Sperm motility in the presence of boundaries

The fluid dynamics of sperm motility near both rigid and elastic walls is studied using the immersed boundary method. Simulations of both single and interacting organisms are presented. In particular, we find that nearby organisms originally undulating with a 90° phase shift may adjust their relative swimming velocities and phase-lock. Comparisons with previous analytical results are also discussed. The tendency of a near-wall to attract organisms is demonstrated.     

Regulation of insulin-like growth factor (IGF) binding protein-2 synthesis and degradation by platelet-derived growth factor and the IGFs is enhanced by serum deprivation in vascular smooth muscle cells

Growth factors such as platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF-1) stimulate proliferation and migration of vascular smooth muscle cells (SMC). IGF-l bioactivity is modulated by high-affinity binding proteins (IGFBP) which are important regulators of these processes. Procine vascular SMC synthesize IGFBP-2 and IGFBP-4 in vitro. In the present study, levels of IGFBP-2 in conditioned media (CM) were increased approximately 1.6 to 2.2-fold when cells were exposed to PDGF (20 ng.ml) or insulin (5 μg/ml) for 24 hr following a 24 hr incubation in serum-free media, or following a 72 hr exposure to either growth factor. Similar increases in IGFBP-2 mRNA levels were observed. Exposure of cells to PDGF for 24 hr without prior serum deprivation resulted in smaller (47 ± 11%) increases in IGFBP-2 protein levels but failed to alter mRNA levels. IGF-1, FGF-b? and EGF failed to increase IGFBP-2 using either experimental paradigm. In contrast, IGFBP-2 protein levels were consistently decreased (75 ± 14%) after 72 hr of exposure to IGF-II without corresponding decreases in IGFBP-2 mRNA levels. Immunoprecipitation of [³⁵S] methionine-labeled IGFBP-2 indicated that this decrease was not due to a decrease in synthesis of IGFBP-2. Immunoblot analysis of CM from cells treated with IGF-II indicated that the decrease in intact protein corresponded with an increase in two non-IGF binding IGFBP-2 fragments of 22 and 14 kD. Increased abundance of these fragements was also observed following IGF-I exposure, although corresponding decreases in intact IGFBP-2 were not usually observed. The relative abundance of these fragments did not appear to be affected by treatment with PDGF or insulin. In contrast to IGFBP-2, regulation of the levels of IGFBP-4 in CM did not appear to be altered by serum deprivation. Insulin consistently increased IGFBP-4 mRNA and protein levels under all situations. PDGF tended to increase IGFBP-4 protein levels, although this effect was less consistent and not as great as the increase observe with insulin. Treatment with IGF-I or -ll consistently decreased IGFBP-4 levels in CM but tended to increase their mRNA levels under all situations. These data indicate that insulin, PDGF, and the IGFs regulate both IGFBP-2 and IGFBP-4. While PDGF and insulin stimulate IGFBP-2 and 4 synthesis, the IGFs appear to activate protease(s) which regulate IGFBP-2 and -4 levels post-translationally. The regulation of IGFBP-2 levels by each of these mechanisms appears to be amplified by serum deprivation, but this is not observed with IGFBP-4. © 1995 Wiley-Liss, Inc.     

Two New Species of Aphelenchoididae (Nemata) from Declining Red Pines in Maryland

Aphelenchoides resinosi n. sp. and Ektaphelenchus joyceae n. sp. are described and illustrated from red pines of the Allegheny plateau of Maryland, USA. The new species were found in trees infested with Bursaphelenchus xylophilus. Primary diagnostic characters of A. resinosi females are constriction of the head, basal stylet knobs, tong postuterine sac, two incisures in the lateral field, and conical tail four to five anal body widths long with a simple terminal mucro. Diagnostic characters of the males are two pairs of subventral caudal papillae and spicule shape: Primary diagnostic characters of E. joyceae females are a slight constriction of the head, six similar lips, conical tail, and short postuterine sac. Diagnostic characters of the males are spicule size and shape, a single row of spermatocytes, and one pair of caudal papillae. Within-tree distributions of A. resinosi and E. joyceae are presented. A total of 70% of both red-needled and chlorotic-needled trees in the study were positive for A. resinosi and E. joyceae. Branch hierarchy was related to the percentage of samples positive for A. resinosi.     

Severe thrombocytopenia associated with acute folic acid deficiency and severe hemorrhage in two patients.

Severe thrombocytopenia associated with acute folic acid deficiency in two inpatients is described. Both patients had severe hemorrhagic manifestations. A similar syndrome has previously been described in patients who have undergone extensive surgery or dialysis or both. The present cases show that acute folic acid deficiency can occur in other circumstances and may go unrecognized because other signs in the peripheral blood of a megaloblastic process may be minimal. A good response was obtained with folic acid therapy.     

Recombination and Chromosome Segregation during the Single Division Meiosis in SPO12–1 and SPO13–1 Diploids

This paper reports a study of chromosome segregation and recombination during sporulation of spo12–1 and spo13–1 diploid strains of S. cerevisiae. These strains undergo a single division to form asci containing two diploid or near-diploid spores. The segregation of centromere-linked markers in the two-spored (dyad) products indicates that the division is generally equational. However, in a small percentage of the spo12–1 and spo13–1 cells, it appears that a meiosis I-like division occurs. Aberrant segregation of the MAT locus on chromosome III, yielding a monosomic and a trisomic spore pair, occurs in 12% of all dyads. The segregation patterns of markers at various distances from their centromeres and several pairs of markers on the same chromosome indicate that recombination takes place in both strains at nearly standard meiotic levels.     

Oxyhemoglobin dissociation curve as expo-exponential paradigm of asymmetric sigmoid function.

From the assumption that the fractional increase of HbO₂ as a function of pO₂ is proportional to HbO₂, and that the proportionality coefficient of that relation decreases exponentially with pO₂, an equation can be derived that gives an excellent fit to the full range of the oxyhemoglobin dissociation curve. To generate this asymmetric sigmoid curve, only one rate constant is required. In addition, the initial and final conditions specify an intermediate constant B, the “shift factor” that determines the horizontal displacement of the curve. The rate constant K specifies the rate of change of the specific rate of increase of HbO₂ with respect to O₂. Governing the slope of the curve, K decreases as temperature and acidity increase, while the B factor remains constant. For Hb in solution, B decreases with decrease of concentration, but K appears to be unchanged. The expo-exponential constants provide convenient specification of the full course and position of the oxyhemoglobin dissociation curve.     

Enzymatic amplification involving glycosyltransferases forms the basis for the increased size of asparagine-linked glycans at the surface of NIH 3T3 cells expressing the N-ras proto-oncogene.

Expression of ras oncogenes in NIH 3T3 fibroblasts results in the acquisition by these cells of an invasive potential concomitant with the appearance of cell surface asparagine-linked complex-type glycan structures of a higher average molecular weight (Bolscher, J.G. M., van der Bijl, M. M. W., Neefjes, J. J., Hall, A., Smets, L.A., and Ploegh, H.L. (1988) EMBO J. 7, 3361-3368). We have investigated the enzymatic basis for the altered glycosylation by assessing the activities of all major Golgi glycosyltransferases involved in the synthesis of these structures. Use was made of a stable transfectant cell line (T15) containing the N-ras-protooncogene under the control of a glucocorticoid-inducible mouse mammary tumor virus promoter. Upon induction of the ras gene with dexamethasone: 1) the levels of N-acetylglucosaminyltransferase I and II were essentially unaltered, indicating an unaffected potential to synthesize complex-type glycans; 2) the activities of the branching N-acetylglucosaminyltransferase III and V were elevated 2- to 2.5-fold suggesting the formation of increased amounts of bisected glycans and of structures carrying a Gal beta 1----GlcNAc beta 1----6Man-branch; 3) the levels of the elongating beta 4-galactosyltransferase and beta 3-N-acetylglucosaminyl-transferase were increased 5- to 7-fold indicating a strongly enhanced capacity to synthesize polylactosaminoglycan chains; 4) the level of the major chain-terminating enzyme, alpha 3-galactosyltransferase, was slightly decreased (0.7-fold), whereas those of the alpha 3- and alpha 6-sialyltransferases were slightly elevated (1.3- and 2-fold, respectively), suggesting a shift from termination by alpha-galactosyl residues to termination by sialic acid moieties. Studies on the acceptor specificities of the different glycosyltransferases indicate that these changes occur in a coordinated manner in which the effects of altered glycosyltransferase expression levels amplify each other. Analysis of the size of cell surface complex-type glycopeptides before and after digestion with neuraminidase and endo-beta-galactosidase suggested an increased sialic acid density, an increase in the number and/or length of polylactosaminoglycan chains, and an increased branching of the glycans upon N-ras induction. The enzymatic results explain these structural changes and allow us to define the alterations in glycosylation pathways associated with ras expression.     

Use of Ultrafiltration To Isolate Viruses from Seawater Which Are Pathogens of Marine Phytoplankton

Viruses may be major structuring elements of phytoplankton communities and hence important regulators of nutrient and energy fluxes in aquatic environments. In order to ascertain whether viruses are potentially important in dictating phytoplankton community structure, it is essential to determine the extent to which representative phytoplankton taxa are susceptible to viral infection. We used a spiral ultrafiltration cartridge (30,000-molecular-weight cutoff) to concentrate viruses from seawater at efficiencies approaching 100%. Natural virus communities were concentrated from stations in the Gulf of Mexico, a barrier island pass, and a hypersaline lagoon (Laguna Madre) and added to cultures of potential phytoplankton hosts. By following changes in in vivo fluorescence over time, it was possible to isolate several viruses that were pathogens to a variety of marine phytoplankton, including a prasinophyte (Micromonas pusilla), a pennate diatom (likely a Navicula sp.), a centric diatom (of unknown taxa), and a chroococcoid cyanobacterium (a Synechococcus sp.). As well, we observed changes in fluorescence in cultures of a cryptophyte (a Rhodomonas sp.) and a chlorophyte (Nannochloropsis oculata) which were consistent with the presence of viral pathogens. Although pathogens were isolated from all stations, all the pathogens were not isolated from every station. Filterability studies on the viruses infecting M. pusilla and the Navicula sp. showed that the viruses were consistently infective after filtration through polycarbonate and glass-fiber filters but were affected by most other filter types. Establishment of phytoplankton-pathogen systems will be important in elucidating the effect that viruses have on primary producers in aquatic systems.