Germination dimorphism and developmental flexibility in the ruderal weed Heterotheca grandiflora

Summary Heterotheca grandiflora Nutt. (Asteraceae, tribe Astereae) is one of the few native Californian plant species increasing its range as a weed. The production of dimorphic seed, together with flexible development in either the annual or biennial habit, may contribute to its range expansion. Well dispersed disc achenes germinate rapidly to high percentages while poorly dispersed ray achenes show considerable dormancy, germinating at a much lower rate to lower final percentages. Ray achenes appear more sensitive to environmental factors and have more specific germination requirements than do disc achenes. Thus, germination is distributed in space and time. Plants growing as annuals have one flowering period while those acting as biennials may flower up to three times, although seed production differs greatly among the stages. These factors aid in forming the general purpose genotype so frequently encountered in weedy species.     

Import of proteins into mitochondria. Energy-dependent, two-step processing of the intermembrane space enzyme cytochrome b2 by isolated yeast mitochondria

Import of in vitro-synthesized cytochrome b2 (a soluble intermembrane space enzyme) was studied wih isolated yeast mitochondria. Import requires an electrochemical gradient across the inner membrane and is accompanied by cleavage of the precursor to the corresponding mature form. This conversion proceeds via an intermediate form of cytochrome b2, which can be detected as a transient species when mitochondria are incubated with the cytochrome b2 precursor for short times or at low temperatures. Conversion of the precursor to the intermediate form is energy-dependent and catalyzed by an o-phenanthroline-sensitive protease located in the soluble matrix. The intermediate is subsequently converted to mature cytochrome b2 in a reaction which is o-phenanthroline-insensitive and requires neither an energized inner membrane nor a soluble component of the intermembrane space. Whereas mature cytochrome b2 is soluble, the intermediate formed by isolated mitochondria is membrane-bound and exposed to the intermembrane space. The same intermediate is detected as a transient species during cytochrome b2 maturation in intact yeast cells (Reid, G. A., Yonetani, T., and Schatz, G (1982) J. Biol. Chem. 257, 13068-13074). The in vitro studies reported here suggest that a part of the cytochrome b2 precursor polypeptide chain is transported to the matrix where it is cleaved to a membrane-bound intermediate form by the same protease that processes polypeptides destined for the matrix space or for the inner membrane. In a second reaction, the cytochrome b2 intermediate is converted to mature cytochrome b2 which is released into the intermembrane space. The binding of heme is not necessary for converting the intermediate to the mature polypeptide.     

Optical super-resolution microscopy in neurobiology

Understanding the highly plastic nature of neurons requires the dynamic visualization of their molecular and cellular organization in a native context. However, due to the limited resolution of standard light microscopy, many of the structural specializations of neurons cannot be resolved. A recent revolution in light microscopy has given rise to several super-resolution light microscopy methods yielding 2-10-fold higher resolution than conventional microscopy. We here describe the principles behind these techniques as well as their application to the analysis of the molecular architecture of the synapse. Furthermore, we discuss the potential for continued development of super-resolution microscopy as necessary for live imaging of neuronal structure and function in the brain.     

Morphological and molecular investigations of Tubulinosema ratisbonensis gen. nov., sp. nov. (Microsporidia: Tubulinosematidae fam. nov.), a parasite infecting a laboratory colony of Drosophila melanogaster (Diptera: Drosophilidae)

A new species of microsporidia from Drosophila melanogaster was investigated by light and electron microscopy and by ribosomal RNA (rRNA) sequencing. This microsporidium and the previously described Nosema kingi and Nosema acridophagus have been transferred to the new genus Tubulinosema gen. nov. with the following characters: nuclei are in diplokaryotic arrangement during the life cycle. All stages are in direct contact with the host cell cytoplasm, slightly anisofilar polar tube with the last coils being smaller in diameter arranged in one or two rows on both sides of the diplokaryon and small tubuli on the surface of late meronts. Spores are oval or slightly pyriform. Thick endospore wall, thinner over anchoring disc. This new genus and the genus Brachiola have been placed in a new family Tubulinosematidae fam. nov. Phylogenetic analysis of small subunit rRNA sequences by different methods placed Tubulinosema spp. in one clade with the genus Brachiola forming its sister clade, which is distant from the clade containing the true Nosema spp. including Nosema bombycis.     

Lineage-specific evolution and gene flow in Listeria monocytogenes are independent of bacteriophages

Listeria monocytogenes is a foodborne pathogen causing systemic infection with high mortality. To allow efficient tracking of outbreaks a clear definition of the genomic signature of a cluster of related isolates is required, but lineage-specific characteristics call for a more detailed understanding of evolution. In our work, we used core genome MLST (cgMLST) to identify new outbreaks combined to core genome SNP analysis to characterize the population structure and gene flow between lineages. Whilst analysing differences between the four lineages of L. monocytogenes we have detected differences in the recombination rate, and interestingly also divergence in the SNP differences between sub-lineages. In addition, the exchange of core genome variation between the lineages exhibited a distinct pattern, with lineage III being the best donor for horizontal gene transfer. Whilst attempting to link bacteriophage-mediated transduction to observed gene transfer, we found an inverse correlation between phage presence in a lineage and the extent of recombination. Irrespective of the profound differences in recombination rates observed between sub-lineages and lineages, we found that the previously proposed cut-off of 10 allelic differences in cgMLST can be still considered valid for the definition of a foodborne outbreak cluster of L. monocytogenes.     

The response of alkaline phosphatase to osmoregulatory changes in the trout,Salmo gairdneri

Summary The relationship between alkaline phosphatase and environmental salinity was examined in the rainbow trout and the migratory rainbow (steelhead),Salmo gairdneri. The enzyme activity in tissues involved in osmoregulation was strongly correlated with the adaptation salinity and thus to the degree of salt and fluid transport in those tissues. After transfer from freshwater to seawater, the specific activity of the enzyme increased over 260% in the intestine, decreased by 50% in kidney, and was unchanged in the liver, an organ not directly involved in osmoregulation. The sea-run steelhead trout response was similar to the nonmigratory rainbow; although, the pre-migratory transformation (smoltification) had no effect on enzyme activity. Amino acid inhibitors of alkaline phosphatase significantly reduced fluid absorption in the isolated intestine of rainbow trout, reaffirming the relationship between the enzyme and fluid movement. Electrophoretic identification of trout alkaline phosphatase isozymes, clearly distinguishes the enzyme from different tissue origins. However, from the analysis of intestinal electrophoretic patterns, osmoregulatory adjustments are not associated with the induction of new alkaline phosphatase isozymes, or in the large scale preferential stimulation of one of the two existing intestinal isozymes over the other.     

Characterization of paired Ig-like receptors in rats

To explore the phylogenetic history of the murine paired Ig-like receptors of activating (PIR-A) and inhibitory (PIR-B) types, we isolated PIR homologues from a rat splenocyte cDNA library. The rat (ra) PIR-A and raPIR-B cDNA sequences predict transmembrane proteins with six highly conserved extracellular Ig-like domains and distinctive membrane proximal, transmembrane, and cytoplasmic regions. The raPIR-B cytoplasmic region contains prototypic inhibitory motifs, whereas raPIR-A features a charged transmembrane region and a short cytoplasmic tail. Southern blot analysis predicts the presence of multiple Pira genes and a single Pirb gene in the rat genome. Although raPIR-A and raPIR-B are coordinately expressed by myeloid cells, analysis of mRNA detected unpaired expression of raPIR-A by B cells and raPIR-B by NK cells. Collectively, these findings indicate that the structural hallmarks of the Pir gene family are conserved in rats and mice, yet suggest divergence of PIR regulatory elements during rodent speciation.