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Neurons are flexible electrophysiological entities in which the distribution and properties of ionic channels control their behaviors. Through simultaneous somatic and axonal whole-cell recording of layer 5 pyramidal cells, we demonstrate a remarkable differential expression of slowly inactivating K ؉ currents. Depolarizing the axon, but not the soma, rapidly activated a lowthreshold, slowly inactivating, outward current that was potently blocked by low doses of 4-aminopyridine, ␣-dendrotoxin, and rTityustoxin-K␣. Block of this slowly inactivating current caused a large increase in spike duration in the axon but only a small increase in the soma and could result in distal axons generating repetitive discharge in response to local current injection. Importantly, this current was also responsible for slow changes in the axonal spike duration that are observed after somatic membrane potential change. These data indicate that low-threshold, slowly inactivating K ؉ currents, containing Kv1.2 ␣ subunits, play a key role in the flexible properties of intracortical axons and may contribute significantly to intracortical processing.axon ͉ cortex ͉ plasticity ͉ synaptic transmission T he precise distribution and properties of ionic channels in cortical neurons strongly influence both the cell's intrinsic electrophysiological properties and its operation within cortical networks. Although the properties of cortical neuronal cell bodies and dendrites have been extensively studied, the study of neocortical axons has been largely confined to recordings from axonal segments near the cell body (e.g., see refs. 1 and 2).Far from being simple static structures that merely communicate spikes, the dynamical properties of intracortical axons may contribute critically to the operation of local cortical networks (reviewed in ref.3). Recently, it was shown that the amplitude of excitatory postsynaptic potentials evoked between excitatory neurons depends on the membrane potential of the presynaptic cell (4, 5). Modest somatic depolarization of presynaptic neocortical pyramidal cells increased the average excitatory postsynaptic potential (EPSP) amplitude evoked in nearby pyramidal cells. Interestingly, simultaneous axonal and somatic patch clamp recordings revealed that these somatic depolarizations increased axonal spike duration over a time course that was similar to the slow component of synaptic facilitation. These results suggest that information transmission within local cortical networks may operate in a mixed

The cellular prion protein, PrPC, is neuroprotective in a number of settings and in particular prevents cerebellar degeneration mediated by CNS‐expressed Doppel or internally deleted PrP (‘ΔPrP’). This paradigm has facilitated mapping of activity determinants in PrPC and implicated a cryptic PrPC‐like protein, ‘π’. Shadoo (Sho) is a hypothetical GPI‐anchored protein encoded by the Sprn gene, exhibiting homology and domain organization similar to the N‐terminus of PrP. Here we demonstrate Sprn expression and Sho protein in the adult CNS. Sho expression overlaps PrPC, but is low in cerebellar granular neurons (CGNs) containing PrPC and high in PrPC‐deficient dendritic processes. In Prnp0/0 CGNs, Sho transgenes were PrPC‐like in their ability to counteract neurotoxic effects of either Doppel or ΔPrP. Additionally, prion‐infected mice exhibit a dramatic reduction in endogenous Sho protein. Sho is a candidate for π, and since it engenders a PrPC‐like neuroprotective activity, compromised neuroprotective activity resulting from reduced levels may exacerbate damage in prion infections. Sho may prove useful in deciphering several unresolved facets of prion biology.

Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimer's disease amyloid-␤ (A␤) peptide. To explore this relationship in vivo, toxic-milk (tx J ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust A␤ deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive tx J mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma A␤ levels. In addition, homozygosity for tx J increased survival of young TgCRND8 mice and lowered endogenous CNS A␤ at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the tx J mutation on CNS A␤ burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of A␤ peptide. A lzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by extracellular deposition of amyloid-␤ (A␤) as senile plaques and intracellular accumulation of hyperphosphorylated tau as neurofibrillary tangles (1). A␤ is generated by secretase-mediated endoproteolysis of the amyloid precursor protein (APP), and familial AD mutations skew APP processing to favor production of pro-amyloidogenic forms of the peptide or net A␤ production and thus drive disease pathogenesis. Although there is growing interest in defining pathogenic subvarieties of A␤ [e.g., secreted oligomeric assemblies such as A␤-derived diffusible ligands (2) and intracellular forms (3)], modulators of APP and A␤ biology in sporadic disease have remained more elusive. One area of particular interest concerns the role of transition metals.Cu and Zn ions are abundant in the normal brain (4-6), and direct measurements of metal levels have indicated altered homeostasis in AD (7-10). Interestingly, APP has a selective, high-affinity Cu-binding site in the extracellular (ecto-) domain that is capable of reducing Cu(II) to Cu(I) (11), and a recent structural analysis of this domain has revealed some similarity to previously identified Cu chaperone proteins (12). In addition to the ectodomain Cu-binding site of APP, A␤ peptide also contains binding sites for . A␤-metal interaction may drive both fibril formation and free radical production (13,(16)(17)(18), findings potentially relevant to AD pathogenesis in vivo, given that metal chelators can resolubilize A␤ aggregates from postmortem AD brain (19). On the other hand, studies of APP processing in cultured cells have revealed stimulation of the ␣-secretase pathway for APP processing by extracellular Cu ions (20). As this pathway cleaves the A␤ domain of APP into two fragments, it has a potential to be anti-amyloidogenic. Prompted by these divergent observations, we devised a genetic experiment to investigate how Cu might modulate A␤-dependent pathologies in vivo by using the transgenic (Tg) CRND8 line of TgAPP mice (21,22) in conjunction with a mutant allele of the CuATPase7b c...

We analyzed the completed human genome for recent segmental duplications (size > or = 1 kb and sequence similarity > or = 90%). We found that approximately 4% of the genome is covered by duplications and that the extent of segmental duplication varies from 1% to 14% among the 24 chromosomes. Intrachromosomal duplication is more frequent than interchromosomal duplication in 15 chromosomes. The duplication frequencies in pericentromeric and subtelomeric regions are greater than the genome average by approximately threefold and fourfold. We examined factors that may affect the frequency of duplication in a region. Within individual chromosomes, the duplication frequency shows little correlation with local gene density, repeat density, recombination rate, and GC content, except chromosomes 7 and Y. For the entire genome, the duplication frequency is correlated with each of the above factors. Based on known genes and Ensembl genes, the proportion of duplications containing complete genes is 3.4% and 10.7%, respectively. The proportion of duplications containing genes is higher in intrachromosomal than in interchromosomal duplications, and duplications containing genes have a higher sequence similarity and tend to be longer than duplications containing no genes. Our simulation suggests that many duplications containing genes have been selectively maintained in the genome.

Although the evolutionary significance of gene duplication has long been recognized, it remains unclear what determines gene duplicability. We find protein complexity to be an important determinant because the proportion of unduplicated genes (P) increases with the number of subunits in a protein. However, P is high (>65%) for both monomers and multimers in yeast, but <30% in human except for subunits of large multimers, implying that organismal complexity is a stronger determinant of gene duplicability than protein complexity. The same conclusion is reached from a comparison of family sizes in yeast and human. Despite Ͼ30 years of effort (1), it remains unclear what determines gene duplicability. Protein complexity, defined as the number of subunits in a protein (n), might be an important factor because duplication of a protein subunit may cause dosage imbalance among the subunits of the protein (2, 3) and the chance of imbalance might increase with the number of subunits in a protein. By using yeast data, Papp et al. (3) found that 33% of the single-copy genes (singletons) participate in protein complexes (multimers), whereas this frequency drops to Ϸ21% for genes with three or more paralogues. They therefore concluded that duplication of a subunit of a protein complex is less likely to be successful than duplication of a monomer. However, no monomers were included in their analysis, so the magnitude of difference in survivability between duplication of a monomer and duplication of a protein complex subunit is not known. It is worth emphasizing that duplication of a monomer may also cause dosage imbalance. This may be particularly true for transcription factors, each of which may control many downstream genes. For example, Drosophila embryos produced by mothers with four dosages of bicoid, a maternal morphogen, tend to develop a larger head, and only Ϸ30% of the embryos produced by mothers with six dosages of bicoid are viable (4). Thus, it is important to include monomers. Indeed, we study the relationship between the survivability of a gene duplication and n by classifying proteins into monomers (n ϭ 1), dimers (n ϭ 2), midsize complexes (3 Յ n Յ 10), and large complexes (n Ͼ 10). Another factor that may affect the survivability of duplicate genes is organismal complexity. It was suggested that, for transcription factors, dosage imbalance occurs more frequently in a complex organism than in yeast because of the long regulatory cascades during multicellular development (3). However, a complex organism may actually be more robust against dosage increase than a simple organism (see below). Thus, we also examine this factor by contrasting human with yeast. Here, organismal complexity is loosely defined as the number of different types of cells.Previously we talked about survivability, which may be defined as the probability for a duplicate gene to survive, but adaptive evolution of duplicate genes may also be important. Because, in the end, we see only whether a gene has been duplicated or not, we will use gene...

Disruption of neurotoxic effects of amyloid β protein (Aβ) is one of the major, but as yet elusive, goals in the treatment of Alzheimer's disease (AD). The amylin receptor, activated by a pancreatic polypeptide isolated from diabetic patients, is a putative target for the actions of Aβ in the brain. Here we show that in primary cultures of human fetal neurons (HFNs), AC253, an amylin receptor antagonist, blocks electrophysiological effects of Aβ. Pharmacological blockade of the amylin receptor or its down-regulation using siRNA in HFNs confers neuroprotection against oligomeric Aβ-induced caspase-dependent and caspase-independent apoptotic cell death. In transgenic mice (TgCRND8) that overexpress amyloid precursor protein, amylin receptor is up-regulated in specific brain regions that also demonstrate an elevated amyloid burden. The expression of Aβ actions through the amylin receptor in human neurons and temporospatial interrelationship of Aβ and the amylin receptor in an in vivo model of AD together provide a persuasive rationale for this receptor as a novel therapeutic target in the treatment of AD.

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