New insights into growth hormone action

It has been 75 years since Evans and Long identified a somatic growth-promoting substance in pituitary extracts, yet it is only in the last 20 years that the molecular basis for this action has been established. Three key elements in this elucidation were the cloning of the GH receptor, the identification of Janus kinase (JAK) 2 as the receptor-associated tyrosine kinase, and the delineation of signal transduction and activators of transcription (STAT) 5a/b as the key transcription factor(s) activated by JAK2. The interaction between these three elements results in enhanced postnatal growth and is the subject of this review. We describe a new model for GH receptor activation based on subunit rotation within a constitutive dimer, together with the phenotype and hepatic transcript profile of mice with targeted knockins to the receptor cytoplasmic domain. These support a central role for STAT5a/b in postnatal growth.

Prismatic dentine in the Australian lungfish, Neoceratodus forsteri (Osteichthyes : Dipnoi)

The Australian lungfish, Neoceratodus forsteri, has a dentition consisting of enamel, mantle dentine and bone, enclosing circumdenteonal, core and interdenteonal dentines. Branching processes from cells that produce interdenteonal dentine leave the cell surface at different angles, with collagen fibrils aligned parallel to the long axis of each process. In the interdenteonal dentine, crystals of calcium hydroxyapatite, form within fibrils of collagen, and grow within a matrix of non-collagenous protein. Crystals are aligned parallel to the cell process, as are the original collagen fibrils. Because the processes are angled to the cell surface, the crystals within the core or interdenteonal dentine are arranged in bundles set at angles to each other. Apatite crystals in circumdenteonal dentine are finer and denser than those of the interdenteonal dentine, and form outside the fibrils of collagen. In mature circumdenteonal dentine the crystals of circumdenteonal dentine form a dense tangled mass, linked to interdenteonal dentine by isolated crystals. The functional lungfish tooth plate contains prisms of large apatite crystals in the interdenteonal dentine and masses of fine tangled crystals around each denteon. This confers mechanical strength on a structure with little enamel that is subjected to heavy wear. (c) 2006 Elsevier Ltd. All rights reserved.

A sensitive HPLC method for measuring bacterial proteolysis and proteinase activity in UHT milk

A sensitive quantitative reversed-phase HPLC method is described for measuring bacterial proteolysis and proteinase activity in UHT milk. The analysis is performed on a TCA filtrate of the milk. The optimum concentration of TCA was found to be 4%; at lower concentrations, non-precipitated protein blocked the HPLC while higher concentrations yielded lower amounts of peptides. The method showed greater sensitivity and reproducibility than a fluorescamine-based method. Quantification of the HPLC method was achieved by use of an external dipeptide standard or a standard proteinase. (c) 2006 Elsevier Ltd. All rights reserved.

Selective modulation of neuronal nicotinic acetylcholine receptor channel subunits by G(o)-protein subunits

protein modulation of neuronal nicotinic acetylcholine receptor ( nAChR) channels in rat intrinsic cardiac ganglia was examined using dialyzed whole-cell and excised membrane patch-recording configurations. Cell dialysis with GTP gamma S increased the agonist affinity of nAChRs, resulting in a potentiation of nicotine-evoked whole-cell currents at low concentrations. ACh- and nicotine-evoked current amplitudes were increased approximately twofold in the presence of GTP gamma S. In inside-out membrane patches, the open probability (NPo) of nAChR-mediated unitary currents was reversibly increased fourfold after bath application of 0.2mM GTP gamma S relative to control but was unchanged in the presence of GDP gamma S. The modulation of nAChR-mediated whole- cell currents was agonist specific; currents evoked by the cholinergic agonists ACh, nicotine, and 1,1-dimethyl-4-phenylpiperazinium iodide, but not cytisine or choline, were potentiated in the presence of GTP gamma S. The direct interaction between G-protein subunits and nAChRs was examined by bath application of either G(o)alpha or G beta gamma subunits to inside-out membrane patches and in glutathione S-transferase pull-down and coimmunoprecipitation experiments. Bath application of 50 nM G beta gamma increased the open probability of ACh- activated single-channel currents fivefold, whereas G(o)alpha( 50 nM) produced no significant increase in NPo. Neuronal nAChR subunits alpha 3-alpha 5 and alpha 2 exhibited a positive interaction with G(o)alpha and G beta gamma, whereas beta 4 and alpha 7 failed to interact with either of the G-protein subunits. These results provide evidence for a direct interaction between nAChR and G-protein subunits, underlying the increased open probability of ACh-activated single-channel currents and potentiation of nAChR-mediated whole-cell currents in parasympathetic neurons of rat intrinsic cardiac ganglia.

The novel cytoskeleton-associated protein Neuronal protein 22: Elevated expression in the developing rat brain

Neuronal development and process targeting is mediated by proteins of the cytoskeleton. However, the signaling pathways underlying these mechanisms are complex and have not yet been fully elucidated. Neuronal protein 22 (NP22) has been identified as a cytoskeleton-associated protein. It colocalizes with microtubules and actin, the two major components of the cytoskeleton. It contains numerous signaling motifs and induces process formation in non-neuronal cells. Expression of rat NP22 (rNP22) rises incrementally at specific time points during brain development, with the greatest elevation occurring during synaptogenesis in the rat brain. its neuronal localization is primarily at the plasma membrane of the soma in the embryonic brain and progresses into homogeneous expression in the postnatal rat brain. Data suggest that NP22 may play a role in mediating the molecular events governing development of the neuronal architecture. Furthermore, its sustained expression in postnatal brain implies a function in the maintenance of neuronal morphology.