The humerus of Aegyptopithecus zeuxis: a primitive anthropoid

Two complete humeri of Aegyptopithecus zeuxis have been recovered from Oligocene deposits in the Fayum Province of Egypt. These new specimens support previous interpretations of the locomotor adaptations of this species and indicate that A. zeuxis was a robust, slowly moving arboreal quadruped. While the previously described distal articular region of the humerus is virtually identical with the same region in many extant ceboids and the Miocene hominoid Pliopithecus vindobonensis, the more proximal parts of the humerus show many primitive "prosimianlike" features not found the limbs of extant anthropoids. The primitive features include the absence of a distinct deltoid plane, a broad shallow bicipital groove, a large brachialis flange, and an entepicondylar foramen. In most features, the humerus of Aegyptopithecus zeuxis is more primitive than the hypothetical last common ancestor of extant cercopithecoids and hominoids based on neontological comparisons. This supports other lines of evidence indicating that the hominoids from the Egyptian Oligocene are morphologically ancestral to both Old World monkeys and apes.     

Calcium changes in immune complex-stimulated human neutrophils. Simultaneous measurement of receptor occupancy and activation reveals full population stimulus binding but subpopulation activation

Immune complexes (ICs) induce an initial transient increase in cytosolic intracellular calcium [( Ca2+]in) levels in human neutrophils (PMN). Changes in PMN [Ca2+]in were measured with the fluorescent calcium indicator Indo-1 ( [1-[2-amino-5-(6-carboxylindol-2-yl]-phenoxyl]-2-(2'-amino-5 '- methylphenoxy]ethane-N,N,N'N'-tetraacetic acid), at the level of individual cells by flow cytometry. Two kinds of immune complexes (ICs) were used in this study: an insoluble (IIC) and a more soluble less valent immune complex (SIC) with fewer available Fc receptor binding ends per molecule of SIC than IIC. Simultaneous binding and activation studies performed on the flow cytometer with fluoresceinated IIC or SIC demonstrated that a majority of the cells bound each stimulus uniformly. However, only an IC dose-dependent proportion of those IC-bound cells responded with an increase in [Ca2+]in. Analysis of Indo-1 fluorescence signals from neutrophils exposed to IIC, corrected for the contribution of the nonresponding population, indicated that every dose of IIC elicited a similar maximum [Ca+2]in within the responding population. In contrast, the magnitude of the increase in [Ca2+]in elicited by low doses of SIC did become dependent on dose. Cells treated with pertussis toxin and exposed to IIC exhibited a normal [Ca2+]in response both in magnitude and expression. Therefore, [Ca2+]in responses induced by immune complexes are expressed by subpopulations of PMN, in a response which is dependent on the valency of the stimulus. In addition, pertussis toxin sensitive G protein(s) appear not to have a major role in IIC-induced [Ca2+]in changes, membrane potential changes, production of superoxide anions, and elastase release.     

Aerobic 2-ketogluconate metabolism of Klebsiella pneumoniae NCTC 418 grown in chemostat culture.

Klebsiella pneumoniae NCTC 418 is able to convert 2-ketogluconate intracellularly to 6-phosphogluconate by the combined action of an NADPH-dependent 2-ketogluconate reductase and gluconate kinase. Synthesis of the former enzyme was maximal under 2-ketogluconate-limited growth conditions. An instantaneous transition to a 2-ketogluconate-excess condition resulted in an acceleration of catabolism of this carbon source, accompanied by complete inhibition of biosynthesis. It is suggested that the cause of this inhibition resides in depletion of the NADPH pool due to the high rate at which NADPH is oxidized by 2-ketogluconate reductase.     

Intracellular free zinc and zinc buffering in human red blood cells

Summary The effect of vasopressin on voltage-sensitive Ca²⁺ currents in the rat insulinoma cell line RINm5F has been investigated in patch-clamp whole-cell and single-channel current recording experiments. In the whole-cell recording configuration the dominant inward current in the presence of tetrodotoxin was noninactivating and had a high voltage threshold. This current was much enhanced when external Ca²⁺ was replaced by Ba²⁺ and was blocked by 1 m nifedipine. It can therefore be classified as an L-current. Vasopressin enhanced the L-current without changing the voltage threshold of activation or the voltage at which the peak current was observed. Vasopressin effects were seen at concentrations as low as 0.01nm, and the maximal effect was observed at about 1nm. In higher concentrations the vasopressin effects were weaker, with effects at 50nm of about the same magnitude as at 0.01nm. In single-channel current recording experiments carried out with the cell-attached configuration there were no effects on single L-channel currents when vasopressin was added to the bath solution, but in experiments in which vasopressin (5nm) was infused into the patch pipette a marked increase in the apparent channel open state probability was observed. We conclude that vasopressin, a peptide that is known to markedly enhance glucose-evoked insulin secretion, stimulates opening of the voltage-sensitive Ca²⁺ channels in insulin-secreting cells.     

Calcium-dependent zinc efflux in human red blood cells

Summary Zinc efflux from human red blood cells is largely brought about by a saturable mechanism that depends upon extracellular Ca²⁺ ions. It has aV _max of about 35 mol/10¹³ cells hr, aK _m for external Ca²⁺ of 1×10^–4 m, and aK _m for internal Zn²⁺ of 1×10^–9 m. External Zn²⁺ inhibits with aK _0.5 of 3×10^–6 m. Sr²⁺ is a substitute for external Ca²⁺, but changes in monovalent anions or cations have little effect on the Zn²⁺ efflux mechanism. It is unaffected by most inhibitors of red cell transport systems, although amiloride and D-600 (methoxyverapamil, a Ca²⁺ channel blocker) are weakly inhibitory. The transport is capable of bringing about the net efflux of Zn²⁺, against an electrochemical gradient, provided Ca²⁺ is present externally. This suggests it may be a Zn²⁺:Ca²⁺ exchange, which would be able to catalyze the uphill movement of Zn²⁺ at the expense of an inward Ca²⁺ gradient, which is it self maintained by the Ca²⁺ pump.     

Axonal and dendritic endocytic pathways in cultured neurons

The endocytic pathways from the axonal and dendritic surfaces of cultured polarized hippocampal neurons were examined. The dendrites and cell body contained extensive networks of tubular early endosomes which received endocytosed markers from the somatodendritic domain. In axons early endosomes were confined to presynaptic terminals and to varicosities. The somatodendritic but not the presynaptic early endosomes were labeled by internalized transferrin. In contrast to early endosomes, late endosomes and lysosomes were shown to be predominantly located in the cell body. Video microscopy was used to follow the transport of internalized markers from the periphery of axons and dendrites back to the cell body. Labeled structures in both domains moved unidirectionally by retrograde fast transport. Axonally transported organelles were sectioned for EM after video microscopic observation and shown to be large multivesicular body-like structures. Similar structures accumulated at the distal side of an axonal lesion. Multivesicular bodies therefore appear to be the major structures mediating transport of endocytosed markers between the nerve terminals and the cell body. Late endocytic structures were also shown to be highly mobile and were observed moving within the cell body and proximal dendritic segments. The results show that the organization of the endosomes differs in the axons and dendrites of cultured rat hippocampal neurons and that the different compartments or stages of the endocytic pathways can be resolved spatially.     

Poliovirus-specific major histocompatibility complex class I-restricted cytolytic T-cell epitopes in mice localize to neutralizing antigenic regions.

A major histocompatibility complex (MHC) class I-restricted cytotoxic T-lymphocyte (CTL) response is induced in BALB/c mice upon immunization with poliovirus serotype 1 (Mahoney strain). A similar class I-restricted response is also induced upon immunization with purified VP1 capsid proteins. Thus, poliovirus-specific MHC class I CTL responses can be induced independently of viral infection in murine hosts. In experiments using recombinant vaccinia virus vectors expressing different segments of the poliovirus capsid proteins and synthetic peptides, two regions of the VP1 capsid protein appear to contain epitopes recognized by this bulk CTL population. These epitope regions contain a Kd-restricted peptide-binding motif. Interestingly, each of these CTL epitopes is located near previously defined neutralizing antigenic sites.     

Comparison of learning in related generalist and specialist eucoilid parasitoids

Effects of learning in two microhabitat specialists, Leptopilina boulardia Barbotin et al. and L. fimbriata Kieffer were compared to previous and new results of learning in the microhabitat generalist L. heterotoma Thomson. Females were given one or more oviposition experiences on hosts in different types of substrate. In all species oviposition experience affected the choice for a substrate, although this effect of learning was considerably less in L. fimbriata compared to the other two species. Patch times, known to be highly determined by experience in the generalist L. heterotoma, were much less flexible in the specialists. L. boulardi and L. fimbriata have fixed patch times on their natural substrate and have variable patch times on other substrates only. In all three species one oviposition affected the choice for a substrate. Additional ovipositions showed no different effect. An accumulative effect of the number of ovipositions on patch times was found in L. heterotoma only. Retention of the learning effect was only studied in L. boulardi, and was shown to be similar to that reported for L. heterotoma, i.e. two to three days. Although learning was found in both the generalist and the specialist species studied, it seems to affect their foraging behaviour differently.     

Flow cytometric kinetic measurements of neutrophil phospholipase A activation.

The interrelationships between activation of phospholipases and neutrophil stimulus-induced Ca2+ responses remain unclear. We report here that immune complexes activate a phosphatidylcholine-specific phospholipase A in a neutrophil only after the cytoplasmic Ca2+ transient has been initiated in the same cell, while chemotactic peptide activation does not proceed via such a phospholipase A-mediated mechanism. Measurements of [Ca2+] changes and of phosphatidylcholine-specific phospholipase A activity were made by flow cytometry, using Indo-1 for Ca2+ indication, and a new fluorescent probe, bis-BODIPY-phosphatidylcholine, localized in the inner leaflet of the plasma membrane, to measure phospholipase A activation. Both 100 nM formyl-methionyl-leucyl-phenylalanine (with or without cytochalasin B) and 60 micrograms/ml insoluble immune complexes elicited cytoplasmic Ca2+ transients, but only insoluble immune complexes stimulated phospholipase A activation in a subpopulation of cells exhibiting an elevation of [Ca2+]in. Phospholipase A activation followed the Ca2+ transient, starting, in each cell, after [Ca2+]in had begun to decrease as Ca2+ redistributed in the activated cell. The products of this phospholipase activation were confirmed by thin layer chromatography. We conclude that neutrophils respond to immune complexes with an elevated cytoplasmic Ca(2+)-requiring phosphatidylcholine-specific phospholipase A activation and to chemotactic peptides by a different mechanism.     

Stress response induced by DNA damage leads to specific, delayed and untargeted mutations

Summary Cells of the mouse T-lymphoma line GRSL13 were treated with 8-methoxy-psoralen plus longwave ultraviolet light (PUVA) under conditions where the biological effects are mainly due to non-persistent DNA crosslinks (PUVA-CL treatment). Fluctuation analysis showed that PUVA-CL treatment resulted in an enhancement of the mutation rate in the progeny of treated cells, which persisted until the eleventh generation after treatment. Since only 5 cross-links are available to account for 52 mutational events observed in the coding region, about 90% of the induced mutational events must have been untargeted. This was confirmed by molecular analysis of these mutations, which showed that 53% of the point mutations arose at sites which are not a target for psoralens. This supports the hypothesis that stress responses may give rise to untargeted mutagenesis. Further support for this hypothesis is provided by the observation that 8-methoxy-psoralen (8-MOP) or UVA alone (both of which are known to induce many pleiotropic effects) each acted as indirect mutagen by enhancing the mutation rate 2–4 fold in the progeny of treated cells.