Purification and properties of theDrosophila zen protein

Summary The zen protein is encoded by the zerknullt gene required for normal early development inDrosophila. Like many regulatory proteins of this type, zen contains a 60 amino acid homeobox sequence. We have purified the zen protein and studied its solution behavior and its interaction with DNA. The zen protein exists as a monomer in solution with a molecular weight of about 40000. It binds specifically to a site about 900 bases upstream from thezen gene. Within this binding site DNase protection experiments indicate that binding is confined to two regions approximately 11 and 14 bases in length that are separated by about 30 base pairs. The protein concentration dependence of the binding curve suggests that protein binding is non cooperative.     

Post-castration rebound of an androgen regulated prostatic gene

Summary After castration, the rat dorsolateral prostate M-40 mRNA initially decreased then rebounded to precastrated levels. The cellular site of M-40 expression and its renewed expression after castration was defined by in situ hybridization histochemistry. In situ hybridization with either a ³²P-labeled or biotin-labeled M-40 cDNA probe demonstrated that M-40 mRNA levels were higher in the lateral than dorsal prostate. A second androgen regulated gene, RWB, also was highly expressed in the lateral prostate. The biotinylated cDNA probes provided microscopic resolution of the expressing cells, revealing two distinct morphologies of lateral epithelium which expressed both the M-40 and RWB mRNA. These morphologies appeared in ducts which contained either epithelial cell sheets that were highly convoluted or thinner epithelial cells with a minimal degree of convolution. The RWB mRNA decreased in both cell populations in response to androgen withdrawal. The decline and reappearance of M-40 mRNA also appeared in both epithelial cell types. These data demonstrated that after castration the M-40 mRNA initially decreased as expected for an androgen sensitive gene and then progressed to a fully inducible state. The mechanism of this progression remains to be elucidated.     

The regions of alpha-neurotoxin binding on the extracellular part of the alpha-subunit of human acetylcholine receptor

A set of 18 synthetic uniform overlapping peptides spanning the entire extracellular part (residues 1–210) of the -subunit of human acetylcholine receptor were studied for their binding activity of¹²⁵I-labeled -bungarotoxin and cobratoxin. A major toxin-binding region was found to reside within peptide 122–138. In addition, low-binding activities were obtained with peptides 34–49 and 194–210. It is concluded that the region within residues 122–138 constitutes a universal major toxin-binding region for acetylcholine receptor of various species.     

AFDX-116 discriminates between muscarinic M2 receptors of the heart and the iris smooth muscle

Summary Studies with the atypical muscarinic antagonist pirenzepine provide convincing evidence for the classification of muscarinic acetylcholine receptors (mAChRs) into two subtypes, M₁ and M₂. The present study examines the heterogeneity of the M₂ subtype employing the newly developed competitive muscarinic antagonist, AFDX-116. Comparison of the binding affinities of pirenzepine, atropine, and AFDX-116 to mAChRs in microsomes from the rabbit cerebral cortex, heart, and iris smooth muscle shows that iris mAChRs, which are pharmacologically of the M₂ subtype, can be distinguished from M₂ cardiac receptors based on their affinity for AFDX-116. These results are consistent with the hypothesis that the M₂ receptor subtype consists of a heterogeneous population of receptors.Abbreviations mAChRs Muscarinic Acetylcholine Receptors - CCh Carbachol - NMS N-Methylscopolamine - AFDX-116 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6Hpyrido[2,3-b][1,4]benzodiazepine-6-one     

Effects of muscimol and baclofen on levels of monoamines and their metabolites in the El mouse brain

We compared the changes in monoamines and their metabolites in the El mouse brain induced by GABA-A and GABA-B receptor agonists. Muscimol was used as a GABA-A receptor agonist, and baclofen as a GABA-B receptor agonist. Muscimol (3 mg/kg) significantly increased the DOPAC level in all parts of the mouse brain and the HVA level in the cortex, striatum, and midbrain. No significant change was observed in the dopamine (DA) level. These findings suggest that muscimol may accelerate both the synthesis and catabolism of DA. Baclofen (20 mg/kg) increased the DA level in the hippocampus and midbrain, and the DOPAC level in the hippocampus. Muscimol increased 5-HIAA levels and decreased 5-HT levels. This result suggests that 5-HT metabolism is accelerated by muscimol. No change in 5-HT or 5-HIAA levels was induced by baclofen. The GABA-A receptor system seems to have a potent effect not only on DA neurons, but on 5-HT neurons. However, the GABA-B receptor system appears to have almost no effect on 5-HT neurons, though it appears to have some effect on DA neurons.     

Interactions of piperidine derivatives with the nicotinic cholinergic receptor complex from Torpedo electric organ

The interactions of eight piperidine derivatives with nicotinic receptor complexes fromTorpedo californica electric organ were studied using [¹²⁵I]alpha-bungarotoxin ([¹²⁵I]BGT) as a probe for the acetylcholine binding site and [³H]perhydrohistrionicotoxin ([³H]H₁₂-HTX) as a probe for a site associated with the receptor-gated ion channel.Cis- andtrans-2-methyl-6-n-undecanyl piperidines (MUP), major constituents of fire ant venom, had a high-affinity for [³H]H₁₂-HTX binding sites (K_i=0.08–0.24 M), but had no affect on receptor binding. MUP affinity for [³H]H₁₂-HTX binding sites was approximately doubled in the presence of 1 M carbamylcholine. Introduction of a 2-hydroxyl group to the undecanyl side channel had little effect on activity of the alkaloid. The analog 2,6- (but not 3,5-) dimethylpiperidine was a moderately active inhibitor of [³H]H₁₂-HTX binding (K _i-8.8 M). 2-Methylpiperidine was considerably less active (K _i=600 M), although it was more potent than either 3- or 4-methylpiperidine. The affinities of 2,6-dimethylpiperidine and 2-methylpiperidine for [³H]H₁₂-HTX binding sites were decreased in the presence of 1 M carbamylcholine. Carbamylcholine affinity for the receptor was increased by up to 7 fold in the presence of 10 and 32 M MUP, but was decreased in the presence of 2,6-dimethylpiperidine and 2-methylpiperidine. Thecis- andtrans-isomers of MUP were equipotent in producing each of its effects. In these actions, MUP resembles a variety of other compounds derived from 2,6-disubstituted piperidines, including histrionicotoxins, gephyrotoxins and pumiliotoxins. These studies establish the importance of alkyl substitutions in theortho position of the piperidine ring in conferring ion channel specificity, and the importance of substantial alkyl side chains in conferring the ability of channel blockers to stabilize the nicotinic receptor complex in high affinity, desensitized conformations.     

Temporal relationship between nerve-stump-length-dependent changes in the autophosphorylation of a cyclic AMP-dependent protein kinase and the acetylcholine receptor content in skeletal muscle

The acetylcholine receptor (AChR) content and the autorphosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rat soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [¹²⁵I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro³²P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the³²P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the³²P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.Abbreviations ACh acetylcholine - AChR acetylcholine receptor(s) - BUTX alpha-bungarotoxin - Kd kilodalton - PAGE polyacrylamide gel electrophoresis - R-II regulatory subunit of cyclic AMP-dependent protein kinase type II - SDS sodium dodecyl sulfate