Serotonin in the developing stomatogastric system of the lobster,Homarus americanus

We studied the development of the serotonergic modulation of the stomatogastric nervous system of the lobster, Homarus americanus. Although the stomatogastric ganglion (STG) is present early in embryonic development, serotonin immunoreactivity is not visible in the STG until the second larval stage. However, incubation of the STG with exogenous serotonin showed that a serotonin transporter is present in embryonic and early larval stages. Serotonin uptake was blocked by paroxetine and 0% Na(+) saline. The presence of a serotonin transporter in the embryonic STG suggests that hormonally liberated serotonin could be taken up by the STG, and potentially released as a "borrowed transmitter". Consistent with a potential hormonal role, serotonin is found in the pericardial organs, a major neurosecretory structure, by midembryonic development. The rhythmic motor patterns produced by embryonic and larval STGs were decreased in frequency by serotonin. Lateral Pyloric (LP) neuron-evoked excitatory junctional potentials (EJPs) in the embryos and the first larval stage (LI) were larger, slower, and more variable than those in the adult. The amplitude of adult LP neuron-evoked EJPs was increased more than twofold in serotonin, but in embryos and LI preparations this effect was negligible. In embryos and LI preparations, serotonin increased the occurrence of muscle fiber action potentials and altered the EJP wave-form. These data demonstrate that serotonin receptors are present in the stomatogastric nervous system early in development, and suggest that the role of serotonin changes from modulation of muscle fiber excitability early in development to enhancement of neurally evoked EJPs in the adult.     

Presence of cyclic nucleotide phosphodiesterases PDE1A,existing as a stable complex with calmodulin,and PDE3A in human spermatozoa

Mammalian sperm motility, capacitation, and the acrosome reaction are regulated by signal transduction systems involving cAMP as a second messenger. Levels of cAMP are controlled by two key enzymes, adenylyl cyclase and phosphodiesterases (PDEs), the latter being involved in cAMP degradation. Calmodulin-dependent PDE (PDE1) and cAMP-specific PDE (PDE4) activities were previously identified in spermatozoa via the use of specific inhibitors. Here we report that human sperm PDEs are associated with the plasma membrane (50%-60%) as well as with the particulate fraction (30%-50%) and have more affinity for cAMP than cGMP. Immunocytochemical data indicated that PDE1A, a variant of PDE1, is localized on the equatorial segment of the sperm head as well as on the mid and principal pieces of the flagellum, and that PDE3A is found on the postacrosomal segment of the sperm head. Immunoblotting confirmed the presence of PDE1A and PDE3A isoforms in spermatozoa. Milrinone, a PDE3 inhibitor, increased intracellular levels of cAMP by about 15% but did not affect sperm functions, possibly because PDE3 represents only a small proportion of the sperm total PDE activity (10% and 25% in Triton X-100 soluble and particulate fractions, respectively). PDE1A activity in whole sperm extract or after partial purification by anion-exchange chromatography was not stimulated by calcium + calmodulin. Results obtained with electrophoresis in native conditions indicated that calmodulin is tightly bound to PDE1A. Incubation with EGTA + EDTA, trifluoperazine, or urea did not dissociate the PDE1A-calmodulin complex. These results suggest that PDE1A is permanently activated in human spermatozoa.     

The heavy chain of conventional kinesin interacts with the SNARE proteins SNAP25 and SNAP23

Recent studies on the conventional motor protein kinesin have identified a putative cargo-binding domain (residues 827-906) within the heavy chain. To identify possible cargo proteins which bind to this kinesin domain, we employed a yeast two-hybrid assay. A human brain cDNA library was screened, using as bait residues 814-963 of human ubiquitous kinesin heavy chain. This screen initially identified synaptosome-associated protein of 25 kDa (SNAP25) as a kinesin-binding protein. Subsequently, synaptosome-associated protein of 23 kDa (SNAP23), the nonneuronal homologue of SNAP25, was also confirmed to interact with kinesin. The sites of interaction, determined from in vivo and in vitro assays, are the N-terminus of SNAP25 (residues 1-84) and the cargo-binding domain of kinesin heavy chain (residues 814-907). Both regions are composed almost entirely of heptad repeats, suggesting the interaction between heavy chain and SNAP25 is that of a coiled-coil. The observation that SNAP23 also binds to residues 814-907 of heavy chain would indicate that the minimal kinesin-binding domain of SNAP23 and SNAP25 is most likely residues 45-84 (SNAP25 numbering), a heptad-repeat region in both proteins. The major binding site for kinesin light chain in kinesin heavy chain was mapped to residues 789-813 at the C-terminal end of the heavy chain stalk domain. Weak binding of light chain was also detected at the N-terminus of the heavy chain tail domain (residues 814-854). In support of separate binding sites on heavy chain for light chain and SNAPs, a complex of heavy and light chains was observed to interact with SNAP25 and SNAP23.     

Strong memory CD8+ T cell responses against immunodominant and three new subdominant HLA-B27-restricted influenza A CTL epitopes following secondary infection of HLA-B27 transgenic mice

We previously showed that the known HLA-B27-restricted influenza A epitope identified from human studies, NP.383-391, was recognized by CTLs following influenza A infection of transgenic (Tg) HLA-B27/H2 class I-deficient (H2 DKO) mice. Here, we examined the kinetics of the primary NP.383-391-specific response in Tg HLA-B27/H2 DKO mice at the site of respiratory infection, along with the profile of additional influenza A epitopes recognized. While the temporal kinetics of the Tg HLA-B27/NP.383-391-specific CD8+ T cell response paralleled the H2-D(b)/NP.366-374-specific response of non-Tg H2b mice, the magnitude was less. Using epitope prediction programs, we identified three novel B27-restricted influenza A epitopes, PB2.702-710, PB1.571-579, and PB2.368-376, recognized during both the primary and secondary response to infection. Although the secondary NP.383-391-specific response was dominant, PB1.571-579 and PB2.368-376 stimulated stronger proliferative expansion in memory T cells. Our results indicate a broader B27/influenza A CTL repertoire than previously known. Together with results for other HLA class I alleles, this information will become important in improving vaccine strategies for influenza A and other human pathogens.     

Dd-Alix, a conserved endosome-associated protein, controls Dictyostelium development

We have characterized the Dictyostelium homolog of the mammalian protein Alix. Dd-Alix is encoded by a single gene and is expressed during vegetative growth and multicellular development. We showed that the alx null strain fails to complete its developmental program. Past the tight aggregate stage, morphogenesis is impaired, leading to markedly aberrant structures containing vacuolated and undifferentiated cells but no mature spores. The developmental defect is cell-autonomous as most cells remain of the PstB type even when mixed with wild-type cells. Complementation analysis with different Alix constructs allowed the identification of a 101-residue stretch containing a coiled-coil domain essential for Alix function. In addition, we showed that the protein associates in part with vesicular structures and that its distribution on a Percoll gradient overlaps that of the endocytic marker Vamp7. Dd-Alix also co-localizes with Dd-Vps32. In view of our data, and given the role of Vps32 proteins in membrane protein sorting and multivesicular body formation in yeast and mammals, we hypothesize that the developmental defects of the alx null strain result from abnormal trafficking of cell-surface receptors.     

Xestospongin B, a competitive inhibitor of IP3-mediated Ca2+ signalling in cultured rat myotubes, isolated myonuclei, and neuroblastoma (NG108-15) cells

Xestospongin B, a macrocyclic bis-1-oxaquinolizidine alkaloid extracted from the marine sponge Xestospongia exigua, was highly purified and tested for its ability to block inositol 1,4,5-trisphosphate (IP(3))-induced Ca(2+) release. In a concentration-dependent manner xestospongin B displaced [(3)H]IP(3) from both rat cerebellar membranes and rat skeletal myotube homogenates with an EC(50) of 44.6 +/- 1.1 microM and 27.4 +/- 1.1 microM, respectively. Xestospongin B, depending on the dose, suppressed bradykinin-induced Ca(2+) signals in neuroblastoma (NG108-15) cells, and also selectively blocked the slow intracellular Ca(2+) signal induced by membrane depolarization with high external K(+) (47 mM) in rat skeletal myotubes. This slow Ca(2+) signal is unrelated to muscle contraction, and involves IP(3) receptors. In highly purified isolated nuclei from rat skeletal myotubes, Xestospongin B reduced, or suppressed IP(3)-induced Ca(2+) oscillations with an EC(50) = 18.9 +/- 1.35 microM. In rat myotubes exposed to a Ca(2+)-free medium, Xestospongin B neither depleted sarcoplasmic reticulum Ca(2+) stores, nor modified thapsigargin action and did not affect capacitative Ca(2+) entry after thapsigargin-induced depletion of Ca(2+) stores. Ca(2+)-ATPase activity measured in skeletal myotube homogenates remained unaffected by Xestospongin B. It is concluded that xestospongin B is an effective cell-permeant, competitive inhibitor of IP(3) receptors in cultured rat myotubes, isolated myonuclei, and neuroblastoma (NG108-15) cells.