Purification and cDNA cloning of ARPP-16, a cAMP-regulated phosphoprotein enriched in basal ganglia, and of a related phosphoprotein, ARPP-19

ARPP-16 (cAMP-regulated phosphoprotein of Mr = 16,000) is a substrate for cAMP-dependent protein kinase and is enriched in the basal ganglia. ARPP-16 has been purified to homogeneity from the soluble fraction of bovine caudate nuclei. An additional substrate for cAMP-dependent protein kinase of Mr = 19,000 (ARPP-19) was found to cross-react with rabbit anti-serum prepared against purified ARPP-16. Immunological analysis indicated that ARPP-16 was enriched in the basal ganglia while ARPP-19 was present in similar levels in all brain regions studied and was also present in non-neuronal tissues. ARPP-19 was also purified to homogeneity from bovine caudate nucleus cytosol. Using oligonucleotide probes based on the partial amino acid sequence of purified ARPP-16, cDNA clones for ARPP-16 and ARPP-19 were isolated from a bovine caudate nucleus cDNA library and sequenced. The predicted amino acid sequences of the two proteins were identical except that ARPP-19 had an additional 16 amino acids at the NH2-terminal. The two cDNA clones share an identical 3'-untranslated region of 756 nucleotides. The cDNA clone for ARPP-16 contained 806 additional nucleotides located 3' to this common sequence. The 5'-untranslated regions of the two clones were entirely different. The results suggest the possibility that ARPP-16 and ARPP-19 are produced by alternative transcription and splicing.

The synapsins and the regulation of synaptic function

Synapsin I and II are a family of synaptic vesicle-associated phosphoproteins involved in the short-term regulation of neurotransmitter release. In this review, we discuss a working model for the molecular mechanisms by which the synapsins act. We propose that synapsin I links synaptic vesicles to actin filaments in the presynaptic nerve terminal and that these interactions are modulated by the reversible phosphorylation of synapsin I through various signal transduction pathways. The high degree of homology between the synapsins suggests that some of the functional properties of synapsin I are also shared by synapsin II.

Localization of the MARCKS (87 kDa) protein, a major specific substrate for protein kinase C, in rat brain

The localization of MARCKS (myristoylated, alanine-rich C-kinase substrate), a major specific substrate for protein kinase C, has been studied in the rat brain. Light microscopic immunocytochemistry and biochemical analysis demonstrated that the protein is widespread throughout the brain and enriched in certain regions, including the piriform and entorhinal cortices, portions of the amygdaloid complex, the intralaminar thalamic nuclei, the hypothalamus, the nucleus of the solitary tract, nucleus ambiguus, and many catecholaminergic and serotonergic nuclei. Electron microscopic analysis revealed immunoreactivity in axons, axon terminals, small dendritic branches, and occasionally in dendritic spines. In neuronal processes, immunoreactivity was particularly prominent in association with microtubules, but reaction product was also seen in cytosol and adjacent to plasma membranes. No reaction product was observed in large dendrites, somata, or nuclei. A population of strongly immunoreactive glial cells was also observed. Many of these glial cells were morphologically similar to microglial cells, although some resembled astrocytes. In glial cells, both cytoplasm and plasma membranes were heavily labeled. The distribution of the MARCKS protein did not coincide precisely with the distribution of any of the subspecies of protein kinase C. The results indicate that the MARCKS protein is expressed in the majority of cell types in the CNS, and they suggest that the protein may be involved both in glial cell functions and in neuronal functions involving cytoskeletal elements in small dendritic branches and axon terminals.

Comparison of gene expression of the dopamine D-2 receptor and DARPP-32 in rat brain, pituitary and adrenal gland

In situ hybridization histochemistry was used to compare the distribution of dopamine D-2 receptor mRNA and DARPP-32 mRNA in rat brain, pituitary and adrenal gland. In many regions such as the caudate nucleus, nucleus accumbens and olfactory tubercle, there was an excellent correlation with dopamine receptor binding studies, whereas in some discrete brain regions mismatches were observed.

Differential expression of ARPP-16 and ARPP-19, two highly related cAMP-regulated phosphoproteins, one of which is specifically associated with dopamine-innervated brain regions

ARPP-16 and ARPP-19 are 2 cAMP-regulated phosphoproteins of Mr = 16,000 and 19,000, respectively, which are identical except for the presence of 15 additional amino acids on the NH2-terminus of ARPP-19. The phosphorylation of these 2 proteins is regulated by cAMP and vasoactive intestinal peptide in reaggregate striatal cultures (Girault et al., 1988). Using immunoblots and immunocytochemistry, we have compared the regional, subcellular, phylogenetic, and ontogenetic distributions of these 2 proteins. ARPP-19 was found in all vertebrate species studied and, at various levels, in all tissues of adult rat. ARPP-19 was also present at high levels in malignant cell lines. During development ARPP-19 concentrations were highest in the embryo and decreased during the pre- and postnatal periods. In contrast, ARPP-16 was detected only in some specific neurons of the dopamine-innervated regions of the basal ganglia and the cerebral cortex, which are known to possess D1 dopamine receptors, in particular the striatonigral neurons. ARPP-16 is phylogenetically recent, being found only in birds and mammals, and appears late in ontogenesis, increasing during the postnatal period. These 2 proteins provide a unique model for studying the specificity of signal transduction and gene expression in dopaminoceptive neurons.

Localization of DARPP-32 immunoreactive neurons in the bed nucleus of the stria terminalis and central nucleus of the amygdala: co-distribution with axons containing tyrosine hydroxylase, vasoactive intestinal polypeptide, and calcitonin gene-related peptide

The distribution and morphology of neurons containing the dopamine- and cyclic AMP-regulated phosphoprotein, DARPP-32, were investigated in the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (CeA). DARPP-32 immunoreactive neurons are numerous in both regions, but are restricted to the lateral dorsal and the lateral juxtacapsular subdivisions of the BST, and the central lateral and lateral capsular subdivisions of the CeA. Immunoreactive neurons in the lateral dorsal BST, and the central lateral and lateral capsular CeA are similar morphologically, while those in the juxtacapsular BST appear to be a subpopulation of striatal medium-sized spiny neurons. The distribution of DARPP-32 immunoreactive neurons in the BST and CeA overlaps considerably with axonal plexuses containing tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP). These studies provide further evidence of the close relationship between the CeA and BST, and also provide anatomical evidence for possible interactions between neurotransmitters, neuropeptides, and phosphoproteins.

Calcium/calmodulin-dependent protein kinase II increases glutamate and noradrenaline release from synaptosomes

A variety of evidence indicates that calcium-dependent protein phosphorylation modulates the release of neurotransmitter from nerve terminals. For instance, the injection of rat calcium/calmodulin-dependent protein kinase II (Ca2+/CaM-dependent PK II) into the preterminal digit of the squid giant synapse leads to an increase in the release of a so-far unidentified neurotransmitter induced by presynaptic depolarization. But until now, it has not been demonstrated that Ca2+/CaM-dependent PK II can also regulate neurotransmitter release in the vertebrate nervous system. Here we report that the introduction of Ca2+/CaM-dependent PK II, autoactivated by thiophosphorylation, into rat brain synaptosomes (isolated nerve terminals) increases the initial rate of induced release of two neurotransmitters, glutamate and noradrenaline. We also show that introduction of a selective peptidergic inhibitor of Ca2+/CaM-dependent PK II inhibits the initial rate of induced glutamate release. These results support the hypothesis that activation of Ca2+/CaM-dependent PK II in the nerve terminal removes a constraint on neurotransmitter release.

Distribution and cellular localization of DARPP-32 mRNA in rat brain

In situ hybridization histochemistry has been used to determine the regional distribution and cellular localization of DARPP-32 mRNA in the rat brain. Results support the concept that DARPP-32 is present primarily in cells expressing the dopamine D1 subtype receptor, and that DARPP-32 is not synthesized in dopamine-containing cells. Strongly labelled neuronal cell bodies were found in the caudate nucleus, nucleus accumbens, olfactory tubercle, parts of the bed nucleus of the stria terminalis, and the amygdaloid complex. In addition large amounts of DARPP-32 mRNA were visualized in the medial habenula and around the third ventricle, in ependymal cells and tanycytes, and in the cerebellar Purkinje cells. A less pronounced activity was seen in layers II-III and VI throughout the cerebral cortex. The present studies together with previous biochemical and immunocytochemical studies demonstrate that DARPP-32 gene expression is greatest primarily in D1 dopaminoceptive cells, although there are exceptions. In situ hybridization may thus be used to quantitate regulation of DARPP-32 mRNA in discrete brain regions.

Distribution of DARPP-32 in the basal ganglia: an electron microscopic study

DARPP-32, a dopamine and cyclic AMP-regulated phosphoprotein, has been studied by light and electron microscopical immunocytochemistry in the rat caudatoputamen, globus pallidus and substantia nigra. In the caudatoputamen, DARPP-32 was present in neurons of the medium-sized spiny type. Immunoreactivity for DARPP-32 was present in dendritic spines, dendrites, perikaryal cytoplasm, most but not all nuclei, axons and a small number of axon terminals. Immunoreactive axon terminals in the caudatoputamen formed symmetrical synapses with immunolabeled dendritic shafts or somata. Neurons having indented nuclei were never immunoreactive. In the globus pallidus and substantia nigra pars reticulata, DARPP-32 was present in myelinated and unmyelinated axons and in axon terminals. The labelled axon terminals in these regions formed symmetrical synaptic contacts on unlabelled dendritic shafts or on unlabelled somata. These data suggest that DARPP-32 is present in striatal neurons of the medium-sized spiny type and that these DARPP-32-immunoreactive neurons form symmetrical synapses on target neurons in the globus pallidus and substantia nigra. The presence of DARPP-32 in these striatal neurons and in their axon terminals suggests that DARPP-32 mediates part of the response of medium-size spiny neurons in the striatum to dopamine D-1 receptor activation.

Redistribution of synaptophysin and synapsin I during alpha-latrotoxin-induced release of neurotransmitter at the neuromuscular junction

The distribution of two synaptic vesicle-specific phosphoproteins, synaptophysin and synapsin I, during intense quantal secretion was studied by applying an immunogold labeling technique to ultrathin frozen sections. In nerve-muscle preparations treated for 1 h with a low dose of alpha-latrotoxin in the absence of extracellular Ca2+ (a condition under which nerve terminals are depleted of both quanta of neurotransmitter and synaptic vesicles), the immunolabeling for both proteins was distributed along the axolemma. These findings indicate that, in the presence of a block of endocytosis, exocytosis leads to the permanent incorporation of the synaptic vesicle membrane into the axolemma and suggest that, under this condition, at least some of the synapsin I molecules remain associated with the vesicle membrane after fusion. When the same dose of alpha-latrotoxin was applied in the presence of extracellular Ca2+, the immunoreactivity patterns resembled those obtained in resting preparations: immunogold particles were selectively associated with the membrane of synaptic vesicles, whereas the axolemma was virtually unlabeled. Under this condition an active recycling of both quanta of neurotransmitter and vesicles operates. These findings indicate that the retrieval of components of the synaptic vesicle membrane is an efficient process that does not involve extensive intermixing between molecular components of the vesicle and plasma membrane, and show that synaptic vesicles that are rapidly recycling still have the bulk of synapsin I associated with their membrane.

Activation of NMDA receptors induces dephosphorylation of DARPP-32 in rat striatal slices

In the caudate-putamen the glutamatergic cortical input and the dopaminergic nigrostriatal input have opposite effects on the firing rate of striatal neurons. Although little is known of the biochemical mechanisms underlying this antagonism, one action of dopamine is to stimulate the cyclic AMP-dependent phosphorylation of DARPP-32 (dopamine and cAMP-regulated phospho-protein, of relative molecular mass 32,000 (32K]. This phosphorylation converts DARPP-32 from an inactive molecule into a potent inhibitor of protein phosphatase-1. Here we show that activation of the NMDA (N-methyl-D-aspartate) subclass of glutamate receptors reverses the cAMP-stimulated phosphorylation of DARPP-32 in striatal slices through NMDA-induced dephosphorylation of DARPP-32. Thus, the antagonistic effects of dopamine and glutamate on the excitability of striatal neurons are reflected in antagonistic effects of these neurotransmitters on the state of phosphorylation of DARPP-32. Our results indicate that stimulation of NMDA receptors leads to the activation of a neuronal protein phosphatase, presumably the calcium-dependent phosphatase calcineurin, and show, in an intact cell preparation, that signal transduction in the nervous system can be mediated by protein dephosphorylation.

ARPP-21, a cAMP-regulated phosphoprotein enriched in dopamine-innervated brain regions: tissue distribution and regulation of phosphorylation in rat brain

ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate), a phosphoprotein substrate for cAMP-dependent protein kinase, is unevenly distributed in adult rat brain. Using immunoblotting and phosphorylation in vitro followed by immunoprecipitation, ARPP-21 was found to be enriched in caudate-putamen, substantia nigra, nucleus accumbens and olfactory tubercle. Intermediate levels were found in cerebral cortex and hippocampus. ARPP-21 was very low in most other brain areas and was not detected in any of the peripheral tissues studied. Following unilateral lesion of the caudate-putamen with quinolinic acid, a marked decrease in the levels of ARPP-21 was observed in both the lesioned caudate-putamen (-75%) and the ipsilateral substantia nigra (-70%) compared with the unlesioned side. This result demonstrates the enrichment of ARPP-21 in striatonigral neurons. In slices of caudate-putamen, substantia nigra or cerebral cortex incubated in vitro, the phosphorylation of ARPP-21 was enhanced by 8-Br-cAMP, a stable analog of cAMP. In striatal slices, forskolin, a compound which stimulates adenylate cyclase directly, enhanced the phosphorylation of ARPP-21 with an EC50 of 0.5 microM. In conclusion, ARPP-21 is a neuron-specific phosphoprotein enriched in specific brain areas which are known to receive a rich dopaminergic innervation and to contain high levels of D1 dopamine receptors. The phosphorylation of ARPP-21 is likely to mediate some of the intracellular effects of neurotransmitters which stimulate adenylate cyclase in these regions, in particular dopamine and vasoactive intestinal peptide.

Phosphorylation of DARPP-32, a dopamine- and cAMP-regulated phosphoprotein, by casein kinase II

DARPP-32 (dopamine- and cAMP-regulated phosphorprotein, Mr = 32,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) is an inhibitor of protein phosphatase-1 and is enriched in dopaminoceptive neurons possessing the D1 dopamine receptor. Purified bovine DARPP-32 was phosphorylated in vitro by casein kinase II to a stoichiometry greater than 2 mol of phosphate/mol of protein whereas two structurally and functionally related proteins, protein phosphatase inhibitor-1 and G-substrate, were poor substrates for this enzyme. Sequencing of chymotryptic and thermolytic phosphopeptides from bovine DARPP-32 phosphorylated by casein kinase II suggested that the main phosphorylated residues were Ser45 and Ser102. In the case of rat DARPP-32, the identification of these phosphorylation sites was confirmed by manual Edman degradation. The phosphorylated residues are located NH2-terminal to acidic amino acid residues, a characteristic of casein kinase II phosphorylation sites. Casein kinase II phosphorylated DARPP-32 with an apparent Km value of 3.4 microM and a kcat value of 0.32 s-1. The kcat value for phosphorylation of Ser102 was 5-6 times greater than that for Ser45. Studies employing synthetic peptides encompassing each phosphorylation site confirmed this difference between the kcat values for phosphorylation of the two sites. In slices of rat caudate-putamen prelabeled with [32P]phosphate, DARPP-32 was phosphorylated on seryl residues under basal conditions. Comparison of thermolytic phosphopeptide maps and determination of the phosphorylated residue by manual Edman degradation identified the main phosphorylation site in intact cells as Ser102. In vitro, DARPP-32 phosphorylated by casein kinase II was dephosphorylated by protein phosphatases-1 and -2A. Phosphorylation by casein kinase II did not affect the potency of DARPP-32 as an inhibitor of protein phosphatase-1, which depended only on phosphorylation of Thr34 by cAMP-dependent protein kinase. However, phosphorylation of DARPP-32 by casein kinase II facilitated phosphorylation of Thr34 by cAMP-dependent protein kinase with a 2.2-fold increase in the Vmax and a 1.4-fold increase in the apparent Km. Phosphorylation of DARPP-32 by casein kinase II in intact cells may therefore modulate its phosphorylation in response to increased levels of cAMP.

Microvesicles of the neurohypophysis are biochemically related to small synaptic vesicles of presynaptic nerve terminals

Nerve endings of the posterior pituitary are densely populated by dense-core neurosecretory granules which are the storage sites for peptide neurohormones. In addition, they contain numerous clear microvesicles which are the same size as small synaptic vesicles of typical presynaptic nerve terminals. Several of the major proteins of small synaptic vesicles of presynaptic nerve terminals are present at high concentration in the posterior pituitary. We have now investigated the subcellular localization of such proteins. By immunogold electron microscopy carried out on bovine neurohypophysis we have found that three of these proteins, synapsin I, Protein III, and synaptophysin (protein p38) were concentrated on microvesicles but were not detectable in the membranes of neurosecretory granules. In addition, we have studied the distribution of the same proteins and of the synaptic vesicle protein p65 in subcellular fractions of bovine posterior pituitaries obtained by sucrose density centrifugation. We have found that the intrinsic membrane proteins synaptophysin and p65 had an identical distribution and were restricted to low density fractions of the gradient which contained numerous clear microvesicles with a size range the same as that of small synaptic vesicles. The peripheral membrane proteins synapsin I and Protein III exhibited a broader distribution extending into the denser part of the gradient. However, the amount of these proteins clearly declined in the fractions preceding the peak of neurosecretory granules. Our results suggest that microvesicles of the neurohypophysis are biochemically related to small synaptic vesicles of all other nerve terminals and argue against the hypothesis that such vesicles represent an endocytic byproduct of exocytosis of neurosecretory granules.

Phosphorylation-dependent inhibition by synapsin I of organelle movement in squid axoplasm

Synapsin I, a neuron-specific, synaptic vesicle-associated phosphoprotein, is thought to play an important role in synaptic vesicle function. Recent microinjection studies have shown that synapsin I inhibits neurotransmitter release at the squid giant synapse and that the inhibitory effect is abolished by phosphorylation of the synapsin I molecule (Llinas et al., 1985). We have considered the possibility that synapsin I might modulate release by regulating the ability of synaptic vesicles to move to, or fuse with, the plasma membrane. Since it is not yet possible to examine these mechanisms in the intact nerve terminal, we have used video-enhanced microscopy to study synaptic vesicle mobility in axoplasm extruded from the squid giant axon. We report here that the dephosphorylated form of synapsin I inhibits organelle movement along microtubules within the interior of extruded axoplasm and that phosphorylation of synapsin I on sites 2 and 3 by calcium/calmodulin-dependent protein kinase II removes this inhibitory effect. Phosphorylation of synapsin I on site 1 by the catalytic subunit of cAMP-dependent protein kinase only partially reduces the inhibitory effect. In contrast to the inhibition of movement along microtubules seen within the interior of the axoplasm, movement along isolated microtubules protruding from the edges of the axoplasm is unaffected by dephospho-synapsin I, despite the fact that the synapsin I concentration is higher there. Thus, synapsin I does not appear to inhibit the fast axonal transport mechanism itself. Rather, these results are consistent with the possibility that dephospho-synapsin I acts by a crosslinking mechanism involving some component(s) of the cytoskeleton, such as F-actin, to create a dense network that restricts organelle movement. The relevance of the present observations to regulation of neurotransmitter release is discussed.

Synaptophysin and synapsin I as tools for the study of the exo-endocytotic cycle

Synaptophysin, an integral protein of the synaptic vesicle membrane, and synapsin I, a phosphoprotein associated with the cytoplasmic side of synaptic vesicles, represent useful markers that allow to follow the movements of the vesicle membrane during recycling. The use of antibodies against these proteins to label nerve terminals during experimental treatments which stimulate secretion has provided evidence that during the exo-endocytotic cycle synaptic vesicles transiently fuse with the axolemma, from which they are specifically recovered. When recycling is blocked, exocytosis leads to the permanent incorporation of the synaptic vesicle membrane into the axolemma and to diffusion of the vesicle components in the plane of the membrane.

Synapsin I, a neuron-specific phosphoprotein interacting with small synaptic vesicles and F-actin

Synapsin I is a neuron-specific phosphoprotein which is a substrate for cAMP- and Ca2+/calmodulin-dependent protein kinases. It is specifically localized to the cytoplasmic side of small synaptic vesicles. The interaction of synapsin I with the synaptic vesicle membrane is complex in nature, since it is modulated by phosphorylation and involves binding of different domains of the molecule to phospholipid and protein components of synaptic vesicles. Synapsin I is also able to interact with actin filaments in a phosphorylation-dependent manner. Because of these properties, it has been hypothesized that synapsin I acts as a dynamic link between synaptic vesicles an the actin meshwork of the nerve terminal, thereby modulating the release of neurotransmitter.

Inhibition of Ca2+/calmodulin-dependent protein kinase II by arachidonic acid and its metabolites

A variety of evidence indicates that activation of Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) in nerve terminals leads to enhanced neurotransmitter release. Arachidonic acid and its 12-lipoxygenase metabolite, 12-hydroperoxyeicosatetraenoic acid (12-HPETE), have been suggested to act as second messengers mediating presynaptic inhibition of neurotransmitter release. In the present study it was found that CaM-kinase II, purified from rat brain cortex, was inhibited both by arachidonic acid (IC50 = 24 microM) and by 12-HPETE (IC50 = 0.7 microM). Neither substance inhibited CaM-kinase I or III, protein kinase C, or the catalytic subunit of cAMP-dependent protein kinase. Specific inhibition of Ca2+/calmodulin-dependent protein phosphorylation by arachidonic acid was also demonstrated in intact synaptic terminals (synaptosomes) isolated from rat forebrain. These results suggest that arachidonate and its metabolites may modulate synaptic function through the inhibition of CaM-kinase II-dependent protein phosphorylation.

Correlated light and electron microscopic study of dopaminergic neurons and their synaptic junctions with DARPP-32-containing cells in three-dimensional reaggregate tissue culture

An antibody to tyrosine hydroxylase has been used in a correlated light and electron microscopic study to characterize dopaminergic neurons and synaptic junctions in three-dimensional reaggregate cell culture. Dissociated fetal mesencephalic cells containing dopamine neurons were coaggregated with dissociated fetal striatal cells in rotatory culture for 21 days. Sections of the coaggregates were stained by the peroxidase anti-peroxidase technique to reveal tyrosine hydroxylase-immunoreactive structures. Clusters of immunoreactive perikarya as well as dendrites and axons were observed. Immunolabeled perikarya were round or oval and approximately 20 microns in diameter. Boutons immunoreactive for tyrosine hydroxylase formed symmetric synapses, primarily with unlabeled dendritic shafts. Symmetric membrane specializations were also observed between tyrosine hydroxylase-positive boutons and unlabeled dendritic spines as well as with the perikaryon of an unlabeled medium-size neuron possessing a slightly indented nucleus. To characterize the neurochemical nature of the neurons postsynaptic to tyrosine hydroxylase-positive boutons in the reaggregates, an antibody against DARPP-32 (a dopamine and adenosine 3':5'-monophosphate-regulated phosphoprotein) and an antibody against tyrosine hydroxylase were employed to visualize striatal dopaminoceptive neurons and dopaminergic structures, respectively, in the same section. Examination of reaggregate sections at the light microscopic level demonstrated that DARPP-32-immunoreactive cells were distributed into discrete clusters that were associated with patches of tyrosine hydroxylase-positive axonal varicosities. Ultrastructural analysis of tyrosine hydroxylase-positive boutons in such clusters revealed that dopaminergic axons synaptically contacted DARPP-32-immunoreactive neurons as well as unlabeled neuronal structures.

An analysis of postmortem brain samples from 32 alcoholic and nonalcoholic individuals for protein III, a neuronal phosphoprotein

Protein phosphorylation is a primary mechanism of intracellular signal transduction, and abnormalities in protein phosphorylation have been implicated in the pathogenesis of several specific diseases. Protein III is a neuronal phosphoprotein that is associated with synaptic vesicles and is probably involved in the regulation of neurotransmitter release. Analysis of 32 postmortem brains has confirmed our previous report that variant forms of protein III with higher apparent molecular weights are found frequently in the brains of alcoholic individuals but rarely in the brains of nonalcoholic individuals who did not suffer from any other medical or neuropsychiatric disorders. Eight of 14 (57%) brain samples from alcoholic individuals and four of eight (50%) brain samples from suspected alcoholic individuals had variant forms, while none of 10 samples from nonalcoholic individuals had variant forms. Previous data indicate that variant forms of protein III are also associated with other neurodegenerative conditions, including various dementias, and, possibly, normal aging.

ARPP-21, a cyclic AMP-regulated phosphoprotein enriched in dopamine-innervated brain regions. II. Molecular cloning and nucleotide sequence

A cDNA clone for the mRNA of bovine ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 as determined by SDS-PAGE) was isolated from a modified Okayama-Berg plasmid library. Transformed Escherichia coli colonies were screened by in situ colony hybridization with 2 different oligonucleotide probes derived from the amino acid sequence of the bovine protein. Sequence analysis of the longest cDNA clone, pTKAI [2407 nucleotides plus a poly(A) tail], revealed a 267-nucleotide-long coding region in agreement with the bovine ARPP-21 amino acid sequence (Williams et al., 1989). Southern blot analysis of total bovine genomic DNA raised the possibility that there may be 2 genes coding for ARPP-21. Northern blot analysis of total cellular RNA from bovine caudate nucleus and other brain regions demonstrated the existence of 2 major mRNA species, 2.5 and 1.0 kb in length, probably derived from use of alternate polyadenylation sites. There was a differential expression of these 2 mRNAs within the brain. Both ARPP-21 mRNAs were most abundant in the caudate nucleus, where the concentration of the protein is highly enriched.

Improving the quality of immunoblots by chromatography of polyclonal antisera on keratin affinity columns

Unwanted reactivity of polyclonal antisera against keratins ("fingerprint proteins") is a problem commonly encountered when proteins transferred to nitrocellulose are studied by immunoblotting. Immunoreactivity against keratins is generally accompanied by a spotted background. This antikeratin immunoreactivity could be removed by adsorption of the antisera to human keratin bound to nitrocellulose. Larger amounts of antisera were purified from contaminant antikeratin antibodies by a single passage over a column of human keratin coupled to activated CH-Sepharose 4B. In contrast to nonpurified antisera and their IgG fractions, the column effluent no longer recognized the Mr 55,000-70,000 keratin proteins and exhibited a marked decrease in background labeling. We propose this simple method as a valuable alternative when affinity purification of polyclonal antisera on antigen columns is not practical.

Calcium/diacylglycerol-dependent protein kinase and its major 87-kilodalton protein substrate are differentially distributed in rat basal ganglia

When brain tissue is subjected to subcellular fractionation, both calcium/diacylglycerol-dependent protein kinase (protein kinase C) and an 87-kilodalton (kDa) protein substrate for this enzyme are enriched in the crude nerve terminal fraction. The present study, using chemical and surgical lesions of neurons in the rat neostriatum and substantia nigra, has examined whether the 87-kDa protein is colocalized with protein kinase C in identified neurons and nerve terminals. Our results show that, in the basal ganglia, protein kinase C is highly enriched in local striatal neurons and the striatonigral fibers and terminals. In contrast, the 87-kDa protein appears to be widely and evenly distributed in both neuronal and nonneuronal cells. The 87-kDa protein may therefore mediate functions of protein kinase C not restricted to nerve terminals.