A light- and electron-microscopic investigation of gametogenesis in Typosyllis pulchra (Berkeley and Berkeley) (polychaeta: Syllidae)

Summary Typosyllis pulchra reproduces by the production of three to four gamete-bearing stolons (schizogamy) during consecutive 30-day periods. Although gonads are found in a large number of segments, only those in the posterior-most segments produce gametes and become incorporated into the developing stolon. The more anterior gonads remain undifferentiated and probably sexually undetermined until they are needed in future stolonizations. Gonial cells, which will eventually become either male or female, are ultrastructurally identical at the onset of each stolonization period. Spermatogenesis is marked by a short proliferative period followed by differentiation and spermiogenesis. The first ultrastructural signs of spermatogenesis were found in coelomic spermatogonia on day 10 of stolon formation. Spermatogonia are joined by intercellular bridges, which are maintained until the early spermatid stage. Synaptonemal complexes mark the onset of meiosis, which is apparently synchronized in the syncytial clusters of primary spermatocytes. Spermiogenesis occurs during the final 10 days of stolonization and a variety of stages is present within a single animal. All sperm mature by the time the stolon detaches. Acrosome formation and nuclear condensation are described in addition to the ultrastructure of mature sperm.     

Host-dependent modification of bacteriophage T7 and SAMase-negative T3 derivatives affecting their adsorption ability

Summary When passaging phage T7 and SAMase-negative T3 mutants betweenE. coli strains with identical (EcoB) or without (EcoO) DNA host specificity, phenotypically a host-controlled modification and restriction is observed. This phenomenon is not due to classical modification and restriction of the bacteriophage DNA but depends on the reversibly altered adsorption capacity of the phages on the different host strains.     

Natural occurrence of sterigmatocystin in in-shell pecans.

The natural occurrence of sterigmatocystin (S) in in-shell pecans is reported. Aspergillus versicolor was not isolated from contaminated samples. Incidence of A. flavus and A. glaucus, species known to produce sterigmatocystin under laboratory conditions, was high (43 and 35%, respectively). Isolation data suggest sterigmatocystin may have been produced by one or both of these species.     

An unusual phenotypic expression of Hb-Leiden

After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal β and δ genes.     

Interaction of fatty acids with recombinant rat intestinal and liver fatty acid-binding proteins

Intestinal enterocytes contain two homologous fatty acid-binding proteins, intestinal fatty acid-binding protein (I-FABP)2 and liver fatty acid-binding protein (L-FABP). Since the functional basis for this multiplicity is not known, the fatty acid-binding specificity of recombinant forms of both rat I-FABP and rat L-FABP was examined. A systematic comparative analysis of the 18 carbon chain length fatty acid binding parameters, using both radiolabeled (stearic, oleic, and linoleic) and fluorescent (trans-parinaric and cis-parinaric) fatty acids, was undertaken. Results obtained with a classical Lipidex-1000 binding assay, which requires separation of bound from free fatty acid, were confirmed with a fluorescent fatty acid-binding assay not requiring separation of bound and unbound ligand. Depending on the nature of the fatty acid ligand, I-FABP bound fatty acid had dissociation constants between 0.2 and 3.1 microM and a consistent 1:1 molar ratio. The dissociation constants for L-FABP bound fatty acids ranged between 0.9 and 2.6 microM and the protein bound up to 2 mol fatty acid per mole of protein. Both fatty acid-binding proteins exhibited relatively higher affinity for unsaturated fatty acids as compared to saturated fatty acids of the same chain length. cis-Parinaric acid or trans-parinaric acid (each containing four double bonds) bound to L-FABP and I-FABP were displaced in a competitive manner by non-fluorescent fatty acid. Hill plots of the binding of cis- and trans- parinaric acid to L-FABP showed that the binding affinities of the two sites were very similar and did not exhibit cooperativity. The lack of fluorescence self-quenching upon binding 2 mol of either trans- or cis-parinaric acid/mol L-FABP is consistent with the presence of two binding sites with dissimilar orientation in the L-FABP. Thus, the difference in binding capacity between I-FABP and L-FABP predicts a structurally different binding site or sites.     

Constitutive production of lymphocyte activating factors by normal tissues in the adult rat

Lymphocyte activating factors (LAFs), e.g., interleukin-1 (IL-1) and IL-1-like factors, have previously been demonstrated outside the immune system in the skin, thymus epithelium, and the human and rat testis. We have studied the presence of LAFs in normal tissues of the adult rat, utilizing a highly IL-1 sensitive murine thymocyte proliferation assay. We have demonstrated high amounts of LAF activity in the tongue, esophagus, proventricular part of the stomach, and the liver. Some activity was also demonstrated in the duodenum, placenta, spleen, Peyer's patches, glandular stomach, and jejunum, but no bioactivity was present in other gastrointestinal, endocrine, lymphoid, or haematopoeitic tissues. We were also unable to detect any LAF activity in the reproductive organs (except for the testis), urinary tract, skeletal and muscular tissues, brain, eyes, salivary glands, or lung. In the esophagus the activity was mainly localized to the mucosa. The LAF activity in the skin was partly inhibited by treatment with a mixture of antibodies against human IL-1 alpha and IL-1 beta. Dose response curves and gel filtration on a Sephacryl S-200 column suggested the presence of a high molecular weight (90,000-100,000 Da) LAF inhibitory factor in the liver. In all positive tissues, the demonstrated LAFs had a molecular weight of 15,000-25,000 Da, as determined by Sephacryl S-200 gel filtration. Of the positive tissues, the skin, tongue, esophagus, and the proventricular part of the stomach all contain stratified squamous epithelium. It is tempting to suggest that the detected LAFs have a similar function in these barrier tissues, e.g., to serve as host defence factors, or, alternatively or additionally, as tissue growth factors.     

Static lung-lung interactions in unilateral emphysema.

Motivated by the introduction of single-lung transplantation into clinical practice, we compared the static mechanical properties of the respiratory system in six supine dogs before (at baseline) with those after the induction of unilateral emphysema. Relaxation volume (Vrel), total lung capacity (TLC), and static compliance of the emphysematous lung increased to 214 +/- 68, 186 +/- 39, and 253 +/- 95% (SD) of baseline, respectively. Vrel of the nonemphysematous lung fell to 81 +/- 28% of baseline, with no significant change in TLC of the nonemphysematous lung or its pressure-volume relationship, indicating that unilateral hyperinflation does not cause dropout of contralateral lung units. After unilateral emphysema, the chest wall shifted to a higher unstressed or neutral volume (when pleural pressure equals atmospheric pressure) in three of six animals, minimizing the anticipated decrease in lung recoil pressure at the higher respiratory system Vrel. The pattern of relative lung emptying in the intact dog and in the excised lungs was similar during stepwise deflations from TLC, suggesting that mean pleural pressure of the hemithoraces is equal. We conclude that in the dog the static volume distribution between emphysematous and nonemphysematous lungs is determined only by differences in lung recoil and compliance.     

Middle cerebral artery flow velocity and blood flow during exercise and muscle ischemia in humans.

Changes in middle cerebral artery flow velocity (Vmean), measured by transcranial Doppler ultrasound, were used to determine whether increases in mean arterial pressure (MAP) or brain activation enhance cerebral perfusion during exercise. We also evaluated the role of "central command," mechanoreceptors, and/or muscle "metaboreceptors" on cerebral perfusion. Ten healthy subjects performed two levels of dynamic exercise corresponding to a heart rate of 110 (range 89-134) and 148 (129-170) beats/min, respectively, and exhaustive one-legged static knee extension. Measurements were continued during 2-2.5 min of muscle ischemia. MAP increased similarly during static [114 (102-133) mmHg] and heavy dynamic exercise [121 (104-136) mmHg] and increased during muscle ischemia after dynamic exercise. During heavy dynamic exercise, Vmean increased 24% (10-47%; P less than 0.01) over approximately 3 min despite constant arterial carbon dioxide tension. In contrast, static exercise with a higher rate of perceived exertion [18 (13-20) vs. 15 (12-18) units; P less than 0.01] was associated with no significant change in Vmean. Muscle ischemia after exercise was not associated with an elevation in Vmean, and it did not provoke an increase in Vmean after static exercise. Changes in Vmean during exercise were similar to those recorded with the initial slope index of the 133Xe clearance method. The data show that middle cerebral artery mean flow velocity reflects changes in cerebral perfusion during exercise. Furthermore, they support the hypothesis that cerebral perfusion during exercise reflects an increase in brain activation that is independent of MAP, central command, and muscle metaboreceptors but is likely to depend on influence of mechanoreceptors.     

Altered membrane structure in transfected mouse L-cell fibroblasts expressing rat liver fatty acid-binding protein

Mouse L cell fibroblasts were transfected with cloned cDNA encoding rat liver fatty acid binding protein (L-FABP) also known as sterol carrier protein. Stable transfectant cell lines were selected and expression of L-FABP determined using Western blot analysis. The nontransfected controls and low expression cells did not differ significantly in any of the properties examined. All cell lines showed similar doubling times but cells expressing high levels of L-FABP attained 2-fold higher cell saturation density and differed significantly in their lipid metabolism as indicated by 1) higher cholesterol ester and phospholipid content, and 2) decreased sterol/phospholipid ratio. The observed changes in the lipid composition predicted a lower degree of membrane-lipid order (higher fluidity) in the plasma membranes of cells expressing high levels of L-FABP. Therefore, fluorescent molecule, 1,6-diphenyl-1,3,5-hexatriene, and multifrequency (1-250 MHz) phase and modulation fluorometry were used to probe the effect of L-FABP expression on membrane structure. Steady-state polarization and limiting anisotropy of diphenylhexatriene were significantly lower in the isolated plasma membrane vesicles from the high expression clones. The observed changes in L-cells as a result of de novo expression of L-FABP are consistent with the ability of this protein to bind sterols and fatty acids, stimulate sterol esterification, and stimulate phospholipid biosynthesis. This evidence is supportive of a physiologic role for L-FABP in modulating cellular lipid metabolism and membrane structure.     

Role of polyunsaturated fatty acids and lipid peroxidation in LM fibroblast plasma membrane transbilayer structure

The effects of polyunsaturated fatty acids and lipid peroxidation on LM fibroblast plasma membrane individual leaflet sterol distribution and structural order were examined. The cytofacial (inner) leaflet was more rigid and contained more sterol than the exofacial (outer) leaflet. The static (limiting anisotropy) and dynamic (rotational relaxation time) structural components of diphenylhexatriene (DPH) motion in each leaflet were determined by phase and modulation fluorometry measurements combined with leaflet-specific quenching by trinitrophenyl groups. Polyunsaturated fatty acids, incorporated into the membrane phospholipids by culture medium supplementation, decreased the limiting anisotrophy of DPH in the cytofacial but not the exofacial leaflet thereby abolishing the transbilayer difference in fluidity. Peroxidation by Fe(II) + H2O2 resulted in a rigidification (increase in limiting anisotropy and rotational relaxation time) of the plasma membrane exofacial leaflet, regardless of whether the membranes contained saturated and monounsaturated fatty acids or were enriched in either linoleate or linolenate. The structure of the cytofacial leaflet reported by DPH was unaffected. Plasma membrane transbilayer sterol distribution, measured by leaflet-specific quenching of dehydroergosterol fluorescence, indicated that 20-28% of the sterol was localized in the exofacial leaflet. Polyunsaturated fatty acid supplementation of LM fibroblasts resulted in a complete reversal of plasma membrane transbilayer sterol distribution (72-76% exofacial leaflet). Sterol transbilayer distribution between the membrane leaflets was completely resistant to alteration by exposure to crosslinking agents and peroxidation in control plasma membranes and by peroxidation in linoleate- or linolenate-supplemented membranes.