Developmental changes in protein phosphorylation in chicken forebrain. II. Calmodulin stimulated phosphorylation

Molecular changes in the intermediate medial mesopallium after a one trial avoidance learning in immature and mature chickens

Because brain maturation in chickens is protracted and occurs well after the major developmental period of synaptogenesis, chicken forebrain is suitable to investigate whether the molecular mechanisms underlying memory consolidation are different in immature and mature animals. We have used antibodies and western blotting to analyze subcellular fractions from the intermediate medial mesopallium region of 14-day and 8-week chicken forebrain prepared 0, 45, and 120 min after learning a discriminative taste avoidance task. At both ages learning induced changes in the phosphorylation of the glutamate receptor subunit 1 at Ser831, the levels of calcium-calmodulin stimulated/dependent protein kinase II and the phosphorylation of calcium-calmodulin stimulated/dependent protein kinase II at Thr286 were observed only in the fraction enriched in post-synaptic densities. The changes were of the same type at the two ages but occurred faster in mature animals. The changes in extracellular signal regulated kinase and phosphorylated-extracellular signal regulated kinase were more complex with different subcellular fractions showing different patterns of change at the two ages. These results imply that the molecular changes induced by learning a behavioral task are faster in mature than immature brain and may involve a different balance of intracellular signaling pathways.

Maturational Changes in the Subunit Composition of AMPA Receptors and the Functional Consequences of Their Activation in Chicken Forebrain

AMPA receptors play a critical role in synaptic plasticity and brain development. Here we show that Ca(2+) uptake in response to AMPA receptor activation decreases dramatically during maturation in chicken brain microslices without a change in tissue AMPA receptor content. We found that during maturation the relative concentration of GluR2 subunits increased, the concentration of the AMPA receptor-associated scaffold proteins SAP97 and GRIP decreased and that depolarization increased GluR1 phosphorylation at Ser831 in subcellular fractions enriched in postsynaptic densities at 2 weeks but not at 10 weeks. These changes are all consistent with a decreased Ca(2+) entry through AMPA receptor channels in response to receptor activation and may account for the changes in the functional properties of the receptor, which are thought to underlie, at least in part, the physiological changes that occur with maturation.

EEG as a measure of developmental changes in the chicken brain

Scalp-applied recording electrodes were used to monitor changes in basal EEG patterns in chickens during posthatch development. Frequency spectra produced by Fast Fourier Transform show a biphasic morphology in all chickens with one peak at about 6 Hz and another at 26 Hz. Changes in the lower frequency band show progressive development and provide a possible index of brain development. Both amplitude and dominant frequency of the spectra decrease between Weeks 3 and 8 posthatch, reaching adult levels between Weeks 5 and 7. These results suggest that modifications of basal EEG reflect the widespread functional changes in neuronal circuits occurring in chicken during the "synapse maturation" period between 3 and 8 weeks' posthatch.

Presynaptic long-term depression at a central glutamatergic synapse: a role for CaMKII

CaMKII is a calcium-activated kinase that is abundant in neurons and has been strongly implicated in memory and learning. Here we show that low-frequency stimulation of glutamatergic afferents in hippocampal slices from juvenile domestic chicks results in long-term depression of synaptic transmission. This reduction does not require activation of NMDA or metabotropic glutamate receptors and does not require a rise in postsynaptic calcium. However, buffering presynaptic calcium prevents the reduction of the excitatory postsynaptic potential or current that is induced by low-frequency stimulation. In addition, application of the calmodulin antagonist calmidazolium, or the specific CaMKII antagonist KN-93, completely blocks long-term depression. These findings demonstrate a newly discovered form of long-term synaptic depression in the avian hippocampus.

Developmental regulation of protein phosphatase types 1 and 2A in post-hatch chicken brain

The activity and subcellular distribution of protein phosphatases 1 and 2A were measured in chicken forebrain and cerebellum during post-hatch development. At all post-hatch ages, a large proportion of PP1 and PP2A was membrane bound and these enzymes were less active than their cytosolic counterparts. The protein concentration of PP1 in the membranes increased 40% between 2 and 14 days and a further 60% between 14 days and adult, whereas the PP1 enzyme activity in the membranes progressively decreased. In contrast to PP1, the protein concentration of PP2A remained constant in all fractions during post-hatch development, and the enzyme activity of PP2A did not change except for a decrease in the membrane-bound activity between 2 and 14 days. These results show that the subcellular distribution and activity of PP1 is selectively regulated during post-hatch development and that membrane association and inactivation of PP1 are independent events.

Long-term potentiation of synaptic transmission in the avian hippocampus

The avian hippocampus plays a pivotal role in memory required for spatial navigation and food storing. Here we have examined synaptic transmission and plasticity within the hippocampal formation of the domestic chicken using an in vitro slice preparation. With the use of sharp microelectrodes we have shown that excitatory synaptic inputs in this structure are glutamatergic and activate both NMDA- and AMPA-type receptors on the postsynaptic membrane. In response to tetanic stimulation, the EPSP displayed a robust long-term potentiation (LTP) lasting >1 hr. This LTP was unaffected by blockade of NMDA receptors or chelation of postsynaptic calcium. Application of forskolin increased the EPSP and reduced paired-pulse facilitation (PPF), indicating an increase in release probability. In contrast, LTP was not associated with a change in the PPF ratio. Induction of LTP did not occlude the effects of forskolin. Thus, in contrast to NMDA receptor-independent LTP in the mammalian brain, LTP in the chicken hippocampus is not attributable to a change in the probability of transmitter release and does not require activation of adenylyl cyclase. These findings indicate that a novel form of synaptic plasticity might underlie learning in the avian hippocampus.

Retinoic acid stimulates alpha-CAMKII gene expression in PC12 cells at a distinct transcription initiation site

The promoter region of the alpha-subunit of the calcium/calmodulin-dependent protein kinase II (alpha-CaMKII) gene was inserted into a beta-galactosidase (beta-gal) reporter plasmid, and beta-gal activities were examined in neuroblastoma (NB2a) and pheochromocytoma (PC12) cells after transient or stable transfections. The alpha-CaMKII promoter was 12- to 45-fold more active in NB2a compared with PC12 cells after transient or stable transfections. All-trans retinoic acid (RA) stimulated reporter gene expression at both protein and mRNA levels in transfected PC12 cells. RA increased the level of endogenous alpha-CaMKII mRNA in untransfected PC12 cells by 4.4-fold. The transcription initiation site(s) (TIS) of the alpha-CaMKII gene in PC12 cells and rat brain was examined by RNase protection assays (RPA) and reverse transcriptase PCRs. The TIS for the alpha-CaMKII/beta-gal reporter gene in transfected PC12 cells was indistinguishable from the TIS+1 in rat hippocampus. In contrast, the only detectable TIS for the alpha-CaMKII gene in untransfected PC12 cells was located near the ATG translation start codon, 147 nucleotides 3' to TIS+1 in hippocampus. This unusual TIS was also the predominant TIS in rat cerebellum. These results suggest that the alpha-CaMKII promoter may contain sequences that respond directly or indirectly to RA. In addition, the unusual TIS of the alpha-CaMKII gene in PC12 cells and rat cerebellum may contribute to the very low expression of this gene compared with that in hippocampus.

Functional identification of the promoter for the gene encoding the alpha subunit of calcium/calmodulin-dependent protein kinase II

To examine the expression of the alpha subunit of calcium/calmodulin-dependent protein kinase II, various 5' flanking genomic sequences were inserted into a chloramphenicol acetyltransferase (CAT) reporter plasmid and CAT enzyme activities were analyzed in transfected NB2a neuroblastoma cells and mRNA transcription was analyzed by nuclease protection assays. A core promoter was identified which contained an essential TATA element located 162 nt 5' to the transcription start site. Sequences 3' to the transcription start site, as well as 5' to the TATA element, increased levels of CAT activity in transfected cells. The alpha-subunit gene promoter displayed higher CAT activities, relative to a simian virus 40 promoter, in transfected neuronal cell lines than in nonneuronal cell lines. Results also suggested that sequence surrounding the natural alpha-gene transcription initiation site may be important for targeting transcription initiation 162 nt downstream of its TATA element.

[3H]MK-801 binding in immature and mature chicken forebrain

Previous studies have shown that the rate of calcium uptake stimulated by N-methyl-D-aspartate (NMDA) increased during the maturation phase of synapse development in chicken forebrain. To investigate whether this change in function is due to a change in the properties of NMDA receptor associated ion channels, we measured the binding of [3H]MK-801 (a ligand which binds to the NMDA receptor associated ion channel) to membranes from immature and mature chicken brain. The binding properties of MK-801 in chicken brain were similar to those in mammalian brain. There was no significant difference in any of the binding parameters measured at the two ages, i.e. KD, Bmax and optimal glutamate concentration for and maximal enhancement by glutamate of MK-801 binding. These results suggest that there is no change in the NMDA operated ion-channels during maturation. Thus the maturational change in NMDA receptor function could be due to: a change in the agonist portion of the NMDA receptor, a change in the regulation of the receptor/ionophore complex, perhaps by the postsynaptic density whose structure and composition changes during the same period, or a change in the number of voltage-sensitive calcium channels recruited as a result of NMDA receptor activation.

Mechanisms of synaptic plasticity. Changes in postsynaptic densities and glutamate receptors in chicken forebrain during maturation

We have shown that the synapse maturation phase of synaptogenesis is a model for synaptic plasticity that can be particularly well-studied in chicken forebrain because for most forebrain synapses, the maturation changes occur slowly and are temporally well-separated from the synapse formation phase. We have used the synapse maturation phase of neuronal development in chicken forebrain to investigate the possible link between changes in the morphology and biochemical composition of the postsynaptic density (PSD) and the functional properties of glutamate receptors overlying the PSD. Morphometric studies of PSDs in forebrains and superior cervical ganglia of chickens and rats have shown that the morphological features of synapse maturation are characteristic of a synaptic type, but that the rate at which these changes occur can vary between types of synapses within one animal and between synapses of the same type in different species. We have investigated, during maturation in the chicken forebrain, the properties of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptors, which are concentrated in the junctional membranes overlying thick PSDs in the adult. There was no change in the number of NMDA receptors during maturation, but there was an increase in the rate of NMDA-stimulated uptake of 45Ca2+ into brain prisms. This functional change was not seen with the other ionotropic subtypes of the glutamate receptor and was NMDA receptor-mediated. The functional change also correlated with the increase in thickness of the PSD during maturation that has previously been shown to be due to an increase in the amount of PSD associated Ca(2+)-calmodulin stimulated protein kinase II (CaM-PK II). Our results provide strong circumstantial evidence for the regulation of NMDA receptors by the PSD and implicate changing local concentrations of CaM-PK II in this process. The results also indicate some of the ways in which properties of existing synapses can be modified by changes at the molecular level.

Developmental changes in phosphorylation of MAP-2 and synapsin I in cytosol and taxol polymerised microtubules from chicken brain

In cytosol, cyclic AMP stimulated phosphorylation of microtubule associated protein-2 (MAP-2) increased from 2 days to adult in proportion to the increase in the concentration of MAP-2. By contrast, the calmodulin stimulated phosphorylation of MAP-2 decreased in proportion to the decrease in the concentration of calmodulin stimulated protein kinase II (CMK II). Similarly, the cAMP stimulated phosphorylation of the site on synapsin I labeled by the cAMP stimulated protein kinase (PKA) changed little during development whereas the calcium/calmodulin stimulated phosphorylation of the CMK II site decreased dramatically in proportion to the decrease in the concentration of CMK II. The decrease in the concentration of CMK II which occurs in cytosol during synapse maturation was also observed in taxol polymerised microtubules and the effects of the change in the relative concentrations of CMK II and PKA on the phosphorylation of MAP-2 and synapsin I in this fraction were similar to that observed in the cytosol. These results are consistent with the hypothesis that the developmental changes in phosphorylation of endogenous substrates by PKA is controlled largely by changes in the concentration of those substrates, whereas the concentration of CMK II is limiting so that the developmental changes in the phosphorylation of endogenous substrates by CMK II are a function of the concentration of CMK II itself as well as the concentration of endogenous substrates. Some possible functional consequences of this during synapse maturation are discussed.

A lead-associated nuclear protein which increases in maturing brain and in differentiating neuroblastoma 2A cells exposed to cyclic AMP-elevating agents

The lead-associated nuclear protein, p32/6.3, increases significantly in the postnatally developing rat cerebral cortex (Egle and Shelton, J. Biol. Chem., 261 (1986) 2294-2298). In the present study, this increase has been identified with late development of the cerebral cortex or forebrain because p32/6.3 reached adult levels 10 to 14 days after birth in guinea pig (a precocial animal) and after hatching in chicken. Comparison with other developmental processes indicates that p32/6.3 reaches adult levels just before or during the period of synapse maturation. Thus p32/6.3 may prove useful as a biochemical indicator of nuclear maturation in this period. The developmental regulation of p32/6.3 was further studied in mouse neuroblastoma 2a (Nb2a) cells. In vitro induction of differentiation of Nb2a cells by serum withdrawal from the culture medium increased p32/6.3, implicating p32/6.3 with differentiating neurons. This association was further strengthened when treatment of the Nb2a cells for 24 h with dibutyryl cAMP (1-5 mM), papaverine (5-12.5 micrograms/ml) or 3-isobutyl-1-methylxanthine (IBMX; 50-250 microM) increased the abundance of p32/6.3 1.5- to 3-fold more than serum withdrawal alone. 8-Bromo-cAMP (2-4 mM), N6-benzoyl cAMP (4 mM) and forskolin (10 microM) also increased the abundance of p32/6.3 in Nb2a cells, arguing that cAMP is involved in p32/6.3 regulation. These results, in conjunction with the postnatal increase of p32/6.3 in cerebral cortex, suggest a relationship between p32/6.3 levels and neuronal maturation.

The differential influence of protein kinase inhibitors on retinal arbor morphology and eye-specific stripes in the frog retinotectal system

We investigated retinal axon morphology and eye-specific afferent termination zones in the optic tectum of three-eyed tadpoles that were chronically treated with protein kinase inhibitors. The kinase inhibitors sphingosine, H-7, and phorbol ester, which down-regulates protein kinase C with chronic exposure, were applied to the tecta in a slow release plastic, Elvax. In vivo protein phosphorylation assays in drug-treated tadpoles indicated that the treatments decreased 32P incorporation into some protein bands by as much as 60%. Although the drugs did not cause a desegregation of the eye-specific stripes, treated retinal axon arbors covered about half the area covered by untreated arbors or arbors treated with inactive analogs of the drugs. We conclude that eye-specific segregation can be maintained under conditions that markedly alter retinal ganglion cell axon arbor size and that significantly perturb protein phosphorylation. Furthermore, we conclude that the protein kinase(s) that we blocked with these treatments is involved in the growth of axon arbors.

Developmental expression of neuronal calmodulin-binding proteins in rat brain

The developmental patterns of calmodulin-binding proteins (CaM-BPS) in rat brain were examined using biotinylated calmodulin overlays of one- and two-dimensional gels. Hippocampus showed the earliest onset of CaM-BP expression (postnatal day 5; PND5), followed by cerebral cortex and striatum, both of which had detectable levels of CaM-BPs by PND7. Cerebellum had the latest onset of CaM-BP expression; CaM-BPs were not detectable until PND9. Very few CaM-BPs were present in brain before PND5 and all regions reached near adult levels by PND20. However, several unique CaM-BPs were seen in embryonic brain and these proteins may have an important role in developing neurons. These data suggest an orderly, complex expression of CaM-BPs which increases during times of synaptogenesis and synaptic maturation.

Phosphorylation of proteins of the postsynaptic density: effect of development on protein tyrosine kinase and phosphorylation of the postsynaptic density glycoprotein, PSD-GP180

The effect of development on the tyrosine kinase activity of postsynaptic densities (PSDs) has been determined. PSDs were prepared from the forebrains of rats ranging in postnatal age from 13 to 90 days and the phosphorylation of both exogenous and endogenous substrates by tyrosine kinase measured. PSDs exhibited tyrosine kinase activity at all ages examined. Phosphorylation of the exogenous substrates polyglutamyltyrosine (4:1) and [val5] angiotensin II increased twofold between days 17 and 22 and then decreased between days 30 and 90 to levels slightly lower than those present at 13 days. The phosphorylation of endogenous PSD proteins on tyrosine residues, assessed by alkali digestion of polyacrylamide gels of 32P-labelled PSD proteins and by measuring the formation of [32P] phosphotyrosine by PSDs incubated in the presence of [gamma-32P] ATP, closely paralleled the changes in total tyrosine kinase activity. Tyrosine phosphorylation of the PSD-specific glycoprotein, PSD-GP180, also showed a transient increase between days 22 and 30, although its concentration within the PSD continued to increase slowly up to 90 days. The results indicate that the tyrosine kinase activity of PSDs is developmentally regulated and that tyrosine phosphorylation of PSD proteins is limited by enzyme rather than substrate availability.

Quantitation of synaptic, neuronal and glial development in the intermediate and medial hyperstriatum ventrale (IMHV) of the chick Gallus domesticus, pre- and post-hatch

A quantitative analysis was made of the development of synapses, neurons and glia in both left and right intermediate and medial hyperstriatum ventrale (IMVH) of the forebrain of the domestic chick, Gallus domesticus from 16 days in ovo to 9 days post-hatch. There was a marked increase in total synapse numerical density (NVsyn), from 10 synapses per 100 microns3 at 16 days in ovo to 50 synapses per 100 microns3 at 9 days post-hatch; no significant left/right hemispheric differences were evident but there were differences between the development profiles for synapses with asymmetric as compared to symmetrical synaptic junctions. In contrast to synaptic development, the number of neurons per unit volume, NVneu, decreased by approximately 50% from the value at 16 days in ovo to that at day 0 (hatching). The neuronal population density remained unchanged to 3 days post-hatch and then, in 9-day-old birds, declined to almost a quarter of the original population size; no significant left/right hemisphere differences were evident. Glial cells declined in number from 16 days in ovo to 19 days in ovo, and then gradually increased to 9 days post-hatch. When the synapse to neuron ratio was examined, a trend was observed of a gradual increase with age, but no hemispheric differences were present. It is concluded that these changes are major events which must be considered in experiments aimed at determining the effects of behavioural, and/or environmental manipulations, on the morphology of the IMHV because they may mask other, more subtle, structural changes that occur as a result of behavioural experiences.

Purification and characterization of calmodulin-stimulated protein kinase II from two-day and adult chicken forebrain

Soluble calmodulin-stimulated protein kinase II has been purified from 2-day and adult chicken forebrain. At both ages the holoenzyme eluted from a Superose-6B column with an apparent molecular weight of approximately 700,000 daltons and contained three subunits. The subunits were found to be the counterparts of the alpha, beta, and beta' subunits of the enzyme purified from adult rat brain in that they had one-dimensional phosphopeptide maps that were indistinguishable from those of the corresponding subunit in the rat enzyme and they migrated in SDS-polyacrylamide gels with the same apparent molecular weights. However, the doublet formed by the beta subunit was much more clearly resolved in the chicken enzyme and the beta' subunit, which was much more abundant in the adult chicken than in the adult rat, was also found to be a doublet. The ratio of the concentrations of the alpha and beta subunits changed during development. By autoradiography following autophosphorylation, the alpha:beta ratios of the 2-day and adult enzymes were 0.89 +/- 0.07 and 1.92 +/- 0.26, respectively; by silver staining the alpha:beta ratios were 0.95 +/- 0.11 and 1.85 +/- 0.17, respectively. The concentration of the beta' subunit was equal to that of the beta subunit at both ages. Autophosphorylation produced a decrease in the electrophoretic mobility of the alpha and beta subunits in SDS-polyacrylamide gels and a marked decrease in the calcium dependence of the substrate phosphorylation activity of the enzyme at both ages. The purified enzyme from chicken brain appeared to be more stable under standard in vitro assay conditions than the rat enzyme, and this was particularly so for the enzyme from 2-day forebrain.

Developmental changes in protein phosphorylation in chicken forebrain. I. cAMP-stimulated phosphorylation

The net level of cyclic AMP-stimulated protein phosphorylation was investigated in cytosolic and membrane fractions from chicken forebrain between embryonic day 13 (E13) and 52 days post-hatching. Throughout this period the majority of the net level of cAMP-stimulated phosphorylation of endogenous proteins was in the cytosolic fractions. Between day -8 (E13) and adult, the net level of cAMP-stimulated phosphorylation of endogenous proteins in the cytosol (S3) and crude synaptic plasma membrane (P2-M) fractions fell by 3 and 4 fold, respectively, when expressed per mg protein and rose by 5 and 10 fold, respectively, when expressed per fraction. The changes in specific activity were completed by 6-15 days post-hatching. The occluded cytosol (P2-S) fraction showed little change in the net level of cAMP-stimulated phosphorylation of endogenous proteins per mg protein. Major changes in phosphoprotein patterns involving both decreases and increases in phosphorylation occurred in all fractions from day -8 (E13) to day 6 post-hatch; thereafter the phosphoprotein bands and their relative intensities were unchanged. Three bands (P90 in S3; P41 and P31 in P2-M) contained major cAMP-stimulated phosphoproteins in embryonic brain but were absent after hatching. When cAMP-stimulated phosphorylation activity was measured in S3 and P-2M using an exogenous peptide substrate (Kemptide) there was no change in kinase activity per mg protein between day -8 (E13) and 30 days post-hatch. This suggests that the decrease in the net level of cAMP stimulated phosphorylation of endogenous proteins was due to the decrease in levels of endogenous phosphoproteins rather than protein kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)