A molecular phylogeny for the South African limbless lizard taxa of the subfamily Acontinae (Sauria: Scincidae) with special emphasis on relationships within Acontias

In the present study, relationships among three genera Acontias, Acontophiops, and Typhlosaurus, that comprise the South African limbless lizard subfamily Acontinae, were assessed with partial sequences of the 16S rRNA mitochondrial DNA gene. In addition, relationships within Acontias were further investigated using sequence data from the cytochrome oxidase I gene (COI). Maximum likelihood and maximum parsimony analyses of the 16S rRNA mtDNA data revealed that within this subfamily, Typhlosaurus is basal while Acontophiops and Acontias are sister taxa. Based on the 16S rRNA mtDNA data, the relationships within Acontias placed A. meleagris orientalis as the sister taxon of A. percivali tasmani, with A. m. orientalis lineacauda morph and A. m. meleagrus being the sister taxa to this group. The small-bodied skinks A. lineatus lineatus and A. l. tristis formed a monophyletic group, with the medium-bodied species A. gracilicauda gracilicauda being their sister taxon. Analyses of the COI gene for Acontias place A. m. orientalis as the sister taxon of A. p. tasmani with both A. meleagris meleagris and A. m. orientalis lineacauda being distinct. In contrast to the 16S rRNA mtDNA data, the COI data placed A. g. gracilicauda as the sister taxon to these medium-bodied species; while the subspecies status of the small-bodied taxa A. l. lineatus and A. l. tristis is reaffirmed. Combined analysis of both gene fragments for Acontias taxa recovered the same clades as found using only COI data. Systematic affinities in Acontias are discussed. These results indicate that Acontias is more species rich than previously thought.     

Phylogenetic relationships of the southern African freshwater crab fauna (Decapoda: Potamonautidae: Potamonautes) derived from multiple data sets reveal biogeographic patterning

The phylogenetic relationships among the southern African freshwater crab species were examined using partial sequence data from three mitochondrial genes (12S rRNA, 16S rRNA, and mtDNA COI) 26 morphological characters and 14 allozyme loci. The aims of the present study were firstly to determine whether freshwater crab species that live in the same geographic region share a close phylogenetic relationship. Secondly, to investigate whether hybridizing species are genetically closely related and thirdly, to test for the validity of subgenera based on the genetic data sets. Phylogenetic analysis based on sequence data revealed largely congruent tree topologies and some associations had consistently high bootstrap support, and these data did not support Bott's subgeneric divisions. The morphological data were less informative for phylogenetic reconstruction while the allozyme data generally supported patterns recovered by the sequence data. A combined analysis of all the data recovered two monophyletic clades, one comprised of small-bodied mountain stream species and the other clade consisting of large-bodied riverine species. The combined analyses reflected clear biogeographic patterning for these river crabs. In addition, there was a clear correlation between genetic distance values and the ability of sympatric species to hybridize.     

Dynamic conditionally linear mixed models for longitudinal data

We develop a new class of models, dynamic conditionally linear mixed models, for longitudinal data by decomposing the within-subject covariance matrix using a special Cholesky decomposition. Here 'dynamic' means using past responses as covariates and 'conditional linearity' means that parameters entering the model linearly may be random, but nonlinear parameters are nonrandom. This setup offers several advantages and is surprisingly similar to models obtained from the first-order linearization method applied to nonlinear mixed models. First, it allows for flexible and computationally tractable models that include a wide array of covariance structures; these structures may depend on covariates and hence may differ across subjects. This class of models includes, e.g., all standard linear mixed models, antedependence models, and Vonesh-Carter models. Second, it guarantees the fitted marginal covariance matrix of the data is positive definite. We develop methods for Bayesian inference and motivate the usefulness of these models using a series of longitudinal depression studies for which the features of these new models are well suited.     

Torpor-associated fluctuations in surfactant activity in Gould's wattled bat

The primary function of pulmonary surfactant is to reduce the surface tension (ST) created at the air-liquid interface in the lung. Surfactant is a complex mixture of lipids and proteins and its function is influenced by physiological parameters such as metabolic rate, body temperature and breathing. In the microchiropteran bat Chalinolobus gouldii these parameters fluctuate throughout a 24 h period. Here we examine the surface activity of surfactant from warm-active and torpid bats at both 24 degrees C and 37 degrees C to establish whether alterations in surfactant composition correlate with changes in surface activity. Bats were housed in a specially constructed bat room at Adelaide University, at 24 degrees C and on a 8:16 h light:dark cycle. Surfactant was collected from bats sampled during torpor (2535 degrees C). Alterations in the lipid composition of surfactant occur with changes in the activity cycle. Most notable is an increase in surfactant cholesterol (Chol) with decreases in body temperature [Codd et al., Physiol. Biochem. Zool. 73 (2000) 605-612]. Surfactant from active bats was more surface active at higher temperatures, indicated by lower ST(min) and less film area compression required to reach ST(min) at 37 degrees C than at 24 degrees C. Conversely, surfactant from torpid bats was more active at lower temperatures, indicated by lower ST(min) and less area compression required to reach ST(min) at 24 degrees C than at 37 degrees C. Alterations in the Chol content of bat surfactant appear to be crucial to allow it to achieve low STs during torpor.     

N-linked glycans direct the cotranslational folding pathway of influenza hemagglutinin

For proteins that traverse the secretory pathway, folding commences cotranslationally upon translocation into the endoplasmic reticulum. In this study, we have comprehensively analyzed the earliest maturation steps of the model glycoprotein influenza hemagglutinin (HA). These steps include cleavage of the signal sequence, glycosylation, binding by the chaperones calnexin and calreticulin, and the oxidoreductase ERp57, and oxidation. Our results show that the molecular choreography of the nascent HA chain is largely directed by multiple glycans that are strategically placed to elicit the binding of lectin chaperones. These chaperones are recruited to specific nascent chain locations to regulate and facilitate glycoprotein folding, thereby suggesting that the positioning of N-linked glycans in critical regions has evolved to optimize the folding process in the cell.     

Alpha-pheromone-induced "shmooing" and gene regulation require white-opaque switching during Candida albicans mating

A 14-mer α-pheromone peptide of Candida albicans was chemically synthesized and used to analyze the role of white-opaque switching in the mating process. The α-pheromone peptide blocked cell multiplication and induced “shmooing” in a/a cells expressing the opaque-phase phenotype but not in a/a cells expressing the white-phase phenotype. The α-pheromone peptide induced these effects at 25°C but not at 37°C. An analysis of mating-associated gene expression revealed several categories of gene regulation, including (i) MTL-homozygous-specific, pheromone stimulated, switching-independent (CAG1 and STE4); (ii) mating type-specific, pheromone-induced, switching-independent (STE2); and (iii) pheromone-induced, switching-dependent (FIG1, KAR4, and HWP1). An analysis of switching-regulated genes revealed an additional category of opaque-phase-specific genes that are downregulated by α-pheromone only in a/a cells (OP4, SAP1, and SAP3). These results demonstrate that α-pheromone causes shmooing, the initial step in the mating process, only in a/a cells expressing the opaque phenotype and only at temperatures below that in the human host. These results further demonstrate that although some mating-associated genes are stimulated by the α-pheromone peptide in both white- and opaque-phase cells, others are stimulated only in opaque-phase cells, revealing a category of gene regulation unique to C. albicans in which α-pheromone induction requires the white-opaque transition. These results demonstrate that in C. albicans, the mating process and associated gene regulation must be examined within the context of white-opaque switching.     

The adhesin Hwp1 and the first daughter cell localize to the a/a portion of the conjugation bridge during Candida albicans mating

The cell wall protein Hwp1 was originally demonstrated to be expressed exclusively in hyphae of Candida albicans and cross-linked to human epithelium by mammalian transglutaminase. Hwp1 is expressed on the walls of hyphae formed by a/alpha, a/a, and alpha/alpha cells. Hence, it is expressed on hyphae independently of mating type. However, Hwp1 is selectively expressed on the wall of conjugation tubes formed by a/a cells, but not alpha/alpha cells, in the mating process. This was demonstrated in all possible crosses between four unrelated natural a/a strains and four unrelated alpha/alpha strains. In zygotes, Hwp1 is restricted to that portion of the wall of the conjugation bridge contributed by the a/a parent cell. Hwp1 staining further revealed that the first daughter bud that emerges from the conjugation bridge does so from the a/a-contributed portion. Hwp1 expression and localization during the mating process is, therefore, mating type specific, opaque phase specific, and alpha-pheromone induced. These results indicate that the mating type-specific contributions to the conjugation bridge during the mating process in C. albicans are qualitatively and functionally distinct and that the a/a portion of the bridge, which selectively contains Hwp1, bears the first daughter cell in the mating process.     

CysG structure reveals tetrapyrrole-binding features and novel regulation of siroheme biosynthesis

Sulfur metabolism depends on the iron-containing porphinoid siroheme. In Salmonella enterica, the S-adenosyl-L-methionine (SAM)-dependent bismethyltransferase, dehydrogenase and ferrochelatase, CysG, synthesizes siroheme from uroporphyrinogen III (uro'gen III). The reactions mediated by CysG encompass two branchpoint intermediates in tetrapyrrole biosynthesis, diverting flux first from protoporphyrin IX biosynthesis and then from cobalamin (vitamin B(12)) biosynthesis. We determined the first structure of this multifunctional siroheme synthase by X-ray crystallography. CysG is a homodimeric gene fusion product containing two structurally independent modules: a bismethyltransferase and a dual-function dehydrogenase-chelatase. The methyltransferase active site is a deep groove with a hydrophobic patch surrounded by hydrogen bond donors. This asymmetric arrangement of amino acids may be important in directing substrate binding. Notably, our structure shows that CysG is a phosphoprotein. From mutational analysis of the post-translationally modified serine, we suggest a conserved role for phosphorylation in inhibiting dehydrogenase activity and modulating metabolic flux between siroheme and cobalamin pathways.     

Neurochemical and thermal control of surfactant secretion by alveolar type II cells isolated from the marsupial, Sminthopsis crassicaudata

Pulmonary surfactant is synthesised in alveolar type II cells and secreted into the lining of the lung in response to ventilation, temperature changes and autonomic neurotransmitters. Type II cells were isolated from the heterothermic marsupial, Sminthopsis crassicaudata. The neurotransmitters, isoproterenol and carbamylcholine chloride significantly increased phosphatidylcholine secretion at 37 degrees C (basal: 14.2%, isoproterenol: 20.1%, carbamylcholine: 17.0%). Temperature reduced the rate of secretion from dunnart type II cells (e.g. basal: 14.2% at 37 degrees C; 7.2% at 18 degrees C). However, the change in secretory rate between 37 degrees C and 18 degrees C was less than expected if due to temperature alone (Q10= 1.4). The surfactant secretory pathway is therefore modulated by factors other than and in addition to, temperature. The response of dunnart type II cells to the agonists remained the same at both temperatures. Basal secretion was higher in dunnart type II cells (14.2% in 4 h) than has been reported in rat type II cells (1.9% in 3 h) and consequently, the agonist-stimulated increases in secretion from dunnart type II cells (41% above basal in 4 h) were much lower than observed for rat type II cells (200% above basal in 1.5 h).