'STRATIGRAPHY VERSUS PALEONTOLOGY IN NOVA SCOTIA.'     

Matthew GF 《Science (New York, N.Y.)》1902,16(404):513-514

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PALEONTOLOGICAL NOTES     

Matthew WD 《Science (New York, N.Y.)》1906,24(624):786-788

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Crystal structure of an ancient protein: evolution by conformational epistasis   总被引：1，自引：0，他引：1  

Ortlund EA  Bridgham JT  Redinbo MR  Thornton JW 《Science (New York, N.Y.)》2007,317(5844):1544-1548

The structural mechanisms by which proteins have evolved new functions are known only indirectly. We report x-ray crystal structures of a resurrected ancestral protein-the approximately 450 million-year-old precursor of vertebrate glucocorticoid (GR) and mineralocorticoid (MR) receptors. Using structural, phylogenetic, and functional analysis, we identify the specific set of historical mutations that recapitulate the evolution of GR's hormone specificity from an MR-like ancestor. These substitutions repositioned crucial residues to create new receptor-ligand and intraprotein contacts. Strong epistatic interactions occur because one substitution changes the conformational position of another site. "Permissive" mutations-substitutions of no immediate consequence, which stabilize specific elements of the protein and allow it to tolerate subsequent function-switching changes-played a major role in determining GR's evolutionary trajectory.  相似文献   

An in vitro neurite-promoting antigen functions in axonal regeneration in vivo   总被引：6，自引：0，他引：6  

A W Sandrock  W D Matthew 《Science (New York, N.Y.)》1987,237(4822):1605-1608

The function of the neurite growth-promoting antigen INO has been tested in an in vivo neurite regeneration system, the rat iris. The sympathetic innervation of the irides was removed by a single systemic injection of 6-hydroxydopamine. The subsequent regeneration of sympathetic axons into the iris of one eye bathed by the INO antibody, which inhibits neurite growth in vitro, was compared with the regrowth of sympathetic axons into the iris of the animal's other eye, which contained control antibody. Antibodies were released within the eye by implanted hybridoma cells. Neurite regeneration was measured by assaying [3H]norepinephrine uptake into freshly explained irides. The blockage of the function of the INO antigen by the antibody resulted in a decreased rate of axonal regeneration, thus suggesting the involvement of the INO antigen in the process of neurite regeneration in vivo.  相似文献   

Early γ oscillations synchronize developing thalamus and cortex     

Minlebaev M  Colonnese M  Tsintsadze T  Sirota A  Khazipov R 《Science (New York, N.Y.)》2011,334(6053):226-229

During development, formation of topographic maps in sensory cortex requires precise temporal binding in thalamocortical networks. However, the physiological substrate for such synchronization is unknown. We report that early gamma oscillations (EGOs) enable precise spatiotemporal thalamocortical synchronization in the neonatal rat whisker sensory system. Driven by a thalamic gamma oscillator and initially independent of cortical inhibition, EGOs synchronize neurons in a single thalamic barreloid and corresponding cortical barrel and support plasticity at developing thalamocortical synapses. We propose that the multiple replay of sensory input in thalamocortical circuits during EGOs allows thalamic and cortical neurons to be organized into vertical topographic functional units before the development of horizontal binding in adult brain.  相似文献   

Sex differences in the brain: implications for explaining autism     

Baron-Cohen S  Knickmeyer RC  Belmonte MK 《Science (New York, N.Y.)》2005,310(5749):819-823

Empathizing is the capacity to predict and to respond to the behavior of agents (usually people) by inferring their mental states and responding to these with an appropriate emotion. Systemizing is the capacity to predict and to respond to the behavior of nonagentive deterministic systems by analyzing input-operation-output relations and inferring the rules that govern such systems. At a population level, females are stronger empathizers and males are stronger systemizers. The "extreme male brain" theory posits that autism represents an extreme of the male pattern (impaired empathizing and enhanced systemizing). Here we suggest that specific aspects of autistic neuroanatomy may also be extremes of typical male neuroanatomy.  相似文献   

Rewarding reviewers     

Metz MA 《Science (New York, N.Y.)》2008,319(5868):1335

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Conservation with sense     

Lim ML  Sodhi NS  Endler JA 《Science (New York, N.Y.)》2008,319(5861):281

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The impact of comet Shoemaker-Levy 9 sends ripples through the rings of Jupiter     

Showalter MR  Hedman MM  Burns JA 《Science (New York, N.Y.)》2011,332(6030):711-713

Jupiter's main ring shows vertical corrugations reminiscent of those recently detected in the rings of Saturn. The Galileo spacecraft imaged a pair of superimposed ripple patterns in 1996 and again in 2000. These patterns behave as two independent spirals, each winding up at a rate defined by Jupiter's gravity field. The dominant pattern originated between July and October 1994, when the entire ring was tilted by about 2 kilometers. We associate this with the Shoemaker-Levy 9 impacts of July 1994. New Horizons images still show this pattern 13 years later and suggest that subsequent events may also have tilted the ring. Impacts by comets or their dust streams are regular occurrences in planetary rings, altering them in ways that remain detectable decades later.  相似文献   

A fluoroquinolone resistance protein from Mycobacterium tuberculosis that mimics DNA     

Hegde SS  Vetting MW  Roderick SL  Mitchenall LA  Maxwell A  Takiff HE  Blanchard JS 《Science (New York, N.Y.)》2005,308(5727):1480-1483

Fluoroquinolones are gaining increasing importance in the treatment of tuberculosis. The expression of MfpA, a member of the pentapeptide repeat family of proteins from Mycobacterium tuberculosis, causes resistance to ciprofloxacin and sparfloxacin. This protein binds to DNA gyrase and inhibits its activity. Its three-dimensional structure reveals a fold, which we have named the right-handed quadrilateral beta helix, that exhibits size, shape, and electrostatic similarity to B-form DNA. This represents a form of DNA mimicry and explains both its inhibitory effect on DNA gyrase and fluoroquinolone resistance resulting from the protein's expression in vivo.  相似文献