A 4-Mb BAC/PAC contig and complete genomic structure of the GPC5/GPC6 gene cluster on chromosome 13q32.

The glypicans compose a family of glycosylphosphatidylinositol-anchored heparan sulfate proteoglycans that may play a role in the control of cell division and growth regulation. So far, six members (GPC1-6) of this family are known in vertebrates. We report the construction of a high-resolution 4 Mb sequence-ready BAC/PAC contig of the GPC5/GPC6 gene cluster on chromosome region 13q32. The contig indicates that, like the GPC3/GPC4 genes on Xq26, GPC5 and GPC6 are arranged in tandem array. Both GPC5 and GPC6 are very large genes, with sizes well over 1 Mb. With a size of approximately 2 Mb, GPC5 would be the second largest human gene identified to date. Comparison of the long range gene organisation on 13q and Xq, suggests that these chromosomes share several regions of homology. Mutations and deletions affecting GPC3 are associated with the Simpson-Golabi-Behmel overgrowth syndrome. Mutational analysis of GPC5 and GPC6 in 19 patients with somatic overgrowth failed to reveal pathologic mutations in either of these genes, but identified several coding region polymorphisms.     

Control of artifacts in plasma adenosine determinations

The literature concerning the role of adenosine (ADO) in physiology reveals no agreement about plasma ADO concentrations and suggests two main sources of error in these determinations: rapid ADO uptake by red blood cells or rapid ADO production from ADO nucleotides, which may be released by any cell lysis or platelet aggregation during plasma preparation. We therefore studied ADO concentrations in plasma from normal human forearm venous blood. ADO was determined by a high-performance liquid chromatographic procedure with a sensitivity of 3 nM (original plasma). Observed ADO concentrations ranged from 894 nM to 8.2 nM depending on the conditions of plasma preparation. In plasma prepared in plastic tubes from 4.5 ml of blood drawn into a plastic syringe containing 1.5 ml of an isotonic stopping solution (pH 7.4) containing heparin (60 units ml), dilazep (40 microM), EGTA (40 mM, EDTA (40 mM), erythro-9-(2-hydroxy-3-nonyl) adenine (40 microM), and alpha, beta-methylene adenosine-5'-diphosphate (525 nM), the plasma ADO concentration was 13.3 +/- 1.88 nM (SE) after correction for a simultaneous ADO recovery determination. The mean ADO recovery was 78% +/- 3.39. The mean plasma ADO concentration found by this method of collection and preparation is lower then reported by others. Proper collection methods are required to avoid artifacts when determining plasma ADO concentrations.     

Interleukin-4 activates ion channels in B lymphocytes.

The lymphokine interleukin-4 (IL-4) has been shown to induce dramatic changes in the physiology of resting B cells. We have applied the patch clamp technique in the cell attached and inside/out configurations to resting and IL-4-treated B cells to determine whether specific ion conductances result as a consequence of IL-4 action. We report here that two distinct ion channel events occur in B lymphocytes after treatment with IL-4, (i) induction of an inward rectifying K+ channel that is not observed in untreated cells, and (ii) activation of a large conductance anion channel that is normally silent in non-treated cells in the cell attached patch configuration. These data present the first evidence of a direct effect by IL-4 on ion channels and we suggest roles for these two ionic conductances in IL-4-induced B cell activation.     

Sulfation of mono- and diaryl oximes by aryl sulfotransferase isozymes

Aryl sulfotransferases (3'-phosphoadenylsulfate:phenol sulfotransferase, EC 2.8.2.1) catalyze the sulfonation of a wide variety of hydroxyl-containing substrates, including numerous xenobiotics. The chemical diversity of aryl sulfotransferase substrates is in part attributable to the presence of multiple isozymes, each of which has broad substrate specificity. Of the aryl sulfotransferase isozymes in rat liver cytosol, two (designated isozymes I and II) have previously been shown to sulfonate phenolic compounds exclusively and, moreover, have very similar substrate specificity patterns. The recently reported unusually efficient, rapid isozyme I-catalyzed sulfonation of 9-fluorenone oxime (Mangold, J.B., Mangold, B.L.K. and Spina, A. (1986) Biochim. Biophys. Acta 874, 37-43) was therefore unexpected and suggested that aryl oximes may represent a useful class of model compounds to probe isozymic differences in substrate steric and electronic requirements. In the present study, several mono- and diaryl oximes have been prepared and tested as potential substrates for partially purified aryl sulfotransferases I and II from rat liver cytosol. The results indicate that steric factors, specifically planarity and hydroxyl group position, appear to be important requirements for enzyme-catalyzed sulfonation. In addition, although isozymes I and II had comparable activity with diaryl oximes, some striking differences in the ability of these two isozymes to sulfonate both substituted and unsubstituted monoaryl oximes were observed. This dissimilarity is consistent with distinct differences in the active sites of these isozymes.     

Strike Fast,Strike Hard: The Red-Throated Caracara Exploits Absconding Behavior of Social Wasps during Nest Predation

Red-throated Caracaras Ibycter americanus (Falconidae) are specialist predators of social wasps in the Neotropics. It had been proposed that these caracaras possess chemical repellents that allow them to take the brood of wasp nests without being attacked by worker wasps. To determine how caracaras exploit nests of social wasps and whether chemical repellents facilitate predation, we: (1) video recorded the birds attacking wasp nests; (2) analyzed surface extracts of the birds'' faces, feet, and feathers for potential chemical repellents; and (3) inflicted mechanical damage on wasp nests to determine the defensive behavior of wasps in response to varying levels of disturbance. During caracara predation events, two species of large-bodied wasps mounted stinging attacks on caracaras, whereas three smaller-bodied wasp species did not. The “hit-and-run” predation tactic of caracaras when they attacked nests of large and aggressive wasps reduced the risk of getting stung. Our data reveal that the predation strategy of caracaras is based on mechanical disturbance of, and damage to, target wasp nests. Caracara attacks and severe experimental disturbance of nests invariably caused wasps to abscond (abandon their nests). Two compounds in caracara foot extracts [sulcatone and iridodial] elicited electrophysiological responses from wasp antennae, and were also present in defensive secretions of sympatric arboreal-nesting Azteca ants. These compounds appear not to be wasp repellents but to be acquired coincidentally by caracaras when they perch on trees inhabited with Azteca ants. We conclude that caracara predation success does not depend on wasp repellents but relies on the absconding response that is typical of swarm-founding polistine wasps. Our study highlights the potential importance of vertebrate predators in the ecology and evolution of social wasps.