Bacterial Symbiont Transmission in the Wood-Boring Shipworm Bankia setacea (Bivalvia: Teredinidae)

The Teredinidae (shipworms) are a morphologically diverse group of marine wood-boring bivalves that are responsible each year for millions of dollars of damage to wooden structures in estuarine and marine habitats worldwide. They exist in a symbiosis with cellulolytic nitrogen-fixing bacteria that provide the host with the necessary enzymes for survival on a diet of wood cellulose. These symbiotic bacteria reside in distinct structures lining the interlamellar junctions of the gill. This study investigated the mode by which these nutritionally essential bacterial symbionts are acquired in the teredinid Bankia setacea. Through 16S ribosomal DNA (rDNA) sequencing, the symbiont residing within the B. setacea gill was phylogenetically characterized and shown to be distinct from previously described shipworm symbionts. In situ hybridization using symbiont-specific 16S rRNA-directed probes bound to bacterial ribosome targets located within the host gill coincident with the known location of the gill symbionts. These specific probes were then used as primers in a PCR-based assay which consistently detected bacterial rDNA in host gill (symbiont containing), gonad tissue, and recently spawned eggs, demonstrating the presence of symbiont cells in host ovary and offspring. These results suggest that B. setacea ensures successful inoculation of offspring through a vertical mode of symbiont transmission and thereby enables a broad distribution of larval settlement.     

Binding to cellular receptors results in increased iron release from transferrin at mildly acidic pH

In order to better understand the cellular delivery of iron from serum transferrin (Tf), we compared iron release from receptor-bound and free Tf. While free Tf did not release all iron until below pH 4.6, receptor-bound Tf released significantly more iron at mildly acidic pH, with essentially all iron released between pH 5.6 and 6.0. Since Tf is acidified to a minimum pH of 5.4 in K562 cells, this result accounts for the nearly complete extraction of iron from Tf by these cells. Comparison of fluorescence from Tf conjugated with lissamine rhodamine sulfonyl chloride (LRSC-Tf) free in solution and bound to receptor provides further evidence that the Tf receptor modulates low pH-mediated conformational changes in Tf. As pH was decreased from neutrality, the fluorescence of free LRSC-Tf began to increase below pH 6.2; the fluorescence of LRSC-Tf bound to human receptors did not increase until below pH 5.6. Binding to the Tf receptor, while facilitating iron release from Tf, appears to partially inhibit a conformational change that causes the increase in LRSC-Tf fluorescence at low pH. The fluorescence of human LRSC-Tf bound to murine receptors increases at a higher pH, 6.0, indicating that there are differences in conformational stabilization of Tf by receptors of different species. The results suggest that the Tf receptor, in addition to providing a means by which cells may internalize Tf, functions to increase the release of iron from Tf in the endosome.     

Amyloid fibril protein AA: purification and properties of the antigenically related serum component as determined by solid phase radioimmunoassay.

The isolation by gel filtration of a serum component (SAA), antigenically related to the major filbrillar amyloid protein (AA), associated with "secondary" amyloidosis, has been monitored by a solid phase radioimmunoassay for the AA protein to detect cross-reacting serum fractions. Evidence is presented that not all cross-reacting antigenic determinants are accessible in native SAA, since additional determinants are revealed during the isolation procedure. The native structure of SAA appears to be quite labile. SAA from freshly collected serum has a m.w. of 180,000 and co-chromatographs with IgG. However, species of higher m.w. are observed after storage of serum at 4 degrees C or upon chromatography of serum in ammonium bicarbonate. Denatured SAA has a tendency to aggregate under strong dissociating conditions. A 12.500 m.w. antigenic species (SAAL) was detected upon guanidine-HCl denaturation of SAA, by earlier studies employing double immunodiffusion. However, evidence is presented here that the major part of the antigenic acitivity after guanidine-HCl treatment was of m.w. greater than 12,500, but was unreactive in double immunodiffusion. Formic acid treatment of cross-reacting serum fractions does result in virtually complete dissociation of SAA to SAAL, however. Furthermore, Formic acid-dissociated SAAL is of comparable immunoreactivity with AA, on a molar basis, unlike SAAL obtained from SAA by guanidine-HCl denaturation.     

The genetic architecture of fitness in a seed beetle: assessing the potential for indirect genetic benefits of female choice

Background  

Quantifying the amount of standing genetic variation in fitness represents an empirical challenge. Unfortunately, the shortage of detailed studies of the genetic architecture of fitness has hampered progress in several domains of evolutionary biology. One such area is the study of sexual selection. In particular, the evolution of adaptive female choice by indirect genetic benefits relies on the presence of genetic variation for fitness. Female choice by genetic benefits fall broadly into good genes (additive) models and compatibility (non-additive) models where the strength of selection is dictated by the genetic architecture of fitness. To characterize the genetic architecture of fitness, we employed a quantitative genetic design (the diallel cross) in a population of the seed beetle Callosobruchus maculatus, which is known to exhibit post-copulatory female choice. From reciprocal crosses of inbred lines, we assayed egg production, egg-to-adult survival, and lifetime offspring production of the outbred F1 daughters (F1 productivity).