The human myosin light chain kinase (MLCK) from hippocampus: cloning, sequencing, expression, and localization to 3qcen-q21

Myosin light chain kinase (MLCK), a key enzyme in muscle contraction, has been shown by immunohistology to be present in neurons and glia. We describe here the cloning of the cDNA for human MLCK from hippocampus, encoding a protein sequence 95% similar to smooth muscle MLCKs but less than 60% similar to skeletal muscle MLCKs. The cDNA clone detected two RNA transcripts in human frontal and entorhinal cortex, in hippocampus, and in jejunum, one corresponding to MLCK and the other probably to telokin, the carboxy-terminal 154 codons of MLCK expressed as an independent protein in smooth muscle. Levels of expression were lower in brain compared to smooth muscle. We show that within the protein sequence, a motif of 28 or 24 residues is repeated five times, the second repeat ending with the putative methionine start codon. These repeats overlap with a second previously reported module of 12 residues repeated five times in the human sequence. In addition, the acidic C-terminus of all MLCKs from both brain and smooth muscle resembles the C-terminus of tubulins. The chromosomal localization of the gene for human MLCK is shown to be at 3qcen-q21, as determined by PCR and Southern blotting using two somatic cell hybrid panels.

Kainate receptor subunits expressed in single cultured hippocampal neurons: molecular and functional variants by RNA editing

To determine the kainate receptor subunits that are found in native kainate receptors, we have applied a multiplex PCR of cDNAs reverse transcribed from mRNA harvested from single cultured hippocampal neurons after electrophysiological recording. We found that all the cells showing rapidly desensitizing currents in response to kainate express the GluR6 subunit mRNA, and that some of them also express the GluR5 subunit mRNA. No GluR7, KA-1, or KA-2 subunit mRNAs were detected. Analysis of the editing sites of the GluR6 mRNA demonstrated that the three editing sites present in these subunits are edited to a different extent. Predominant expression of the unedited variant (Q) was observed, but edited and unedited variants may coexist in the same cell. In addition, we show that the Q/R site from the GluR6 subunit controls functional properties of native kainate receptors.

Single cell RT-PCR proceeds without the risk of genomic DNA amplification

We have previously described a method for detection of mRNAs expressed in single cells after patch-clamp recordings. The method, termed single cell RT-PCR, involves aspiration of the cell content, a reverse transcription (RT) step, and a polymerase chain reaction (PCR) using specific primers. Since the nucleus is frequently harvested together with the cytosol, genomic DNA may generate false positive results. Thus, we demonstrated that dilutions containing a few copies of plasmid could be detected by PCR in a range which, according to the Poisson law, suggests that the PCR method can amplify from the two genomic alleles. We performed single cell RT-PCR of intronless GluR2 or GluR5 fragments by comparing cerebellar cell types where these mRNAs are known to be present or absent. For each cell the nucleus was harvested together with the cytosol. Following RT-PCR with GluR5 primers, all Purkinje cells (n = 6) yielded the expected PCR product, whereas it was not generated from any of the granule cells (n = 5). In corresponding experiments with GluR2 primers, we obtained the GluR2 product from all Purkinje cells (n = 5), but not from any of the glial cells (n = 5). These results are in agreement with the known cellular expression of GluR2 and GluR5 mRNAs. We conclude that the single cell RT-PCR method does not amplify the genomic DNA when the nucleus is aspirated together with the cytosol. We suggest that genomic DNA amplification is avoided, because the genomic alleles are not exposed during the procedure.

Electrospray mass spectrometry for the characterization of the purity of natural and modified oligodeoxynucleotides

Electrospray ionization mass spectrometry is an accurate and sensitive analytical method to characterize the purity of oligodeoxynucleotides being tested for pharmacological studies. We report the preparation procedure ('desalting') of natural and modified oligodeoxynucleotides (ODNs) and their analysis by negative-ion electrospray mass spectrometry. We evaluate the sensitivity and the accuracy of the method for two antisense ODN sequences. Mass analysis of the 25-mer phosphorothioate can be performed to within 0.001% accuracy (standard error of 0.05 Da) for a sample concentration of 12 pmol/microL. In addition, the adduct ion and the failure sequence can be identified to characterize the antisense ODN.

Polyglycylation of tubulin: a posttranslational modification in axonemal microtubules

A posttranslational modification was detected in the carboxyl-terminal region of axonemal tubulin from Paramecium. Tubulin carboxyl-terminal peptides were isolated and analyzed by Edman degradation sequencing, mass spectrometry, and amino acid analysis. All of the peptides, derived from both alpha and beta tubulin subunits, were modified by polyglycylation, containing up to 34 glycyl units covalently bound to the gamma carboxyl group of glutamyl residues. This modification, present in one of the most stable microtubular systems, may influence microtubule stability or axoneme function, or both.

Activity-dependent regulation of N-methyl-D-aspartate receptor subunit expression in rat cerebellar granule cells

The glutamate receptor channels of the N-methyl-D-aspartate (NMDA) subtype are composed of different subunits named NR1 and NR2A-D. These subunits can combine in different oligomers with diverging properties and their expression is developmentally regulated. We have used rat cerebellar slice cultures to test the involvement of bioelectrical activity and synaptic transmission in the changes in NR2A-C expression observed in developing granule cells. A correlation between the functional properties of the NMDA receptors and expression of the NR2A-C mRNAs was obtained in single granule cells by coupling patch-clamp recording and reverse transcription followed by polymerase chain reaction. Granule cells grown under standard culture conditions expressed mainly NR2A mRNA when examined after 15-40 days in vitro. Consistent with this observation, their responses to NMDA were only weakly reduced by 3 microM ifenprodil, a non-competitive antagonist which discriminates between NR2A and NR2B subunits in expression systems. In cerebellar cultures chronically exposed to tetrodotoxin to eliminate spontaneous electrical activity, granule cells maintained a predominant expression of NR2B subunits and their responses to NMDA were largely inhibited by 3 microM ifenprodil. These results provide evidence that the expression of the NR2A and B subunits is regulated through an activity-dependent mechanism leading to the formation of NMDA receptors with different pharmacological properties. Finally, the NR2C subunit, abundantly expressed in vivo by adult granule cells, was only rarely detected in slice cultures, even when excitatory synapses were formed between granule cells and fibres originating from co-cultured brainstem explants. These data suggest that the induction of NR2C expression observed in vivo requires an additional factor(s) that remains to be identified.

Cellular locus of the nitric oxide-synthase involved in cerebellar long-term depression induced by high external potassium concentration

The cellular location of the NO-synthase involved in long-term depression (LTD) of parallel fiber (PF)-mediated EPSCs induced by raising the external potassium (K) concentration has been investigated by using both whole-cell patch-clamp recordings (WCR) of Purkinje cells (PCs) in thin slices in vitro, and reverse transcription followed by polymerase chain reaction (PCR) applied to mRNAs harvested from these single PCs during WCR. In all tested cells in the control group, a large LTD of PF-mediated EPSCs was induced by perfusing the slices for 3 min with a high (30 mM) K perfusing medium. In a second group of cells for which the protein kinase C (PKC) inhibitor peptide 19-36 was added to the intrapipette solution at a concentration of 10 microM, the LTD following complete wash out of the high K solution was significantly less prominent than in the control group. Very similar results were also obtained when 30 microM NG-methyl-L-arginine (L-NMMA) was added to the perfusing medium. In contrast, when both the PKC inhibitor peptide 19-36 and L-NMMA were added to the intrapipette solution at a concentration of 10 and 30 microM respectively, no LTD was revealed following wash out of the high K solution. Finally, the PCR amplification of mRNAs harvested from these single PCs during WCR, as well as from granule cells from the same slices, confirms that mRNAs encoding the NO-synthase are expressed by granule cells, whereas they are not detected in PCs.

Class I and IVa beta-tubulin isotypes expressed in adult mouse brain are glutamylated

Several types of post-translational modifications contribute to the high level of tubulin heterogeneity in the brain. An important modification is glutamylation of the major brain-specific isotypes, such as class Ia/b of alpha-tubulin and classes II and III of beta-tubulin. Here we describe experiments to determine if additional, minor tubulin isotypes, expressed in adult mouse brain, could also be glutamylated. Purified tubulin from adult mouse brain was cleaved with thermolysin. Proteolytically released carboxy-terminal peptides of both alpha- and beta-tubulin were isolated by sequential anion exchange and reverse-phase column-chromatography. Anionic peptides were then characterized by amino acid sequencing and mass spectrometry. We show that brain-specific class IVa and constitutive class I beta-tubulin isotypes can be glutamylated, at Glu434 and Glu441, respectively.

Cloning and characterization of a 135- to 500-kb region of homology on the long arm of human chromosome 21

The polymorphic marker D21S190 was initially isolated from a chromosome 21 phage library and mapped to two loci: one in 21q11.1 (proximal locus) and the other one in 21q22.1 (distal locus). To characterize the region of homology revealed with D21S190, we have screened two different chromosome 21 YAC libraries and one chromosome 21 cosmid library. Fluorescence in situ hybridization on normal human chromosomes of YACs, cosmids, and phages positive with D21S190 confirmed the existence of two homologous regions on the long arm of chromosome 21. Among the positive YACs, four (HY67, 2D7y21, 2D11y21, and 1B1y21) were selected and oriented relative to each other, forming a 2-Mb contig in the distal locus, including D21S54. Hybridization of YAC extremities to a panel of somatic cell hybrids containing various portions of chromosome 21 showed that the proximal locus is located between the breakpoints of 2Fu(r)1 and ACEM and the distal locus between the breakpoints of ACEM and 6918. The proximal and the distal breakpoints of JC6 are both included in the region of homology. We have constructed a restriction map of HY67, 2D7y21, and 2D11y21 spanning 1 Mb and including several markers: D21S294, D21S296, and the new STSs corresponding to YAC extremities. The region of homology encompasses 135-500 kb and has the same orientation in the distal and in the proximal locus, which are at least 12 Mb apart. It is lacking a NotI site but does contain clusters of GC-rich restriction sites, which are candidate regions for as yet unidentified genes.

Evidence for a conformational polymorphism of invertebrate neurohormones. D-amino acid residue in crustacean hyperglycemic peptides

Several large peptidic neurohormones have been isolated in crustaceans. In lobster and other related species, each of these neurohormones, and particularly the crustacean hyperglycemic hormone, occurs as two isoforms having the same peptidic sequence and molecular mass. We report here that these isoforms differ by the configuration of a single amino acid residue. The third residue (Phe3) of the lobster hyperglycemic hormones is in either the L- or D-configuration. In addition, we have shown that the biological activity of the two isoforms differs when considering the kinetics of their hyperglycemic effect.

Subunit composition at the single-cell level explains functional properties of a glutamate-gated channel

The diversity of known glutamate-gated channels has been markedly increased by the discovery of multiple subunits and their spliced and edited variants. These subunits can potentially form different oligomeric complexes with diverging properties. A crucial question is therefore to determine the actual subunit composition of naturally occurring glutamate receptors. We have coupled patch-clamp recordings and reverse transcription followed by PCR amplification to correlate the presence of mRNAs for each subunit and the functional properties of native glutamate receptors at the single-cell level. In a homogeneous population of functionally identified hippocampal neurons (type II) in culture bearing a glutamate receptor of the AMPA subtype with a high calcium permeability, we found that, among the multiple subunits, only two, the flop forms of GluR1 and GluR4, were expressed. In particular, GluR2 was never detected. This composition explains the uncommon properties of AMPA receptors in type II neurons.

The pseudo-posterior limiting layer syndrome: a vitreoretinal heredodegeneration with autosomal dominant transmission

A new vitreoretinal heredodegenerative syndrome with a high incidence (> 40%) of retinal detachment is described. It has been observed in five families (altogether 27 subjects) without consanguinity. The affection is autosomal dominant, bilateral, and more often than not (> 70%) coupled with axial myopia exceeding 5 D. Peripheral retinal degenerations are found in about 90% of the eyes. The syndrome is characterized by a pathognomonic membrane-like structure in the vitreous cavity, the pseudo-posterior limiting layer. The pseudo-PLL is a purely intravitreal phenomenon: in contrast to other vitreoretinal syndromes, there are no vitreous condensations connected to the retina.

Electrospray ionization mass spectrometry on hydrophobic peptides electroeluted from sodium dodecyl sulfate-polyacrylamide gel electrophoresis application to the topology of the sarcoplasmic reticulum Ca2+ ATPase

We describe a method to prepare proteins and peptides in a state suitable for exact determination of molecular mass by electrospray ionization mass spectrometry after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution. The utility of the procedure, in conjunction with N-terminal sequencing, in defining the C-terminal end of the peptide fragments produced by proteolysis of sarcoplasmic reticulum Ca2+ ATPase with V8 is demonstrated. The application of mass spectrometry aids significantly the use of proteolytic enzymes for topological studies of membrane proteins, and SDS-PAGE is preferable to reverse-phase HPLC for separation of membraneous, hydrophobic peptides and proteins.

Frog prodermorphin expressed in mammalian cells is partly converted to the hydroxyproline containing precursor

Using recombinant vaccinia virus, we have expressed in mammalian cells the cDNA coding for the precursor of dermorphin, a D-alanine containing opioid peptide from the skin of the South American frog Phyllomedusa sauvagei. HeLa cells and AtT-20 cells produced prodermorphin where proline-6 of dermorphin was partly hydroxylated. This was demonstrated by digesting the partially purified precursors with trypsin and carboxypeptidase B. After immunoprecipitation and separation by HPLC, two decapeptides were detected which differed by the presence of proline or hydroxy-proline at position 6. This demonstrates that HeLa cells as well as AtT-20 cells can perform the post-translational conversion of certain proline residues to hydroxyproline in a foreign hormone precursor expressed in these cells.

Photo-cross-linking of CRP to nonspecific DNA in the absence of cAMP. DNA interacts with both the N- and C-terminal parts of the protein

Adenosine cyclic 3',5'-phosphate receptor protein (CRP or CAP) is a regulatory protein involved in the transcription of several operons in Escherichia coli. cAMP-independent, nonspecific complexes of CRP and DNA were investigated by photochemical cross-linking of the protein to nonspecific DNA, whose thymines are substituted by 5-bromouracil (BrUra). The cross-linked protein was completely digested by trypsin, and the covalently bound peptides were sequenced. We identified two regions of the protein in close contact with DNA: one in the C-terminal part, overlapping the canonical helix-turn-helix motif, and the other one in the N-terminal part, which is usually not considered to belong to the DNA-interacting domain of CRP. This result lead us to propose models for nonspecific interaction, where the DNA is in contact with both the N- and C-terminal parts of the protein.

Molecular biology of excitatory amino acid receptors: subtypes and subunits

Glutamate receptors coupled to ion channels have been named according to their selective agonist: N-methyl-D-Aspartate (NMDA), kainate, quisqualate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA). The pharmacology of the NMDA receptor is clearly different from that of the kainate, quisqualate and AMPA receptors, thus differentiating two types: NMDA and non-NMDA receptors. Molecular cloning and expression of non-NMDA receptor subunits have now established that the different neuronal responses to kainate, quisqualate and AMPA are mediated by at least two subtypes of ligand-gated channels: one responding to the three ligands, the other responding to kainate and quisqualate but not to AMPA.

Electron microscopic localization of photoaffinity-labelled delta opioid receptors in the neostriatum of the rat

The distribution of delta opioid receptors, selectively labelled in vitro with the photoaffinity probe monoiodo azido-DTLET ([D-Thr2,pN3Phe4, Leu5]enkephaly-Thr6), was analyzed by light and electron microscopic radioautography in sections from rat neostriatum. Preliminary experiments indicated that up to 65% of specific 125I-azido-DTLET binding to rat striatal sections was still detectable following prefixation of the brain with 0.5% glutaraldehyde. These experiments also showed that up to 20-30% of the specifically bound radioactivity was covalently linked following ultraviolet irradiation and was thereby retained in tissue during subsequent postfixation and dehydration steps. Accordingly, the topographic distribution of the covalently attached azido-DTLET molecules was similar to that seen in fresh frozen sections and characteristic of that previously described for delta sites. Light and electron microscopic examination of the label in prefixed, striatal sections irradiated with ultraviolet light revealed that a significant proportion of specifically bound 125I-azido-DTLET molecules was intraneuronal. Specifically, 16% of the labelled binding sites were found in dendrites, 12% in perikarya and 4% in axon terminals. These results suggest that an important proportion of delta opioid binding sites labelled in the neostriatum correspond to receptors that are undergoing synthesis, transport and/or recycling. They also imply that a major fraction of delta sites are associated with intrastriatal neurons, as opposed to afferent axons. Approximately 44% of the labelled binding sites were associated with neuronal plasma membranes. Although most of these were found at the level of axodendritic (20%) and dendrodendritic (7%) appositions, comparison of the labelling incidence of these two compartments with their frequency of occurrence in tissue suggested that delta sites are fairly widely dispersed along neuronal plasma membranes. Only a small proportion (smaller than that of mu or kappa sites labelled in the same region) was associated with synaptic specializations. These results support the concept that delta receptors correspond to molecular entities that are distinct from mu and kappa sites and suggest that delta ligands act primarily nonjunctionally on the plasma membrane of striatal neurons.

Effects of convulsant ligands of the GABA-benzodiazepine receptor complex in conflict and learning tasks in mice

A systematic study of the effects of convulsants acting at the GABA-benzodiazepine receptor complex was undertaken in mice to estimate their potential anxiogenic effects and/or performance enhancing effects in learning and memory tasks. Anxiogenic effects were assessed in a conflict task where lever presses delivered both a food pellet and a mild electric foot shock. Effects on learning were assessed through analysis of habituation to a new environment. The convulsant agents pentylenetetrazol (PTZ) and picrotoxin (PX), both acting through the GABA-benzodiazepine receptor complex, and strychnine, a convulsant acting through the glycine transmission were used. Our data show that non convulsive doses of PTZ (25 mg/kg) and PX (0.85 mg/kg), but not of strychnine (0.8 mg/kg), are anxiogenic in the conflict model. At lower doses PTZ (10 mg/kg) and PX (0.3 mg/kg), but not strychnine (0.1 to 0.6 mg/kg), enhance performance in the habituation model. Our results contribute to the validation of the idea that small decreases in GABAergic transmission are accompanied by improvement of learning whereas medium decreases induce anxiogenic effects.

AMPA receptor subunits expressed by single Purkinje cells

Several subunits of the glutamate receptor of the AMPA subtype have been cloned recently. These subunits, named GluR1, GluR2, GluR3, and GluR4, exist as two splicing variants (flip and flop). We have determined the subset of AMPA receptor subunits expressed by single cerebellar Purkinje cells in culture. This was achieved by combining whole-cell patch-clamp recordings and a molecular analysis, based on the polymerase chain reaction, of the messenger RNAs harvested into the patch pipette at the end of each recording. We found that each single cell expresses the messenger RNAs encoding the following five subunits: the flip and flop versions of GluR1 and GluR2 as well as GluR3flip, GluR2 being the most abundant. In addition, GluR3flop and GluR4flip were scarcely expressed in half of these neurons, and GluR4flop was never detected.

BEN, a surface glycoprotein of the immunoglobulin superfamily, is expressed in a variety of developing systems

We have previously identified a 95- to 100-kDa cell surface glycoprotein, which we named BEN (for bursal epithelium and neurons), that is widely expressed during chicken embryonic development. In the central nervous system, it is restricted to subsets of neurons including the motoneurons and the inferior olivary nucleus neurons (which provide the cerebellum with the climbing fibers) where its expression occurs during the phase of axonogenesis and synaptogenesis. In the present work, we show that BEN expression extends to a variety of tissues originating from the three embryonic germ layers. We have found that BEN immunopurified from neural, epithelial, and hemopoietic tissues is differently glycosylated and may or may not carry the HNK-1 epitope. We then cloned a full-length cDNA encoding this protein. Analysis of its sequence reveals that BEN is a member of the immunoglobulin superfamily. Two molecules with an identical cDNA sequence were recently reported: DM-GRASP [Burns, F. R., Von Kannen, S., Guy, L., Raper, J. A., Kamholz, J. & Chang, S. (1991) Neuron 7, 209-220] and SC1 [Tanaka, H., Matsui, T., Agata, A., Tomura, M., Kubota, I., Mcfarland, K. C., Kohr, B., Lee, A., Phillips, H. S. & Shelton, D. L. (1991) Neuron 7, 535-545]. Their pattern of expression and structural properties are consistent with those reported for BEN. Therefore BEN, DM-GRASP, and SC1 are likely to be the same molecule of the immunoglobulin superfamily.