significantly improved the activation of virus-specific T cells. In vaccination experiments DCs loaded with viral Ag targeted to CD11c provided improved rejection of FV-derived tumors and efficiently primed virus-specific CTL responses after virus challenge. Since the induction of strong virus-specific T cell responses is critical in viral infections, CD11c targeted protein vaccines might provide means to enhance the cellular immune response to prophylactic or therapeutic levels.