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At least 1,531 records · Page 85Linked to original sources
PubMed2006

Oogenesis in the leech Glossiphonia heteroclita (Annelida, Hirudinea, Glossiphoniidae) II. Vitellogenesis, follicle cell structure and egg shell formation.

By the end of previtellogenesis, the oocytes of Glossiphonia heteroclita gradually protrude into the ovary cavity. As a result they lose contact with the ovary cord (which begins to degenerate) and float freely within the hemocoelomic fluid. The oocyte's ooplasm is rich in numerous well-developed Golgi complexes showing high secretory activity, normal and transforming mitochondria, cisternae of rER and vast amounts of ribosomes. The transforming mitochondria become small lipid droplets as vitellogenesis progresses. The oolemma forms microvilli, numerous coated pits and vesicles occur at the base of the microvilli, and the first yolk spheres appear in the peripheral ooplasm. A mixed mechanism of vitellogenesis is suggested. The eggs are covered by a thin vitelline envelope with microvilli projecting through it. The envelope is formed by the oocyte. The vitelline envelope is produced by exocytosis of vesicles containing two kinds of material, one of which is electron-dense and seems not to participate in envelope formation. The cortical ooplasm of fully grown oocytes contains many cytoskeletal elements (F-actin) and numerous membrane-bound vesicles filled with stratified content. Those vesicles probably are cortical granules. The follicle cells surrounding growing oocytes have the following features: (1) they do not lie on a basal lamina; (2) their plasma membrane folds deeply, forming invaginations which eventually seem to form channels throughout their cytoplasm; (3) the plasma membrane facing the ovary lumen is lined with a layer of dense material; and (4) the plasma membrane facing the oocyte forms thin projections which intermingle with the oocyte microvilli. In late oogenesis, the follicle cells detach from the oocytes and degenerate in the ovary lumen.

Animals↗
PubMed2003

Multiple forms of medicinal leech destabilase-lysozyme.

Earlier, three genes Ds1, Ds2, and Ds3 encoding corresponding destabilase-lysozyme isoforms were identified. However only one form of the enzyme encoded by Ds3 gene coincided with the protein CNBr fragments [Mol. Gen. Genet. 253 (1996) 20]. In this work we found by ESI-TOF mass spectrometry that the enzyme preparation consists of at least three forms with molecular masses of 12677.6, 12839.7, and 12938.2Da, each of which contains seven disulfide bridges. Only one mass (12839.7Da) fits to the calculated mass for the protein encoded by Ds3 gene. Further analysis of the CNBr fragments of the enzyme showed the heterogeneity of large 5.5 kDa peptide at positions 64 (threonine or arginine) and 67 (histidine or arginine) in the wild-type amino acid sequence. One CNBr peptide, with Arg and His at positions 64 and 67, respectively, correlates in the molecular mass with the protein encoded by Ds3. In addition, we have found a new acid form of destabilase-lysozyme, P-Ac, which differs from all known destabilase-lysozyme structures by its N-terminal amino acid sequence.

Amino Acid Sequence↗
PubMed1996

Three-dimensional reconstruction of Macrobdella decora (leech) hemoglobin by cryoelectron microscopy.

Macrobdella decora hemoglobin was observed in vitreous ice by cryoelectron microscopy and subjected to three-dimensional reconstruction by the method of random conical tilt series. The refined volume has a resolution of 40 A and a D6 point-group symmetry. Its architecture, with its hexagonal bilayer appearance, resembles those of Lumbricus terrestris (oligochaete) and Eudistylia vancouverii (polychaete). When the reconstruction volume is viewed along its sixfold axis, the vertices of the upper hexagonal layer are rotated 16 degrees clockwise compared to those of the lower layer. In agreement with the "bracelet" model of Vinogradov et al., a central linker complex is decorated by 12 hollow globular substructures. The linker complex is made up of a central hexagonal toroid linked by 12 c5 connections to two bracelets of c3 connections, which are themselves linked via six c4 connections. The portion of the hollow globular substructure corresponding to the dodecamer of globin chains has a local pseudo threefold symmetry and is composed of three elongated structures visible when the volume is displayed at high threshold. The main difference between Macrobdella, Lumbricus, and Eudistylia hemoglobins is the presence in Macrobdella of a central hexagonal toroid instead of a compact flat hexagonal structure.

Animals↗
PubMed1997

Single potassium channels in neuropile glial cells of the leech central nervous system.

We performed patch-clamp experiments to identify distinct K+ channels underlying the high K+ conductance and K+ uptake mechanism of the neuropile glial cell membrane on the single-channel level. In the soma membrane four different types of K+ channels were characterized, which were found to be distributed in clusters. Since no other types of K+ channels were observed, these appear to be the complete repertoire of K+ channels expressed in the soma region of this cell type. The outward rectifying 42 pS K+ channel could markedly contribute to the high K+ conductance and the maintenance of the membrane potential, since it shows the highest open probability of all channels. The channel gating occurred in bursts and patch excision decreased the open probability. The outward rectifying 74 pS K+ channel was rarely active in the cell-attached configuration; however, patch excision enhanced its open probability considerably. This type of channel may be involved in neuron-glial crosstalk, since it is activated by both depolarizations and increases in the intracellular Ca2+ concentration, which are known to be induced by neurotransmitter release following the activation of neurons. The 40 pS and 83 pS K+ channels showed inward rectifying properties, suggesting their involvement in the regulation of the extracellular K+ content. The 40 pS K+ channel could only be observed in the inside-out configuration. The 83 pS channel was activated following patch excision. At membrane potentials more negative than -60 mV, flickering events indicated voltage-dependent gating.

4-Aminopyridine↗
PubMed1999

Ionic mechanism of 4-aminopyridine action on leech neuropile glial cells.

Extracellular 4-aminopyridine (4-AP), tetraethylammonium chloride (TEA) and quinine depolarized the neuropile glial cell membrane and decreased its input resistance. As 4-AP induced the most pronounced effects, we focused on the action of 4-AP and clarified the ionic mechanisms involved. 4-AP did not only block glial K+ channels, but also induced Na+ and Ca2+ influx via other than voltage-gated channels. The reversal potential of the 4-AP-induced current was -5 mV. Application of 5 mM Ni2+ or 0.1 mM d-tubocurarine reduced the 4-AP-induced depolarization and the associated decrease in input resistance. We therefore suggest that 4-AP mediates neuronal acetylcholine release, apparently by a presynaptic mechanism. Activation of glial nicotinic acetylcholine receptors contributes to the depolarization, the decrease in input resistance, and the 4-AP-induced inward current. Furthermore, the 4-AP-induced depolarization activates additional voltage-sensitive K+ and Cl- channels and 4-AP-induced Ca2+ influx could activate Ca2+-sensitive K+ and Cl- channels. Together these effects compensate and even exceed the 4-AP-mediated reduction in K+ conductance. Therefore, the 4-AP-induced depolarization was paralleled by a decreasing input resistance.

4-Aminopyridine↗
PubMed1976

On the distribution and role of acid phosphatase in the sub-pharyngeal ganglia of Indian cattle leech, Poecilobdella granulosa.

Histoenzymatic studies on the sub-pharyngeal ganglia have shown two types of neurons, enclosed in a packet-glial-cell. One of these kinds of cells is larger than the other and vesiculated, while the other is non-vesiculated. Interestingly, all the neurons have reacted very violently for acid phosphatase. The reaction is predominently cytoplasmic, masking the cellular organelles in most of the cells. Smaller cells are more in number and of two kinds. The neuronal processes (axons) have manifested mild enzymatic activity. The neuropile shows predominently granular reaction, each dot probably representing a synaptic site. Intersegmental tracts have provided intense enzymatic activity. Possible physiological significance has been discussed.

Acid Phosphatase↗