Two genes encoding midgut-specific maltase-like polypeptides from Anopheles gambiae

Full-length cDNA clones of two genes have been isolated from the African malaria vector mosquito, Anopheles gambiae. These genes, designated Agm1 and Agm2, encode maltase-like polypeptides of 498 and 599 residues, respectively. Deduced amino acid sequences contain a putative signal peptide sequence and four potential glycosylation sites. Agm1 and Agm2 show highest similarities to the Mal1 gene from Aedes aegypti and three clustered maltase genes from Drosophila melanogaster. Both genes are located at position 46D, in the terminal division of the left arm of the third chromosome. Agm2 has very strict tissue and temporal specificity, being expressed exclusively in the adult midgut. The specificity of Agm1 is similar but appears slightly broader; transcripts of this gene are detected at a low level in the pupae, and occasionally in the adult carcass after removal of the midgut.

[Pathologic observations of hepatitis C]

The morphological changes in liver biopsies from 70 patients with a clinical diagnosis of hepatitis C were studied. Sixty-two of the patients had history of blood transfusions. All patients were seropositive for anti-HCV by first and second generation test and/or were seropositive for HCV RNA by PCR method. Clinically, twenty cases diagnosed as acute hepatitis, fifty were chronic including 7 cases with both HBV and HCV infection. The main morphological changes in acute cases being 1. Focal degeneration of liver cells, including large and small droplet fatty changes. 2. Focal necrosis and acidophilic bodies usually being surrounded by T lymphocytes. 3. Sinusoidal inflammatory cell infiltration. 4. Lymphoid aggregation with bile duct epithelial damage was found in 60% of portal tracts. The chronic cases included 17 chronic persistent hepatitis cases (CPH) and 33 chronic active hepatitis cases (CAH). The main histopathologic changes in CAH included dense clusters of lymphocytes (lymphoid aggregates) present in the enlarged portal tracts with bridging necrosis and fibrosis, lobular inflammation including acidophilic bodies, focal necrosis and fatty degeneration. The sinusoidal cells were often hyperplastic. These changes may provide useful diagnostic clues for hepatitis C.

Induction of apoptosis in mature T cells by tumour necrosis factor

T-cell receptor-induced apoptosis regulates immune responses and can result from interactions between Fas (Apo1/CD95) and Fas ligand (FasL). Mutations in the genes for Fas and FasL cause disorders resembling human autoimmune diseases in lpr and gld mice, respectively. However, peripheral T-cell deletion takes place in lpr mice, and autoimmune syndromes occur in mouse strains without Fas or FasL defects. Here we show that tumour necrosis factor (TNF) can mediate mature T-cell receptor-induced apoptosis through the p75 TNF receptor. Blockage of both TNF and FasL is required to abrogate T-cell death and TNF mediates the death of most CD8+ T cells, whereas FasL mediates the death of most CD4+ T cells. Our results suggest that autoregulatory apoptosis of the mature T cells can occur by two distinct molecular mechanisms.

Temporal and spatial expression of amygdalin hydrolase and (R)-(+)-mandelonitrile lyase in black cherry seeds

In black cherry (Prunus serotina Ehrh.) macerates, the cyanogenic diglucoside (R)-amygdalin undergoes stepwise degradation to HCN catalyzed by amygdalin hydrolase (AH), prunasin hydrolase, and (R)-(+)-mandelonitrile lyase (MDL). A near full-length AH cDNA clone (pAH1), whose insert encodes the isozyme AH I, has been isolated and sequenced. AH I exhibits several features characteristic of beta-glucosidases of the BGA family, including their likely nucleophile center (isoleucine-threonine-glutamic acid-asparagine-glycine) and acid catalyst (asparagine-glutamic acid-proline/isoleucine) motifs. The temporal expression of AH and MDL in ripening fruit was analyzed by northern blotting. Neither mRNA was detectable until approximately 40 days after flowering (DAF), when embryos first became visible to the naked eye. Both mRNAs peaked at approximately 49 DAF before declining to negligible levels when the fruit matured (82 DAF). Taken together with enzyme activity data, these time courses suggest that AH and MDL expression may be under transcriptional control during fruit maturation. In situ hybridization analysis indicated that AH transcripts are restricted to the procambium, whereas MDL transcripts are localized within cotyledonary parenchyma cells. These tissue-specific distributions are consistent with the major locations of AH and MDL protein in mature seeds previously determined by immunocytochemistry (E. Swain, C.P. Li, and J.E. Poulton [1992] Plant Physiol 100:291-300).

Alveolar macrophage TNF-alpha release and BAL cell phenotypes in sarcoidosis

The aim of this study was to investigate the relationship between release of tumor necrosis factor-alpha (TNF-alpha) by alveolar macrophages (AM) and the phenotypic characteristics of bronchoalveolar lavage (BAL) cells in sarcoidosis. We studied the spontaneous release of TNF-alpha by AM in vitro and the phenotypic characteristics of freshly recovered BAL T-cells and AM in 31 individuals (13 with active sarcoidosis, nine with inactive sarcoidosis, and nine normal controls). TNF-alpha was measured by enzyme-linked immunosorbent assay (ELISA) in supernatants from unstimulated AM after 24 h culture. Phenotypic markers of BAL cells were determined by an immunocytochemical assay. AM of patients with active sarcoidosis released more TNF-alpha (1,355 +/- 133 pg/ml/ 10(6) AM/24 h) than those of the inactive group (651 +/- 142 pg/ml/10(6) AM/24 h) or the normal controls (425 +/- 121 pg/ml/10(6) AM/24 h), with p < 0.001 for both comparisons. The amount of TNF-alpha released correlated positively with the percentage expression of CD4 (r = 0.72) and CD25 (r = 0.70) by lymphocytes, and of CD14 (r = 0.63), VLA-4 (r = 0.59), FRD1 (r = 0.67) and 27E10 (r = 0.67) by AM, with p < 0.001 for all correlations. In conclusion, this relationship suggests that these antigens may be considered as cellular activation markers, and that some of these AM antigens may indirectly characterize the AM phenotype that is capable of producing TNF-alpha.

frizzled regulates mirror-symmetric pattern formation in the Drosophila eye

Coordinated morphogenesis of ommatidia during Drosophila eye development establishes a mirror-image symmetric pattern across the entire eye bisected by an anteroposterior equator. We have investigated the mechanisms by which this pattern formation occurs and our results suggest that morphogenesis is coordinated by a graded signal transmitted bidirectionally from the presumptive equator to the dorsal and ventral poles. This signal is mediated by frizzled, which encodes a cell surface transmembrane protein. Mosaic analysis indicates that frizzled acts non-autonomously in an equatorial to polar direction. It also indicates that relative levels of frizzled in photoreceptor cells R3 and R4 of each ommatidium affect their positional fate choices such that the cell with greater frizzled activity becomes an R3 cell and the cell with less frizzled activity becomes an R4 cell. Moreover, this bias affects the choice an ommatidium makes as to which direction to rotate. Equator-outwards progression of elav expression and expression of the nemo gene in the morphogenetic furrow are regulated by frizzled, which itself is dynamically expressed about the morphogenetic furrow. We propose that frizzled mediates a bidirectional signal emanating from the equator.

Analysis of the CD4 coreceptor and activation-induced costimulatory molecules in antigen-mediated mature T lymphocyte death

We have compared the signaling requirements for activation and lymphokine production in mature T lymphocytes to those required for TCR-driven programmed cell death (PCD). Both processes require TCR engagement and ligation of the CD4 coreceptor in the case of a T cell clone that recognizes Ag in the context of an MHC class II molecule. By contrast, stimulation through the CD28/B7 pathway does not appear to positively or negatively influence TCR-induced PCD, although it was required for IL-2 production in both resting and proliferating T cells. T cells that had been activated and induced to proliferate with IL-2 were found to express high levels of IL-2 mRNA upon TCR rechallenge, without a requirement for accessory cells. This was due to a strong up-regulation of the B7-1 molecule, but not the B7-2 molecule, on the T cell surface. These T cells that strongly costimulate each other are highly susceptible to TCR-induced death providing independent evidence that costimulatory signals are not protective. Thus, these results provide evidence that in mature T cells there exists a difference in the requirement for CD28 to achieve activation and IL-2 production compared with TCR-mediated PCD.

Analysis of the CD4 coreceptor and activation-induced costimulatory molecules in antigen-mediated mature T lymphocyte death

We have compared the signaling requirements for activation and lymphokine production in mature T lymphocytes to those required for TCR-driven programmed cell death (PCD). Both processes require TCR engagement and ligation of the CD4 coreceptor in the case of a T cell clone that recognizes Ag in the context of an MHC class II molecule. By contrast, stimulation through the CD28/B7 pathway does not appear to positively or negatively influence TCR-induced PCD, although it was required for IL-2 production in both resting and proliferating T cells. T cells that had been activated and induced to proliferate with IL-2 were found to express high levels of IL-2 mRNA upon TCR rechallenge, without a requirement for accessory cells. This was due to a strong up-regulation of the B7-1 molecule, but not the B7-2 molecule, on the T cell surface. These T cells that strongly costimulate each other are highly susceptible to TCR-induced death providing independent evidence that costimulatory signals are not protective. Thus, these results provide evidence that in mature T cells there exists a difference in the requirement for CD28 to achieve activation and IL-2 production compared with TCR-mediated PCD.

Mechanisms of transport of quinapril in Caco-2 cell monolayers: comparison with cephalexin

PURPOSE

To determine the transport mechanisms of quinapril and cephalexin in Caco-2 cell monolayers, a cell culture model of the human small intestinal epithelium.

METHODS

Uptake, transepithelial transport and intracellular accumulations of these two drugs were measured using Caco-2 cell monolayers grown onto Millicells and magnetically stirred diffusion chambers.

RESULTS

Transepithelial transport, apical (AP)4 uptake and intracellular accumulation of both drugs depended on the maintenance of a transepithelial proton gradient and temperature of the medium. However, quinapril transport and accumulation, which did not display a maximum at approximately pH 6, was more sensitive to proton gradient change, whereas cephalexin transport was more sensitive to concentration change (range 0.5-5 mM). In addition, quinapril (1 mM) transport was decreased significantly (p < 0.05) by 10 mM cephalexin, loracarbef, Gly-Pro and Phe-Pro, but not by enalapril; whereas cephalexin (0.1 mM) transport was decreased significantly (p < 0.05) by all four compounds. Similarly, AP quinapril (1 mM) uptake was also decreased by 10 mM loracarbef, Gly-Pro, cephalexin, and enalapril, but these inhibitory effects (20-50%) were quantitatively less than their inhibitory effects on cephalexin uptake (50-90%). Finally, the AP uptake of quinapril was also significantly (p < 0.05) inhibited by FCCP (10 micrograms/ml), amiloride (0.5 mM), DEP (0.5 mM), and staurosporine (5 nM).

CONCLUSIONS

The transport of quinapril in the Caco-2 cells is via a combination of the carrier-mediated proton gradient-dependent peptide transporter and passive diffusion.

Influence of thyroid status on postnatal maturation of calcium channels, beta-adrenoceptors and cation transport ATPases in rat ventricular tissue

In order to examine the influence of thyroid hormones on the postnatal development of cardiac excitation-contraction coupling, newborn rats were made hypo- or hyperthyroid, and several key factors involved, directly or indirectly, in Ca2+ signaling: L-type Ca2+ channels (1,4-dihydropyridine receptors), Ca(2+)-release channels of sarcoplasmic reticulum (ryanodine receptors), beta-adrenoceptors, thapsigargin-sensitive Ca(2+)-ATPase and Na(+)-K(+)-ATPase (enzyme activity and ouabain receptors), were investigated in membrane fractions from ventricular tissue, collected on day 21. Hypothyroidism induced a moderately lower myocardial density of 1,4-dihydropyridine and ryanodinerece receptors (reduced by 23% and 31%, respectively, with respect to euthyroid controls), and much reduced levels of beta-adrenoceptors, Ca(2+)-ATPase and Na(+)-K(+)-ATPase activities. Hyperthyroidism induced only a moderate (22%) decrease in the myocardial density of 1,4-dihydropyridine receptors and a marked (240%) increase of the alpha 2 isoform of Na(+)-K(+)-ATPase. To analyse the subsarcolemmal localization of L-type channels, microsomal fractions were subfractionated by density equilibration in sucrose gradient. In gradients from control and hyperthyroid rats, most 1,4-dihydropyridine receptors were recovered in high-density subfractions, their distribution following that of ryanodine receptors, whereas, in gradients from hypothyroid rats, most 1,4-dihydropyridine receptors were recovered in low-density subfractions, together with beta-adrenoceptors and Na(+)-K(+)-ATPase. We conclude that thyroid hormones are important for the postnatal changes in the myocardial density of several channels and pumps involved in Ca2+ fluxes, as well as for the postnatal redistribution of L-type Ca2+ channels from non-junctional sarcolemma to junctional structures, a key process for the efficient operation of excitation-contraction coupling in adult ventricular tissue.

[Trigeminal neuralgia caused by microvascular compression of perforation type]

Of 512 patients of trigeminal neuralgia who had undergone microvascular decompression through a retromastoid craniotomy, 4 were caused by microvascular compression of perforation type. In 3 patients, the perineurium of trigeminal nerve was cut longitudinally, the nerve-tract was separated, the perforating blood vessel was pushed to the distal end, and the vessel was made to leave the nerve sensitive area and then decompression materials were put between the separated nerve-tract. The patients were pain-free and the facial sensation was preserved after operation, and no recurrence occurred in 1 to 3 years after operation. The authors realized that there is a sensitive area near the trigeminal nerve sensory root entry zone. When the blood vessel compresses the sensitive area, trigeminal neuralgia is induced, whereas the vessel decompresses the area, the pain is free. So it is a good evidence for the microvascular compression theory and it is more important than the non-perforation type.

Cyclosporin A, rapamycin and FK506 decrease prolactin release from rat pituitary cells in primary culture

It is at present well established that prolactin exerts a non-specific immunoactivating function. In this work we tested whether the immunosuppressant drugs cyclosporin A, FK506 and rapamycin influence prolactin release from rat pituitary cells in primary culture. The tested drugs had no effect on the prolactin release measured during a 2h incubation period, indicating that they do not influence the secretion of prolactin from intracellular stores into the culture medium. During longer incubation times (48h), however, prolactin release was diminished to 56% +/- 18 (10 microM cyclosporin A), 64% +/- 14 (1 microM rapamycin) or 64% +/- 7 (1 microM FK506), suggesting an effect on prolactin production. At these drug concentrations no toxic effects were observed. The data indicate that inhibition of pituitary prolactin synthesis might contribute to the immunosuppressant action of cyclosporin A, rapamycin and FK506.

Gonadotropin-releasing hormone-induced sensitization of calcium-dependent exocytosis in pituitary gonadotrophs

Agonist-induced increases in cytoplasmic calcium concentration ([Ca2+]i) play a pivotal role in regulated exocytosis by promoting the fusion of secretory vesicles with the plasma membrane. In permeabilized and ATP-primed pituitary cells, increases in ambient [Ca2+]i stimulated the release of LH from gonadotrophs with an EC50 of 2-3 microM. In contrast, the responses of intact gonadotrophs to agonist stimulation by GnRH were characterized by transient [Ca2+]i elevations of up to 1.5 microM, followed by a plateau of 300-400 nM. The sensitivity of the exocytotic response of permeabilized cells to [Ca2+]i was significantly increased by GnRH, which reduced the EC50 for [Ca2+]i to the submicromolar concentration range. The stimulatory action of GnRH on LH release in permeabilized cells was not a consequence of intracellular Ca2+ release, but was associated with increased cytidine diphosphate diacylglycerol production. Activation of protein kinase C by phorbol esters caused a similar increase in the Ca2+ sensitivity of LH release from permeabilized cells, and this effect was not additive to that of GnRH. Furthermore, the GnRH-induced increase in the sensitivity of the exocytotic response to Ca2+ was attenuated by inhibitors of protein kinase C. These findings indicate that although elevated [Ca2+]i per se can promote LH release from permeabilized gonadotrophs, concomitant activation of protein kinase C is necessary to support exocytosis at the physiological [Ca2+]i levels that prevail in GnRH-stimulated intact cells. Such sensitization of the Ca(2+)-dependent secretory mechanism by protein kinase C may be an important step in the agonist-induced release of LH from pituitary gonadotrophs.

Dependence of stimulus-transcription coupling on phospholipase D in agonist-stimulated pituitary cells

Stimulation of phospholipase D activity is frequently observed during agonist activation of Ca(2+)-mobilizing receptors, but the cellular functions of this signaling pathway are not well defined. Pituitary gonadotrophs express Ca(2+)-mobilizing receptors for gonadotropin-releasing hormone (GnRH) and endothelin (ET), activation of which stimulates luteinizing hormone secretion and transient expression of c-fos. In pituitary cells and alpha T3-1 gonadotrophs, GnRH action was associated with both initial and sustained diacylglycerol (DG) production, whereas ET-1 induced only a transient DG response. Also, phospholipase D activity, estimated by the production of phosphatidylethanol from phosphatidylcholine in the presence of ethanol, was stimulated by GnRH but not ET-1. Such formation of phosphatidylethanol at the expense of phosphatidic acid (PA) during GnRH-induced activation of phospholipase D significantly reduced the production of PA, DG, and cytidine diphosphate diacylglycerol. Inhibition of PA-phosphohydrolase activity by propranolol also decreased GnRH-induced DG production and, in contrast to ethanol, increased PA and cytidine diphosphate diacylglycerol levels. The fall in DG production caused by ethanol and propranolol was accompanied by inhibition of GnRH-induced c-fos expression, whereas agonist-induced luteinizing hormone release was not affected. In contrast to their inhibitory actions on GnRH-induced early gene expression, neither ethanol nor propranolol affected ET-1-induced c-fos expression, or GnRH- and ET-1-induced inositol trisphosphate/Ca2+ signaling. These findings demonstrate that phospholipase D participates in stimulus-transcription but not stimulus-secretion coupling, and indicate that DG is the primary signal for this action.

Role of protein kinase C isozymes in Fc gamma receptor-mediated intracellular killing of Staphylococcus aureus by human monocytes

Intracellular killing of Staphylococcus aureus by human monocytes after cross-linking Fc gamma R is known to be a phospholipase C (PLC)-dependent process. Activation of PLC leads to the formation of second messengers that synergistically activate protein kinase C (PKC). The aim of this study was to obtain more insight into the role of PKC in Fc gamma R-mediated killing process. PKC inhibitors H-7 and staurosporine markedly suppressed the killing of S. aureus by monocytes stimulated by cross-linking Fc gamma RI or -II. Cross-linking Fc gamma R caused a transient increase in PKC activity in the membranes of monocytes, as measured by Ca2+/phospholipid-dependent phosphorylation of histone. Western blot analysis revealed that cross-linking Fc gamma R stimulated a transient increase in PKC-beta in the membranes of monocytes with kinetics that correlated closely with the translocation of PKC activity. Cross-linking Fc gamma R on monocytes also stimulated the translocation of PKC-epsilon but not PKC-alpha. PMA and 1-oleoyl-2-acetylglycerol (OAG), which caused translocation of PKC-alpha, -beta, and -epsilon, did not stimulate the killing process. Incubation with these PKC activators for 10 min rendered monocytes unresponsive to stimulation of killing of S. aureus via Fc gamma R. It could be that activation of certain PKC isozymes, probably PKC-alpha and -epsilon, by these activators causes feedback inhibition of PLC and, consequently, the killing in monocytes, because PMA blocks the Fc gamma R-mediated intracellular inositol(1,4,5)P3 formation and PKC translocation. Together, our results indicate that PKC isozymes play an important role in both stimulation and inhibition of the Fc gamma R-mediated intracellular killing of bacteria by monocytes.

Role of protein kinase C isozymes in Fc gamma receptor-mediated intracellular killing of Staphylococcus aureus by human monocytes

Intracellular killing of Staphylococcus aureus by human monocytes after cross-linking Fc gamma R is known to be a phospholipase C (PLC)-dependent process. Activation of PLC leads to the formation of second messengers that synergistically activate protein kinase C (PKC). The aim of this study was to obtain more insight into the role of PKC in Fc gamma R-mediated killing process. PKC inhibitors H-7 and staurosporine markedly suppressed the killing of S. aureus by monocytes stimulated by cross-linking Fc gamma RI or -II. Cross-linking Fc gamma R caused a transient increase in PKC activity in the membranes of monocytes, as measured by Ca2+/phospholipid-dependent phosphorylation of histone. Western blot analysis revealed that cross-linking Fc gamma R stimulated a transient increase in PKC-beta in the membranes of monocytes with kinetics that correlated closely with the translocation of PKC activity. Cross-linking Fc gamma R on monocytes also stimulated the translocation of PKC-epsilon but not PKC-alpha. PMA and 1-oleoyl-2-acetylglycerol (OAG), which caused translocation of PKC-alpha, -beta, and -epsilon, did not stimulate the killing process. Incubation with these PKC activators for 10 min rendered monocytes unresponsive to stimulation of killing of S. aureus via Fc gamma R. It could be that activation of certain PKC isozymes, probably PKC-alpha and -epsilon, by these activators causes feedback inhibition of PLC and, consequently, the killing in monocytes, because PMA blocks the Fc gamma R-mediated intracellular inositol(1,4,5)P3 formation and PKC translocation. Together, our results indicate that PKC isozymes play an important role in both stimulation and inhibition of the Fc gamma R-mediated intracellular killing of bacteria by monocytes.

Lymphocyte subsets in bronchoalveolar lavage fluid of children without bronchopulmonary disease

Bronchoalveolar lavage (BAL) is increasingly used in the pediatric age group. However, normal values for BAL fluid (BALF) constituents are lacking. As part of an investigation to define reference values in children, we studied lymphocyte surface markers of BALF in 28 children 3 to 16 yr of age without bronchopulmonary disease. All of them were undergoing elective surgery for nonpulmonary illnesses. BAL was performed under general anaesthesia with tracheal intubation. A flexible bronchoscope (Pentax 3.5 or 4.9 mm) was wedged into the middle lobe or into one of its segments, and 3 x 1 ml/kg body weight normal saline warmed to body temperature were instilled and immediately withdrawn. The first sample was studied separately; subsequent samples were pooled for analysis. Studies on lymphocyte surface markers were performed on the pooled sample only. The distribution of B-cells, pan T-cells, and CD57 positive cells was within the range reported for adult subjects. However, CD4/CD8 ratios were lower than in adults (0.7 +/- 0.4, mean +/- SD). This decrease in the CD4/CD8 ratio was caused by an increase in CD8 cells. Comparative analysis of blood and BALF lymphocytes in a subgroup of children showed that CD4/CD8 ratios in blood were within the normal range reported for this age group and significantly higher when compared with BALF. The lower CD4/CD8 ratios in normal children have to be considered in the interpretation of BALF in children with pulmonary diseases.

Effect of intracerebroventricular injection of somatostatin or GABA on pain threshold and contents of GABA or somatostatin in rat brain

AIM

To study the interactive influence of somatostatin (Som) and GABA in the brain and its relation to the pain modulation.

METHOD

Using radioimmunoassay, amino acid analyzer and measurement of pain threshold.

RESULTS

Som 10 micrograms i.c.v. increased the pain threshold (from 4.2 +/- 0.2 to 7.0 +/- 1.1 s) of the rat, but reduced the content of GABA from 2.3 +/- 0.3 to 1.6 +/- 0.4 mumol g-1 in hippocampus and from 2.4 +/- 0.4 to 1.5 +/- 0.2 mmol kg-1 in brain stem. After depletion of the Som in brain by i.c.v. cysteamine (Cys, 600 micrograms), the content of GABA in hippocampus and brain stem was also reduced without modification of the pain threshold. GABA 1500 micrograms i.c.v. had no effect on the pain threshold, however, caused a decrease of Som content from 55 +/- 4 to 37 +/- 5 ng g-1 in hippocampus and from 84 +/- 4 to 55 +/- 6 ng g-1 in brain stem, which was blocked by bicuculline (10 micrograms). After reduced of the GABA content in brain by subcutaneous injection of isoniazid (300 mg kg-1), Som content of the hippocampus and rain stem was markedly elevated.

CONCLUSION

Som and GABA inhibited each other, unrelated to their pain modulation.

MCML--Monte Carlo modeling of light transport in multi-layered tissues

A Monte Carlo model of steady-state light transport in multi-layered tissues (MCML) has been coded in ANSI Standard C; therefore, the program can be used on various computers. Dynamic data allocation is used for MCML, hence the number of tissue layers and grid elements of the grid system can be varied by users at run time. The coordinates of the simulated data for each grid element in the radial and angular directions are optimized. Some of the MCML computational results have been verified with those of other theories or other investigators. The program, including the source code, has been in the public domain since 1992.

Microsatellite DNA and isozyme variability in a west African population of Anopheles gambiae

Microsatellites are defined as tracts of tandemly repeated short DNA sequences. Polymorphisms in this class of DNA are currently being used to generate a genetic map of the mosquito Anopheles gambiae. In the present study we explore the potential of microsatellites as a tool for studying the genetic structure of natural populations of this malaria vector. Genetic polymorphism at twenty enzyme coding gene loci and eleven microsatellite DNA loci was surveyed in a population of An. gambiae from Mali, West Africa. All of the microsatellite loci surveyed were polymorphic, as compared to 40% of the isozyme loci. The mean heterozygosity for the isozyme loci was only 0.097 (+/- 0.0035), but for the microsatellite loci it was 0.732 (+/- 0.060). The pattern of variability was very different between isozymes and microsatellites. Typically, at an isozyme locus a single allele occurred at a frequency > or = 0.75, whereas at microsatellite loci the most common allele had a frequency < 0.50. We conclude that microsatellites provide a rich source of genetic polymorphisms for the study of the population genetics of An. gambiae and are in many ways superior to isozymes for this purpose. We discuss the potential for utilizing genetically mapped microsatellite loci to explore the effect of chromosomal inversions on the distribution of genetic polymorphisms in An. gambiae.

[A study on expression of epidermal growth factor receptor in pleomorphic adenoma of lacrimal gland]

Expression of epidermal growth factor (EGF) receptor was examined in 32 cases of pleomorphic adenoma of lacrimal gland by means of an immunohistochemical method. While normal lacrimal glands were all negative for the antigen, EGF receptor was positive in 10 pleomorphic adenomas and the positive staining was mainly limited in the tumor cells in trabecular or duct-like arrangement or squamous metaplastic epithelium. These data suggest that the expression of EGF receptor be significantly higher in pleomorphic adenoma than in normal lacrimal gland, and also suggest that EGF receptor be expressed in the neoplastic cells which are considered to be of duct origin.

[Experimental study on in vivo hematopoietic regulation of interleukin-6 gene therapy]

Interleukin-6 (IL-6), a pleiotropic cytokine, is involved in extensive immune regulation and hematopoietic regulation. We observed the effect of fibroblast mediated human IL-6 gene therapy on hematopoiesis. The platelet counts started to increase at day 4 after implantation of IL-6 highly secreting fibroblast cells and peaked at day 10 and lasted at high level for 22 days. The neutrophil counts were elevated after their implantation, but WBC did not show any remarkable increase. The CFU-GM and CFU-MK in bone marrow and spleen were also increased significantly. The results demonstrated that fibroblasts mediated human IL-6 gene therapy can significantly augment in vivo hematopoietic functions in bone marrow and spleen and elevate the number of nuetrophils and platelets. This study provides a new approach to treat thrombopenia and chemotherapy or radiotherapy-induced hematopoietic suppression.

Effects of the phospholipase-C inhibitor, U73122, on signaling and secretion in pituitary gonadotrophs

The effects of inhibition of phosphoinositide hydrolysis by U73122 [1-(6-[17 beta-3-methoxyestra-1,3,5- (10) triene-17-yl] amino/hexyl) 1H-pyrroledione] and neomycin on agonist-stimulated intracellular signaling and secretory responses were analyzed in cultured pituitary cells and alpha T3-1 gonadotrophs. GnRH (100 nM)- and endothelin-1 (ET-1; 100 nM)-induced inositol (1,4,5)-trisphosphate and diacylglycerol formation in normal cells and immortalized gonadotrophs were reduced by U73122 in a concentration-dependent manner, with IC50 values of about 2 microM and complete inhibition at 10 microM U73122. Neomycin also reduced GnRH- and ET-induced inositol phosphate production in both cell types. Agonist-induced intracellular Ca2+ responses were also inhibited in both cell types by U73122 and neomycin at the same concentrations that inhibited their inositol phosphate responses. In cultured pituitary cells, agonist-induced LH release was inhibited by U73122 and neomycin in a dose-dependent manner. In perifused pituitary cells, U73122 completely inhibited GnRH- and ET-1-induced LH release, but after 10 min caused a progressive and substantial increase in basal LH release. In static cultures, U73122 inhibited agonist-induced LH response at low concentrations (up to 3 microM), but stimulated LH release at higher concentrations due to direct activation of exocytosis by the compound. When added alone, U73122 caused a concentration-dependent increase in LH release with an EC50 of about 7 microM and a maximum response similar that that elicited by GnRH. The stimulatory action of U73122 on LH release was not reduced in the absence of extracellular Ca2+. In contrast to cultured pituitary cells, alpha T3-1 gonadotrophs showed only constitutive exocytosis that was not affected by either neomycin or U73122. These results demonstrate that GnRH and ET(A) receptors are coupled to the phosphoinositide/Ca2+ transduction system in pituitary gonadotrophs, and provide evidence for the dependence of agonist-regulated exocytosis on this signaling pathway. The ability of U73122 to stimulate LH release could reflect an additional action of the compound at late steps in the exocytic pathway.

Soluble CD14 is increased in bronchoalveolar lavage of active sarcoidosis and correlates with alveolar macrophage membrane-bound CD14

CD14 is a myeloid differentiation antigen which exists in a membrane-bound (55 kD) and a soluble (48 kD) form. This antigen is a receptor for lipopolysaccharide (LPS) structures and triggers the production of various cytokines. The aim of this study was to evaluate whether in active sarcoidosis, a disease with increased proportions of alveolar macrophages (AM) with CD14 expression in BAL fluid, the soluble form of CD14 (sCD14) is also increased. The sCD14 levels were measured in BAL fluid with an ELISA, and membrane-bound CD14 was determined by an immunoperoxidase assay, in active sarcoidosis (n = 13), inactive sarcoidosis (n = 9), idiopathic pulmonary fibrosis (IPF) (n = 6), and control subjects (n = 8). Higher concentrations of sCD14 were present in BAL fluid of patients with active sarcoidosis (58 +/- 34 ng/ml) than in those with inactive disease (13 +/- 10 ng/ml), patients with IPF (5 +/- 5 ng/ml), or control subjects (10 +/- 8% ng/ml) (p < 0.01). Similarly, the proportions of AM expressing membrane-bound CD14 were increased in active sarcoidosis (91 +/- 6%) compared with inactive sarcoidosis (82 +/- 6%), patients with IPF (76 +/- 13%), and control subjects (79 +/- 9%) (p < .05). In sarcoidosis, a significant correlation was found between the sCD14 concentration in BAL fluid and AM membrane expression of CD14 (r = 0.57, p < 0.01). We conclude that sCD14 is increased in BAL of active sarcoidosis suggesting a potential role for this substance as marker of activity and in the pathogenesis of pulmonary sarcoidosis.

Peptide transporter function and prolidase activities in Caco-2 cells: a lack of coordinated expression

Peptide transport and prolidase activities were measured to determine whether the expression of these two components of protein nutrition are coordinately regulated; i.e., whether an increase in the peptide transporter function will necessarily lead to a higher prolidase activity, or vice versa. The results indicated that peptide transporter function and prolidase activity respond differently to cell differentiation and feeding schedules. The results also indicated that peptide transport and prolidase activities were different in two Caco-2 cell "clones", with S-K cells transported peptides at higher rates but had lower total prolidase activities, when compared to ATCC cells. These results suggest that the expression of the peptide transporter function and prolidase activity is not coordinated. In addition, both the transporter and the prolidase activities affected the overall transport of Phe when given as the dipeptide Phe-Pro, supporting the notion that intestinal absorption of peptides is an essential component of amino acid absorption. In conclusion, the evidence suggests that the peptide transporter function and prolidase activity are not coordinately expressed by the human intestinal Caco-2 cells.

Autocrine feedback death and the regulation of mature T lymphocyte antigen responses

Antigen-induced T cell death is an important regulatory mechanism in the peripheral immune system. Evidence suggests that this process depends on T cell growth-inducing lymphokines such as IL-2 and occurs in proportion to the degree of T cell receptor occupancy. Strong T cell receptor stimulation leads to the synthesis of death molecules such as Fas ligand and tumor necrosis factor that cause T cell suicide. We propose that T cell death under these circumstances is the culmination of a feedback control mechanism termed propriocidal regulation or autocrine feedback death that regulates the expansion of specific T cell clones under conditions of high lymphokine and antigen load. In a quasi-stochastic system such as the antigen receptor repertoire, feedback information may be essential for the appropriate regulation of peripheral immune responses. Our understanding of this feedback mechanism affords a means to manipulate antigen-specific T cell death in vivo. The application of this approach to the therapy of T cell-medicated immunological diseases is discussed.

Comparison of the transport characteristics of D- and L-methionine in a human intestinal epithelial model (Caco-2) and in a perfused rat intestinal model

Absorption mechanisms of L- and D-methionine (MET) in an in vitro cultured human intestinal epithelial cell model (Caco-2) and an in situ perfused rat intestinal model were investigated to determine if the kinetic characteristics of absorption are comparable in these two popular absorption models. The results indicate that the transport of L- and D-MET were concentration-dependent in both model systems, and displayed comparable Km values. The Km value for L-MET is 1.34 mM in the Caco-2 model and 3.6 mM in the perfused rat intestinal model, while the Km value for D-MET is 1.79 mM in the Caco-2 model and 2.87 mM in the perfused rat intestinal model. Although the Jmax values were not comparable because of significant methodology differences, the Jmax values for L-MET were always higher than that for D-MET. In addition, transport of L- and D-MET across the Caco-2 cell monolayers were also inhibited by 10 mM Phe and Lys while MeAIB, Pro and Glu were generally ineffective. Similar results were also observed with these inhibitors in the perfused rat intestinal model with the exception that a combination of Pro and Glu stimulated the uptake of L-MET. In conclusion, the transport characteristics of L- and D-MET are comparable in both model systems.

Reduction of tomato polygalacturonase beta subunit expression affects pectin solubilization and degradation during fruit ripening

The developmental changes that accompany tomato fruit ripening include increased solubilization and depolymerization of pectins due to the action of polygalacturonase (PG). Two PG isoenzymes can be extracted from ripe fruit: PG2, which is a single catalytic PG polypeptide, and PG1, which is composed of PG2 tightly associated with a second noncatalytic protein, the beta subunit. Previous studies have correlated ripening-associated increases in pectin solubilization and depolymerization with the presence of extractable PG1 activity, prior to the appearance of PG2, suggesting a functional role for the beta subunit and PG1 in pectin metabolism. To assess the function of the beta subunit, we produced and characterized transgenic tomatoes constitutively expressing a beta subunit antisense gene. Fruit from antisense lines had greatly reduced levels of beta subunit mRNA and protein and accumulated < 1% of their total extractable PG activity in ripe fruit as PG1, as compared with 25% for wild type. Inhibition of beta subunit expression resulted in significantly elevated levels of EDTA-soluble polyuronides at all stages of fruit ripening and a significantly higher degree of depolymerization at later ripening stages. Decreased beta subunit protein and extractable PG1 enzyme activity and increased pectin solubility and depolymerization all cosegregated with the beta subunit antisense transgene in T2 progeny. These results indicate (1) that PG2 is responsible for pectin solubilization and depolymerization in vivo and (2) that the beta subunit protein is not required for PG2 activity in vivo but (3) does play a significant role in regulating pectin metabolism in wild-type fruit by limiting the extent of pectin solubilization and depolymerization that can occur during ripening. Whether this occurs by direct interaction of the beta subunit with PG2 or indirectly by interaction of the beta subunit with the pectic substrate remains to be determined.

Protein tyrosine kinase activity is essential for Fc gamma receptor-mediated intracellular killing of Staphylococcus aureus by human monocytes

Our previous study revealed that the intracellular killing of Staphylococcus aureus by human monocytes after cross-linking Fc gamma receptor I (Fc gamma RI) or Fc gamma RII is a phospholipase C (PLC)-dependent process. The aim of the present study was to investigate whether protein tyrosine kinase (PTK) activity plays a role in the Fc gamma R-mediated intracellular killing of bacteria and activation of PLC in these cells. The results showed that phagocytosis of bacteria by monocytes was not affected by the PTK inhibitors genistein and tyrphostin-47. The intracellular killing of S. aureus by monocytes after cross-linking Fc gamma RII or Fc gamma RII with anti-Fc gamma R monoclonal antibody and a bridging antibody or with human immunoglobulin G (IgG) was inhibited by these compounds in a dose-dependent fashion. The production of O2- by monocytes after stimulation with IgG or IgG-opsonized S. aureus was almost completely blocked by the PTK inhibitor. These results indicate that inhibition of PTK impairs the oxygen-dependent bactericidal mechanisms of monocytes. Genistein and tyrphostin-47, which do not affect the enzymatic activity of purified PLC, prevented activation of PLC after cross-linking Fc gamma RI or Fc gamma RII, measured as an increase in the intracellular inositol 1,4,5-trisphosphate concentration. Cross-linking Fc gamma RI or Fc gamma RII induced rapid tyrosine phosphorylation of several proteins in monocytes, one of which was identified as PLC-gamma 1, and the phosphorylation could be completely blocked by PTK inhibitors, leading to the conclusion that activation of PLC after cross-linking Fc gamma R in monocytes is regulated by PTK activity. Together, these results demonstrate that PTK activity is essential for the activation of PLC which is involved in the Fc gamma R-mediated intracellular killing of S. aureus by human monocytes.

Effect of pituitary adenylate cyclase-activating polypeptide 38 on growth hormone and prolactin expression

Time- and dose-dependent effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on prolactin (PRL) and growth hormone (GH) release were examined in static and dynamic rat pituitary cell incubations and on different pituitary cell (sub)populations separated according to their density on a discontinuous Percoll gradient. Quantitative in situ hybridization histochemistry allowed us to examine in parallel the effects of PACAP on PRL and GH gene expression. PACAP did not alter GH or PRL secretion in a dynamic superfusion system, in any cell population tested. Static incubations (30 min, 2-36 h) with PACAP 38 resulted in a significant increase in GH release and stimulated GH synthesis, as measured by the cytoplasmic accumulation of GH mRNA in the somatotrophs. These effects on synthesis and release were also observed after the enrichment of GH cells on Percoll gradients. PRL release was not altered by longer periods of incubation. Although no significant changes were observed in PRL secretion after 38 h, accumulation of cytoplasmic PRL mRNA was significantly stimulated in total pituitary cell suspension. After fractioning lactotrophs on Percoll gradients, the stimulatory effect of PACAP on PRL synthesis was lost. These results suggest that PACAP stimulates GH release and synthesis, and that it may act as a physiological regulator of this cell type. The PRL cell is not the most likely target cell type for PACAP. Effects observed on PRL synthesis in the total cell population may involve paracrine action of other hormone- or non-hormone-secreting cell types.

Specific beta-adrenergic receptor binding of carazolol measured with PET

Carazolol is a promising high-affinity beta-adrenergic receptor ligand for the noninvasive determination of beta receptor status using PET. Earlier investigations demonstrated specific receptor binding of carazolol in mice. These PET studies with S(-)-[2"-11C]carazolol in pigs were performed to explore the utility of the tracer for PET receptor studies.

METHODS

Tracer uptake in the heart and lung was measured by PET as a function of time. Receptors were blocked with propranolol and different doses of ICI 118,551 to estimate specific binding. Fluorine-18-1"-Fluorocarazolol and the less active R-enantiomer of [11C]-carazolol were also studied.

RESULTS

Specific receptor binding was 75% of the total uptake in the heart, preventable and displaceable by propranolol. Dose-dependent competition showed that carazolol binds in vivo to beta 1 and to beta 2 subtypes. Uptake of the labeled R(+) enantiomer of carazolol was not receptor-specific.

CONCLUSIONS

Carazolol labeled with 11C or 18F is a strong candidate for use in receptor estimation with PET. The in vivo observations were consistent with its known high affinity and slow receptor dissociation rate. Its high specific receptor uptake and low metabolism allow existing kinetic models to be applied for receptor measurements. The 11C label is convenient for repeated administrations, though 18F allowed the long observation periods necessary for measurement of the receptor dissociation rate. If needed, nonspecific uptake can be estimated without pharmacologic intervention by using the labeled R enantiomer.

Synthesis, binding properties, and 18F labeling of fluorocarazolol, a high-affinity beta-adrenergic receptor antagonist

New beta-adrenergic receptor antagonists, 2-(R)-(+)- and 2-(S)-(-)-1-(9H-carbazol-4-yl-oxy)-3-[[1-(fluoromethyl)ethyl]amino ]-2-propanol ((S)- and (R)-fluorocarazolols), were labeled with fluorine-18 at the no-carrier-added level by reductive alkylation of desisopropylcarazolol (4-(2-hydroxy-3-amino-1-propoxy)carbazole) with [18F]fluoroacetone. The latter was prepared by nucleophilic substitution of fluoride on acetol tosylate and may serve as a useful synthetic precursor for other radiotracers. The radiochemical yield of [18F]fluorocarazolol (500-1200 Ci/mmol) from [18F]fluoride was 40 +/- 10% at the end of the 45 min synthesis. Chiral HPLC showed > 99% enantiomeric purity of 2-(S)- and 2-(R)-[18F]fluorocarazolols. The log P of fluorocarazolol was 2.2 at pH 7.4. The in vitro KD values of (S)- and (R)-fluorocarazolol for the beta-adrenergic receptor were measured in a rat heart preparation to be KD = 68 and 1128 pM, respectively. Biodistribution experiments in mice demonstrated specific beta-adrenergic receptor binding of (S)-[18F]fluorocarazolol. (R)-[18F]fluorocarazolol showed no observable specific binding to beta-receptors in vivo. The uptake of (R)-[18F]fluorocarazolol may therefore be used as an estimation of nonspecific binding. Positron emission tomography images of pigs showed receptor-specific uptake of (S)-[18F]fluorocarazolol in the heart and lung. Washout of dissociated ligand from the tissue was observed only after 70 min postinjection. The maximum ratio of specific to nonspecific uptake in pig heart and lung was ca. 10 at 150 min postinjection. Observed levels of fluorocarazolol metabolites in mouse and pig blood were relatively low and remained fairly constant during the period from 10 to 180 min postinjection. These results indicate that (S)-(-)-[18F]fluorocarazolol is of interest for use as a radiopharmaceutical for estimation of beta-adrenergic receptors with positron tomography.

Cloning and expression of phosphatidylcholine-hydrolyzing phospholipase D from Ricinus communis L

Phosphatidylcholine-hydrolyzing phospholipase D (PLD; EC 3.1.4.4) has been proposed to play an important role in the signal transduction pathways in animals and in various cellular processes in plants. To unravel the structure of PLD and further the investigation of its modes of regulation and cellular function, we have isolated a PLD cDNA from castor bean (Ricinus communis L. var. Hale) by using oligonucleotide probes based on the N-terminal amino acid sequence of purified PLD protein. The nucleotide sequence of the castor bean PLD cDNA clone contains an open reading frame of 2424 bases encoding an 808-amino acid protein of 92,400 daltons. Expression of this PLD cDNA clone in Escherichia coli resulted in the accumulation of a functional PLD able to catalyze hydrolysis and transphosphatidylation reactions, demonstrating that the introduction of this single gene product was sufficient to confer PLD activity and that both the hydrolysis and transphosphatidylation reactions are catalyzed the single PLD protein. Comparison of the deduced protein sequence of the clone to the N-terminal amino acid sequence of purified PLD revealed that the mature PLD protein is preceded by a 30-amino acid leader peptide. Removal of this leader peptide resulted in accumulation of non-functional PLD and also increased PLD degradation in E. coli, suggesting that this leader peptide may be involved in proper folding of PLD. The primary structure of the castor bean PLD exhibits no significant similarities with sequences of other cloned lipolytic enzymes.

Differential Expression of the Two Subunits of Tomato Polygalacturonase Isoenzyme 1 in Wild-Type and rin Tomato Fruit

The [beta] subunit of tomato (Lycopersicon esculentum Mill.) fruit polygalacturonase 1 is a cell wall glycoprotein that binds to and apparently regulates the catalytic PG2 polypeptide in vivo. [beta] Subunit and polygalacturonase 2 (PG2) expression have been investigated in both wild-type and ripening inhibitor (rin) mutant fruit. During fruit development and ripening, [beta] subunit expression was unrelated to expression of the catalytic PG2 protein. In wild-type fruit, [beta] subunit mRNA and protein were first detected early in development and increased to maximal levels before PG2 mRNA and protein were detected. At the onset of ripening [beta] subunit mRNA decreased dramatically, but [beta] subunit protein levels remained stable. In rin fruit, which fail to ripen, [beta] subunit expression was similar to that in wild type, although PG2 mRNA and protein were not detected. These data suggest that [beta] subunit expression is ethylene independent and regulated primarily by developmental cues. This conclusion is supported by results from ethylene-treated immature (20 days after pollination) wild-type and rin fruit in which no significant differences were observed in [beta] subunit expression patterns in response to ethylene treatment. Surprisingly, RNA blot analysis indicated that catalytic PG2 mRNA was induced in immature rin fruit after 3 d of exogenous ethylene treatment. In addition, [beta] subunit mRNA and protein were also detected at lower levels in root, leaf, and flower tissues of both genotypes, suggesting a broader functional role for the protein.

Catalytic formation of a nitrogenase iron-sulfur cluster

Biological nitrogen fixation is catalyzed by nitrogenase, an enzyme comprised of two component proteins called the Fe protein and the MoFe protein. Both nitrogenase component proteins contain metalloclusters. The Azotobacter vinelandii nifS gene product (NifS), which is required for full activation of the nitrogenase component proteins, is a pyridoxal phosphate enzyme and is able to catalyze the desulfurization of L-cysteine to yield sulfur and L-alanine (Zheng, L., White, R. H., Cash, V.L., Jack, R.F., and Dean, D.R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2754-2758). An enzyme-bound persulfide that was identified as an intermediate in the cysteine desulfurization reaction catalyzed by NifS has been suggested as a possible S-donor in formation of the iron-sulfide cores of the nitrogenase metalloclusters. In the present work it is shown that NifS is able to effectively catalyze activation of an apo-form of the Fe protein that was prepared by removal of its Fe4S4 cluster using the chelator, alpha,alpha'-dipyridyl. The reconstitution reaction includes apo-Fe protein, NifS, L-cysteine, ferrous ion, dithiothreitol, and MgATP. Reconstitution of the inactive apo-Fe protein catalyzed by NifS results in 80-95% recovery of the original activity and yields an Fe protein having the normal electron paramagnetic resonance spectra properties associated with the Fe protein's Fe4S4 cluster. An altered NifS protein, NifS-Ala325, which lacks the desulfurase activity and is unable to from the NifS-bound persulfide, is not able to catalyze reactivation of the apo-Fe protein. These in vitro results support the proposal that NifS activity provides the inorganic sulfide necessary for in vivo formation of the nitrogenase metalloclusters. Moreover, because NifS has recently been shown to be a member of a highly homologous gene family, it appears that pyridoxal phosphate chemistry might play a general role in iron-sulfur cluster assembly.

Mechanism for the desulfurization of L-cysteine catalyzed by the nifS gene product

The nifS gene product (NIFS) is a pyridoxal phosphate binding enzyme that catalyzes the desulfurization of L-cysteine to yield L-alanine and sulfur. In Azotobacter vinelandii this activity is required for the full activation of the nitrogenase component proteins. Because the nitrogenase component proteins, Fe protein and MoFe protein, both contain metalloclusters which are required for their respective activities, it is suggested that NIFS participates in the biosynthesis of the nitrogenase metalloclusters by providing the inorganic sulfur required for Fe-S core formation [Zheng, L., White, R. H., Cash, V. L. Jack, R. F., & Dean, D. R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2754-2758]. In the present study the mechanism for the desulfurization of L-cysteine catalyzed by NIFS was determined in the following ways. First, the substrate analogs, L-allylglycine and vinylglycine, were shown to irreversibly inactivate NIFS by formation of a gamma-methylcystathionyl or cystathionyl residue, respectively, through nucleophilic attack by an active site cysteinyl residue on the corresponding analog-pyridoxal phosphate adduct. Second, this reactive cysteinyl residue, which is required for L-cysteine desulfurization activity, was identified as Cys325 by the specific alkylation of that residue and by site-directed mutagenesis experiments. Third, the formation of an enzyme-bound cysteinyl persulfide was identified as an intermediate in the NIFS-catalyzed reaction. Fourth, evidence was obtained for an enamine intermediate in the formation of L-alanine.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential activation of phospholipase-C and -D in agonist-stimulated gonadotrophs

The contributions of phospholipase-C and -D to diacylglycerol (DG) formation during agonist-induced cell signaling were investigated in rat pituitary cells and alpha T3-1 gonadotrophs. In both cell types, GnRH caused a biphasic increase in DG formation, with an initial spike within 60 sec, followed by a larger and sustained rise to reach a second peak after 15 min of stimulation. Both phases of DG production were temporally correlated with inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] formation, consistent with the dependence of DG formation on phospholipase-C-mediated phosphoinositide hydrolysis. However, the ability of GnRH to stimulate phosphatidylethanol (PEt) in the presence of ethanol suggested that phospholipase-D may also participate in DG formation. Two inhibitors of phospholipase-C-dependent phosphoinositide hydrolysis, U73122 and neomycin sulfate, reduced the PEt as well as the Ins(1,4,5)P3 response to GnRH, indicating that phospholipase-D is activated during phospholipase-C-dependent signaling in pituitary gonadotrophs. The production of both DG and PEt was increased by treatment with the active phorbol ester phorbol 12-myristate 13-acetate (PMA), but not with inactive 4 alpha-phorbol 13-didecanoate, indicating that stimulation of protein kinase-C leads to activation of phospholipase-D. In accord with this, GnRH- and PMA-induced elevations of DG and PEt production were attenuated or abolished in protein kinase-C-depleted cells. In contrast, short and long term stimulation with PMA had no effect on basal inositol phosphate production. Also, GnRH-induced inositol phosphate production was not affected by protein kinase-C depletion. Finally, U73122 and neomycin sulfate did not inhibit PMA-induced PEt formation. These data indicate that GnRH activates a dual phospholipase pathway in a sequential and synchronized manner; phospholipase-C initiates the biphasic increase in Ins(1,4,5)P3 and DG formation, and protein kinase-C mediates the integration of phospholipase-D into the signaling response during the sustained phase of agonist stimulation.

Optimization by trees on simple adaptive landscapes

We evaluate the optimizing ability (rate of adaptation) of trees on simple adaptive landscapes. At points away from a peak, there is a strong negative relationship between rate of adaptation and tree precision P, a relationship that is independent of the size of the tree. P measures the variability among trial solutions generated by the tree: high precision trees have low variability, low precision trees have high variability. Near a peak, the situation reverses, with high precision trees showing higher rates of adaptation than low precision trees; however, for all trees, the absolute rate of adaptation is uniformly low. On multiple-peak landscapes, the probability of crossing an adaptive valley from a lower peak to a higher peak is also negatively correlated with tree precision. These results suggest that under a wide range of conditions, trees with low precision are, on average, the best optimizers.