When terrestrial slugs (Limax maximus) are dehydrated to 65-70% of their initial body weight (IBW) their feeding responsiveness is greatly decreased. There is a 90% decrease in feeding responsiveness ...when slugs are injected with hyperosmotic mannitol solution that raises the haemolymph osmolality to that of slugs dehydrated to 65-70% IBW (i.e. 200 mosmol kg-1 H2O). The duration of the Feeding Motor Programme (FMP) that can be recorded from an isolated CNS-lip preparation is reduced by increasing the osmolality of the saline bathing the preparation. The osmolality of the saline that can modify the FMP corresponds to that of the haemolymph of a slug dehydrated to 65-70% IBW. The pattern of the motor programme is not affected. A gradual increase in saline osmolality which temporally mimics the progressive increase in haemolymph osmolality of a dehydrating slug also causes a decrease in the duration of the FMP. The neural network underlying the FMP appears to adapt to hyperosmotic saline since the duration of FMP bouts gradually returns to normal levels after long-term exposure (6-8 h).
Research over the past few years has demonstrated the central role of protein phosphorylation in regulating mitosis and the cell cycle. However, little is known about how the mechanisms regulating ...the entry into mitosis contribute to the positional and temporal regulation of the actomyosin-based contractile ring formed during cytokinesis. Recent studies implicate p34cdc2 as a negative regulator of myosin II activity, suggesting a link between the mitotic cycle and cytokinesis. In an effort to study the relationship between protein phosphorylation and cytokinesis, we examined the in vivo and in vitro phosphorylation of actin-associated cortical cytoskeletal (CSK) proteins in an isolated model of the sea urchin egg cortex. Examination of cortices derived from eggs or zygotes labeled with 32P-orthophosphate reveals a number of cortex-associated phosphorylated proteins, including polypeptides of 20, 43 and 66 kDa. These three major phosphoproteins are also detected when isolated cortices are incubated with 32PATP in vitro, suggesting that the kinases that phosphorylate these substrates are also specifically associated with the cortex. The kinase activities in vivo and in vitro are stimulated by fertilization and display cell cycle-dependent activities. Gel autophosphorylation assays, kinase assays and immunoblot analysis reveal the presence of p34cdc2 as well as members of the mitogen-activated protein kinase family, whose activities in the CSK peak at cell division. Nocodazole, which inhibits microtubule formation and thus blocks cytokinesis, significantly delays the time of peak cortical protein phosphorylation as well as the peak in whole-cell histone H1 kinase activity. These results suggest that a key element regulating cortical contraction during cytokinesis is the timing of protein kinase activities associated with the cortical cytoskeleton that is in turn regulated by the mitotic apparatus.
Mouse submandibular salivary gland cells were grown in primary explant culture. After an initial period of degeneration within the explant, surviving epithelial cells proliferated rapidly and ...duct-like structures recolonized the explant. Autoradiographic studies showed that a peak of DNA synthesis occurred after 4 days in vitro and that proliferation was enhanced by insulin and hydrocortisone. These cells retained specialized secretory function (protease activity) for at least 2 weeks in vitro. This enzyme is a differentiated product of granular tubule cells in vivo. Between 6 and 10 days, explants attached to the substrate. An outgrowth developed, consisting largely of ultrastructurally identifiable epithelial cells which formed pseudoglandular structures in the monolayer. Epithelium survived for over 6 months in primary culture but could not be serially transferred. Secondary cultures were rapidly overgrown by mesenchymal cells.
In this study, we have examined the capacity of various cell types, which express cell surface hyaluronan receptors, to organize a chondrocyte-like pericellular matrix when given chondrocyte-derived ...extracellular matrix macromolecules exogenously. The assembly of a pericellular matrix was visualized by a particle exclusion assay. Without the addition of exogenous macromolecular components, none of the cell types studied exhibited significant pericellular matrices extending from their plasma membranes. However, upon the addition of high molecular weight hyaluronan in combination with aggregating cartilage proteoglycan monomers, large pericellular matrices were formed within two hours of incubation. No pericellular matrices were formed if these macromolecular components were added separately at equivalent concentrations or if the components were added in the presence of hyaluronan hexasaccharide, a competitive inhibitor of hyaluronan interaction with cell surface hyaluronan receptors. Fully assembled pericellular matrices could also be displaced by the subsequent addition of hyaluronan hexasaccharides. Nonliving, glutaraldehyde-fixed cells, which retained functional hyaluronan receptors, maintained the capacity to assembly pericellular matrices with exogenous components, in serum-containing or serum-free medium. Cells that were incubated with exogenous matrix macromolecules for 24 h, followed by a chase incubation in medium minus the exogenous macromolecules, continued to maintain the matrix for up to 6 h on live cells and more than 24 h on glutaraldehyde-fixed cells. Cell types that did not express hyaluronan receptors were not capable of organizing such pericellular matrices when incubated with these exogenous components. These findings suggest that cells expressing hyaluronan receptors have a significant capacity to organize their immediate extracellular environment via hyaluronan-hyaluronan receptor interactions. Possible physiological functions for this type of matrix organizing capacity are discussed.
In endothelial cells, a bolus of hydrogen peroxide (H2O2) or oxygen metabolites generated by hypoxanthine-xanthine oxidase (HX-XO) increased the mitochondrial calcium concentration Ca2+m. Both agents ...caused a biphasic increase in Ca2+m which was preceded by a rise in cytosolic free calcium concentration Ca2+c (18 and 6 seconds for H2O2 and HX-XO, respectively). The peak and plateau elevations of Ca2+ were consistently higher in the mitochondrial matrix than in the cytosol. In Ca2+-free/EGTA medium, the plateau phase of elevated Ca2+ evoked by H2O2 due to capacitative Ca2+ influx was abolished in the cytosol, but was maintained in the mitochondria. In contrast to H2O2 and HX-XO, ATP which binds the P2Y purinoceptors induced an increase in Ca2+m that was similar to that of Ca2+c. When cells were first stimulated with inositol 1,4, 5-trisphosphate-generating agonists or the Ca2+-ATPase inhibitor cyclopiazonic acid (CPA), subsequent addition of H2O2 did not affect Ca2+c, but still caused an elevation of Ca2+m. Moreover, the specific inhibitor of the mitochondrial Ca2+/Na+ exchanger, 7-chloro-3,5-dihydro-5-phenyl-1H-4.1-benzothiazepine-2-on (CGP37157), did not potentiate the effects of H2O2 and HX-XO on Ca2+m, while causing a marked increase in the peak Ca2+m and a significant attenuation of the rate of Ca2+m efflux upon addition of histamine or CPA. In permeabilized cells, H2O2 mimicked the effects of CGP37157 causing an increase in the basal level of matrix free Ca2+ and decreased efflux. Dissipation of the electrochemical proton gradient by carbonylcyanide p-(trifluoromethoxy) phenylhydrazone (FCCP), and blocade of the Ca2+ uptake by ruthenium red prevented Ca2+m increases evoked by H2O2. These results demonstrate that the H2O2-induced elevation in Ca2+m results from a transfer of Ca2+ secondary to increased Ca2+c, and an inhibition of the Ca2+/Na+ electroneutral exchanger of the mitochondria.
The investment of nitrogenous materials by female and male German cockroaches Blattella germanica (L.) into their progeny was examined. Adult females maintained on dog food invested 34% of their dry ...mass and 26% of their nitrogen into an oothecae during their first gonadotrophic cycle. Females maintained on a low- (5%) protein diet and injected simultaneously with 3Hleucine and 14Chypoxanthine incorporated less 3Hleucine-derived radiolabel in their oothecae than those on a dog food diet (25% crude protein). Females on the low-protein diet incorporated more 14Chypoxanthine-derived material (primarily as 14Curates) into their oothecae than they retained in their bodies. Stored 14Curates were metabolized more readily by females on the low-protein diet. Oothecae obtained from females provided with an 15Nurate-amended diet contained at least four 15N-enriched amino acids, which supports the hypothesis that urates are utilized as a nitrogen resource in these insects. Dietary effects on paternal investment were also found to be significant. Females fed a low-protein diet and their oothecae contained 63% of the radiolabel made available to them at mating when paired with males injected simultaneously with 3Hleucine and 14Chypoxanthine, whereas dog-food-fed females and their oothecae contained only 17% of the total radiolabel made available to them at mating.
Nopp44/46 is a phosphoprotein of the protozoan parasite Trypanosoma brucei that is localized to the nucleolus. Based on the primary sequence, Nopp44/46 appears to be a protein composed of distinct ...domains. This communication describes the relationship of these domains to the known functional interactions of the molecule and suggests that the amino-terminal region defines a novel homology region that functions in nucleolar targeting. We have previously shown that Nopp44/46 is capable of interacting with nucleic acids and associating with a protein kinase. Using in vitro transcription and translation, we now demonstrate that the nucleic acid binding function maps to the carboxy-terminal domain of the molecule, a region rich in arginine-glycine-glycine motifs. Our experiments reveal that a central region containing a high proportion of acidic residues is required for association with the protein kinase. Analysis of transfectants expressing epitope-tagged Nopp44/46 deletion constructs showed that the amino-terminal 96 amino acids allowed nuclear and nucleolar accumulation of the protein. This region of the molecule shows homology to several recently described nucleolar proteins. Deletion of a 27-amino-acid region within this domain abrogated nucleolar, but not nuclear, localization. These studies show that Nopp44/46 is composed of distinct modules, each of which plays a different role in molecular interactions. We suggest that this protein could facilitate interactions between sets of nucleolar molecules.
mec-12 is one of a dozen genes required for touch receptor neuron function in Caenorhabditis elegans. Some mec-12 mutants (mechanosensory-defective) lack the large-diameter microtubules that are ...characteristic of these neurons (15 protofilaments, as opposed to 11). Mutants of mec-7, a alpha-tubulin encoding gene, have a similar phenotype. We have identified the nature of mec-12 by germline transformation rescue and characterization of a point mutation. Sequence analysis of the mec-12 encoded product (MEC-12) indicates that it corresponds to a novel C. elegans alpha-tubulin. MEC-12 is the only identified C. elegans alpha-tubulin that contains a lysine at position 40, a known site of post-translational acetylation. Some mec-12 mutations eliminate microtubule acetylation as assayed immunocyto-chemically; phenotypic rescue using a MEC-12 variant lacking the lysine-40 showed that acetylation is not required for MEC-12 activity. Although functionally needed only in the touch neurons, mec-12 is expressed in several other neuron types. These results support the notion that tubulin isotype diversity contributes to the formation of distinct classes of microtubules; 15-protofilament microtubule assembly requires MEC-12 alpha-tubulin and MEC-7 beta-tubulin, which are both highly expressed in the touch receptor neurons. MEC-12 is the first reported alpha-tubulin isotype that appears to be required in a single class of neuronal microtubules.
Histochemical staining of the epiphysial growth plate revealed that free hyaluronan (i.e. available to the staining probe) was restricted to the zone of hypertrophy, where it was located in the ...pericellular space between the chondrocytes and the edge of the lacunae. Furthermore, the amount of hyaluronan staining was directly proportional to the size of the lacunae. Autoradiographic analysis of growth plates cultured with isotopically labeled glucosamine indicated that at least a portion of this hyaluronan was newly synthesized by the hypertrophic chondrocytes. Since hyaluronan can adsorb large amounts of water, it is possible that it exerted a hydrostatic pressure on the surrounding territorial matrix and thereby caused the expansion of hypertrophic lacunae. To assess this possibility, segments of the growth plate were placed in organ culture under different conditions. Under normal culture conditions, a band of hyaluronan staining migrated across the segments coinciding with the enlargement of lacunae in these regions, and the segments, as a whole, increased in size. In contrast, when the segments were cultured in the presence of hyaluronidase, which degraded the pericellular hyaluronan, the lacunae did not undergo enlargement and the overall size of the segments did not increase. These results suggest that the production of hyaluronan contributes to the enlargement of hypertrophic lacunae which is important for determining both the body's stature and proportions.
In the present study, we have examined the distribution of both hyaluronan and its receptor, CD44, during the process of endochondral ossification in the mouse tibia. Histochemical staining revealed ...that a large amount of hyaluronan was present in the lacunae located in the zone of hypertrophy, but it was greatly reduced or absent from the zone of erosion. In addition, hyaluronan was present in the cytoplasm of osteoprogenitor cells located in the zone of erosion. These cells also expressed CD44 on their surfaces, as revealed by double-label immunohistochemistry. These results suggested that the osteoprogenitor cells may use CD44 to bind and internalize hyaluronan, and subsequently degrade it with lysosomal enzymes. To test this possibility, we examined the human cell line, MG-63, which closely resembles osteoprogenitor cells. These cells produced several different forms of CD44, as determined by western blotting (85, 116 and 150 kDa). In addition, the binding of isotopically labeled hyaluronan to detergent extracts of these cells was blocked by a monoclonal antibody to CD44. Similarly, the degradation of hyaluronan by these cultured cells was also inhibited by a monoclonal antibody to CD44. To determine if these cells could remove hyaluronan from the growth plate, the cells were cultured directly on top of thin sections of the epiphysial region of long bone. After 16 hours, the sections were stained for hyaluronan. The MG-63 cells removed significant amounts of hyaluronan present in the zone of hypertrophy, and this effect was blocked by an excess of soluble hyaluronan and by a monoclonal antibody to CD44.
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