Cooperative transcriptional activity of Jun and Stat3 beta, a short form of Stat3.

To identify proteins that regulate the transcriptional activity of c-Jun, we have used the yeast two-hybrid screen to detect mammalian polypeptides that might interact functionally with the N-terminal segment of c-Jun, a known regulatory region. Among the proteins identified is a short form of Stat3 (designated Stat3 beta). Stat3 beta is missing the 55 C-terminal amino acid residues of the long form (Stat3 alpha) and has 7 additional amino acid residues at its C terminus. In the absence of added cytokines, expression of Stat3 beta (but not Stat3 alpha) in transfected cells activated a promoter containing the interleukin 6 responsive element of the rat alpha 2-macroglobulin gene; coexpression of Stat3 beta and c-Jun led to enhanced cooperative activation of the promoter. Nuclear extracts of cells transfected with a Stat3 beta expression plasmid formed a complex with an oligonucleotide containing a Stat3 binding site, whereas extracts of cells transfected with a Stat3 alpha plasmid did not. We conclude that there is a short form of Stat3 (Stat3 beta), that Stat3 beta is transcriptionally active under conditions where Stat3 alpha is not, and that Stat3 beta and c-Jun are capable of cooperative activation of certain promoters.

Down syndrome-critical region contains a gene homologous to Drosophila sim expressed during rat and human central nervous system development.

Many features of Down syndrome might result from the overdosage of only a few genes located in a critical region of chromosome 21. To search for these genes, cosmids mapping in this region were isolated and used for trapping exons. One of the trapped exons obtained has a sequence very similar to part of the Drosophila single-minded (sim) gene, a master regulator of the early development of the fly central nervous system midline. Mapping data indicated that this exonic sequence is only present in the Down syndrome-critical region in the human genome. Hybridization of this exonic sequence with human fetal kidney poly(A)+ RNA revealed two transcripts of 6 and 4.3 kb. In situ hybridization of a probe derived from this exon with human and rat fetuses showed that the corresponding gene is expressed during early fetal life in the central nervous system and in other tissues, including the facial, skull, palate, and vertebra primordia. The expression pattern of this gene suggests that it might be involved in the pathogenesis of some of the morphological features and brain anomalies observed in Down syndrome.

Jasmonic acid distribution and action in plants: regulation during development and response to biotic and abiotic stress.

Jasmonic acid (JA) is a naturally occurring growth regulator found in higher plants. Several physiological roles have been described for this compound (or a related compound, methyl jasmonate) during plant development and in response to biotic and abiotic stress. To accurately determine JA levels in plant tissue, we have synthesized JA containing 13C for use as an internal standard with an isotopic composition of [225]:[224] 0.98:0.02 compared with [225]:[224] 0.15:0.85 for natural material. GC analysis (flame ionization detection and MS) indicate that the internal standard is composed of 92% 2-(+/-)-[13C]JA and 8% 2-(+/-)-7-iso-[13C]JA. In soybean plants, JA levels were highest in young leaves, flowers, and fruit (highest in the pericarp). In soybean seeds and seedlings, JA levels were highest in the youngest organs including the hypocotyl hook, plumule, and 12-h axis. In soybean leaves that had been dehydrated to cause a 15% decrease in fresh weight, JA levels increased approximately 5-fold within 2 h and declined to approximately control levels by 4 h. In contrast, a lag time of 1-2 h occurred before abscisic acid accumulation reached a maximum. These results will be discussed in the context of multiple pathways for JA biosynthesis and the role of JA in plant development and responses to environmental signals.

Nonneuronal expression of Rab3A: induction during adipogenesis and association with different intracellular membranes than Rab3D.

Rab3A is a small GTP-binding protein expressed predominantly in brain and neuroendocrine cells, in which it is associated with synaptic and synaptic-like vesicles, respectively. Here we report that adult mouse fat cells and 3T3-L1 adipocytes also express Rab3A mRNA and protein. They do not express synaptophysin, an abundant protein in synaptic vesicles or synaptic-like vesicles. The amount of Rab3A mRNA and protein, like that of the highly homologous isoform Rab3D, increases severalfold during differentiation of 3T3-L1 fibroblasts into mature adipocytes. In fat cells, most Rab3D and Rab3A protein is bound to membrane, irrespective of insulin addition. Rab3A and Rab3D are localized in different subcellular compartments, since about half of the Rab3A, but none of the Rab3D, is associated with a low-density organelle(s). Rab3D and Rab3A may be involved in different pathways of regulated exocytosis in adipocytes. Moreover, in adipocytes Rab3A may define an exocytic organelle that is different from synaptic vesicles or synaptic-like microvesicles found in neuronal and endocrine cells.