Historic and recent fragmentation coupled with altitude affect the genetic population structure of one of the world's highest tropical tree line species

Aim To assess the effects of altitude and historic and recent forest fragmentation on the genetic diversity and structure of the wind‐pollinated tropical tree line species Polylepis incana. Location One of the highest mountain forest regions of the world, located in the Eastern Cordillera of the Ecuadorian Andes. Methods We compared genetic diversity and structure of adult trees with those of seedlings (n= 118 in both cases) in nine forest stands spanning an altitudinal gradient from 3500 to 4100 m a.s.l. using amplified fragment length polymorphisms (AFLPs). Genetic diversity was calculated as percentage of polymorphic bands (P) and Nei's expected heterozygosity (He); genetic differentiation was assessed using analysis of molecular variance, Φ_ST statistics and Bayesian cluster analysis. Results Estimates of genetic diversity at the population level were significantly lower in seedlings than in adults. Genetic diversity (He‐value) was, in both cases, negatively correlated to altitude and positively correlated to population size in the seedlings. Genetic differentiation of the seedlings was approximately as high (φ_ST= 0.298) as that of the adults (φ_ST= 0.307), and geographical differentiation was clearly reflected in both AFLP profiles, with mountain ridges acting as barriers to gene flow. Main conclusions Our study provides evidence of a historic upslope migration of P. incana in central Ecuador. In addition, it highlights the detrimental effects of unexpectedly strong genetic isolation, both recent and historical, particularly for our wind‐pollinated species where the distance between forest stands was less than 25 km. We therefore additionally propose that in habitats with pronounced high‐mountain landscape structures, gene flow may be hampered to such an extent that species have a more pronounced sensitivity to habitat fragmentation, even among populations of wind‐pollinated trees.     

A2BR adenosine receptor modulates sweet taste in circumvallate taste buds

In response to taste stimulation, taste buds release ATP, which activates ionotropic ATP receptors (P2X2/P2X3) on taste nerves as well as metabotropic (P2Y) purinergic receptors on taste bud cells. The action of the extracellular ATP is terminated by ectonucleotidases, ultimately generating adenosine, which itself can activate one or more G-protein coupled adenosine receptors: A1, A2A, A2B, and A3. Here we investigated the expression of adenosine receptors in mouse taste buds at both the nucleotide and protein expression levels. Of the adenosine receptors, only A2B receptor (A2BR) is expressed specifically in taste epithelia. Further, A2BR is expressed abundantly only in a subset of taste bud cells of posterior (circumvallate, foliate), but not anterior (fungiform, palate) taste fields in mice. Analysis of double-labeled tissue indicates that A2BR occurs on Type II taste bud cells that also express Gα14, which is present only in sweet-sensitive taste cells of the foliate and circumvallate papillae. Glossopharyngeal nerve recordings from A2BR knockout mice show significantly reduced responses to both sucrose and synthetic sweeteners, but normal responses to tastants representing other qualities. Thus, our study identified a novel regulator of sweet taste, the A2BR, which functions to potentiate sweet responses in posterior lingual taste fields.     

Testosterone replacement in hypogonadal men alters the HDL proteome but not HDL cholesterol efflux capacity

The effects of androgens on cardiovascular disease (CVD) risk in men remain unclear. To better characterize the relationship between androgens and HDL, we investigated the effects of testosterone replacement on HDL protein composition and serum HDL-mediated cholesterol efflux in hypogonadal men. Twenty-three older hypogonadal men (ages 51-83, baseline testosterone < 280 ng/dl) were administered replacement testosterone therapy (1% transdermal gel) with or without the 5α-reductase inhibitor dutasteride. At baseline and after three months of treatment, we determined fasting lipid concentrations, HDL protein composition, and the cholesterol efflux capacity of serum HDL. Testosterone replacement did not affect HDL cholesterol (HDL-C) concentrations but conferred significant increases in HDL-associated paraoxonase 1 (PON1) and fibrinogen α chain (FGA) (P = 0.022 and P = 0.023, respectively) and a decrease in apolipoprotein A-IV (apoA-IV) (P = 0.016). Exogenous testosterone did not affect the cholesterol efflux capacity of serum HDL. No differences were observed between men who received testosterone alone and those who also received dutasteride. Testosterone replacement in older hypogonadal men alters the protein composition of HDL but does not significantly change serum HDL-mediated cholesterol efflux. These effects appear independent of testosterone conversion to dihydrotestosterone. Further research is needed to determine how changes in HDL protein content affect CVD risk in men.     

A cyclic peptide inhibitor of apoC-II peptide fibril formation: mechanistic insight from NMR and molecular dynamics analysis

The misfolding and aggregation of proteins to form amyloid fibrils is a characteristic feature of several common age-related diseases. Agents that directly inhibit formation of amyloid fibrils represent one approach to combating these diseases. We have investigated the potential of a cyclic peptide to inhibit fibril formation by fibrillogenic peptides from human apolipoprotein C-II (apoC-II). Cyc[60-70] was formed by disulfide cross-linking of cysteine residues added to the termini of the fibrillogenic peptide comprising apoC-II residues 60-70. This cyclic peptide did not self-associate into fibrils. However, substoichiometric concentrations of cyc[60-70] significantly delayed fibril formation by the fibrillogenic, linear peptides apoC-II[60-70] and apoC-II[56-76]. Reduction of the disulfide bond or scrambling the amino acid sequence within cyc[60-70] significantly impaired its inhibitory activity. The solution structure of cyc[60-70] was solved using NMR spectroscopy, revealing a well-defined structure comprising a hydrophilic face and a more hydrophobic face containing the Met60, Tyr63, Ile66 and Phe67 side chains. Molecular dynamics (MD) studies identified a flexible central region within cyc[60-70], while MD simulations of "scrambled" cyc[60-70] indicated an increased formation of intramolecular hydrogen bonds and a reduction in the overall flexibility of the peptide. Our structural studies suggest that the inhibitory activity of cyc[60-70] is mediated by an elongated structure with inherent flexibility and distinct hydrophobic and hydrophilic faces, enabling cyc[60-70] to interact transiently with fibrillogenic peptides and inhibit fibril assembly. These results suggest that cyclic peptides based on amyloidogenic core peptides could be useful as specific inhibitors of amyloid fibril formation.     

Spontaneous recurrent mutations and a complex rearrangement in the MECP2 gene in the light of current models of mutagenesis

Mutations in the methyl-CpG-binding protein 2 (MECP2) gene are associated with Rett syndrome (RTT). The MECP2 gene has some unique characteristics: (1) it is mainly affected by de novo mutations, due to recurrent independent mutational events in a defined "hot spot" regions or positions; (2) complex mutational events along a single allele are frequently found in this gene; (3) most mutations arise on paternal X chromosome. The recurrent point mutations involve mainly CpG dinucleotides, where C>T transitions are explained by methylation-mediated deamination. The complex mutational events might be explained by the genomic architecture of the region involving the MECP2 gene. The finding that most spontaneous mutations arise on paternal X-chromosome supports the higher contribution of replication-mediated mechanism of mutagenesis. We present 9 types of mutations in the MECP2 gene, detected in a group of 22 Bulgarian and 6 Romanian classical RTT patients. Thirteen patients were clarified on molecular level (46.4%). The point mutations in our sample account for 61.5%. One intraexonic deletion was detected in the present study (7.7%). One novel insertion c.321_322insGAAG, p.(Lys107_Leu108insGluAlafs2*) was found (7.7%). Large deletions and complex mutations account for 23%. A novel complex mutational event c.[584_624del41insTT; 638delTinsCA] was detected in a Romanian patient. We discuss different types of the MECP2 mutations detected in our sample in the light of the possible mechanisms of mutagenesis. Complex gene rearrangements involving a combination of deletions and insertions have always been most difficult to detect, to specify precisely and hence to explain in terms of their underlying mutational mechanisms.     

Acute sex steroid withdrawal increases cholesterol efflux capacity and HDL-associated clusterin in men

Exogenous androgens can lower HDL-cholesterol (HDL-C) concentrations, yet men with low serum testosterone have elevated rates of cardiovascular disease (CVD). HDL function may better predict CVD risk than absolute HDL-C quantity. We evaluated the acute effects of medical castration in men on HDL-C, cholesterol efflux capacity and HDL protein composition. Twenty-one healthy men, ages 18-55, received the GnRH antagonist acyline and one of the following for 28days: Group 1: placebo, Group 2: transdermal testosterone gel and placebo, Group 3: transdermal testosterone gel and an aromatase inhibitor. Sex steroids, fasting lipids, and cholesterol efflux to apoB-depleted serum were measured in all subjects. The HDL proteome was assessed in Group 1 subjects only. In Group 1, serum testosterone concentrations were reduced by >95%, and HDL-C and cholesterol efflux capacity increased (p=0.02 and p=0.03 vs. baseline, respectively). HDL-associated clusterin increased significantly with sex steroid withdrawal (p=0.007 vs. baseline). Testosterone withdrawal in young, healthy men increases HDL-C and cholesterol efflux capacity. Moreover, sex steroid deprivation changes HDL protein composition. Further investigation of the effects of sex steroids on HDL composition and function may help resolve the apparently conflicting data regarding testosterone, HDL-C, and CVD risk.     

Lachemilla jaramilloi and L. talamanquensis spp. nov. (Rosaceae) from Ecuador and Costa Rica

Two new species of Lachemilla (Rosaceae) are described and illustrated. Lachemilla jaramilloi Romoleroux &Morales‐Briones from Ecuador is characterized by its decumbent habit, villous‐hirsute pubescence, long basal petiole, and deeply tri‐parted leaf blades. The flowers are sessile to subsessile and subtended by episepals, and the hypanthia elongated and glabrescent. Lachemilla talamanquensis Romoleroux & Morales‐Briones from Costa Rica is distinguished by its sericeous‐villous, ascending branches, sub‐sessile distal leaves, tri‐lobed leaf blades, forming whorls with the stipule. The flowers are solitary or arranged in few‐flowered inflorescences, with big, dark, villous hypanthia, containing several achenes.     

Antitumor Effects of Combining Docetaxel (Taxotere) with the Antivascular Action of Ultrasound Stimulated Microbubbles

Ultrasound stimulated microbubbles (USMB) are being investigated for their potential to promote the uptake of anticancer agents into tumor tissue by exploiting their ability to enhance microvascular permeability. At sufficiently high ultrasound transmit amplitudes it has also recently been shown that USMB treatments can, on their own, induce vascular damage, shutdown blood flow, and inhibit tumor growth. The objective of this study is to examine the antitumor effects of ‘antivascular’ USMB treatments in conjunction with chemotherapy, which differs from previous work which has sought to enhance drug uptake with USMBs by increasing vascular permeability. Conceptually this is a strategy similar to combining vascular disrupting agents with a chemotherapy, and we have selected the taxane docetaxel (Taxotere) for evaluating this approach as it has previously been shown to have potent antitumor effects when combined with small molecule vascular disrupting agents. Experiments were conducted on PC3 tumors implanted in athymic mice. USMB treatments were performed at a frequency of 1 MHz employing sequences of 50 ms bursts (0.00024 duty cycle) at 1.65 MPa. USMB treatments were administered on a weekly basis for 4 weeks with docetaxel (DTX) being given intravenously at a dose level of 5 mg/kg. The USMB treatments, either alone or in combination with DTX, induced an acute reduction in tumor perfusion which was accompanied at the 24 hour point by significantly enhanced necrosis and apoptosis. Longitudinal experiments showed a modest prolongation in survival but no significant growth inhibition occurred in DTX–only and USMB-only treatment groups relative to control tumors. The combined USMB-DTX treatment group produced tumor shrinkage in weeks 4–6, and significant growth inhibition and survival prolongation relative to the control (p<0.001), USMB-only (p<0.01) and DTX-only treatment groups (p<0.01). These results suggest the potential of enhancing the antitumor activity of docetaxel by combining it with antivascular USMB effects.     

Gap junctional intercellular communication is required to maintain embryonic stem cells in a non-differentiated and proliferative state

Pluripotent embryonic stem (ES) cells are capable of maintaining a self-renewal state and have the potential to differentiate into derivatives of all three embryonic germ layers. Despite their importance in cell therapy and developmental biology, the mechanisms whereby ES cells remain in a proliferative and pluripotent state are still not fully understood. Here we establish a critical role of gap junctional intercellular communication (GJIC) and connexin43 (Cx43) in both processes. Pharmacological blockers of GJIC and Cx43 down-regulation by small interfering RNA (siRNA) caused a profound inhibitory effect on GJIC, as evidenced by experiments of fluorescence recovery after photobleaching. This deficient intercellular communication in ES cells induced a loss of their pluripotent state, which was manifested in morphological changes, a decrease in alkaline phosphatase activity, Oct-3/4 and Nanog expression, as well as an up-regulation of several differentiation markers. A decrease in the proliferation rate was also detected. Under these conditions, the formation of embryoid bodies from mouse ES cells was impaired, although this inhibition was reversible upon restoration of GJIC. Our findings define a major function of GJIC in the regulation of self-renewal and maintenance of pluripotency in ES cells.     

Roads to polyploidy: the megakaryocyte example.

Polyploidy, recognized by multiple copies of the haploid chromosome number, has been described in plants, insects, and in mammalian cells such as, the platelet precursors, the megakaryocytes. Several of these cell types reach high ploidy via a different cell cycle. Megakaryocytes undergo an endomitotic cell cycle, which consists of an S phase interrupted by a gap, during which the cells enter mitosis but skip anaphase B and cytokinesis. Here, we review the mechanisms that lead to this cell cycle and to polyploidy in megakaryocytes, while also comparing them to those described for other systems in which high ploidy is achieved. Overall, polyploidy is associated with an orchestrated change in expression of several genes, of which, some may be a result of high ploidy and hence a determinant of a new cell physiology, while others are inducers of polyploidization. Future studies will aim to further explore these two groups of genes.