Complex population of mRNA sequences in large polyadenylylated nuclear RNA molecules.

Polyadenylylated heterogeneous nuclear RNA [poly(A)-hnRNA] from mouse brain was subjected to electrophoresis in agarose gels containing CH3HgOH, and molecules larger than 8 kilobases or 13 kilobases were recovered. cDNA was then transcribed from polyadenylylated RNA fragments cleaved from these large molecules. The resulting cDNA hybridized almost to completion with poly(A)-mRNA isolated from mouse brain polysomes. From the hybridization kinetics of this cDNA with its template RNA, it was estimated that the sequence complexity of the 3'-proximal sequences (of the same average size as mRNA) of the greater than 8 kilobase poly(A)-hnRNA was about 57,000 kilobases. The sequence complexity of poly(A)-mRNA, estimated from the template-driven hybridization kinetics of its respective cDNA, was about 110,000 kilobases. It is concluded that most, if not all, of the 3'-proximal sequences of large poly(A)-hnRNA molecules are homologous with mRNA in the mouse brain and that at least 40,000 different mRNA sequences (or portions of mRNA sequences) are represented in the 3'-proximal sequences of greater than 8 kilobase poly(A)-hnRNA.     

Early auxin-regulated polyadenylylated mRNA sequences in pea stem tissue

Polyadenylylated mRNA from etiolated pea stem segments treated with or without 20 μM indoleacetic acid (IAA) for various periods of time was assayed by translating it in a wheat germ extract containing [³⁵S]methionine and separating the translation products by two-dimensional gel electrophoresis. Within 2 hr IAA causes at least five mRNA sequences to increase in translational activity, relative to initial levels and to simultaneous controls; three of these rise significantly within 20 min after exposure of tissue to IAA but are apparently not elevated at 10 min, whereas the others begin to increase at successive times later than 30 min, and still others begin to change only later than 2 hr. These observations indicate an early, highly selective IAA regulation of mRNA amounts or activities, becoming progressively more extensive with time. The earliest detected enhancement seems close to the primary action of IAA but appears not to be rapid enough to be responsible for auxin induction of cell enlargement.     

mRNA coding for oxytocin is present in axons of the hypothalamo-neurohypophysial tract.

Neuronal mRNA is thought to be restricted to perikaryal and dendritic compartments containing rough endoplasmic reticulum. We have used both in situ hybridization and DNA polymerase chain reaction methods to determine the precise intracellular distribution of oxytocin mRNA. Using light- and electron-microscopic detection of in situ hybridization with 5'-bromo-2'-deoxyuridine-labeled oligonucleotide probes, we found oxytocin mRNA in axons and Herring bodies in the lateral and ventral hypothalamus, the median eminence, and the posterior lobe of the pituitary in postpartum lactating rats. Southern blot analysis of the amplification products confirmed the presence of oxytocin mRNA in all three tissue samples. The present findings indicate that oxytocin mRNA can be transported axonally. Such transport could reflect an adventitious compartmentalization or a functional storage in Herring bodies for subsequent secretion.     

Insulin receptor substrate-1 is present in hepatocyte nuclei from intact rats

Insulin receptor substrate-1 (IRS-1), the primary substrate for the insulin receptor tyrosine kinase in most cells and tissues, is a key component of the insulin signaling network. Numerous studies have documented the trafficking of IRS-1 from the cell membrane to intracellular, extranuclear compartments. During the course of our previous studies aimed at defining the ontogeny of insulin signaling in the rat, Western immunoblotting showed minimal IRS-1 content in late gestation fetal liver. Immunohistochemical analyses, aimed at corroborating these Western immunoblotting results, showed hepatocyte nuclear staining for IRS-1 in adult liver but not fetal liver. Further analysis of fixed tissue as well as immunofluorescent staining of liver cryosections confirmed the localization of IRS-1 to the nuclear matrix and nucleoli of adult hepatocytes within intact liver. Tissue fractionation and Western immunoblotting also showed nuclear localization of IRS-1, with this fraction accounting for approximately 25% of total liver IRS-1. Administration of insulin to intact animals did not stimulate nuclear translocation of hepatic IRS-1 or the p85 regulatory subunit of phosphatidylinositol-3 kinase. However, insulin did activate IRS-1-associated phosphatidylinositol-3 kinase in nuclear extracts. Our results indicate that insulin signaling, which terminates in an array of nuclear events, may originate at the immediate postreceptor level with IRS-1 activation within the nucleus of normal hepatocytes.     

A tRNA-like structure is present in 10Sa RNA, a small stable RNA from Escherichia coli.

We have determined that 10Sa RNA (one of the small stable RNAs found in Escherichia coli) has an interesting structural feature: the 5' end and the 3' end of 10Sa RNA can be arranged in a structure that is equivalent to a half-molecule (acceptor stem and TFC stem-loop) of alanine tRNA of E. coli. Primer-extension analysis of 10Sa RNA extracted from a bacterial mutant with temperature-sensitive RNase P function revealed that the precursor to 10Sa RNA (pre-10Sa RNA) is folded into a pre-tRNA-like structure in vivo such that it can be cleaved by RNase P to generate the 5' end of the mature 10Sa RNA. The purified 10Sa RNA can be charged with alanine in vitro. Disruption of the gene encoding 10Sa RNA (ssrA) caused a reduction in the rate of cell growth, which was especially apparent at 45 degrees C, and a reduction in motility on semisolid agar. These phenotypic characteristics of the deletion strain (delta ssrA) allowed us to investigate the effects of some mutations in 10Sa RNA in vivo, although the exact function of 10Sa RNA still remains unclear. When the G.U pair (G3.U357) in 10Sa RNA, which may be equivalent to the determinant G.U pair of alanine tRNA, was changed to a G.A or G.C pair, the ability to complement the phenotypic mutations of the delta ssrA strain was lost. Furthermore, this inability to complement the mutant phenotypes that was caused by the substitution of the determinant bases by a G.A pair could be overcome by the introduction of a gene encoding alanyl-tRNA synthetase (alaS) on a multicopy plasmid. The evidence suggests that the proposed structural features of 10Sa RNA are indeed manifested in vivo.     

Apolipoprotein E mRNA is abundant in the brain and adrenals, as well as in the liver, and is present in other peripheral tissues of rats and marmosets.

The relative amount of apolipoprotein (apo-) E mRNA in 12 different tissues of the rat and marmoset was examined by dot blot hybridization using cloned cDNA probes. As expected, it was found to be most abundant in the liver. However, substantial amounts of apo-E mRNA were found in the brain and adrenals at relative levels about one-third of that found in the liver. Significant quantities of apo-E mRNA were detected in all of the other peripheral tissues as well. The apo-E mRNA levels in these tissues were 2-10% of that found in the liver of the rat and 10-30% of that found in the liver of the marmoset. Apo-E mRNA was also abundant in human brain and in each species examined; it was distributed throughout all major areas of this organ. In contrast, apo-A-I mRNA was detected in abundant amounts only in the small intestine and in the liver. Extrahepatic apo-E mRNA appears to be functional, generating a translation product similar or identical to that generated by the liver. During fetal and neonatal development, apo-E mRNA is rapidly induced from low levels to approximately equal to 60% of adult levels in liver at parturition. The fetal yolk sac contains more apo-E mRNA than the fetal liver, suggesting a significant role for the yolk sac as a source of apo-E during gestation.     

Presence of albumin mRNA precursors in nuclei of analbuminemic rat liver lacking cytoplasmic albumin mRNA.

Analbuminemic rats, which lack serum albumin, were previously found to have no albumin mRNA in the cytoplasm of the liver. In the present study, the existence of nuclear albumin mRNA precursors in the liver of analbuminemic rats was examined by RNA X cDNA hybridization kinetics. Albumin mRNA precursors were present in the nuclei of analbuminemic rat liver at almost normal levels, despite the absence of albumin mRNA from the cytoplasm. Nuclear RNA of analbuminemic rat liver was subjected to electrophoresis on 1% agarose gel in parallel with nuclear RNA of normal rat liver. RNA was transferred from the gel to diazobenzyloxymethyl-paper and hybridized to cloned cDNA. Several bands of putative albumin mRNA precursors were obtained with nuclear RNA of analbuminemic rat liver and some of them were indistinguishable from those of normal rat liver. Nuclear RNA of analbuminemic rats was hybridized to 3'-end-labeled cloned cDNA under the conditions of RNA excess and then digested completely with S1 nuclease and subjected to electrophoresis on polyacrylamide gel. By this technique, nuclear RNA that could hybridized to cDNA was found to have the albumin mRNA sequence in at least the 3' half of the mRNa that was covered by cloned cDNA. For comparison of the structures of the albumin genes of analbuminemic and normal rats, DNAs from rat livers of both types were digested completely with EcoRI, HindIII, and Pst I; the fragments were separated by electrophoresis on 1% agarose gel, transferred to nitrocellulose paper, and hybridized to cloned cDNA. The intensities of the corresponding bands and the digestion patterns of the analbuminemic and normal rat genes were indistinguishable. From these data, it is concluded that analbuminemic rats have a unique type of mutation(s) affecting albumin mRNA maturation.     

Tyrosine hydroxylase mRNA is increased by hyperosmotic stimuli in the paraventricular and supraoptic nuclei

In situ hybridization histochemistry was used to locate cells containing tyrosine hydroxylase (TH) mRNA in the hypothalami of salt-loaded and Brattleboro rats. The hyperosmotic plasma conditions found in these animals, as compared to control animals, was associated with an increase in detectable TH mRNA-producing cells in the paraventricular and supraoptic nuclei. These results suggest that dopamine synthesized by neurons of those nuclei may participate in the regulation of neuropeptide synthesis and release within the nuclei and the posterior pituitary.     

Structure of psoralen-crosslinked ribosomal RNA from Drosophila melanogaster.

Ribosomal RNA from Drosophila melanogaster photoreacted with hydroxymethyltrioxsalen has been examined by electron microscopy. Reproducible patterns of hairpins were found in both the 26S and 18S RNA. The frequency of these hairpins and the amount of incorporated drug were dependent upon the conditions under which the crosslinking was performed. A prominent central hairpin occurs in the 26S RNA and the break that interrupts the continuity of the RNA chain is located within it. In addition to several small hairpins, the crosslinked 18S RNA contains a large open loop.     

Xanthine oxidoreductase is present in human synovium.

It is postulated that the mobile inflamed joint may be subject to cyclical ischaemic reperfusion injury. Xanthine oxidoreductase is an enzyme thought to contribute to oxidative reperfusion injury, and the detection of this activity in human synovium is described. Three normal and five rheumatoid tissues were assayed with a carbon-14 radioassay detecting the conversion of [14C]xanthine to [14C]uric acid. Rheumatoid synovia contained 0.67-305 microU/g tissue (n = 5), while normal synovia contained 1.2-5.0 microU/g tissue (n = 3).     

Meiosis in Drosophila: seeing is believing.

Recently many exciting advances have been achieved in our understanding of Drosophila meiosis due to combined cytological and genetic approaches. New techniques have permitted the characterization of chromosome position and spindle formation in female meiosis I. The proteins encoded by the nod and ncd genes, two genes known to be needed for the proper partitioning of chromosomes lacking exchange events, have been identified and found to be kinesin-like motors. The effects of mutations in these genes on the spindle and chromosomes, together with the localization of the proteins, have yielded a model for the mechanism of female meiosis I. In male meiosis I, the chromosomal regions responsible for homolog pairing have been resolved to the level of specific DNA sequences. This provides a foundation for elucidating the molecular basis of meiotic pairing. The cytological techniques available in Drosophila also have permitted inroads into the regulation of sister-chromatid segregation. The products of two genes (mei-S332 and ord) essential for sister-chromatid cohesion have been identified recently. Additional advances in understanding Drosophila meiosis are the delineation of a functional centromere by using minichromosome derivatives and the identification of several regulatory genes for the meiotic cell cycle.     

Genome-linked protein VPg of poliovirus is present as free VPg and VPg-pUpU in poliovirus-infected cells.

VPg is a virus-encoded protein covalently attached to the 5' end of poliovirus virion RNA. We have used antibody prepared against chemically synthesized VPg to detect two forms of VPg in infected cells. Both forms were specifically immunoprecipitated from lysates of infected cells labeled with [3H]-leucine. One appears to be unmodified VPg because it had the same electrophoretic mobility as synthetic VPg. The other had a larger apparent molecular weight than VPg and could be labeled in vivo with 32Pi. Its structure is VPg-pUpU, the UMP dinucleotide being attached to VPg via a phosphodiester bond to tyrosine, the third amino acid from the NH2 terminus of VPg. This structure is identical to that found at the 5' end of virion and minus-strand RNA.