Neurotrophic effect of Semaphorin 4D in PC12 cells

Semaphorins provide crucial attractive and repulsive cues involved in axon guidance during neural development. Out of them, Semaphorin 4D (Sema4D) is enriched in the nervous and immune tissues, and acts as proliferative and survival factors of peripheral lymphocytes in the immune system, but is poorly understood in the nervous system. By using PC12 cells which are well known to differentiate into neural cells in response to nerve growth factor (NGF), we found that soluble forms of Sema4D had neurotrophic effects which were inhibited by neutralizing antibodies to Sema4D. Sema4D strikingly potentiated neurite outgrowth in the presence of 50 ng/ml NGF and increased sensitivity to NGF. Cells responded to very low concentrations of NGF in the presence of 1 nM Sema4D. Activation of following signal proteins, protein kinase C (PKC), L-type of voltage-dependent Ca(2+) channel, and phosphatidylinositol (PI) 3-kinase mediated neurotrophic neurite-outgrowth action of Sema4D. These findings suggest a new function of Sema4D as a neurotrophic signal in PC12 cells.     

Bromodeoxyuridine-immunohistochemistry on cellular differentiation and migration in the fundic gland of Xenopus laevis during development

Summary Cellular differentiation and migration in the fundic glands of adult and larval Xenopus laevis have been examined using bromodeoxyuridine-immunohistochemistry. In the adult fundic gland, cumulative labeling with bromodeoxyuridine revealed a proliferative cell zone between the surface mucous cells and mucous neck cells, in what is referred to as the neck portion of the gland. The labeling-index of mucous neck cells had rapidly increased by week-5. The labeling-index of oxynticopeptic cells showed a more delayed increase until week-7, coincident with the decrease in the labeling of mucous neck cells. In the immature fundic glands of larvae, the labeled proliferating cells were randomly distributed throughout the developing gastric mucosa. During metamorphosis, the labeling-index of immature epithelial cells was highest at stage 63. Following administration of bromodeoxyurdine at this, stage, there was no significant loss of labeled epithelial cells during the metamorphosing period. Furthermore, there was no significant difference in the labeling-indices among the epithelial cells, such as surface mucous cells/generative cells, mucous neck cells, and oxynticopeptic cells, 7 days after administration. Cellular differentiation and migration pathways of epithelial cells in the fundic gland of adult X. laevis and its larvae are discussed.     

V domain of human SLAM (CDw150) is essential for its function as a measles virus receptor

Human signaling lymphocytic activation molecule (SLAM; also known as CDw150) has been shown to be a cellular receptor for measles virus (MV). Chinese hamster ovary cells transfected with a mouse SLAM cDNA were not susceptible to MV and the vesicular stomatitis virus pseudotype bearing MV envelope proteins alone, indicating that mouse SLAM cannot act as an MV receptor. To determine the functional domain of the receptor, we tested the abilities of several chimeric SLAM proteins to function as MV receptors. The ectodomain of SLAM comprises the two immunoglobulin superfamily domains (V and C2). Various chimeric transmembrane proteins possessing the V domain of human SLAM were able to act as MV receptors, whereas a chimera consisting of human SLAM containing the mouse V domain instead of the human V domain no longer acted as a receptor. To examine the interaction between SLAM and MV envelope proteins, recombinant soluble forms of SLAM were produced. The soluble molecules possessing the V domain of human SLAM were shown to bind to cells expressing the MV hemagglutinin (H) protein but not to cells expressing the MV fusion protein or irrelevant envelope proteins. These results indicate that the V domain of human SLAM is necessary and sufficient to interact with the MV H protein and allow MV entry.     

Fractionation of Nitrogen Isotopes during the Uptake and Assimilation of Ammonia by Plants

Two varieties (Nihonbare and Koshihikari) of rice plants (Oryzasativa L.) were grown hydro-ponically with two levels (20 and100 mg N liter ^–1) of ammonia. Variations in levels ofnatural abundance of ¹⁵N (¹⁵N) were analyzed in the ammoniaand organic nitrogen of shoots and roots, as well as in theammonia in the culture solution. There was substantial fractionationof nitrogen isotopes during the uptake of ammonia. When plantsabsorbed a large proportion of ammonia from a solution witha low concentration, less negative ¹⁵N values in plants andhigh positive ¹⁵N values in the ammonia remaining in solutionwere observed. The reverse was found when a smaller fractionof ammonia was absorbed from a solution with a higher concentrationof ammonia. The ^l5N values of ammonia in shoots and roots werehigher than in the respective constituent organic nitrogen,suggesting the fractionation of nitrogen isotopes during theassimilation of ammonia. Wild-type and mutant cells of the cyanobacterium(blue-green alga) Synechococcus PCC 7942 were grown in nitrate-or ammonia-containing medium as the source of nitrogen. Fractionationof nitrogen isotopes during the uptake of nitrate was limited,whereas that during the uptake of ammonia was considerable. ¹ In this report, the term ammonia refers indiscriminately toboth NH₃ or NH₄⁺. (Received June 13, 1991; Accepted September 12, 1991)     

Regulation of nitrate reductase by non-modifiable derivatives of PII in the cells of Synechococcus elongatus strain PCC 7942

In Synechococcus elongatus, the PII protein inhibits both transport and reduction of nitrate when ammonium is present in the medium. Using a transporter mutant having ammonium-resistant nitrate transport activity as the genetic background, we analyzed specific effects of PII on in vivo nitrate reductase activity by measuring uptake of nitrate from the medium. The results showed that the regulation of nitrate reductase does not require changes in the electric charge or size of the side chain at the phosphorylation site of PII. Phosphorylation of PII is thus unlikely to play a role in the regulation of nitrate reductase.     

Two lignan dimers from bamboo stems (Phyllostachys edulis)

Phyllostadimers A and B, two bis-lignans in which the two lignan units are directly connected by a C-C bond, were isolated from stems of bamboo, Phyllostachys edulis. Their structures were determined on the basis of spectral evidence. In addition, 14 known compounds were also obtained throughout the investigation. Phyllostadimer A significantly inhibited liposomal lipid peroxidation.     

Phosphorylation of ribosomal protein S19 at Ser59 by CaM Kinase Iα

In order to examine the possible involvements of Ca²⁺/calmodulin-dependent protein kinases (CaM kinases) in the regulation of ribosomal functions, we tested the phosphorylation of rat ribosomal protein S19 (RPS19) by various CaM kinases in vitro . We found that CaM kinase Iα, but not CaM kinase Iβ1, Iβ2, II, or IV, robustly phosphorylated RPS19. From the consensus phosphorylation site sequence, Ser59, Ser90, and Thr124 were likely to be phosphorylated; therefore, we mutated each amino acid to alanine and found that the mutation of Ser59 to alanine strongly attenuated phosphorylation by CaM kinase Iα, suggesting that Ser59 was a major phosphorylation site. Furthermore, we produced a specific antibody against RPS19 phosphorylated at Ser59, and found that Ser59 was phosphorylated both in GT1-7 cells and rat brain. Phosphorylation of RPS19 in GT1-7 cells was inhibited by KN93, an inhibitor of CaM kinases. Immunoblot analysis after subcellular fractionation of rat brain demonstrated that phosphorylated RPS19 was present in 80S ribosomes. Phosphorylation of RPS19 by CaM kinase Iα augmented the interaction of RPS19 with the previously identified S19 binding protein. These results suggest that CaM kinase Iα regulates the functions of RPS19 through phosphorylation of Ser59.     

Arginine inhibits Na-driven flagellar motors of alkaliphilic Bacillus

L-arginine has attracted a great deal of attention as an agent for refolding denatured proteins, and the mildness of its effects offer hope for a wide range of potential applications for this substance, including medicines with few side effects. We report that both L- and D-arginine inhibits Na+-driven flagellar motors of alkaliphilic Bacillus by competing with Na+, which we take as evidence that arginine specifically binds to a molecular target.