Chromogranin A-derived peptides: interaction with the rat posterior cerebral artery

Chromogranin A (CgA), an acidic granule protein of the regulated secretory pathway in the diffuse neuroendocrine system, is postulated to serve as a prohormone for regulatory peptides. Betagranin (rCgA(1-128)), the first N-terminal cleavage product of rat CgA, is 87% homologous to the bovine vasostatin I (bCgA(1-76)), previously shown to be vasoinhibitory in bovine resistance arteries. In this study the vasoactivity of homologous rat and bovine peptides was investigated in the rat posterior cerebral artery. Firstly, we examined the interaction of rhodamine (Rh)-labelled bCgA(7-40) and bCgA(47-70) with elements of the arterial wall by fluorescence microscopy. Secondly, rCgA(7-57), bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin) were studied for effects on arterial tone and intracellular calcium as function of pressure in an arteriograph. Although without dilator or constrictor responses at 60-150 mm Hg, the rat peptide (rCgA(7-57)) evoked a significant delay in the onset of forced dilatation at 170 mm Hg, in contrast to the bovine peptides bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin). Neither Rh-bCgA(7-40) nor Rh-bCgA(47-70) stained the endothelial layer, while Rh-bCgA(47-70) but not Rh-bCgA(7-40) stained the smooth muscle compartment. Analogously, bCgA(47-66) but not bCgA(7-40) reduced intracellular calcium, however without modifying the myogenic response. Thus, the betagranin peptide rCgA(7-57) and the two bovine chromofungin-containing peptides, highly homologous to the corresponding sequence (rCgA(47-66)), affected the rat cerebral artery without vasodilator effects, indicating significant species differences in vasoactivity of the N-terminal domain of CgA.     

Genomic imprinting,disrupted placental expression,and speciation

The importance of regulatory incompatibilities to the early stages of speciation remains unclear. Hybrid mammals often show extreme parent‐of‐origin growth effects that are thought to be a consequence of disrupted genetic imprinting (parent‐specific epigenetic gene silencing) during early development. Here, we test the long‐standing hypothesis that abnormal hybrid growth reflects disrupted gene expression due to loss of imprinting (LOI) in hybrid placentas, resulting in dosage imbalances between paternal growth factors and maternal growth repressors. We analyzed placental gene expression in reciprocal dwarf hamster hybrids that show extreme parent‐of‐origin growth effects relative to their parental species. In massively enlarged hybrid placentas, we observed both extensive transgressive expression of growth‐related genes and biallelic expression of many genes that were paternally silenced in normal sized hybrids. However, the apparent widespread disruption of paternal silencing was coupled with reduced gene expression levels overall. These patterns are contrary to the predictions of the LOI model and indicate that hybrid misexpression of dosage‐sensitive genes is caused by other regulatory mechanisms in this system. Collectively, our results support a central role for disrupted gene expression and imprinting in the evolution of mammalian hybrid inviability, but call into question the generality of the widely invoked LOI model.     

5 Alpha-reductase in the non-secretory cells of the rat ventral prostate epithelium

Kinetic constants for the 5 alpha-reductase were determined in freshly isolated epithelial cells from the rat ventral prostate. Studies were also performed on stromal tissue but not isolated stromal cells for comparison. Secretory and non-secretory epithelial cells were separated by centrifugation in a Percoll gradient. Both epithelial cell populations metabolized testosterone to predominantly 5 alpha-dihydrotestosterone (5 alpha-DHT), although when expressed per cell the capacity for conversion was 3-4-fold higher for secretory cells (7.4 pmol/min/10(6) cells) than for non-secretory cells (2.3 pmol/min/10(6) cells; P less than 0.01 in 4 separate studies). When compared per mg cytosol protein this difference became non-significant. Stromal tissue contained a 5 alpha-reductase Vmax (expressed) per mg protein) which was comparable to the non-secretory cell enzyme. Lineweaver-Burke plots revealed different Km values for the different cell populations (12.5, 5.9 and 4.7 microM for secretory, non-secretory and stromal cells, respectively) suggesting the presence of different isoforms of the enzyme, or differences in the intracellular concentrations of enzyme antagonists.     

Systematic review of avian hatching failure and implications for conservation

Avian hatching failure is a widespread phenomenon, affecting around 10% of all eggs that are laid and not lost to predation, damage, or desertion. Our understanding of hatching failure is limited in terms of both its underpinning mechanisms and its occurrence across different populations. It is widely acknowledged that rates of hatching failure are higher in threatened species and in populations maintained in captivity compared to wild, non-threatened species, but these differences have rarely been quantified and any broader patterns remain unexplored. To examine the associations between threat status, management interventions, and hatching failure across populations we conducted a phylogenetically controlled multilevel meta-analysis across 231 studies and 241 species of birds. Our data set included both threatened (Critically Endangered, Endangered, and Vulnerable) and non-threatened (Near Threatened and Least Concern) species across wild and captive populations, as well as ‘wild managed’ (‘free-living’) populations. We found the mean overall rate of hatching failure across all populations to be 16.79%, with the hatching failure rate of wild, non-threatened species being 12.40%. We found that populations of threatened species experienced significantly higher mean hatching failure than populations of non-threatened species. Different levels of management were also associated with different rates of hatching failure, with wild populations experiencing the lowest rate of hatching failure, followed by wild managed populations, and populations in captivity experiencing the highest rate. Similarly, populations that were subject to the specific management interventions of artificial incubation, supplementary feeding, and artificial nest provision displayed significantly higher rates of hatching failure than populations without these interventions. The driver of this correlation between hatching failure and management remains unclear, but could be an indirect result of threatened species being more likely to have lower hatching success and also being more likely to be subject to management, indicating that conservation efforts are fittingly being focused towards the species potentially most at risk from extinction. This is the most comprehensive comparative analysis of avian hatching failure that has been conducted to date, and the first to quantify explicitly how threat status and management are associated with the rate of hatching failure in a population. We discuss the implications of our results, focusing on their potential applications to conservation. Although we identified several factors clearly associated with variation in hatching failure, a significant amount of heterogeneity was not explained by our meta-analytical model, indicating that other factors influencing hatching failure were not included here. We discuss what these factors might be and suggest avenues for further research. Finally, we discuss the inconsistency in how hatching failure is defined and reported within the literature, and propose a standardised definition to be used in future studies which will enable better comparison across populations and ensure that the most accurate information is used to support management decisions.     

Separation and characterization of the troponin components from bovine cardiac muscle.

The three major components of bovine cardiac troponin were separated by successive chromatography on sulfopropyl-Sephadex and DEAE-Sephadex columns in the presence of 6 M urea. All three of the bovine cardiac troponin subunits were necessary to restore full troponin activity in both skeletal and cardiac actomyosin ATPase assay systems. The 38,000-dalton subunit bound tropomyosin, and the 20,000-dalton subunit bound calcium, like skeletal TN-T and TN-C, respectively. The 28,000 component, although presumably analogous to skeletal TN-I, gave very little inhibition of actomyosin ATPase activity. Differences between cardiac and skeletal troponin subunits were also found in the elution patterns from ion exchange columns and in amino acid composition, thus demonstrating a significant muscle-type specificity.