Sex differences in song perception in Bengalese finches measured by the cardiac response

Birdsong may be perceived and processed differently by males and females because the production and function of this behaviour are often sexually dimorphic. However, examination of this hypothesis has been difficult, since different behavioural measures have been used to describe the perceptual process for each sex. We analysed changes in heart rate as an index of song perception in Bengalese finches, Lonchura striata var. domestica. In this species, only males sing, and song is used exclusively for mate attraction. This species is not territorial and songs are never used in aggressive contexts. In both sexes, repeated presentation of a song resulted in a waning of the heart rate response. Presentation of heterospecific songs did not increase the heart rate. When a novel conspecific song was presented, the heart rate increased only in females with each presentation of the stimulus, not in males. These results correspond to the sex differences in song usage in this species. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Ca2+-dependent and phorbol ester activating phosphorylation of a 36K-dalton protein of rat basophilic leukemia cell membranes and immunoprecipitation of the phosphorylated protein with IgE-anti IgE system

Endogeneous phosphorylation of rat basophilic leukemia cell membranes was investigated. EGTA specifically inhibited the phosphorylation of a protein having an approximate molecular weight of 36,000 dalton (36K-Da protein). Phosphorylation of this protein was enhanced by phorbol-12-myristate-13-acetate in the presence of phosphatidylserine. The phosphorylated 36K-Da protein was specifically immunoprecipitated with IgE and anti IgE antibody. These results suggest that the phosphorylated 36K-Da protein is the beta-chain of the receptor for IgE and that protein kinase C is involved in the phosphorylation mechanism.     

Changes in N-glycosylation of human stromal cells by telomerase expression

It was established that remarkable changes in the N-glycosylation are induced in immortalized cancer cells. Whether changes were induced in human stromal cells immortalized by transfection with the human telomerase catalytic subunit (hTert) cDNA was examined by lectin blot analysis. Morphological appearance and growth rate of the gene-transfected stromal cells were not changed significantly. However, lectin blot analysis of membrane glycoprotein samples showed that bindings of Ricinus communis agglutinin-I (RCA-I) and of leuko-agglutinating phytohemagglutinin to glycoprotein bands increase significantly in the gene-transfected cells. No lectin binding was observed when blotted filters were treated with diplococcal beta-1,4-galactosidase or N-glycanase prior to incubation with RCA-I. In contrast, no changes in Coomassie brilliant blue-staining and in binding of concanavalin A were obtained between the primary and gene-transfected stromal cells. These results indicate that the highly branched N-glycosylation with augmented galactosylation is induced in human stromal cells immortalized by the telomerase expression.     

Moderate hypothermia increases the chance of spiral wave collision in favor of self-termination of ventricular tachycardia/fibrillation

In cardiac arrest due to ventricular fibrillation (VF), moderate hypothermia (MH, 33 degrees C) has been shown to improve defibrillation success compared with normothermia (NR, 37 degrees C) and severe hypothermia (SH, 30 degrees C). The underlying mechanisms remain unclear. We hypothesized that MH might prevent reentrant excitations rotating around functional obstacles (rotors) that are responsible for the genesis of VF. In two-dimensional Langendorff-perfused rabbit hearts prepared by cryoablation (n = 13), action potential signals were recorded by a high-resolution optical mapping system. During basic stimulation (2.5-5.0 Hz), MH and SH caused significant prolongation of action potential duration and significant reduction of conduction velocity. Wavelength was unchanged at MH, whereas it was shortened significantly at SH at higher stimulation frequencies (4.0-5.0 Hz). The duration of direct current stimulation-induced ventricular tachycardia (VT)/VF was reduced dramatically at MH compared with NR and SH. The spiral wave (SW) excitations documented during VT at NR were by and large organized, whereas those during VT/VF at MH and SH were characterized by disorganization with frequent breakup. Phase maps during VT/VF at MH showed a higher incidence of SW collision (mutual annihilation or exit from the anatomical boundaries), which caused a temporal disappearance of phase singularity points (PS-0), compared with that at NR and SH. There was an inverse relation between PS-0 period in the observation area and VT/VF duration. MH data points were located in a longer PS-0 period and a shorter VT/VF duration zone compared with SH. MH causes a modification of SW dynamics, leading to an increase in the chance of SW collision in favor of self-termination of VT/VF.     

Rho-kinase is involved in mouse blastocyst cavity formation

During mammalian embryonic development, the formation and subsequent expansion of a fluid-filled cavity, the blastocoel, is crucial for successful implantation. Our present experiments were aimed at exploring the contribution of Rho-kinase, a downstream effector of the small GTP-binding protein RhoA, to mouse blastocoel formation. RT-PCR analysis showed that Rho-kinase mRNA is present throughout mouse preimplantation development. When 2-cell embryos were cultured in the presence of a specific inhibitor of Rho-kinase, Y-27632, they developed to the morula stage but failed to develop to the blastocyst stage. Y-27632 inhibited the formation of the blastocoel cavity from the morula stage, and this inhibitory effect was reversible when embryos were returned to medium without Y-27632. Moreover, Y-27632 reduced the rate of re-expansion of blastocysts collapsed by cytochalasin D upon transfer to the control medium. These results suggest that Rho-kinase is likely involved in blastocyst formation.     

Mitochondrial Ribosomal Protein L11 Gene of Dictyostelium discoideum Resides not in the Nuclear Genome but in the Mitochondrial Genome

During the course of analysis of the mitochondrial genome ofthe cellular slime mold, Dictyostelium discoideum, we founda gene (rpl11) for mitochondrial ribosomal protein L11 (RPL11),having 172 amino acid residues. Southern blot analysis revealedthat the gene resided in the mitochondrial DNA as a singlecopybut not in the nuclear DNA. From Northern blot experiments,one major mRNA (about 27 kb) and two minor mRNAs (about 4 and5 kb) for the gene were detected in the mitochondria. This isthe first report showing that the active gene for RPL11 stillresides in the mitochondrial genome and has not been transferredto the nuclear genome in D. discoideum.     

Exocytotic insertion of calcium channels constrains compensatory endocytosis to sites of exocytosis

Proteins inserted into the cell surface by exocytosis are thought to be retrieved by compensatory endocytosis, suggesting that retrieval requires granule proteins. In sea urchin eggs, calcium influx through P-type calcium channels is required for retrieval, and the large size of sea urchin secretory granules permits the direct observation of retrieval. Here we demonstrate that retrieval is limited to sites of prior exocytosis. We tested whether channel distribution can account for the localization of retrieval at exocytotic sites. We find that P-channels reside on secretory granules before fertilization, and are translocated to the egg surface by exocytosis. Our study provides strong evidence that the transitory insertion of P-type calcium channels in the surface membrane plays an obligatory role in the mechanism coupling exocytosis and compensatory endocytosis.     

Fusion of cell ghosts with intact cells in Dictyostelium discoideum: Differential response of opposite mating-type cells

The sexual cycle of Dictyostelium discoideum is initiated by the fusion of cells that are of opposite mating types (e.g. NC4- and HM1-type cells). Cells grown in light on agar plates are not capable of sexual cell fusion, but become capable when cultured in the dark in a liquid medium. Cells in the incapable state are called fusion-incompetent cells, and cells in the latter state, fusion-competent cells. To gain some understanding of the mechanism of cell fusion, cell ghosts prepared by freeze-thawing intact cells were incubated with intact cells. The cell ghosts killed the intact cells by directly fusing with them, the extent of fusion depending on the particular strains employed and the fusion-competency of the intact cells and of the cells from which the cell ghosts had been prepared. A detailed examination revealed that fusion-competent NC4 cells were always more easily killed by cell ghosts than fusion-incompetent NC4 cells. It also became apparent that cell ghosts prepared from fusion-competent NC4 cells killed all cell types far more efficiently than did those prepared from fusion-incompetent NC4 cells. However, fusion-competent and fusion-incompetent HM1 cells were equally sensitive to cell ghosts, and cell ghosts prepared from fusion-competent HM1 cells had the same ability to kill as those prepared from fusion-incompetent HM1 cells. From these findings, it thus appears that opposite mating-type cells have distinct membrane properties related to sexual cell fusion.