Stimulation of GABAB receptors increases the expression of the proenkephalin gene in slice cultures of rat neocortex.

In rat neocortex the proenkephalin gene is expressed in GABAergic interneurons. Immunocytochemistry and in situ hybridisation show only a small number of cells in layers II to VI which express the gene. In organotypic slices of rat neocortex, the GABAA receptor inhibitor bicuculline methiodide enhances the expression of the gene in numerous cells. In the present study, we have investigated how GABA regulates the expression of the proenkephalin gene. The GABAA receptor antagonist bicuculline methiodide and the inhibitor of ligand-gated Cl- channels picrotoxin strongly enhanced the expression of the gene in numerous cells which were arranged in neocortical layers II/III and V/VI. Since bicuculline methiodide can also block Ca(++)-activated K+ channels, the possible involvement of such channels was tested. However, apamin which blocks only Ca(++)-activated K+ channels had no effect on the expression of the proenkephalin gene indicating that the effect of bicuculline methiodide was due to inhibition of GABAA receptors. In addition, the GABAB receptor agonist baclofen increased the neocortical expression of the proenkephalin gene mainly in cells located in layers V/VI of the neocortex. The effect of baclofen was inhibited by the GABAB receptor antagonists CGP35348 and CGP52432. Also muscimol, an agonist at GABAA receptors, enhanced the expression of the proenkephalin gene. This effect was blocked by CGP52432 confirming previous observations that muscimol can also stimulate GABAB receptors. Our results indicate that GABA can regulate the expression of the opioid peptide in neocortical neurons in a bidirectional manner. The expression is suppressed via GABAA and enhanced via GABAB receptors.

A LIM-domain protein from sunflower is localized to the cytoplasm and/or nucleus in a wide variety of tissues and is associated with the phragmoplast in dividing cells.

LIM proteins are important eucaryotic developmental regulators characterized by the presence of one or several double zinc finger motifs, the LIM domains, which are protein-interacting domains. Using the cDNA of the previously described pollen LIM protein PLIM1 from sunflower as a hybridization probe we have isolated the coding sequence for a related protein from cDNA libraries from various sunflower organs. This protein, WLIM1, is 188 amino acids long and, like the pollen protein PLIM1, contains two LIM domains, separated by a 48 residue spacer region. The two sunflower proteins are structurally related to the animal LIM proteins CRP and MLP. A WLIM1 gene transcript was detected by RT-PCR in all vegetative and reproductive plant organs tested. Polyclonal antibodies raised against the bacterially expressed and affinity-purified protein recognize a polypeptide of ca. 50 kDa in these organs. Immunocytochemical studies detect the protein in many cell types in each of these organs where it is localized either to the cytoplasm, the nucleus, or both. The protein is often associated with plastids and smaller cellular structures or organelles. In late anaphase and early telophase of dividing cells from ovaries, stems and roots it accumulates in the phragmoplast, and may therefore also play a role in cytokinesis.