Isolation of an actin polymerization stimulator from bovine thyroid plasma membranes

An actin polymerization stimulator was purified from bovine thyroid plasma membranes by DNase I affinity column chromatography. Although the molecular weight of the protein was about 42,000 (42K) by sodium dodecyl sulfate polyacrylamide gel electrophoresis, it did not comigrate with actin. In the presence of 30 mM KCl, the 42K protein facilitated formation of actin filaments when analyzed by a centrifugation method, accelerated the initial phase of actin polymerization as measured in an Ostwald viscometer and increased the length of filaments as shown by electron microscopy. The 42K protein also accelerated the initial phase of actin polymerization in the presence of 100 mM KCl and 2 mM MgCl₂ but did not affect the final viscosity. The effect of the 42K protein was diminished by 5 uM cytochalasin B or 1 uM cytochalasin D. This 42K protein may anchor actin filaments onto the thyroid plasma membrane.     

Contribution of maternal mRNA for maintenance of Ca2+-dependent reaggregating activity in dissociated cells of Xenopus laevis embryos

Dissociated Xenopus laevis blastula cells, where reaggregation was inhibited in Ca2+-free medium, reaggregated immediately after the addition of Ca2+. This reaggregation was not inhibited by cordycepin or actinomycin D treatment during culture, although cycloheximide and puromycin were inhibitory. The reaggregation was not inhibited even when fertilized eggs were microinjected with cordycepin and their RNA synthesis was continuously inhibited through cleavage to blastula stages. In neurula cells, cordycepin treatment induced significant reduction in sizes of aggregates formed. These results suggest that the Ca2+-dependent reaggregating activity of blastula cells is maintained by the translation of maternal, rather than newly synthesized, mRNA.     

Milky Disease Bacteria

A comparative study was made of all available milky-disease species and strains that have been isolated around the world from beetle larvae (family Scarabaeidae). Included in the study were Bacillus popilliae Dutky, B. lentimorbus Dutky, and B. lentimorbus var. maryland from the United States; B. euloomarahae Beard and B. lentimorbus var. australis Beard from Australia; B. fribourgensis Wille from Switzerland; and New Zealand milky disease (Dumbleton). The organisms were classified into three groups: (i) those containing parasporal bodies, including B. popilliae Dutky, B. fribourgensis Wille, and New Zealand milky disease (Dumbleton); (ii) those without a visible parasporal body and with spore morphology similar to B. lentimorbus Dutky, including B. lentimorbus var. australis Beard; and (iii) those with very tiny spores and no parasporal body, including B. euloomarahae Beard and B. lentimorbus var. maryland. All available milky-disease species and strains were cultivated in vitro on Brain Heart Infusion Agar plates. However, the most fastidious organisms—B. euloomarahae and B. lentimorbus var. maryland—could not be grown until they were passed through a life cycle in larvae of a large scarabaeid beetle infesting rotting wood. Then they remained stable for only one or two subcultures. All the milky-disease organisms produced larger cells in vitro than they did in vivo. The pattern of sugar fermentations was similar for all milky-disease species. It appears that there is a very low percentage of strains of B. popilliae, B. lentimorbus, and the other milky-disease organisms that have the inherent genetic makeup to permit them to sporulate on artificial media, if conditions are favorable. Among these conditions are a sufficiently high cell population and a reduced oxygen tension. Spores produced in vitro may have a low virulence via the normal ingestion pathway, even though they show apparent virulence when injected directly into the hemocoel.     

Organ tropism of Sendai virus in mice: proteolytic activation of the fusion glycoprotein in mouse organs and budding site at the bronchial epithelium.

Wild-type Sendai virus is exclusively pneumotropic in mice, while a host range mutant, F1-R, is pantropic. The latter was attributed to structural changes in the fusion (F) glycoprotein, which was cleaved by ubiquitous proteases present in many organs (M. Tashiro, E. Pritzer, M. A. Khoshnan, M. Yamakawa, K. Kuroda, H.-D. Klenk, R. Rott, and J. T. Seto, Virology 165:577-583, 1988). These studies were extended by investigating, by use of an organ block culture system of mice, whether differences exist in the susceptibility of the lung and the other organs to the viruses and in proteolytic activation of the F protein of the viruses. Block cultures of mouse organs were shown to synthesize the viral polypeptides and to support productive infections by the viruses. These findings ruled out the possibility that pneumotropism of wild-type virus results because only the respiratory organs are susceptible to the virus. Progeny virus of F1-R was produced in the activated form as shown by infectivity assays and proteolytic cleavage of the F protein in the infected organ cultures. On the other hand, much of wild-type virus produced in cultures of organs other than lung remained nonactivated. The findings indicate that the F protein of wild-type virus was poorly activated by ubiquitous proteases which efficiently activated the F protein of F1-R. Thus, the activating protease for wild-type F protein is present only in the respiratory organs. These results, taken together with a comparison of the predicted amino acid substitutions between the viruses, strongly suggest that the different efficiencies among mouse organs in the proteolytic activation of F protein must be the primary determinant for organ tropism of Sendai virus. Additionally, immunoelectron microscopic examination of the mouse bronchus indicated that the budding site of wild-type virus was restricted to the apical domain of the epithelium, whereas budding by F1-R occurred at the apical and basal domains. Bipolar budding was also observed in MDCK monolayers infected with F1-R. The differential budding site at the primary target of infection may be an additional determinant for organ tropism of Sendai virus in mice.     

Tissue Distribution and Immunocytochemical Localization of Neurotrophin-3 in the Brain and Peripheral Tissues of Rats

Abstract: The tissue distribution of neurotrophin-3 (NT-3) was investigated in rats at 1 month of age using a newly established, sensitive two-site enzyme immunoassay system for NT-3, as well as the immunocytochemical localization of this protein. The immunoassay for NT-3 enabled us to quantify NT-3 at levels > 3 pg per assay. In the rat brain, NT-3 was detectable only in the olfactory bulb (0.54 ng/g wet weight), cerebellum (0.71 ng/g), septum (0.91 ng/g), and hippocampus (6.3 ng/g). By contrast, NT-3 was widely distributed in peripheral tissues. Appreciable levels of NT-3 were also found in the thymus (31 ng/g), heart (38 ng/g), diaphragm (21 ng/g), liver (45 ng/g), pancreas (892 ng/g), spleen (133 ng/g), kidney (40 ng/g), and adrenal gland (46 ng/g). An antibody specific for NT-3 bound to pyramidal cells in the CA2-CA4 regions of the hippocampus, to A cells in the islets of Langerhans in the pancreas, to unidentified cells in the red pulp of the spleen, to liver cells, and to muscle fibers in the diaphragm from rats at 1 month of age. Molecular masses of NT-3-immunoreactive proteins in the hippocampus and pancreas were 14 and 12 kDa, respectively. Thus, in rats, NT-3 was detected in restricted regions of the brain and in the visceral targets of the nodose ganglia at high concentrations. Our present results suggest that NT-3 not only functions as a classical target-derived neurotrophic factor but also can play other roles.