Fine structure of microgametogenesis of Eimeria ferrisi Levine and Ivens 1965 in Mus musculus

Summary The microgamogony of Eimeria ferrisi from experimentally infected mice was investigated with the electron microscope. Microgamonts were recognizable by the presence of peripherally arranged nuclei and the presence of single or paired centrioles between each nucleus and the limiting membrane of the parasite. Often an intranuclear centrocone directed toward the centriole was present. Differentiation of the microgamete began when elevations of the limiting membrane, which indicated the commencement of flagellar development, appeared above the centrioles. This event was accompanied by the segregation of nuclear content into a dense osmiophilic portion and an electron-pale portion. Then followed a gradual protrusion of the dense portion of the nucleus and developing flagella into the parasitophorous vacuole. A dense ring developed at the base of the differentiating microgamete, resulting in the formation of a stalk which was occupied by the residual portion of the nucleus. Fully developed microgametes became detached and occupied the parasitophorous vacuole along with the residual cytoplasm. Microgametes had an anterior perforatorium, a dense elongate nucleus, with an anteriorly positioned mitochondrion in a small groove of the nucleus. Usually two flagella were present but one microgamete appeared to have three. Polysaccharide first appeared when differentiation was in progress and increased until large numbers of granules were present in the microgamont cytoplasm.Abbreviations AM Amylopectin - B Basal Body of Flagellum - CC Centrocone - CE Centriole - DR Dense Ring - ER Endoplasmic Reticulum - F Flagellum - HC Host Cell - HN Host Cell Nucleus - MI Mitochondrion - MN Microneme - MP Micropore - MT Microtubule - N Nucleus - P Perforatorium - PL Osmiophilic Plate - PV Parasitophorous Vacuole - RN Residual Nucleus Supported in part by the Deutsche Forschungsgemeinschaft¹, the Alexander von Humboldt Foundation² and a Faculty Development Grant to Andrews University by the Merck Foundation, Rahway, New Jersey, USA     

Localization of corticotropin-releasing activity in the rat hypothalamus

Hypothalamic nuclei were removed from frozen sections of rat brain and examined for their corticotropin-releasing activity. The highest concentration was measured in the median eminence. In addition there was significantly more activity detected in the nuclei paraventricularis, supraopticus, suprachiasmaticus and arcuatus than in the other nuclei.     

Human immunodeficiency virus type 1 Tat binds to Candida albicans, inducing hyphae but augmenting phagocytosis in vitro

Tat, the human immunodeficiency virus type 1 (HIV-1) transactivating protein, binds through its RGD-motif to human integrin receptors. Candida albicans, the commonest cause of mucosal candidiasis in subjects infected with HIV-1, also possesses RGD-binding capacity. The present study reveals that Tat binds to C. albicans but not to C. tropicalis. Tat binding was markedly reduced by laminin and to a lesser extent by a complement C3 peptide containing the RGD motif, but not by a control peptide. The outgrowth of C. albicans was accelerated following binding of Tat, but phagocytosis of opsonized C. albicans was also increased after Tat binding. Thus, Tat binding promotes fungal virulence by inducing hyphae but may also reduce it by augmenting phagocytosis. The net effect of Tat in vivo is difficult to judge but in view of the many disease-promoting effects of Tat we propose that accelerating the formation of hyphae dominates over the augmentation of phagocytosis.     

Using literature-based discovery to identify disease candidate genes

We present BITOLA, an interactive literature-based biomedical discovery support system. The goal of this system is to discover new, potentially meaningful relations between a given starting concept of interest and other concepts, by mining the bibliographic database MEDLINE. To make the system more suitable for disease candidate gene discovery and to decrease the number of candidate relations, we integrate background knowledge about the chromosomal location of the starting disease as well as the chromosomal location of the candidate genes from resources such as LocusLink and Human Genome Organization (HUGO). BITOLA can also be used as an alternative way of searching the MEDLINE database. The system is available at http://www.mf.uni-lj.si/bitola/.     

Compartmental aspects of Na+ saturation kinetics in prog skina

Epithelial membranes are multicompartment structures of microscopic and submicroscopic dimensions. Therefore, interpretations of kinetic data on solute fluxes, based on the standard three compartment model are open to criticism. We have obtained an integrated view of the kinetics of Na⁺ transport in frog skin epidermis by application of the computer simulation method. Epidermis and whole skin models were designed which resemble photomicrographs of these tissues. Justification is given for the way in which internal and external chamber compartments are connected (topology). The epidermis model has eight passive, and two active transfer sites. Our primary aims were 1) simulation of the transepidermal Na⁺ influx and the concomitant Na⁺ backflux saturation kinetics, and 2) localization of the so-called “outer” and “inner” Na⁺ responsive borders in epidermis. The analysis, based on methodical variations of transfer coefficients, suggests involvement of the “composite desmosomes” and the transepithelial Na⁺-pump leak pathway. These are located in the outer and the inner region of the epidermis, respectively. Reasonable functional agreement between epidermis and model was also seen in 1) Na⁺ saturation kinetics in ouabain, poisoned system, 2) relative independence of the two borders to the “trans” [Na⁺] in the external solutions, and 3) equal energy requirement, for the transmembrane Na⁺ pump, Na⁺/O₂∼-20. This work was supported by NIH Grant GM 03545-23     

Modification of collagen matrices for enhancing angiogenesis

The vascularization of engineered tissues in many cases does not keep up with the ingrowth of cells. Nutrient and oxygen supply are not sufficient, which ultimately leads to the death of the invading cells. The enhancement of the angiogenic capabilities of engineered tissues therefore represents a major challenge in the field of tissue engineering. The immobilization of angiogenic growth factors may be useful for enhancing angiogenesis. The most potent angiogenic growth factor specific to endothelial cells, vascular endothelial growth factor (VEGF), occurs in several splice variants. The variant with 165 amino acids both has a high angiogenic activity and a high affinity for heparin. We therefore incorporated heparin molecules into collagen matrices by covalently cross-linking them to amino functions on the collagen. Physical binding of VEGF to the heparin may then prevent a rapid clearance from the implant, while the release rate may become coupled to the degradation of the collagen matrix. The modified matrices were characterized by determination of the extent of the heparin immobilization, the in vitro degradation rate by collagenase. For testing the angiogenic properties, non-modified and heparinized collagen specimens were--either loaded with VEGF or non-loaded--subcutaneously implanted on the back of rats. Specimens were explanted after varying periods of implantation, the dry weights and the hemoglobin contents, as well as immunostained histological sections were evaluated: heparinized collagen matrices loaded with VEGF are vascularized to a substantially higher extent as compared to non-modified matrices.     

An efficient method to generate chromosomal rearrangements by targeted DNA double-strand breaks in Drosophila melanogaster

Homologous recombination (HR) is an indispensable tool to modify the genome of yeast and mammals. More recently HR is also being used for gene targeting in Drosophila. Here we show that HR can be used efficiently to engineer chromosomal rearrangements such as pericentric and paracentric inversions and translocations in Drosophila. Two chromosomal double-strand breaks (DSBs), introduced by the rare-cutting I-SceI endonuclease on two different mobile elements sharing homologous sequences, are sufficient to promote rearrangements at a frequency of 1% to 4%. Such rearrangements, once generated by HR, can be reverted by Cre recombinase. However, Cre-mediated recombination efficiency drops with increasing distance between recombination sites, unlike HR. We therefore speculate that physical constraints on chromosomal movement are modulated during DSB repair, to facilitate the homology search throughout the genome.     

Noise-induced cell death in the mouse medial geniculate body and primary auditory cortex

Noise-induced effects within the inner ear have been well investigated for several years. However, this peripheral damage cannot fully explain the audiological symptoms in noise-induced hearing loss (NIHL), e.g. tinnitus, recruitment, reduced speech intelligibility, hyperacusis. There are few reports on central noise effects. Noise can induce an apoptosis of neuronal tissue within the lower auditory pathway. Higher auditory structures (e.g. medial geniculate body, auditory cortex) are characterized by metabolic changes after noise exposure. However, little is known about the microstructural changes of the higher auditory pathway after noise exposure. The present paper was therefore aimed at investigating the cell density in the medial geniculate body (MGB) and the primary auditory cortex (AI) after noise exposure. Normal hearing mice were exposed to noise (10 kHz center frequency at 115 dB SPL for 3 h) at the age of 21 days under anesthesia (Ketamin/Rompun, 10:1). After 1 week, auditory brainstem response recordings (ABR) were performed in noise exposed and normal hearing animals. After fixation, the brain was microdissected and stained (Kluever-Barrera). The cell density in the MGB subdivisions and the AI were determined by counting the cells within a grid. Noise-exposed animals showed a significant ABR threshold shift over the whole frequency range. Cell density was significantly reduced in all subdivisions of the MGB and in layers IV-VI of AI. The present findings demonstrate a significant noise-induced change of the neuronal cytoarchitecture in central key areas of auditory processing. These changes could contribute to the complex psychoacoustic symptoms after NIHL.