Experience-dependent corticofugal adjustment of midbrain frequency map in bat auditory system

Recent studies of corticofugal modulation of auditory information processing indicate that cortical neurons mediate both a highly focused positive feedback to subcortical neurons “matched” in tuning to a particular acoustic parameter and a widespread lateral inhibition to “unmatched” subcortical neurons. This cortical function for the adjustment and improvement of subcortical information processing is called egocentric selection. Egocentric selection enhances the neural representation of frequently occurring signals in the central auditory system. For our present studies performed with the big brown bat (Eptesicus fuscus), we hypothesized that egocentric selection adjusts the frequency map of the inferior colliculus (IC) according to auditory experience based on associative learning. To test this hypothesis, we delivered acoustic stimuli paired with electric leg stimulation to the bat, because such paired stimuli allowed the animal to learn that the acoustic stimulus was behaviorally important and to make behavioral and neural adjustments based on the acquired importance of the acoustic stimulus. We found that acoustic stimulation alone evokes a change in the frequency map of the IC; that this change in the IC becomes greater when the acoustic stimulation is made behaviorally relevant by pairing it with electrical stimulation; that the collicular change is mediated by the corticofugal system; and that the IC itself can sustain the change evoked by the corticofugal system for some time. Our data support the hypothesis.

Compromised mitochondrial function leads to increased cytosolic calcium and to activation of MAP kinases

We have investigated in rat pheochromacytoma PC12 cells the activation of the mitogen-activated protein kinases ERK1 and ERK2 by the mitochondrial uncoupler carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP). This treatment slowly decreases ATP levels to 30% of control, whereas the internal calcium level rises very rapidly to 250% of control, derived from internal stores. Tyrosine phosphorylation of ERK1 and ERK2 increases gradually, starting after 5 min of treatment, to reach a maximum at 30 min; the kinase activity reaches 250% when measured after 1 hr of treatment. The drop in ATP levels is slower still. Comparison of the time courses of the rapid rise in cytosolic calcium with the slower increase in ERK1 and ERK2 activation suggests one or more intermediate stages in this pathway. Chelation of cytosolic calcium with dimethyl bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid abolished the FCCP-stimulated rise in internal calcium, as well as the tyrosine phosphorylation and the activation of the ERKs. Surprisingly, caffeine, which releases calcium from different internal stores, did not increase the tyrosine phosphorylation and did not activate the ERKs. The FCCP effect on calcium storage may be related to mitochondrial dysfunction in Alzheimer disease, which might result in ineffective buffering of cytosolic calcium that leads to mitogen-activated protein kinase activation and subsequent protein phosphorylations.

Maintenance of a somatotopic cortical map in the face of diminishing thalamocortical inputs

This study addresses the extent of divergence in the ascending somatosensory pathways of primates. Divergence of inputs from a particular body part at each successive synaptic step in these pathways results in a potential magnification of the representation of that body part in the somatosensory cortex, so that the representation can be expanded when peripheral input from other parts is lost, as in nerve lesions or amputations. Lesions of increasing size were placed in the representation of a finger in the ventral posterior thalamic nucleus (VPL) of macaque monkeys. After a survival period of 1–5 weeks, area 3b of the somatosensory cortex ipsilateral to the lesion was mapped physiologically, and the extent of the representation of the affected and adjacent fingers was determined. Lesions affecting less than 30% of the thalamic VPL nucleus were without effect upon the cortical representation of the finger whose thalamic representation was at the center of the lesion. Lesions affecting about 35% of the VPL nucleus resulted in a shrinkage of the cortical representation of the finger whose thalamic representation was lesioned, with concomitant expansion of the representations of adjacent fingers. Beyond 35–40%, the whole cortical representation of the hand became silent. These results suggest that divergence of brainstem and thalamocortical projections, although normally not expressed, are sufficiently great to maintain a representation after a major loss of inputs from the periphery. This is likely to be one mechanism of representational plasticity in the cerebral cortex.

Structural features of the γ subunit of the Escherichia coli F1 ATPase revealed by a 4.4-Å resolution map obtained by x-ray crystallography

The F1 part of the F1FO ATP synthase from Escherichia coli has been crystallized and its structure determined to 4.4-Å resolution by using molecular replacement based on the structure of the beef-heart mitochondrial enzyme. The bacterial F1 consists of five subunits with stoichiometry α3, β3, γ, δ, and ɛ. δ was removed before crystallization. In agreement with the structure of the beef-heart mitochondrial enzyme, although not that from rat liver, the present study suggests that the α and β subunits are arranged in a hexagonal barrel but depart from exact 3-fold symmetry. In the structures of both beef heart and rat-liver mitochondrial F1, less than half of the structure of the γ subunit was seen because of presumed disorder in the crystals. The present electron-density map includes a number of rod-shaped features which appear to correspond to additional α-helical regions within the γ subunit. These suggest that the γ subunit traverses the full length of the stalk that links the F1 and FO parts and makes significant contacts with the c subunit ring of FO.

Comparison of parametric and nonparametric methods to map oligogenes by linkage

A sample of 95 sib pairs affected with insulin-dependent diabetes and typed with their normal parents for 28 markers on chromosome 6 has been analyzed by several methods. When appropriate parameters are efficiently estimated, a parametric model is equivalent to the β model, which is superior to nonparametric alternatives both in single point tests (as found previously) and in multipoint tests. Theory is given for meta-analysis combined with allelic association, and problems that may be associated with errors of map location and/or marker typing are identified. Reducing by multipoint analysis the number of association tests in a dense map can give a 3-fold reduction in the critical lod, and therefore in the cost of positional cloning.

A sensory brain map for each behavior?

Multiple brain maps are commonly found in virtually every vertebrate sensory system. Although their functional significance is generally relatively little understood, they seem to specialize in processing distinct sensory parameters. Nevertheless, to yield the stimulus features that ultimately elicit the adaptive behavior, it appears that information streams have to be combined across maps. Results from current lesion experiments in the electrosensory system, however, suggest an alternative possibility. Inactivations of different maps of the first-order electrosensory nucleus in electric fish, the electrosensory lateral line lobe, resulted in markedly different behavioral deficits. The centromedial map is both necessary and sufficient for a particular electrolocation behavior, the jamming avoidance response, whereas it does not affect the communicative response to external electric signals. Conversely, the lateral map does not affect the jamming avoidance response but is necessary and sufficient to evoke communication behavior. Because the premotor pathways controlling the two behaviors in these fish appear to be separated as well, this system illustrates that sensory–motor control of different behaviors can occur in strictly segregated channels from the sensory input of the brain all through to its motor output. This might reflect an early evolutionary stage where multiplication of brain maps can satisfy the demand on processing a wider range of sensory signals ensuing from an enlarged behavioral repertoire, and bridging across maps is not yet required.

A General RNA-Binding Protein Complex That Includes the Cytoskeleton-associated Protein MAP 1A

Association of mRNA with the cytoskeleton represents a fundamental aspect of RNA physiology likely involved in mRNA transport, anchoring, translation, and turnover. We report the initial characterization of a protein complex that binds RNA in a sequence-independent but size-dependent manner in vitro. The complex includes a ∼160-kDa protein that is bound directly to mRNA and that appears to be either identical or highly related to a ∼1600-kDa protein that binds directly to mRNA in vivo. In addition, the microtubule-associated protein, MAP 1A, a cytoskeletal associated protein is a component of this complex. We suggest that the general attachment of mRNA to the cytoskeleton may be mediated, in part, through the formation of this ribonucleoprotein complex.

Activation of Both MAP Kinase and Phosphatidylinositide 3-Kinase by Ras Is Required for Hepatocyte Growth Factor/Scatter Factor–induced Adherens Junction Disassembly

Hepatocyte growth factor/scatter factor (HGF/SF) stimulates the motility of epithelial cells, initially inducing centrifugal spreading of colonies followed by disruption of cell–cell junctions and subsequent cell scattering. In Madin–Darby canine kidney cells, HGF/SF-induced motility involves actin reorganization mediated by Ras, but whether Ras and downstream signals regulate the breakdown of intercellular adhesions has not been established. Both HGF/SF and V12Ras induced the loss of the adherens junction proteins E-cadherin and β-catenin from intercellular junctions during cell spreading, and the HGF/SF response was blocked by dominant-negative N17Ras. Desmosomes and tight junctions were regulated separately from adherens junctions, because they were not disrupted by V12Ras. MAP kinase, phosphatidylinositide 3-kinase (PI 3-kinase), and Rac were required downstream of Ras, because loss of adherens junctions was blocked by the inhibitors PD098059 and LY294002 or by dominant-inhibitory mutants of MAP kinase kinase 1 or Rac1. All of these inhibitors also prevented HGF/SF-induced cell scattering. Interestingly, activated Raf or the activated p110α subunit of PI 3-kinase alone did not induce disruption of adherens junctions. These results indicate that activation of both MAP kinase and PI 3-kinase by Ras is required for adherens junction disassembly and that this is essential for the motile response to HGF/SF.

The Fission Yeast Mitotic Regulator win1+ Encodes an MAP Kinase Kinase Kinase That Phosphorylates and Activates Wis1 MAP Kinase Kinase in Response to High Osmolarity

The Schizosaccharomyces pombe win1-1 mutant has a defect in the G2-M transition of the cell cycle. Although the defect is suppressed by wis1+ and wis4+, which are components of a stress-activated MAP kinase pathway that links stress response and cell cycle control, the molecular identity of Win1 has not been known. We show here that win1+ encodes a polypeptide of 1436 residues with an apparent molecular size of 180 kDa and demonstrate that Win1 is a MAP kinase kinase kinase that phosphorylates and activates Wis1. Despite extensive similarities between Win1 and Wis4, the two MAP kinase kinase kinases have distinct functions. Wis4 is able to compensate for loss of Win1 only under unstressed conditions to maintain basal Wis1 activity, but it fails to suppress the osmosignaling defect conferred by win1 mutations. The win1-1 mutation is a spontaneous duplication of 16 nucleotides, which leads to a frameshift and production of a truncated protein lacking the kinase domain. We discuss the cell cycle phenotype of the win1-1 cdc25-22 wee1-50 mutant and its suppression by wis genes.

Molecular Interaction Map of the Mammalian Cell Cycle Control and DNA Repair Systems

Eventually to understand the integrated function of the cell cycle regulatory network, we must organize the known interactions in the form of a diagram, map, and/or database. A diagram convention was designed capable of unambiguous representation of networks containing multiprotein complexes, protein modifications, and enzymes that are substrates of other enzymes. To facilitate linkage to a database, each molecular species is symbolically represented only once in each diagram. Molecular species can be located on the map by means of indexed grid coordinates. Each interaction is referenced to an annotation list where pertinent information and references can be found. Parts of the network are grouped into functional subsystems. The map shows how multiprotein complexes could assemble and function at gene promoter sites and at sites of DNA damage. It also portrays the richness of connections between the p53-Mdm2 subsystem and other parts of the network.

A p90rsk Mutant Constitutively Interacting with MAP Kinase Uncouples MAP Kinase from p34cdc2/Cyclin B Activation in Xenopus Oocytes

The efficient activation of p90rsk by MAP kinase requires their interaction through a docking site located at the C-terminal end of p90rsk. The MAP kinase p42mpk1 can associate with p90rsk in G2-arrested but not in mature Xenopus oocytes. In contrast, an N-terminally truncated p90rsk mutant named D2 constitutively interacts with p42mpk1. In this report we show that expression of D2 inhibits Xenopus oocyte maturation. The inhibition requires the p42mpk1 docking site. D2 expression uncouples the activation of p42mpk1 and p34cdc2/cyclin B in response to progesterone but does not prevent signaling through p90rsk. Instead, D2 interferes with a p42mpk1-triggered pathway, which regulates the phosphorylation and activation of Plx1, a potential activator of the Cdc25 phosphatase. This new pathway that links the activation of p42mpk1 and Plx1 during oocyte maturation is independent of p34cdc2/cyclin B activity but requires protein synthesis. Using D2, we also provide evidence that the sustained activation of p42mpk1 can trigger nuclear migration in oocytes. Our results indicate that D2 is a useful tool to study MAP kinase function(s) during oocyte maturation. Truncated substrates such as D2, which constitutively interact with MAP kinases, may also be helpful to study signal transduction by MAP kinases in other cellular processes.

A metric map of humans: 23,500 loci in 850 bands

High-resolution maps integrated with the enhanced location data base software (ldb+) give improved estimates of genetic parameters and reveal characteristics of cytogenetic bands. Chiasma interference is intermediate between Kosambi and Carter–Falconer levels, as in Drosophila and the mouse. The autosomal genetic map is 2832 and 4348 centimorgans in males and females, respectively. Telomeric T-bands are strikingly associated with male recombination and gene density. Position and centromeric heterochromatin have large effects, but nontelomeric R-bands are not significantly different from G-bands. Several possible reasons are discussed. These regularities validate the maps, despite their high resolution and inevitable local errors. No other approach has been demonstrated to integrate such a large number of loci, which are increasing at about 45% per year. The maps and the data and software from which they are constructed are available through the Internet (http://cedar.genetics.soton.ac.uk/public_html). Successive versions of this location data base may also be accessed on CD-ROM.

An alternative pathway to β-carotene formation in plant chromoplasts discovered by map-based cloning of Beta and old-gold color mutations in tomato

Carotenoid pigments in plants fulfill indispensable functions in photosynthesis. Carotenoids that accumulate as secondary metabolites in chromoplasts provide distinct coloration to flowers and fruits. In this work we investigated the genetic mechanisms that regulate accumulation of carotenoids as secondary metabolites during ripening of tomato fruits. We analyzed two mutations that affect fruit pigmentation in tomato (Lycopersicon esculentum): Beta (B), a single dominant gene that increases β-carotene in the fruit, and old-gold (og), a recessive mutation that abolishes β-carotene and increases lycopene. Using a map-based cloning approach we cloned the genes B and og. Molecular analysis revealed that B encodes a novel type of lycopene β-cyclase, an enzyme that converts lycopene to β-carotene. The amino acid sequence of B is similar to capsanthin-capsorubin synthase, an enzyme that produces red xanthophylls in fruits of pepper (Capsicum annum). Our results prove that β-carotene is synthesized de novo during tomato fruit development by the B lycopene cyclase. In wild-type tomatoes B is expressed at low levels during the breaker stage of ripening, whereas in the Beta mutant its transcription is dramatically increased. Null mutations in the gene B are responsible for the phenotype in og, indicating that og is an allele of B. These results confirm that developmentally regulated transcription is the major mechanism that governs lycopene accumulation in ripening fruits. The cloned B genes can be used in various genetic manipulations toward altering pigmentation and enhancing nutritional value of plant foods.

Plasticity of the cochleotopic (frequency) map in specialized and nonspecialized auditory cortices

Auditory conditioning (associative learning) causes reorganization of the cochleotopic (frequency) maps of the primary auditory cortex (AI) and the inferior colliculus. Focal electric stimulation of the AI also evokes basically the same cortical and collicular reorganization as that caused by conditioning. Therefore, part of the neural mechanism for the plasticity of the central auditory system caused by conditioning can be explored by focal electric stimulation of the AI. The reorganization is due to shifts in best frequencies (BFs) together with shifts in frequency-tuning curves of single neurons. In the AI of the Mongolian gerbil (Meriones unguiculatus) and the posterior division of the AI of the mustached bat (Pteronotus parnellii), focal electric stimulation evokes BF shifts of cortical auditory neurons located within a 0.7-mm distance along the frequency axis. The amount and direction of BF shift differ depending on the relationship in BF between stimulated and recorded neurons, and between the gerbil and mustached bat. Comparison in BF shift between different mammalian species and between different cortical areas of a single species indicates that BF shift toward the BF of electrically stimulated cortical neurons (centripetal BF shift) is common in the AI, whereas BF shift away from the BF of electrically stimulated cortical neurons (centrifugal BF shift) is special. Therefore, we propose a hypothesis that reorganization, and accordingly organization, of cortical auditory areas caused by associative learning can be quite different between specialized and nonspecialized (ordinary) areas of the auditory cortex.

Rck2, a member of the calmodulin-protein kinase family, links protein synthesis to high osmolarity MAP kinase signaling in budding yeast

Rck2, a yeast Ser/Thr protein kinase homologous to mammalian calmodulin kinases, requires phosphorylation for activation. We provide evidence that in budding yeast, this step can be executed by the osmostress-activated mitogen-activated protein kinase Hog1. Rck2 phosphorylation was transiently increased during osmostress or in mutants with a hyperactive high osmolarity glycerol (HOG) pathway. This modification depended on catalytically active Hog1 kinase and two putative mitogen-activated protein kinase phosphorylation sites in Rck2. Immunokinase assays showed that Hog1 can directly phosphorylate Rck2 to stimulate its enzymatic activity toward translation elongation factor 2. We demonstrate that Hog1 and Rck2 are necessary for attenuation of protein synthesis in response to osmotic challenge and show that modification of elongation factor 2 induced by osmostress depends on Rck2 and Hog1 in vivo. Therefore, we propose that the transient down-regulation of protein synthesis after osmotic shock is a response not to damage but to an extracellular signal mediated by Hog1 and Rck2.