Transient exposure to HIV-1 Tat protein results in cytokine production in macrophages and astrocytes. A hit and run phenomenon.

The pathological correlates of dementia due to human immunodeficiency virus (HIV) infection are glial cell activation and cytokine dysregulation. These findings occur in the setting of small numbers of productively infected cells within the brain. We determined whether exposure of susceptible cells to Tat protein of HIV could result in the production of select proinflammatory cytokines. In a dose-responsive manner, Tat induced interleukin (IL)-1beta production in monocytic cells, while astrocytic cells showed an increase in mRNA for IL-1beta, but had a translation block for IL-1beta protein production. Conversely, IL-6 protein and mRNA productions were strongly induced in astrocytic cells and minimally in monocytic cells. IL-1beta and IL-6 production were independent of tumor necrosis factor-alpha production. An exposure to Tat for a few minutes was sufficient for sustained releases of cytokines for several hours. This prolonged cytokine production is likely maintained by a positive feed back loop of Tat-induced nuclear factor kappaB activation and cytokine production that is independent of extracellular calcium. Thus a transient exposure may be sufficient to initiate a cascade of events resulting in cerebral dysfunction and a "hit and run" approach may be in effect. Hence cross-sectional measurement of viral load in the brain may not be a useful indicator of the role of viral products in the neuropathogenesis of HIV dementia.     

Independent development of sensory and motor innervation patterns in embryonic chick hindlimbs

Previous studies suggest that sensory axon outgrowth is guided by motoneurons, which are specified to innervate particular target muscles. Here we present evidence that questions this conclusion. We have used a new approach to assess the pathfinding abilities of bona fide sensory neurons, first by eliminating motoneurons after neural crest cells have coalesced into dorsal root ganglia (DRG) and second by challenging sensory neurons to innervate muscles in a novel environment created by shifting a limb bud rostrally. The resulting sensory innervation patterns mapped with the lipophilic dyes DiI and DiA showed that sensory axons projected robustly to muscles in the absence of motoneurons, if motoneurons were eliminated after DRG formation. Moreover, sensory neurons projected appropriately to their usual target muscles under these conditions. In contrast, following limb shifts, muscle sensory innervation was often derived from inappropriate segments. In this novel environment, sensory neurons tended to make more "mistakes" than motoneurons. Whereas motoneurons tended to innervate their embryologically correct muscles, sensory innervation was more widespread and was generally from more rostral segments than normal. Similar results were obtained when motoneurons were eliminated in embryos with limb shifts. These findings show that sensory neurons are capable of navigating through their usual terrain without guidance from motor axons. However, unlike motor axons, sensory axons do not appear to actively seek out appropriate target muscles when confronted with a novel terrain. These findings suggest that sensory neuron identity with regard to pathway and target choice may be unspecified or quite plastic at the time of initial axon outgrowth.     

5-methylcytosine at HpaII sites in p53 is not hypermutable after UVC irradiation

Using a yeast based p53 functional assay we previously demonstrated that the UVC-induced p53 mutation spectrum appears to be indistinguishable from the one observed in Non Melanoma Skin Cancer (NMSC). However, position 742 (codon 248, CpG site) represented the major hot spot in NMSC but was not found mutated in the yeast system. In order to determine whether UVC-induced mutagenic events may be facilitated at methylated cytosine (5mC), a yeast expression vector harbouring a human wild-type p53 cDNA (pLS76) was methylated in vitro by HpaII methylase. Methylation induced 98% protection to HpaII endonuclease. Unmethylated and methylated pLS76 vectors were then UVC irradiated (lambda(max): 254 nm) and transfected into a yeast strain containing the ADE2 gene regulated by a p53-responsive promoter. The results revealed that: (i) 5mC at HpaII sites did not cause any difference in the UVC-induced survival and/or mutagenicity; (ii) none of the 20 mutants derived from methylated pLS76 showed p53 mutations targeted at HpaII sites; (iii) the UVC-induced p53 mutation spectra derived from methylated and unmethylated pLS76 were indistinguishable not only when classes of mutations and hot spots were concerned, but also when compared through a rigorous statistical test to estimate their relatedness (P = 0.85); (iv) the presence of 5mC did not increase the formation of photo-lesions at codon 248, as determined by using a stop polymerase assay. Although based on a limited number of mutants, these results suggest that the mere presence of 5mC at position 742 does not cause a dramatic increase of its mutability after UVC irradiation. We propose that position 742 is a hot spot in NMSC either because of mutagenic events at 5mC caused by other UV components of solarlight and/or because not all the NMSC are directly correlated with UV mutagenesis but may have a "spontaneous" origin.     

Changes in cytosolic pH within Arabidopsis root columella cells play a key role in the early signaling pathway for root gravitropism

Ratiometric wide-field fluorescence microscopy with 1',7'- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran demonstrated that gravistimulation leads to rapid changes in cytoplasmic pH (pHc) in columella cells of Arabidopsis roots. The pHc of unstimulated columella cells in tiers 2 and 3, known sites of graviperception (E.B. Blancaflor, J.B. Fasano, S. Gilroy [1998] Plant Physiol 116: 213-222), was 7.22 +/- 0.02 pH units. Following gravistimulation, the magnitude and direction of pHc changes in these cells depended on their location in the columella. Cells in the lower side of tier 2 became more alkaline by 0.4 unit within 55 s of gravistimulation, whereas alkalinization of the cells on the upper side was slower (100 s). In contrast, all cells in tier 3 acidified by 0.4 pH unit within 480 s after gravistimulation. Disrupting these pHc changes in the columella cells using pHc modifiers at concentrations that do not affect root growth altered the gravitropic response. Acidifying agents, including bafilomycin A1, enhanced curvature, whereas alkalinizing agents disrupted gravitropic bending. These results imply that pHc changes in the gravisensing cells and the resultant pH gradients across the root cap are important at an early stage in the signal cascade leading to the gravitropic response.     

The paleoenvironment of Sivapithecus parvada

Remains of the hominoid Sivapithecus parvada and a diversity of mammalian taxa are preserved at locality Y311 (ca. 10 Ma) in the Siwalik Nagri Formation of northern Pakistan. Bovids (Bovidae, Artiodactyla) are the most abundant mammals next to tragulids (Tragulidae, Artiodactyla) at locality Y311 and provide a means for reconstructing the paleoenvironments that would have been available to Sivapithecus parvada. A functional model indicates a linkage between habitat and several femoral characters among extant bovids. Based on this model, we infer that forested habitats predominated at locality Y311 but that some less densely covered areas may also have been present. Paleoenvironments in the earlier Chinji Formation appear comparable to those at locality Y311, although the presence of a continuous canopy in the former is more certain. Thus, adaptive changes in the bovid fauna from the Chinji through the Nagri Formations appear to have preceded the shift to predominantly C4 grasslands which, based on other lines of evidence, occurred locally (and possibly globally) between 8 and 6 Ma. The paleoenvironments of locality Y311 and the Chinji Formation localities appear different from the paleoenvironment of Kenyapithecus at Fort Ternan in Kenya, where the presence of continuous canopy is unlikely. The Fort Ternan fauna is dominated by two genera of bovids. One of these is adapted to light cover while the other appears better adapted to heavy cover. Sivapithecus and Kenyapithecus lived in different ecological settings probably characterized by varying degrees of vegetative cover.     

The challenge of pollen analysis in palaeoenvironmental studies of hominid beds: the record from Sterkfontein caves

The search for pollen in carbonate-rich sediments from the hominid site Sterkfontein has been justified because previous investigations suggested that although pollen contamination is a problem, speleothems (e.g. travertines and stalagmites) are most likely to contain reliable assemblages. The new results confirm that, although they have some potential, most sediment types from the site, even speleothems, are usually not suitable for analysis and that they contain very low concentrations of pollen, if any. The extraction of pollen from them is complicated by the problem of contamination from the modern environment. Such contamination has shown up in many previous investigations at this and similar sites and judging from published literature, its significance has not been fully appreciated. Cave palynology can be a very valuable tool in palaeoenvironmental research but the caveats associated with palynology of different sediment types especially carbonate impregnated sediments must be emphasized.     

Oxidation of alpha1-proteinase inhibitor by the myeloperoxidase-hydrogen peroxidase system promotes binding to immunoglobulin A

We have demonstrated previously that patients with rheumatoid arthritis (RA) show an increase in serum and synovial fluid levels of complexes between alpha1-proteinase inhibitor (alpha1PI) and IgA. These are believed to form through disulfide binding between the Cys232 residue on alpha1PI and the penultimate cysteine residue (Cys471) of the IgA alpha chain. The mechanism for this has not been elucidated. We show here that alpha1PI oxidized by the myeloperoxidase-hydrogen peroxide (MPO-H2O2) system promotes the formation of IgA-alpha1PI complexes when incubated with IgA and that such complexes have no inhibitory activity against porcine pancreatic elastase (PPE). The activity of alpha1PI was considerably reduced also in IgA-alpha1PI complexes isolated from serum of an RA patient. We suggest that formation of IgA-alpha1PI complexes in inflammation may involve oxidation of alpha1PI, and as a consequence the alpha1PI in such complexes has reduced elastase inhibitory activity.