Evan S. Deneris

Cloning of a novel glutamate receptor subunit, GluR5: Expression in the nervous system during development

We have isolated cDNAs encoding a glutamate receptor subunit, designated GluR5, displaying 40%-41% amino acid identity with the kainate/AMPA receptor subunits GluR1, GluR2, GluR3, and GluR4. This level of sequence similarity is significantly below the approximately 70% intersubunit identity characteristic of kainate/AMPA receptors. The GluR5 protein forms homomeric ion channels in Xenopus oocytes that are weakly responsive to L-glutamate. The GluR5 gene is expressed in subsets of neurons throughout the developing and adult central and peripheral nervous systems. During embryogenesis, GluR5 transcripts are detected in areas of neuronal differentiation and synapse formation.

Members of a nicotinic acetylcholine receptor gene family are expressed in different regions of the mammalian central nervous system

Nicotinic acetylcholine receptors found in the peripheral and central nervous system differ from those found at the neuromuscular junction. Recently we isolated a cDNA clone encoding the alpha subunit of a neuronal acetylcholine receptor expressed in both the peripheral and central nervous system. In this paper we report the isolation of a cDNA encoding the alpha subunit of a second acetylcholine receptor expressed in the central nervous system. Thus it is clear that there is a family of genes coding for proteins with sequence and structural homology to the alpha subunit of the muscle nicotinic acetylcholine receptor. Members of this gene family are expressed in different regions of the central nervous system and, presumably, code for subtypes of the nicotinic acetylcholine receptor.

The functional diversity of the neuronal nicotinic acetylcholine receptors is increased by a novel subunit: β4

A new nicotinic acetylcholine receptor (nAChR) subunit, beta 4, was identified by screening a rat genomic library. In situ hybridization histochemistry revealed expression of the beta 4 gene in the medial habenula of adult rat brains. The primary structure of this subunit was deduced from a cDNA clone isolated from a PC12 cDNA library. Functional nAChRs were detected in Xenopus oocytes injected in pairwise combinations with in vitro synthesized RNAs encoding beta 4 and either the alpha 2, alpha 3, or alpha 4 subunit. Unlike the alpha 3 beta 2 receptor, the alpha 3 beta 4 receptor is not blocked by bungarotoxin 3.1, indicating that the beta subunit can affect the sensitivity of neuronal nAChRs to this toxin. These results extend the functional diversity of nicotinic receptors in the nervous system.

The brain nicotinic acetylcholine receptor gene family

Publisher Summary During the past decade, the availability of radiolabeled nicotine with high specific activity has led to the discovery and mapping of nicotine binding sites in the mammalian brain. These data suggested that the mammalian brain contains an important nicotinic receptor system. This chapter discusses the family of brain nicotinic acetylcholine receptors that have discovered in the past few years through the use of the molecular genetic approach. It identifies seven genes in the rat or mouse genome that code for proteins with homology to the nicotinic acetylcholine receptor. These genes are expressed in the mammalian brain and in some peripheral neurons. The primary structures of the brain nicotinic receptor subunits expressed in the brain have been deduced from the sequences of the cDNA clones. Analysis of the hydrophobicity profiles of the brain nicotinic receptor subunits suggests that they fold through the membrane in an identical manner to the Torpedo fish nicotinic receptor.

The nicotinic receptor genes.

Summary: The causative factor(s) of Alzheimers disease (AD) are presently unknown. However, it has been shown that the number as well as the fraction of high‐ to low‐affinity nicotine binding sites is altered in patients suffering from this disease. This finding, along with the identification of seven genes which code for nicotinic receptors expressed in the mammalian brain, has led to the idea that one nicotinic receptor subtype may be specifically altered in AD. The present article reviews how, through a molecular genetic approach, a family of genes coding for nicotinic acetylcholine receptor subtypes was uncovered. Also discussed is the use of in situ hybridization to determine the distribution of expression of the mRNA encoding for each receptor subtype and the patch clamp technique to characterize their biophysical properties. Determination of the promoters of these genes, as well as the properties of the expressed receptor subtypes, may make it possible to design new specific nicotinic receptor subtype drugs that will treat not only the symptoms of AD but the progression of the disease process as well.

The Nicotinic Acetylcholine Receptor Gene Family

The synapse plays a key role in the nervous system and it is likely that biochemical changes at the synapse underlie some aspects of higher brain function. Most plausible theories of learning, pattern recognition and memory depend upon changes in the efficiency of chemical synapses and changes in the ion channels involved in altering and maintaining the membrane potential, Hopfield 1982. It seems unlikely that these theories will be testable until we have learned more about the structure, function and regulation of receptor and ion channel molecules. It is also now known that receptors can be directly implicated in human disease. Myasthenia gravis is an auto-immune disease involving the production of antibodies against the nicotinic acetylcholine receptor present in skeletal muscle, Patrick and Lindstrom 1973. Degenerative diseases of the brain such as Parkinson’s, Huntington’s and Alzheimer’s disease may involve a breakdown in one or more transmitter systems, Perry et al, 1987.

The Glutamate Receptors: Genes, Structure and Expression

Many plausible theories of learning, pattern recognition and memory depend upon changes in the efficiency of chemical synapses (Cajal 1911; Hebb 1949; Hopfield 1982; Kandel and Schwartz 1982). It seems unlikely that these theories will be testable until the structure, function and regulation of receptor and ion channel molecules are understood in detail.

Brain and Muscle Nicotinic Acetylcholine Receptors: A Gene Family

The synapse plays a key role in the nervous system and it is likely that biochemical changes at the synapse underlie some aspects of higher brain function. Most plausible theories of learning, pattern recognition and memory depend upon changes in the efficiency of chemical synapses and changes in the ion channels involved in altering and maintaining the membrane potential, Cajal, 1911, Hebb,1949, Hopfield 1982. It seems unlikely that these theories will be testable until we have learned more about the structure, function and regulation of receptor and ion channel molecules. It is also now known that receptors can be directly implicated in human disease. Myasthenia gravis is an auto-immune disease involving the production of antibodies against the nicotinic acetylcholine receptor present in skeletal muscle,Patrick and Lindstrom 1973. Degenerative diseases of the brain such as Parkinson’s, Huntington’s and Alzheimer’s disease may involve a breakdown in one or more transmitter systems, Perry et al, 1987.

Molecular Biology of the Neural and Muscle Nicotinic Acetylcholine Receptors

Most theories of nervous system function depend heavily on the existence and properties of the synapse. For this reason, this structure has been a focal point for neuroscience research for many decades. The best understood synapse is the neuromuscular junction because of its accessibility to biochemical and electrophysiological techniques and because of its elegant, well-defined structure. The nicotinic acetylcholine (ACh) receptor found in the postsynaptic membrane binds ACh released from the nerve. The binding of ACh results in a conformational change in the receptor that opens a channel permeable to cations. The resulting ion flux depolarizes the muscle and ultimately leads to muscle contraction. Thus the ACh receptor contains both a ligand-binding domain as well as a channel domain. Biological and structural studies have shown that the muscle nicotinic ACh receptor is a glycoprotein made up of five subunits with the stoichiometry α2βγδ; each of these subunits has a molecular weight between 40,000 and 60,000, and is encoded by a separate gene. This complex has been shown in reconstitution experiments to be a functional receptor containing both a ligand-binding site and a ligand-gated channel (for recent reviews, see Conti-Tronconi and Raftery, 1982; Popot and Changeux, 1984; Stroud and Finer-Moore, 1985; Karlin et al., 1986; McCarthy et al.,1986).

Brain Nicotinic Acetylcholine Receptors: A Gene Family

The synapse plays a key role in the nervous system and it is likely that biochemical changes at the synapse underlie some aspects of higher brain function. Most plausible theories of learning, pattern recognition and memory depend upon changes in the efficiency of chemical synapses and changes in the ion channels involved in altering and maintaining the membrane potential (Cajal, 1911; Hebb, 1949; Hopfield 1982). It seems unlikely that these theories will be testable until we have learned more about the structure, function and regulation of receptor and ion channel molecules. It is also now known that receptors can be directly implicated in human disease. Myasthenia gravis is an auto-immune disease involving the production of antibodies against the nicotinic acetylcholine receptor present in skeletal muscle (Patrick and Lindstrom 1973). Degenerative diseases of the brain such as Parkinson’s, Huntington’s and Alzheimer’s disease may involve a breakdown in one or more transmitter systems (Perry et al., 1987). Most of the therapeutic drugs that have proven to be effective in treating mental illnesses, (such as depression and schizophrenia), are known to act by altering receptor function or by affecting transmitter metabolism or transmitter uptake.