Sequential phases of cortical specification involve Neurogenin-dependent and -independent pathways

Neocortical projection neurons, which segregate into six cortical layers according to their birthdate, have diverse morphologies, axonal projections and molecular profiles, yet they share a common cortical regional identity and glutamatergic neurotransmission phenotype. Here we demonstrate that distinct genetic programs operate at different stages of corticogenesis to specify the properties shared by all neocortical neurons. Ngn1 and Ngn2 are required to specify the cortical (regional), glutamatergic (neurotransmitter) and laminar (temporal) characters of early-born (lower-layer) neurons, while simultaneously repressing an alternative subcortical, GABAergic neuronal phenotype. Subsequently, later-born (upper-layer) cortical neurons are specified in an Ngn-independent manner, requiring instead the synergistic activities of Pax6 and Tlx, which also control a binary choice between cortical/glutamatergic and subcortical/GABAergic fates. Our study thus reveals an unanticipated heterogeneity in the genetic mechanisms specifying the identity of neocortical projection neurons.     

Apoptotic effect of sphingosine 1-phosphate and increased sphingosine 1-phosphate hydrolysis on mesangial cells cultured at low cell density

The lipid mediator sphingosine 1-phosphate (S1P) may alter the proliferation of mesangial cells during pathophysiological processes. Here, S1P stimulated proliferation of rat mesangial cells and phosphorylation of MAPKs at subconfluent cell density. Both effects were inhibited by pertussis toxin treatment. Mesangial cells expressed several S1P receptors of the endothelial differentiation gene family: EDG-1, -3, -5, and -8. Conversely, S1P induced apoptosis at low cell density (2 x 10(4) cells/cm(2)), which was demonstrated by flow cytometry and Hoechst staining. Apoptosis was observed also in quiescent or growing cells and was not reverted by lysophosphatidic acid or platelet-derived growth factor. S1P enhanced phosphorylation of SAPKs. Incubation with [(33)P]S1P, [(3)H]S1P, and [(3)H]sphingosine demonstrated increased S1P hydrolysis, resulting in enhanced intracellular sphingosine levels and decreased S1P levels. A rise in total ceramide levels was also observed; however, ceramide did not originate from [(3)H]sphingosine, and S1P-induced apoptosis was not inhibited by fumonisin B, precluding involvement of de novo ceramide synthesis in apoptosis. Therefore, we suggest that sphingosine accumulation and decreased S1P are primarily responsible for S1P-induced apoptosis. In conclusion, incubation of low-density mesangial cells with S1P results in apoptosis, presumably due to increased S1P hydrolysis.     

Construction of the mobilizable plasmid pMV158GFP,a derivative of pMV158 that carries the gene encoding the green fluorescent protein

Plasmid pMV158 has been employed to construct cloning non-mobilizable vectors for various Gram-positive organisms. Here we report the construction of a mobilizable pMV158-based plasmid that harbors the gene encoding the green fluorescent protein under the control of a promoter inducible by maltose. The plasmid was mobilized between strains of Streptococcus pneumoniae as well as from S. pneumoniae to Lactococcus lactis or Enterococcus faecalis at the same frequency as its parental. Transconjugant that received the GFP-tagged plasmid could be detected by their fluorescence, which was especially high in E. faecalis cells.     

Additive polymorphisms and reticulation in an ITS phylogeny of thrifts (Armeria,Plumbaginaceae)

A parsimony analysis of 133 sequences of the nuclear ribosomal DNA ITS1+5.8S+ITS2 region from 71 taxa in Armeria was carried out. The presence of additive polymorphic sites (APS; occurring in 14 accessions) fits the reticulate scenario proposed in previous work for explaining the ITS pattern of variation on a much smaller scale and is based mainly on the geographical structure of the data, irrespective of taxonomic boundaries. Despite the relatively low bootstrap values and large polytomies, part of which are likely due to disruptive effects of reticulation and concerted evolution in these multicopy sequences, the ITS analysis has phylogenetic and biogeographic implications. APS detected in this study are consistent with hypothesized hybridization events, although biased concerted evolution, previously documented in the genus, needs to be invoked for specific cases and may be responsible for a possible "sink" effect in terminals from a large clade. The causes for sequences of the same species appearing in different clades (here termed transclade) are discussed.     

Jawsfest: new perspectives on neural crest lineages and morphogenesis

The neural crest is a fascinating population of cells that migrate long distances in the developing embryo to generate many different derivatives. It also occupies a central position in the origin and patterning of the vertebrate head, and has generated debates about issues such as cell programming versus plasticity and the role of cell death in early morphogenesis. These aspects of the field were revisited and discussed in a recent meeting organized to honour the retirement of Jim Weston and his contribution to the field.     

Cloning and expression of alpha-amylase from the hyperthermophilic archaeon Pyrococcus woesei in the moderately halophilic bacterium Halomonas elongata

An extracellular alpha-amylase gene from the hyperthermophilic archaeon Pyrococcus woesei has been cloned and sequenced. The 1.4-kb protein-coding sequence is identical to that of the corresponding alpha-amylase gene of the closely related species P. furiosus. By using a shuttle cloning vector for halophilic bacteria, the P. woesei alpha-amylase was expressed in the moderate halophile Halomonas elongata, under the control of a native H. elongata promoter. The hyperthermophilic amylase activity expressed in the halophilic host was recovered completely in the crude membrane fraction of cell homogenates, suggesting the formation of inclusion bodies or that the secretion machinery of H. elongata may fail to recognize and release the pyrococcal alpha-amylase to the extracellular medium. However, thermal stability, metal ion interactions, optimal temperature and pH values for the crude and purified recombinant alpha-amylase were comparable with those of the native pyrococcal enzyme. The P. woesei amylase activity expressed in H. elongata was consistently detected in the cells upon growth on a wide range of NaCl concentrations (0.7-2.5 mol l-1). To our knowledge, this is the first report on the expression of an archaeal gene (P. woesei alpha-amylase) in a moderate halophilic host which serves as a cell factory able to grow under extreme salt conditions and with very simple nutritional requirements.