Metamorphic core complex formation by density inversion and lower-crust extrusion.

Metamorphic core complexes are domal uplifts of metamorphic and plutonic rocks bounded by shear zones that separate them from unmetamorphosed cover rocks. Interpretations of how these features form are varied and controversial, and include models involving extension on low-angle normal faults, plutonic intrusions and flexural rotation of initially high-angle normal faults. The D'Entrecasteaux islands of Papua New Guinea are actively forming metamorphic core complexes located within a continental rift that laterally evolves to sea-floor spreading. The continental rifting is recent (since approximately 6 Myr ago), seismogenic and occurring at a rapid rate ( approximately 25 mm yr-1). Here we present evidence-based on isostatic modelling, geological data and heat-flow measurements-that the D'Entrecasteaux core complexes accommodate extension through the vertical extrusion of ductile lower-crust material, driven by a crustal density inversion. Although buoyant extrusion is accentuated in this region by the geological structure present-which consists of dense ophiolite overlaying less-dense continental crust-this mechanism may be generally applicable to regions where thermal expansion lowers crustal density with depth.     

Plasmid-related anaerobic autotrophy of the novel archaebacterium Sulfolobus ambivalens

Three different species of the genus Sulfolobus, S. acidocaldarius, S. solfataricus (= Caldariella) and S. brierleyi, have been distinguished by the conditions required for optimal growth, by the component patterns of their DNA-dependent RNA polymerases and by DNA sequence data. Many isolates of these species are able to grow chemolithoautotrophically using CO2 as the sole carbon source and the oxidation of S(0) with O2 yielding sulphuric acid, as the energy source, though a few others grow only heterotrophically. We show here that a strain of a novel Sulfolobus species, S. ambivalens, is alternatively able to live by an anaerobic mode of chemolithoautotrophy, also using CO2 as the sole carbon source, but using reduction of S(0) with H2, yielding H2S as the energy source. This mode of growth is correlated with the amplification of a plasmid, pSL10.     

Inositol phosphates and cell signalling

Inositol 1,4,5-trisphosphate is a second messenger which regulates intracellular calcium both by mobilizing calcium from internal stores and, perhaps indirectly, by stimulating calcium entry. In these actions it may function with its phosphorylated metabolite, inositol 1,3,4,5-tetrakisphosphate. The subtlety of calcium regulation by inositol phosphates is emphasized by recent studies that have revealed oscillations in calcium concentration which are perhaps part of a frequency-encoded second-messenger system.     

Heritability of locomotor performance and its correlates in a natural population

Summary Locomotor capacities and their physiological bases are thought to be of considerable selective importance in natural populations. Within this functional complex, organismal performance traits (e.g., speed, stamina) are expected to be of more direct selective importance than their suborganismal determinants (e.g., heart size). Quantitative genetics theory predicts that traits of greater selective importance should generally have lower heritabilities at equilibrium. Contrary to these expectations, we report that organismal performance traits had the highest heritabilities in a natural population of garter snakes.     

Occurrence,distribution and nature of neuropeptide Y in the rat pancreas

Summary Significant quantities of a newly discovered peptide, neuropeptide Y, were found in the rat pancreas, where they were localized to nerves in the exocrine parenchyma and around arterial and ductal structures. Although unaffected by surgical parasympathectomy, the periarterial and periductal nerves were abolished by chemical sympathectomy, suggesting that NPY is partially costored with sympathetic transmitters in nerve fibers.     

Role of myelin P0 protein as a homophilic adhesion molecule.

Peripheral nervous system myelin is an extension of the Schwann cell's plasma membrane that tightly enwraps axons in many layers and permits nerve impulses to be rapidly conducted. It is not known how these multiple membrane layers are held together in this compact form. Here we present evidence supporting the hypothesis that the extracellular leaflets of myelin are held together by the most abundant protein of myelin of the peripheral nervous system, P0, by homophilic interaction of its extracellular domains. Transfected Chinese hamster ovary cells expressing P0 protein adhere to each other in suspension, to form large aggregates, whereas cells that are identical but which do not express P0 do not. We also show that this aggregation is mediated by homophilic binding between P0-expressing cells and that the apposing plasma membranes of these cells specifically form desmosomes, whereas control transfected cells do not. As the only difference between the two cell populations is the expression of P0, this protein is apparently responsible for the changes in morphology and adhesion in the cells that express it. The idea that P0 is a homophilic adhesion molecule is supported by its inclusion in the immunoglobulin supergene family, all members of which are involved in recognition and/or adhesion.