Multiple regulatory domains on the Byr2 protein kinase.

Byr2 protein kinase, a homolog of mammalian mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEKK) and Saccharomyces cerevisiae STE11, is required for pheromone-induced sexual differentiation in the fission yeast Schizosaccharomyces pombe. Byr2 functions downstream of Ste4, Ras1, and the membrane-associated receptor-coupled heterotrimeric G-protein alpha subunit, Gpa1. Byr2 has a distinctive N-terminal kinase regulatory domain and a characteristic C-terminal kinase catalytic domain. Ste4 and Ras1 interact with the regulatory domain of Byr2 directly. Here, we define the domains of Byr2 that bind Ste4 and Ras1 and show that the Byr2 regulatory domain binds to the catalytic domain in the two-hybrid system. Using Byr2 mutants, we demonstrate that these direct physical interactions are all required for proper signaling. In particular, the physical association between Byr2 regulatory and catalytic domains appears to result in autoinhibition, the loss of which results in kinase activation. Furthermore, we provide evidence that Shk1, the S. pombe homolog of the STE20 protein kinase, can directly antagonize the Byr2 intramolecular interaction, possibly by phosphorylating Byr2.     

Human papillomavirus infection and cervical intraepithelial neoplasia in women with renal allografts.

An increased prevalence of cervical cancer has been observed in immunosuppressed women, but controlled studies are rare. Biopsy specimens from 49 women with renal allografts and 69 non-immunosuppressed controls (with no history of cervical intraepithelial neoplasia, vulval warts, or abnormal results of cervical smear tests) were assessed for colposcopic appearance, cytological and histological diagnosis, and the presence of human papillomavirus types 6/11 and 16/18 DNA sequences. At colposcopy 26 (53%) of the women with allografts had cervical abnormalities compared with 20 (29%) of the controls. The prevalence of cervical intraepithelial neoplasia was significantly higher in the women with allografts (24 (49%) compared with 7 (10%]. The overall rate of detection of human papillomavirus DNA did not differ significantly between the two groups. There was however, a significant difference in the rate of detection of human papillomavirus type 16/18 DNA (27% in the women with allografts and 6% in the controls). These data confirm that pathological and virological changes affecting the cervix are significantly increased in immunosuppressed women and emphasise the need for regular colposcopic examination.     

Glycosylation study of the major genetic variants of human alpha1-acid glycoprotein and of their pharmacokinetics in the rat

Human alpha1-acid glycoprotein (AAG) is a mixture of at least two genetic variants, the A variant and the F1 and/or S variant or variants, which are encoded by two different genes. AAG is also an extensively glycosylated protein which possesses five N-linked glycans exhibiting substantial heterogeneity in their structures. The first objective of this study was to investigate the glycosylation of the two major gene products of AAG, i.e. the A variant and a mixture of the F1 and S variants (F1*S). To this end, we combined a chromatographic method for the fractionation of the AAG variants with a lectin-binding assay to characterise the glycosylation of purified glycoproteins. Secondly, because the oligosaccharides can influence the disposition of AAG, a kinetic study of the AAG variants was carried out in the rat. After intravenous administration of whole human AAG, the separation and quantification of the AAG variants in plasma was performed by application of specific methods by isoelectric focusing and immunonephelometry. The binding studies carried out on a panel of lectins showed significant differences in the lectin-binding characteristics of the separated F1*S and A variants, accounting for differences in the degree of branching of their glycan chains and substitution with sialic acid and fucose. The plasma concentration-time profiles of the F1*S and A variants were biphasic, and only small differences were observed between the variants for their initial and terminal half-lives, clearance and distribution volume. This indicates that the structural differences between the two AAG gene products do not affect their pharmacokinetics in the rat. Specific drug transport roles have been previously demonstrated for the F1*S and A variants, calling for further investigations into their effects on the disposition of drugs they bind in plasma. The present study shows that such investigations are possible without being complicated by kinetic differences between these variants.     

Egg patterning is not a reliable indicator of intraspecific brood parasitism in the blue tit Cyanistes caeruleus

A recent study reported the incidence of intraspecific brood parasitism (IBP) in the blue tit, based on differences in pigmentation between eggs within clutches and the appearance of multiple eggs within a nest in a single day. Here we present data from another population of blue tits Cyanistes caeruleus in which we show that such evidence is not necessarily indicative of IBP. As in many other studies of birds, we found that the patterning and degree of pigmentation on eggs is individually highly characteristic of a female. As in the previous study of blue tits, a minority of clutches (about 3% of 904 clutches) contained one, two or three eggs that were distinctly different from the other eggs in the clutch, either in size or patterning, but not both. Molecular genetic analyses of parentage in a sample of these clutches with suspected IBP demonstrated unequivocally that all eggs within each clutch had in fact been laid by a single female, in all cases the social parent. We also found no evidence of IBP from paternity analyses of a sample of 3,529 offspring from 427 broods in this population, adding to previous evidence of the absence of IBP in this species. These findings cast doubt on the utility of purely observational approaches to provide evidence of intraspecific brood parasitism; our study suggests that egg morphology and records of laying patterns are inadequate to enable the identification of IBP.     

Phylogenetic signal in tooth wear dietary niche proxies

In the absence of independent observational data, ecologists and paleoecologists use proxies for the Eltonian niches of species (i.e., the resource or dietary axes of the niche). Some dietary proxies exploit the fact that mammalian teeth experience wear during mastication, due to both tooth‐on‐tooth and food‐on‐tooth interactions. The distribution and types of wear detectible at micro‐ and macroscales are highly correlated with the resource preferences of individuals and, in turn, species. Because methods that quantify the distribution of tooth wear (i.e., analytical tooth wear methods) do so by direct observation of facets and marks on the teeth of individual animals, dietary inferences derived from them are thought to be independent of the clade to which individuals belong. However, an assumption of clade or phylogenetic independence when making species‐level dietary inferences may be misleading if phylogenetic niche conservatism is widespread among mammals. Herein, we test for phylogenetic signal in data from numerous analytical tooth wear studies, incorporating macrowear (i.e., mesowear) and microwear (i.e., low‐magnification microwear and dental microwear texture analysis). Using two measures of phylogenetic signal, heritability (H²) and Pagel's λ, we find that analytical tooth wear data are not independent of phylogeny and failing to account for such nonindependence leads to overestimation of discriminability among species with different dietary preferences. We suggest that morphological traits inherited from ancestral clades (e.g., tooth shape) influence the ways in which the teeth wear during mastication and constrain the foods individuals of a species can effectively exploit. We do not suggest that tooth wear is simply phylogeny in disguise; the tooth wear of individuals and species likely varies within some range that is set by morphological constraints. We therefore recommend the use of phylogenetic comparative methods in studies of mammalian tooth wear, whenever possible.     

Evidence that genes from the male parent may influence the morphology of potato dihaploids

A number of recent studies have provided evidence that potato dihaploids (S. tuberosum) contain and express DNA from the male (dihaploid inducer) parent, S. phureja. The importance of this for breeding programmes that use dihaploid potatoes is to some extent dependent upon whether the S. phureja DNA influences dihaploid morphology. In the present study, 21 characters were used to compare the morphology of six dihaploids with those of their parents: S. tuberosum (cvs `Pentland Dell' and `Pentland Crown') and S. phureja (IVP48). Characteristics of S. phureja were found in all of the dihaploids examined. In principal component analyses, dihaploids formed intermediate groupings positioned between those of the parents, although much closer to S. tuberosum. It is concluded there is evidence that DNA originating from the dihaploid inducer can affect the morphology of potato dihaploids. Implications of the findings are discussed. Received: 26 November 1995 / Accepted: 9 February 1996     

Response of Net Ecosystem Productivity of Three Boreal Forest Stands to Drought

In 2001–03, continuous eddy covariance measurements of carbon dioxide (CO₂) flux were made above mature boreal aspen, black spruce, and jack pine forests in Saskatchewan, Canada, prior to and during a 3−year drought. During the 1st drought year, ecosystem respiration (R) was reduced at the aspen site due to the drying of surface soil layers. Gross ecosystem photosynthesis (GEP) increased as a result of a warm spring and a slow decrease of deep soil moisture. These conditions resulted in the highest annual net ecosystem productivity (NEP) in the 9 years of flux measurements at this site. During 2002 and 2003, a reduction of 6% and 34% in NEP, respectively, compared to 2000 was observed as the result of reductions in both R and GEP, indicating a conservative response to the drought. Although the drought affected most of western Canada, there was considerable spatial variability in summer rainfall over the 100−km extent of the study area; summer rainfalls in 2001 and 2002 at the two conifer sites minimized the impact of the drought. In 2003, however, precipitation was similarly low at all three sites. Due to low topographic position and consequent poor drainage at the black spruce site and the coarse soil with low water-holding capacity at the jack pine site almost no reduction in R, GEP, and NEP was observed at these two sites. This study shows that the impact of drought on carbon sequestration by boreal forest ecosystems strongly depends on rainfall distribution, soil characteristics, topography, and the presence of vegetation that is well adapted to these conditions.     

Application of a subtraction hybridization technique involving photoactivatable biotin and organic extraction to solution hybridization analysis of genomic DNA

We have adapted a subtraction hybridization technique involving photoactivatable biotin, streptavidin binding, and organic extraction for solution hybridization analysis of mammalian genomic DNA. By combining maximal hybridization conditions of high salt, dextran sulfate, and formamide with successive hybridization steps and sequence enrichment by agarose gel electrophoresis, up to 97% of tracer DNA can be reproducibly driven to hybridize with photobiotinylated driver DNA. We demonstrate that the fractionation of hybridized from unhybridized sequences by this technique differs from hydroxyapatite chromatography with respect to the handling of nondenatured tracer, foldback sequences, and tracer-tracer hybrids. Strategies are presented to control the contribution of these species to the final subtracted product thereby making this technology a useful adjunct to solution hybridization approaches such as deletion cloning.