Stellate cells storing retinol in the liver of adult lamprey,Lampetra japonica

Summary Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies, Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11–12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed.     

Splenic outer periarterial lymphoid sheath (PALS): An immunoproliferative microenvironment constituted by antigen-laden marginal metallophils and ED2-positive macrophages in the rat

Summary In an attempt to reveal the role of antigen-laden marginal metallophil (MM) and other macrophages in the intrasplenic immune response of a specific B-cell lineage to a thymus-independent type-2 antigen (Ficoll conjugated with fluorescein isothiocyanate), simultaneous immuno-histological observations of the involved cells were performed in the rat. By newly established methods of double or triple immunostainings, time-kinetics of the following parameters were studied and compared: (1) the antigen, (2) the specific antibody-forming cells (AFC) directed to the fluorescein-isothiocyanate determinant, (3) proliferating cells labeled with 5-bromo-2-deoxyuridine (BrdU), and (4) macrophage subpopulations recognized by monoclonal antibodies (ED2 and ED3). The antigen localized stably not only in the marginal-zone macrophages but also in the MM except around the follicular area. The increase of BrdU-positive cells was observed from day 2 up to day 4 after antigen injection mostly in the periphery of the periarterial lymphoid sheath (outer PALS), which indicated antigen-induced proliferation. As a novel finding, the majority of AFC, both BrdU-positive and -negative, were either closely associated with the antigen-laden MM, or forming cell clusters with ED2-positive macrophages in the outer PALS. In contrast, there were very few AFC in juxtaposition to antigen-free MM in the follicular area or the antigen-laden marginal zone macrophages. The results led to the proposal of a hypothesis that the antigen-laden MM together with ED2-positive macrophages constitute an immunoproliferative microenvironment for the plasmacellular reaction by accumulating the antigen-specific B-cell lineage and promoting these cells to differentiate into the AFC and to proliferate in the outer PALS.Abbreviations AFC specific antibody-forming cells - BrdU 5-bromo-2-deoxyuridine - Fic-F FITC-conjugated Ficoll - FITC fluorescein isothiocyanate - HRP horseradish peroxidase - MM marginal metallophils - MZ marginal zone - PALS periarterial lymphoid sheath - PBS phosphate-buffered saline - TI2 thymus-independent type-2     

Three-dimensional structure of endothelial cells in hepatic sinusoids of the rat as revealed by the Golgi method

Summary The three-dimensional structure of endothelial cells in the hepatic sinusoids of the rat was studied by application of light- and electron microscopy on Golgi-impregnated specimens. A number of endothelial cells could thus be individually delineated throughout the hepatic lobules. The cytoplasm, showing heavy silver deposits, consists of two distinct areas, a thick and thin portion. The thick portion, issuing from the region of the perikaryon, branches and tapers toward the cell periphery. The thin portion, occupying the remainder of the cytoplasm, consists largely of highly fenestrated sieve plates. Some intralobular variation can be noted; the thick portion of the endothelial cells is well developed in the periportal zone, while the cells in the centrilobular zone are relatively rich in thin portions. In addition, the area of distribution of an individual endothelial cell is larger in the centrilobular sinusoids than in the periportal zone. Some endothelial cells also possess unique cytoplasmic processes projecting into the intercellular space between hepatocytes and connecting the sinusoidal walls of neighboring sinusoids. These processes may anchor the endothelial cells to the hepatic plates.     

Effects of solute hydrophobicity and phospholipid composition on permeability of composite membranes containing phospholipids

Permeabilities of several solutes through the composite membranes containing phospholipids have been measured. They were inversely proportional to the content of the phospholipids in the membrane. Both the permeability of solutes and the degree of permeability change around the phase transition temperature of the phospholipids for the hydrophobic solutes such as n-butanol and salicylamide were larger than those for the hydrophilic solutes such as amino acids and pyridoxine. These results suggest thatthe permeation path of hydrophobic solutes is different from that of hydrophilic ones. The addition of phosphatidyl ethanolamine, phosphatidyl serine, or phosphatidic acid to the composite membrane influenced the solute permeability due to the introduced negative charge and/or the change in the molecular packing of phospholipid.     

Effects of various ammonium salts, amines, polyamines and alpha-methylornithine on rRNA synthesis in neurula cells of Xenopus laevis and Xenopus borealis

Xenopus neurula cells were cultured in a medium that contained ammonium salts, amines, polyamines or alpha-methylornithine, and their rRNA synthesis was examined. All the ammonium salts and amines, but not polyamines, were strong and selective inhibitors of rRNA synthesis at 1.25-5.0 mM. alpha-Methylornithine did not inhibit rRNA synthesis, although it inhibited ornithine decarboxylase, an enzyme claimed to be a direct stimulator of rRNA synthesis. During the treatment ammonium ions and monomethylamines were accumulated within the treated cells. However, monomethylamines did not induce the accumulation of ammonium ions, and vice versa. Ammonium salts and amines also selectively inhibited rRNA synthesis in Xenopus borealis neurula cells.     

Structural analysis of ribosomal DNA homologues in nucleolus-less mutant of Xenopus laevis

Sequences homologous to the ribosomal DNA (rDNA) in a Xenopus anucleolate (nucleolus-less) mutant were analyzed by Southern blot analysis. The mutant was found to possess a variety of sequences homologous to non-transcribed spacer (NTS) and/or coding region of rDNA. 65 rDNA-homologous clones were isolated from a genomic DNA library of the mutant. All the clones showed only partial homology to the normal rDNA unit and their restriction maps differed from that of the normal rDNA unit. Based on the hybridization patterns, the rDNA-homologous clones were divided into four groups (I-IV). Structure of group IV, which most strongly hybridized to normal rDNA probe, was analyzed by nucleotide sequencing. The group IV sequence was found to contain a part of the rDNA, including Bam island, enhancer element, promoter region, external transcribed spacer, and a portion of 18S rRNA gene. The blotting analysis suggested that the group IV sequence is specific for a particular strain of Xenopus.     

Inhibitor of ribosomal RNA synthesis in Xenopus laevis embryos: VI. Occurrence in mature oocytes and unfertilized eggs

Occurrence of a factor(s) which can selectively inhibit ribosomal RNA synthesis in isolated neurula cells of Xenopus laevis was examined in oocytes, unfertilized eggs, and embryos of Xenopus laevis. It was found that acid-soluble materials from full-sized oocytes, white-banded mature oocytes, unfertilized eggs, and pregastrular embryos were all active in significantly reducing the relative ratio of the [³H]uridine incorporation into 18S and 28S ribosomal RNA to that into 4S RNA from the control value. These results suggest that the inhibitor appears in the terminal step of oogenesis and, hence, may be assumed as a maternal regulator.     

Existence and stability of periodic travelling wave solutions to Nagumo's nerve equation

Summary Nagumo's nerve conduction equation has a one-parameter family of spatially periodic travelling wave solutions. First, we prove the existence of these solutions by using a topological method. (There are some exceptional cases in which this method cannot be applied in showing the existence.) A periodic travelling wave solution corresponds to a closed orbit of a third-order dynamical system. The Poincaré index of the closed orbit is determined as a direct consequence of the proof of the existence. Second, we prove that the periodic travelling wave solution is unstable if the Poincaré index of the corresponding closed orbit is + 1. By using this result, together with the result of the author's previous paper, it is concluded that the slow periodic travelling wave solutions are always unstable. Third, we consider the stability of the fast periodic travelling wave solutions. We denote by L(c) the spatial period of the travelling wave solution with the propagation speed c. It is shown that the fast solution is unstable if its period is close to L_min, the minimum of L(c).     

Synthesis and transport of various RNA species in developing embryos of Xenopus laevis.

Embryonic cells of Xenopus laevis were labeled for varying lengths of time, and their nuclear and cytoplasmic RNAs were analyzed, with the following results. (1) The synthesis of small nuclear RNAs (snRNAs) is detected from blastula stage on. (2) The initiation of 4 S and 5 S RNA syntheses occurs at blastula stage. However, while the former is transported into the cytoplasm immediately after its synthesis, the latter remains within the nucleus, until its transport starts later, concomitantly with that of 28 S rRNA. (3) As soon as “blastula” cells start to synthesize 40 S rRNA precursor at 5th hr of cultivation, 18 S rRNA is transported first; the transport of 28 S rRNA begins 2 hr later. (4) On a per-cell basis, poly(A)-RNA is synthesized in blastula stage at a much higher rate than in the later stages. About one-third of the total blastula poly(A)-RNA, and about one-fifth in the case of tailbud cells, is transported quickly into the cytoplasm. Then, it appears that the RNAs which are synthesized at early embryonic stages are transported to the cytoplasm without delays, except for 5 S RNA and snRNAs.