Ghrelin can bind to a species of high density lipoprotein associated with paraoxonase

Ghrelin is a 28-residue peptide hormone that is principally released from the stomach during fasting and prior to eating. Two forms are present in human plasma: the unmodified peptide and a less abundant acylated version, in which octanoic acid is attached to the third residue, a serine, via an ester linkage. The acylated form of ghrelin acts as a ligand for the growth hormone secretagogue receptor and can stimulate the release of growth hormone from the pituitary gland. It also initiates behavioral and metabolic adaptations to fasting. Here we show that an immobilized form of ghrelin specifically binds a species of high density lipoprotein associated with the plasma esterase, paraoxonase, and clusterin. Both free ghrelin and paraoxon, a substrate for paraoxonase, can inhibit this interaction. An endogenous species of ghrelin is found to co-purify with high density lipoprotein during density gradient centrifugation and subsequent gel filtration. This interaction links the orexigenic peptide hormone ghrelin to lipid transport and metabolism. Furthermore, the interaction of the esterified hormone ghrelin with a species of HDL containing an esterase suggests a possible mechanism for the conversion of ghrelin to des-acyl ghrelin.     

Estimation of population growth or decline in genetically monitored populations

This article introduces a new general method for genealogical inference that samples independent genealogical histories using importance sampling (IS) and then samples other parameters with Markov chain Monte Carlo (MCMC). It is then possible to more easily utilize the advantages of importance sampling in a fully Bayesian framework. The method is applied to the problem of estimating recent changes in effective population size from temporally spaced gene frequency data. The method gives the posterior distribution of effective population size at the time of the oldest sample and at the time of the most recent sample, assuming a model of exponential growth or decline during the interval. The effect of changes in number of alleles, number of loci, and sample size on the accuracy of the method is described using test simulations, and it is concluded that these have an approximately equivalent effect. The method is used on three example data sets and problems in interpreting the posterior densities are highlighted and discussed.     

Disruption of doubly uniparental inheritance of mitochondrial DNA in hybrid mussels (Mytilus edulis x M. galloprovincialis)

Blue mussels of the genus Mytilus have an unusual mode of mitochondrial DNA inheritance termed doubly uniparental inheritance (DUI). Females are homoplasmic for the F mitotype which is inherited maternally, whereas males are heteroplasmic for this and the paternally inherited M mitotype. In areas where species distributions overlap a varying degree of hybridization occurs; yet genetic differences between allopatric populations are maintained. Observations from natural populations and previous laboratory experiments suggest that DUI may be disrupted by hybridization, giving rise to heteroplasmic females and homoplasmic males. We carried out controlled laboratory crosses between Mytilus edulis and M. galloprovincialis to produce pure species and hybrid larvae of known parentage. DNA markers were used to follow the fate of the F and M mitotypes through larval development. Disruption of the mechanism which determines whether the M mitotype is retained or eliminated occurred in an estimated 38% of M. edulis x M. galloprovincialis hybrid larvae, a level double that previously observed in adult mussels from a natural M. edulis x M. galloprovincialis hybrid population. Furthermore, reciprocal hybrid crosses exhibited contrasting types of DUI disruption. The results indicate that disruption of DUI in hybrid mussels may be associated with increased mortality and hence could be a factor in the maintenance of genetic integrity for each species.     

Testing for genetic evidence of population expansion and contraction: an empirical analysis of microsatellite DNA variation using a hierarchical Bayesian model

The role of past climatic change in shaping the distributions of tropical rain forest vertebrates is central to long-standing hypotheses about the legacy of the Quaternary ice ages. One approach to testing such hypotheses is to use genetic data to infer the demographic history of codistributed species. Population genetic theory that relates the structure of allelic genealogies to historical changes in effective population size can be used to detect a past history of demographic expansion or contraction. The fruit bats Cynopterus sphinx and C. brachyotis (Chiroptera: Pteropodidae) exhibit markedly different distribution patterns across the Indomalayan region and therefore represent an exemplary species pair to use for such tests. The purpose of this study was to test alternative hypotheses about historical patterns of demographic expansion and contraction in C. sphinx and C. brachyotis using a coalescent-based analysis of microsatellite variation. Specifically, we used a hierarchical Bayesian model based on Markov chain Monte Carlo simulations to estimate the posterior distribution of genealogical and demographic parameters. The results revealed strong evidence for population contraction in both species. Evidence for a population contraction in C. brachyotis was expected on the basis of biogeographic considerations. However, similar evidence for population contraction in C. sphinx does not support the hypothesis that this species underwent a pronounced range expansion during the late Quaternary. Genetic evidence for population decline may reflect the consequences of habitat destruction on a more recent time scale.     

Nitrite reductase of Nitrosomonas europaea is not essential for production of gaseous nitrogen oxides and confers tolerance to nitrite

A gene that encodes a periplasmic copper-type nitrite reductase (NirK) was identified in Nitrosomonas europaea. Disruption of this gene resulted in the disappearance of Nir activity in cell extracts. The nitrite tolerance of NirK-deficient cells was lower than that of wild-type cells. Unexpectedly, NirK-deficient cells still produced nitric oxide (NO) and nitrous oxide (N(2)O), the latter in greater amounts than that of wild-type cells. This demonstrates that NirK is not essential for the production of NO and N(2)O by N. europaea. Inactivation of the putative fnr gene showed that Fnr is not essential for the expression of nirK.     

HS1 interacts with Lyn and is critical for erythropoietin-induced differentiation of erythroid cells

Erythroid cells terminally differentiate in response to erythropoietin binding its cognate receptor. Previously we have shown that the tyrosine kinase Lyn associates with the erythropoietin receptor and is essential for hemoglobin synthesis in three erythroleukemic cell lines. To understand Lyn signaling events in erythroid cells, the yeast two-hybrid system was used to analyze interactions with other proteins. Here we show that the hemopoietic-specific protein HS1 interacted directly with the SH3 domain of Lyn, via its proline-rich region. A truncated HS1, bearing the Lyn-binding domain, was introduced into J2E erythroleukemic cells to determine the impact upon responsiveness to erythropoietin. Truncated HS1 had a striking effect on the phenotype of the J2E line-the cells were smaller, more basophilic than the parental proerythoblastoid cells and had fewer surface erythropoietin receptors. Moreover, basal and erythropoietin-induced proliferation and differentiation were markedly suppressed. The inability of cells containing the truncated HS1 to differentiate may be a consequence of markedly reduced levels of Lyn and GATA-1. In addition, erythropoietin stimulation of these cells resulted in rapid, endosome-mediated degradation of endogenous HS1. The truncated HS1 also suppressed the development of erythroid colonies from fetal liver cells. These data show that disrupting HS1 has profoundly influenced the ability of erythroid cells to terminally differentiate.     

Larval growth, juvenile size and heterozygosity in laboratory reared mussels, Mytilus edulis

Studies with marine bivalve juveniles have shown a positive correlation between growth and allozyme multi-locus heterozygosity (MLH), and, in some cases, between larval growth and juvenile growth, but there has been little research on the relationship between allozyme heterozygosity and larval growth. Larvae of M. edulis from different mating systems (half-sib families with a single female, or a single male parent, a reciprocal cross of two malesxtwo females and two mass matings of 13x13 and 8x17 females and males, respectively) were reared in the laboratory and selected into fast and slow growing groups when about 10-30% were undergoing metamorphosis. Offspring were reared to the juvenile stage (>3.00 mm) and both groups of each mating were electrophoresed and genotyped at up to 12 allozyme loci. There was generally good agreement with Mendelian inheritance (half-sibs and reciprocal cross) or the Hardy-Weinberg model (mass matings). Null alleles were detected at the Odh and Lap loci but there was no evidence that null allele heterozygotes grew slower than other genotypes. Over all cohorts, juveniles from the fast growing larval group were not significantly larger, or smaller, than juveniles from the slow growing group which suggests that larval growth rate may be independent of juvenile growth rate. This observation agrees with some, but not all, earlier studies and has commercial relevance. Tests of heterozygosity and juvenile shell length indicated no association between average heterozygosity across all allozyme loci and the size of juveniles in any cohort regardless of the mating system used or their larval growth rate. The association between MLH and juvenile growth in bivalves is seldom detected in cohorts from a limited genetic background. The lack of an association between heterozygosity and size might therefore be expected in the half-sib and reciprocal cross cohorts, but not in the mass matings. The results argue against any significant association between heterozygosity and larval size in mussels.     

Microsatellites reveal heterosis in red deer.

The fitness consequences of inbreeding and outbreeding are poorly understood in natural populations. We explore two microsatellite-based variables, individual heterozygosity (likely to correlate with recent inbreeding) and a new individual-specific internal distance measure, mean d2 (focusing on events deeper in the pedigree), in relation to two measures of fitness expressed early in life, birth weight and neonatal survival, in 670 red deer calves (Cervus elaphus) born on the Isle of Rum between 1982 and 1996. For comparison, we also analyse inbreeding coefficients derived from pedigrees in which paternity was inferred by molecular methods. Only 14 out of 231 calves (6.1%) had non-zero inbreeding coefficients, and neither inbreeding coefficient nor individual heterozygosity was consistently related to birth weight or neonatal survival. However, mean d2 was consistently related to both fitness measures. Low mean d2 was associated with low birth weight, especially following cold Aprils, in which foetal growth is reduced. Low mean d2 was also associated with low neonatal survival, but this effect was probably mediated by birth weight because fitting birth weight to the neonatal survival model displaced mean d2 as an explanatory variable. We conclude that in the deer population fitness measures expressed early in life do not show evidence of inbreeding depression, but they do show evidence of heterosis, possibly as a result of population mixing. We also demonstrate the practical problems of estimating inbreeding via pedigrees compared with a direct marker-based estimate of individual heterozygosity. We suggest that, together, individual heterozygosity and mean d2, estimated using microsatellites, are useful tools for exploring inbreeding and outbreeding in natural population.