Differential effects of brefeldin A on sialylation of N- and O-linked oligosaccharides in low density lipoprotein receptor and epidermal growth factor receptor

Low density lipoprotein receptor (LDL-R) is a membrane glycoprotein carrying both N- and O-linked oligosaccharides, processing of which is reflected in conversion from a precursor to mature form during its synthesis and intracellular transport. Treatment with brefeldin A (BFA) of mouse macrophage-like J774 cells, Chinese hamster ovary cells, and two human cancer cell lines (A431 and IMC-2) resulted in production of LDL-R with a molecular size 5-10 kDa smaller than that of the mature form in the control cells. Treatment with sialidase caused apparent reduction in the molecular size of LDL-R synthesized in all BFA-treated J774, Chinese hamster ovary, A431, and IMC-2 cell lines as observed for the mature form of the control cells. Thus, O-linked sugar chains of LDL-R were apparently sialylated in the BFA-treated cells. We also examined the effect of BFA on the processing of another membranous glycoprotein, epidermal growth factor receptor (EGF-R) carrying only N-linked oligosaccharides. EGF-R synthesized in the presence of BFA was found to have no response to sialidase treatment, suggesting that the drug blocks the sialylation of EGF-R. The results indicate that BFA causes different effects on the sialylation of LDL-R and EGF-R depending upon linkage types of their oligosaccharides.     

Presence of the cytosolic factor stimulating the import of precursor of mitochondrial proteins in rabbit reticulocytes and rat liver cells

Previously we purified a cytosolic factor that stimulates the import of the extrapeptide (the synthetic peptide of the presequence of ornithine aminotransferase) into the mitochondrial matrix (Ono, H., and Tuboi, S., 1988, J. Biol. Chem. 263, 3188-3193). In this work this cytosolic factor was shown also to stimulate the import of the precursors of ornithine aminotransferase, a large subunit of succinate dehydrogenase, and sulfite oxidase. The amounts of these precursors bound to the outer mitochondrial membrane were increased by this cytosolic factor, suggesting that the cytosolic factor participates in the recognition step in the import process of the precursor protein. When the cytosolic factor was applied to an ATP-agarose column, the import-stimulating activity was recovered entirely in the unadsorbed fraction. Immunochemical studies showed that in these conditions the 70-kDa heat shock-related protein (Hsp 70) was present exclusively in the fraction adsorbed to the ATP-agarose column. The cytosolic factor is thus different from the 70-kDa heat shock-related protein, which was identified as a factor required for the import of mitochondrial proteins in yeast. The cytosolic factor was also detected in the cytosol of rat liver cells, and a considerable amount of this factor was recovered from rat liver mitochondria by washing them with high salt buffer, suggesting that the cytosolic factor has affinity to the outer mitochondrial membrane and binds to its receptor on the membrane. From these results, we conclude that the cytosolic factor forms a complex with the precursor of mitochondrial protein and then this complex binds to the outer mitochondrial membrane, probably via the receptor of the cytosolic factor.     

Possible role of rat fatty acid-binding proteins in the intestine as carriers of phenol and phthalate derivatives

Fatty acid-binding proteins of hepatic and intestinal type and gastrotropin-like protein (GTLP) were purified from rat intestinal cytosol by Sephadex G-75 gel filtration and DEAE-cellulose, CM-cellulose, and hydroxylapatite chromatographies. In addition to fatty acids, butylated hydroxytoluene (BHT), phthalate dibutyl, and di(2-ethylhexyl) esters (DBP and DEHP) were identified by gas liquid chromatography and mass spectrometry as endogenous ligands from the extract of either fatty acid-binding protein superfamily. These protein families in the intestine may have an important role as carriers in the initial step of arresting these exogenous pollutants.     

Regulation by induction of branched-chain 2-oxo acid dehydrogenase complex in clofibrate-fed rat liver.

The activity of branched-chain 2-oxo acid dehydrogenase complex increased 3.0-fold in liver of rats fed on 0.1%(w/w) clofibrate. Immunotitration experiments with antibodies against the constituent enzymes of the complex revealed that this increase resulted mainly from the increased amounts of only two(a decarboxylase and a lipoate acyltransferase) of three components of the complex and that the other component(dihydrolipoamide dehydrogenase) remained unchanged in its content, irrespective of clofibrate administration. The increases of both enzyme components were associated with increases in their mRNA levels which were estimated by in vitro translation with poly(A)+ RNA.     

Generality of the action of various maturation-promoting factors

It has been known in amphibians and starfishes that a cytoplasmic factor called maturation-promoting factor (MPF), produced in maturing oocytes under the influence of the maturation-inducing hormones, can induce germinal vesicle breakdown (GVBD) and the subsequent process of meiotic maturation. The present study revealed that injection of cytoplasm of maturing starfish oocytes (starfish MPF) into immature sea cucumber oocytes brought about maturation of the recipients. Amphibian MPF obtained from mature oocytes of Xenopus laevis or Bufo bufo was found to induce maturation of starfish oocytes following injection. Cytoplasm taken from cleaving starfish blastomeres induced maturation when injected into immature starfish oocytes. The maturation-inducing activity of cytoplasm of starfish blastomeres changed along with the mitotic cell cycle during 1- to 4-cell stages so far tested and reached a peak just before cleaving. Furthermore, an extract of mammalian cultured cells, CHO or V-79, synchronized in M phase, induced GVBD in starfish oocytes following injection, whereas S phase extract had little activity. These facts suggest that MPF generally brings about nuclear membrane breakdown in both meiosis and mitosis, and that the nature of MPF is very similar among vertebrates and invertebrates.     

Structure of tendon organs in fishes of the genus Polymixia

Summary Modified branchiostegal rays 1 through 3 support the proximal end of the paired hyoid barbels in the beardfish (Beryciformes: Polymixiidae). The polymixiid barbel is unusual in that it has an unique intrinsic muscular system. Using silver impregnation and electron microscopic techniques, unencapsulated, free nerve endings were located within the tendon of the third modified branchiostegal ray. Branchiostegal rays 1 and 2 do not have any free nerve endings associated with their tendons, however. It is suggested that the free nerve endings are proprioceptors acting as stretch-sensitive mechanoreceptors, and that branchiostegal ray 3 acts as part of a sensory apparatus for monitoring the positional state of the barbel. Branchiostegal rays 1 and 2 merely provide support for the barbel.Abbreviations used in Figures BA barbel - br r 3 branchiostegal ray 3 - IM intermandibularis - IOP interoperculum - LIM interoperculomandibular ligament - MD mandible - MX maxilla - OP operculum - PM premaxilla - POP preoperculum - SOP suboperculum     

Two new subspecies of Bacillus thuringiensis isolated in Japan: Bacillus thuringiensis subsp. kumamotoensis (serotype 18) and Bacillus thuringiensis subsp. tochigiensis (serotype 19)

Bacteriological and serological characteristics of three Bacillus thuringiensis isolates obtained in Japan were investigated. They formed typical rhomboidal parasporal inclusions but flagellar (H) antigens of these isolates were different from those of the known 17 H serotypes of B. thuringiensis. The three isolates were divided into two new serotypes (serotypes 18 and 19). The serotype 18 isolate (3–71) produced thermostable exotoxin and the inclusions of this isolate were toxic to larvae of the silkworm, Bombyx mori, but nontoxic to larvae of the mosquito, Aedes aegypti. The other isolate (119-72) belonging to serotype 18 produced inclusions nontoxic to larvae of B. mori and A. aegypti and did not produce thermostable exotoxin. However, other bacteriological properties of the isolate 119-72 were similar to those of the isolate 3–71. The serotype 19 isolate (117-72) produced inclusions nontoxic to larvae of B. mori and A. aegypti and did not produce thermostable exotoxin. Acid production from saccharose and the production of brownish purple pigment were observed in the two serotype 18 isolates, while neither of them was observed in the serotype 19 isolate. In other 29 biochemical properties tested, there was no difference among the three isolates. Based on these characteristics, the following two subspecies names are proposed: Bacillus thuringiensis subsp. kumamotoensis (serotype 18) for the type strain 3–71 and Bacillus thuringiensis subsp. tochigiensis (serotype 19) for the type strain 117-72.     

Induction of Haploid Callus from Isolated Microspores of Peony in vitro

The in vitro culture of isolated microspores of two cultivarsof Paeonia, P. lactiflora cv. "Kumoinotsuru" (2n=10) and cv."Toyonoakari" (2n = 10), was attempted. With both cultivars,some cultured microspores (3–6%) began to divide afterfive to seven days of culture. Those of "Kumoinotsuru" grewinto calli, whereas the others degenerated. Cytological examinationof the callus developed from a microspore revealed haploids,diploids or a mixture of both. No direct embryo formation frommicrospores was observed in this experiment. (Received December 1, 1980; Accepted January 16, 1981)     

Hydrocephalus in suckling rats infected intracerebrally with mouse hepatitis virus, MHV-A59

After intracerebral inoculation of mouse hepatitis virus, MHV-A59 strain, into 3- to 5-day-old Wistar rats, some survivors at 14 days postinoculation (p.i.) were found to lack the cerebral cortex and to have an accumulation of considerable amount of cerebrospinal fluid. The virus titer in the brain increased exponentially after inoculation, reaching a maximum 4 to 6 days p.i. when immunofluorescence revealed virus-specific antigen within neurons in the cerebral cortex. A small amount of infectious virus was also detectable 14 days p.i. when the cerebral anomaly was evident. This brain malformation causing hydrocephalus was due to cerebral damage by viral infection.