Repetitive changes in Early Pliocene vegetation revealed by high-resolution pollen analysis: revised cyclostratigraphy of southwestern Romania

A high-resolution pollen analysis has been carried out on the Lupoaia section (SW Romania) in order to check whether the repetitive clay–lignite alternations correspond to cyclic changes in climate. Increases in altitudinal tree pollen content appear to have been caused by drops in temperature, while developments of thermophilous elements correspond to rises in temperature, still under humid conditions. Such repeated changes in vegetation, on the whole consistent with the clay–lignite alternations, have been forced by cycles in eccentricity. On the basis of a comparison between the Lupoaia pollen record and (1) European climatostratigraphy (based on reference pollen diagrams documenting global changes), and (2) global climatic curves (eccentricity, δ¹⁸O), the age of the section has been reconsidered. The Lupoaia section (i.e. from lignite IV to lignite XIII) starts just before the C3n.3n Chron and probably ends just before the C3n.1n Chron. The section represents a time span of about 600 kyr, i.e. from about 4.90 Ma to about 4.30 Ma.     

Xenon accumulation in the red blood cell. A process altered by suppressors of the membrane active transport function

Xenon passage across the erythrocyte membrane was investigated by performing several types of tests. The effects of some enzyme inhibitors (ouabain, NaF, dinitrophenol, low temperature), representing various modifications of the mentioned transport phenomenon, led to the conclusion of the existence of a strong correlation between the cellular energetic metabolism (and, hence, the energy supply for membrane processes) and the xenon accumulation into the erythrocyte. The experimental data obtained indicate that the xenon concentration in the cell water exceeds the concentration in the incubation solution by about 20 %. The metabolic inhibitors practically equalise the xenon concentrations in the cell water and in the surrounding medium. The possible theoretical consequences of these facts are taken into account and analysed.     

Sirt7 inhibits Sirt1-mediated activation of Suv39h1

Sirtuins regulate a variety of cellular processes through protein deacetylation. The best-known member of mammalian sirtuin family, Sirt1, plays important roles in the maintenance of cellular homeostasis by regulating cell metabolism, differentiation and stress responses, among others. Sirt1 activity requires tight regulation to meet specific cellular requirements, which is achieved at different levels and by specific mechanisms. Recently, a regulatory loop between Sirt1 and another sirtuin, Sirt7, was identified. Sirt7 inhibits Sirt1 autodeacetylation at K230 and activation thereby preventing Sirt1-mediated repression of adipocyte differentiation by inhibition of the PPARγ gene. Here, we extend the regulatory complexity of Sirt7-dependent restriction of Sirt1 activity by demonstrating that Sirt7 reduces activation of a previously described prominent Sirt1 target, the histone methyltransferase Suv39h1. We show that removal of the acetyl-group at K230 in Sirt1 due to the absence of Sirt7 leads to hyperactivation of Sirt1 and thereby to constantly increased activity of Suv39h1.     

Heterocellular molecular contacts in the mammalian stem cell niche

Adult tissue homeostasis and repair relies on prompt and appropriate intervention by tissue-specific adult stem cells (SCs). SCs have the ability to self-renew; upon appropriate stimulation, they proliferate and give rise to specialized cells. An array of environmental signals is important for maintenance of the SC pool and SC survival, behavior, and fate. Within this special microenvironment, commonly known as the stem cell niche (SCN), SC behavior and fate are regulated by soluble molecules and direct molecular contacts via adhesion molecules providing connections to local supporting cells and the extracellular matrix. Besides the extensively discussed array of soluble molecules, the expression of adhesion molecules and molecular contacts is another fundamental mechanism regulating niche occupancy and SC mobilization upon activation. Some adhesion molecules are differentially expressed and have tissue-specific consequences, likely reflecting the structural differences in niche composition and design, especially the presence or absence of a stromal counterpart. However, the distribution and identity of intercellular molecular contacts for adhesion and adhesion-mediated signaling within stromal and non-stromal SCN have not been thoroughly studied. This review highlights common details or significant differences in cell-to-cell contacts within representative stromal and non-stromal niches that could unveil new standpoints for stem cell biology and therapy.     

PHOSPHORUS STATUS AND CYTOPLASMIC STRUCTURES IN SCENEDESMUS (CHLOROPHYCEAE) UNDER DIFFERENT METABOLIC REGIMES1

Phosphorus deficiency affects the anatomy of the unicellular green alga Scenedesmus obtusiusculus Chad. and influences the distribution of other inorganic elements in the cell in addition to phosphorus. Scenedesmus was grown under standard conditions with or without phosphorus. Cells were then cultured with phosphorus under conditions favouring glycolysis, respiration, or photophosphorylation for 2 h or photosynthesis for up to 8 h. The dominating features of phosphorus starvation, were loss of phosphorus and coions from polyphosphate bodies, accumulation of starch, decrease in the volume density of ribosomes both in the chloroplast and cytoplasm, and an increase in wall thickness. Under conditions favoring photosynthesis the mass fraction for phosphorus is low after 1 h, exceptionally high by 2 h, and diminishes by 8 h. High amounts of phosphorus are also regained under conditions favoring glycolysis and photophosphorylation but not respiration. After 2 h under photosynthetic conditions the volume densities of the chloroplast, cytoplasmic ribosomes, the vacuole, and the mitochondrion increased over controls. By 8 h the relative volume of the single ramified mitochondrion had decreased slightly and recognizable segments of it were sequestered within the vacuome. The autophagic nature of the vacuole was further evidenced by the presence of ribosomes and whorls of lamellae within it. Serial sections showed that all polyphosphate granules and sequestered materials were located within a continuous vacuolar cisterna.     

Asymmetric distribution of metals in the Xenopus laevis oocyte: a synchrotron X-ray fluorescence microprobe study.

The asymmetric distribution of many components of the Xenopus oocyte, including RNA, proteins, and pigment, provides a framework for cellular specialization during development. During maturation, Xenopus oocytes also acquire metals needed for development, but apart from zinc, little is known about their distribution. Synchrotron X-ray fluorescence microprobe was used to map iron, copper, and zinc and the metalloid selenium in a whole oocyte. Iron, zinc, and copper were asymmetrically distributed in the cytoplasm, while selenium and copper were more abundant in the nucleus. A zone of high copper and zinc was seen in the animal pole cytoplasm. Iron was also concentrated in the animal pole but did not colocalize with zinc, copper, or pigment accumulations. This asymmetry of metal deposition may be important for normal development. Synchrotron X-ray fluorescence microprobe will be a useful tool to examine how metals accumulate and redistribute during fertilization and embryonic development.     

In silico-initiated cloning and molecular characterization of a novel human member of the L1 gene family of neural cell adhesion molecules

To discover genes contributing to mental retardation in 3p^- syndrome patients we have used in silico searches for neural genes in NCBI databases (dbEST and UniGene). An EST with strong homology to the rat CAM L1 gene subsequently mapped to 3p26 was used to isolate a full-length cDNA. Molecular analysis of this cDNA, referred to as CALL (cell adhesion L1-like), showed that it is encoded by a chromosome 3p26 locus and is a novel member of the L1 gene family of neural cell adhesion molecules. Multiple lines of evidence suggest CALL is likely the human ortholog of the murine gene CHL1: it is 84% identical on the protein level, has the same domain structure, same membrane topology, and a similar expression pattern. The orthology of CALL and CHL1 was confirmed by phylogenetic analysis. By in situ hybridization, CALL is shown to be expressed regionally in a timely fashion in the central nervous system, spinal cord, and peripheral nervous system during rat development. Northern analysis and EST representation reveal that it is expressed in the brain and also outside the nervous system in some adult human tissues and tumor cell lines. The cytoplasmic domain of CALL is conserved among other members of the L1 subfamily and features sequence motifs that may involve CALL in signal transduction pathways. Received: 14 April 1998 / Accepted: 18 June 1998     

Ultrastructural study of calcium distribution in cardiac muscle cells

Summary To investigate calcium distribution in cardiac muscle cells, two methods, one using oxalate and another using lead acetate, were used concomitantly to determine the subcellular localization of calcium. Particular attention was paid to the specificity of the methods employed. Chemical and physical analyses of the electron-opaque deposits of the reaction end-products was performed by chelation with EGTA or X-ray and electron diffraction. Results obtained show that the distribution of the calcium deposits in the cardiac muscle cells is more complex than that described for striated muscle fibers. The implications of these findings are discussed and an original viewpoint on the calcium distribution and movement in cardiac muscle cells is presented.