Increase In RNA Accumulation Research Articles

Systemic response to aphid infestation by Myzus persicae in the phloem of Apium graveolens

Little is known about the molecular processes involved in the phloem response to aphid feeding. We investigated molecular responses to aphid feeding on celery (Apium graveolenscv. Dulce) plants infested with the aphid Myzus persicae, as a means of identifying changes in phloem function. We used celery as our model species as it is easy to separate the phloem from the surrounding tissues in the petioles of mature leaves of this species. We generated a total of 1187 expressed sequence tags (ESTs), corresponding to 891 non-redundant genes. We analysed these ESTs in silico after cDNA macroarray hybridisation. Aphid feeding led to significant increase in RNA accumulation for 126 different genes. Different patterns of deregulation were observed, including transitory or stable induction 3 or 7 days after infestation. The genes affected belonged to various functional categories and were induced systemically in the phloem after infestation. In particular, genes involved in cell wall modification, water transport, vitamin biosynthesis, photosynthesis, carbon assimilation and nitrogen and carbon mobilisation were up-regulated in the phloem. Further analysis of the response in the phloem or xylem suggested that a component of the response was developed more specifically in the phloem. However, this component was different from the stress responses in the phloem driven by pathogen infection. Our results indicate that the phloem is actively involved in multiple adjustments, recruiting metabolic pathways and in structural changes far from aphid feeding sites. However, they also suggest that the phloem displays specific mechanisms that may not be induced in other tissues.

Regulation of pre-mRNA processing by src.

Changes in gene expression in response to external signals provide a key mechanisms for the regulation of higher eukaryotic cell functions. The importance of transcriptional control in the response of cells to growth factors and cytokines has been extensively documented, but gene expression has also been shown to be controlled at other levels, such as the stability of mRNA in the cytoplasm, its localization and translation. By contrast to transcriptional control, little is known of the contribution of pre-mRNA nuclear processing to the regulation of gene expression, as most of our knowledge of pre-mRNA processing in vivo is indirect, being inferred from comparisons of transcription rates and levels of mRNA accumulation. In this study, we have used as a model the well-characterized maturation pathway of transcripts of the cytokine, tumour necrosis factor beta (TNF beta). We have used the murine TNF beta gene as a reporter for pre-mRNA processing, using a co-transfection approach to investigate whether overproduction of proteins involved in signal transduction influences the processing of TNF beta transcripts. Although transfection of both activated ras and src genes led to an increase in RNA accumulation in the nuclear and cytoplasmic compartments, as expected from their transactivation of the TNF beta expression vector, only src induced a modification of RNA processing. Comparison of several modes of src activation indicated that two distinct effects of src on pre-mRNA processing can be coupled: one involves slowing down splicing and the other allows the export of partially spliced transcripts. These effects can be observed not only on the three introns of TNF beta but also on transcripts from a beta globin expression vector. We have characterized how the processing of transcripts of TNF beta and beta globin is regulated by the signal transduction pathway that includes the Src protein, establishing that external signals have the capacity to regulate gene expression at a post-transcriptional level within the nucleus. Src seems to act on a general mechanism of splicing and/or mRNA transport, but its biologically relevant targets are likely to be restricted to genes for which either alternative processing pathways are in competition, or the kinetics of splicing is critical. This regulation could reflect a modulation by Src of the activity of components of the splicing and transport machineries, but could also involve RNA-binding proteins, which have been shown to interact with Src.

Accumulation of RNA in blastocysts during embryonic diapause and the periimplantation period in the western spotted skunk

The in vivo incorporation of 3H-uridine into RNA was studied in delayed implanting and activated blastocysts obtained from 33 western spotted skunks. 3H-uridine was incorporated into RNA by all blastocysts; however, significantly more label was incorporated as blastocyst diameter increased. Activated blastocysts with diameters of 1.6 mm or greater on average incorporated 65 times more 3H-precursor in 5 hr than diapausing blastocysts with diameters of 1.1 mm or less. Polyadenylated RNA was likewise synthesized by delayed implanting and activated skunk blastocysts; however, the proportion of polyadenylated RNA synthesized by the former was greater than in the latter (43.9% vs. 27.5%). Our data suggest that the transition from embryonic diapause to fully activated blastocysts first occurs gradually for several days before entering a 1-2-day period of rapid development characterized by an abrupt increase in RNA accumulation.

RNA metabolism in human celss during amino acid deprivation. I

1. 1. Uptake of uridine and incorporation into RNA were concentration dependent. Apparent K m for uridine uptake and incorporation into RNA was for normally growing cells 0.04 mM and for glutamine deficient cells 0.1–0.05 mM. 2. 2. Addition of uridine to the culture medium did not appreciably expand the acid-soluble pool labeled from externally added uridine. 3. 3. Uridine incorporation into RNA attained its maximal rate within a few minutes, at a time when the specific activity of the acid-soluble pool was comparatively low, indicating a compartmentalization of the pool. 4. 4. At saturating concentrations, uridine incorporation into RNA was linear for many hours, indicating a feedback regulation of uridine uptake into the nuclear precursor pool and a preferential reutilization of breakdown products of nuclear turnover RNA. The rate of incorporation into RNA of labeled uridine will therefore be proportional to the accumulation of “stable” species of RNA. 5. 5. Leucine and glutamine deprival gradually decreased RNA accumulation. 6. 6. After the addition of the missing amino acid to prestarved cultures there was a lag priod of about 3 h before any increase in RNA accumulation could be seen. Thus a complete restoration of protein synthesis preceded the increase in RNA accumulation.