Regulation of simian virus 40 gene expression in Xenopus laevis oocytes.

Expression of the simian virus 40 (SV40) early and late regions was examined in Xenopus laevis oocytes microinjected with viral DNA. In contrast to the situation in monkey cells, both late-strand-specific (L-strand) RNA and early-strand-specific (E-strand) RNA could be detected as early as 2 h after injection. At all time points tested thereafter, L-strand RNA was synthesized in excess over E-strand RNA. Significantly greater quantities of L-strand, relative to E-strand, RNA were detected over a 100-fold range of DNA concentrations injected. Analysis of the subcellular distribution of [35S]methionine-labeled viral proteins revealed that while the majority of the VP-1 and all detectable small t antigen were found in the oocyte cytoplasm, most of the large T antigen was located in the oocyte nucleus. The presence of the large T antigen in the nucleus led us to investigate whether this viral product influences the relative synthesis of late or early RNA in the oocyte as it does in infected monkey cells. Microinjection of either mutant C6 SV40 DNA, which encodes a large T antigen unable to bind specifically to viral regulatory sequences, or deleted viral DNA lacking part of the large T antigen coding sequences yielded ratios of L-strand to E-strand RNA that were similar to those observed with wild-type SV40 DNA. Taken together, these observations suggest that the regulation of SV40 RNA synthesis in X. laevis oocytes occurs by a fundamentally different mechanism than that observed in infected monkey cells. This notion was further supported by the observation that the major 5' ends of L-strand RNA synthesized in oocytes were different from those detected in infected cells. Furthermore, only a subset of those L-strand RNAs were polyadenylated.     

Regulation of epidermal differentiation by a Distal-less homeodomain gene

The Distal-less-related homeodomain gene Dlx3 is expressed in terminally differentiated murine epidermal cells. Ectopic expression of this gene in the basal cell layer of transgenic skin results in a severely abnormal epidermal phenotype and leads to perinatal lethality. The basal cells of affected mice ceased to proliferate, and expressed the profilaggrin and loricrin genes which are normally transcribed only in the latest stages of epidermal differentiation. All suprabasal cell types were diminished and the stratum corneum was reduced to a single layer. These data indicate that Dlx3 misexpression results in transformation of basal cells into more differentiated keratinocytes, suggesting that this homeoprotein is an important regulator of epidermal differentiation.     

Regulation of plant gene expression by antisense RNA.

Regulation of gene expression by antisense RNA was first discovered as a naturally-occurring phenomenon in bacteria. Recently natural antisense RNAs have been found in a variety of eukaryotic organisms; their in vivo function is, however, obscure. Deliberate expression of antisense RNA in animal and plant systems has lead to successful down-regulation of specific genes. We will review the current status of antisense gene action in plant systems. The recent discovery that 'sense' genes are able to mimic the action of antisense genes indicates that (anti)sense genes must operate by mechanisms other than RNA-RNA interaction.     

Regulation of integrin gene expression by substrate adherence.

Under substrate adherent conditions, integrin gene expression can be regulated by transforming growth factor-beta, interleukin-1 beta, and prostaglandins. This report demonstrates a new mechanism that can differentially control the expression of several integrins. When MG-63 osteosarcoma cells are maintained in suspension, up-regulation of several integrin alpha-subunits takes place. Within as little as 4 h, the mRNA levels for both the alpha 2- and alpha 4-subunits are increased 4- and 6-fold, respectively. It was found that mRNA levels for the alpha 2-, alpha 4-, and alpha v-subunits were markedly increased in several differentiated cell lines under nonadherent conditions; however, cells that did not express a given integrin under substrate adherent conditions also did not express this integrin when maintained in suspension. The alpha 5-subunit did not upregulate during suspension growth. By immunocytochemistry, changes in integrin mRNA levels were confirmed at the protein level. Both cytochalasin B and a phorbol ester were found to induce the expression of the alpha 2-subunit, but not the alpha 4- and alpha 5-subunits, in a dose-dependent fashion. Many investigators have documented changes in gene expression that result from changes in "cell shape." These phenomena may result from up-regulation of integrin gene expression induced by the lack of substrate adherence.