Vision as oculomotor reward: cognitive contributions to the dynamic control of saccadic eye movements

Humans and other primates are equipped with a foveated visual system. As a consequence, we reorient our fovea to objects and targets in the visual field that are conspicuous or that we consider relevant or worth looking at. These reorientations are achieved by means of saccadic eye movements. Where we saccade to depends on various low-level factors such as a targets’ luminance but also crucially on high-level factors like the expected reward or a targets’ relevance for perception and subsequent behavior. Here, we review recent findings how the control of saccadic eye movements is influenced by higher-level cognitive processes. We first describe the pathways by which cognitive contributions can influence the neural oculomotor circuit. Second, we summarize what saccade parameters reveal about cognitive mechanisms, particularly saccade latencies, saccade kinematics and changes in saccade gain. Finally, we review findings on what renders a saccade target valuable, as reflected in oculomotor behavior. We emphasize that foveal vision of the target after the saccade can constitute an internal reward for the visual system and that this is reflected in oculomotor dynamics that serve to quickly and accurately provide detailed foveal vision of relevant targets in the visual field.     

5-Phosphonomethylquinoxalinediones as competitive NMDA receptor antagonists with a preference for the human 1A/2A, rather than 1A/2B receptor composition

NMDA antagonists derived from 5-phosphonomethyl-1,4-dihydroquinoxaline-2,3-dione (3a) are potent anticonvulsant agents, and display strong protective effects in the electroshock-induced convulsion assay in mice. Their preference for the human NMDAR 1A/2A over 1A/2B subunit composition was optimized, leading to (1RS,1'S)-PEAQX (9r), which shows a >100-fold selectivity.     

Tuberous sclerosis genes regulate cellular 14-3-3 protein levels

The genes TSC1, encoding hamartin, and TSC2, encoding tuberin are responsible for tuberous sclerosis. This autosomal dominant tumor suppressor gene syndrome affects about 1 in 6000 individuals. A variety of tumors characteristically occur in different organs of tuberous sclerosis patients and are believed to result from defects in cell cycle/cell size control. We performed a proteomics approach of two-dimensional gel electrophoresis with subsequent mass spectrometrical identification of protein spots after ectopic overexpression of human TSC1 or TSC2. We found the cellular levels of four isoforms of the 14-3-3 protein family, 14-3-3 gamma, 14-3-3, 14-3-3 sigma, and 14-3-3 zeta, to be regulated by the two tuberous sclerosis gene products. In the same experiments the protein levels of keratin 7, capZ alpha-1 subunit, ezrin, and nedasin were not affected by ectopic TSC1 or TSC2. Western blot analyses confirmed the deregulation of 14-3-3 proteins upon ectopic overexpression of TSC1 and TSC2. A TSC1 mutant not encoding the transmembrane domain and the tuberin-binding domain but harbouring most of the coiled-coil region and the ERM protein interaction domain of hamartin did not affect 14-3-3 protein levels. The here presented findings suggest that deregulation of 14-3-3 protein amounts might contribute to the development of tumors in tuberous sclerosis patients. These data provide important new insights into the molecular development of this disease especially since both, the TSC genes and the 14-3-3 proteins, are known to be involved in mammalian cell cycle control.     

Linking anti-predator behaviour and habitat quality: group effect in nest defence of a passerine bird

In habitats where the density of breeding individuals is higher, breeding success has been shown to increase with the number of close conspecific and heterospecific neighbours. However, the mechanisms linking habitat quality, group size of prey individuals and offspring defence are poorly known. In this field study, we examined the relationships between habitat quality and parental nest defence behaviour in the pied flycatcher (Ficedula hypoleuca). We found that mobbing is more intense in unmanaged forests where birds breed in more dense and diverse communities than in heavily managed young forests where heterospecific densities are lower. We also found that the mobbing activities of pied flycatchers breeding in unmanaged mature boreal forests attracted more neighbouring prey individuals than in nearby managed forests. This study shows that habitat quality-mediated effects might be responsible for the decreased group size of mobbing birds in managed forests, which may lead to less effective communal defence.     

Short-term weightlessness produced by parabolic flight maneuvers altered gene expression patterns in human endothelial cells

This study focused on the effects of short-term microgravity (22 s) on the gene expression and morphology of endothelial cells (ECs) and evaluated gravisensitive signaling elements. ECs were investigated during four German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt) parabolic flight campaigns. Hoechst 33342 and acridine orange/ethidium bromide staining showed no signs of cell death in ECs after 31 parabolas (P31). Gene array analysis revealed 320 significantly regulated genes after the first parabola (P1) and P31. COL4A5, COL8A1, ITGA6, ITGA10, and ITGB3 mRNAs were down-regulated after P1. EDN1 and TNFRSF12A mRNAs were up-regulated. ADAM19, CARD8, CD40, GSN, PRKCA (all down-regulated after P1), and PRKAA1 (AMPKα1) mRNAs (up-regulated) provide a very early protective mechanism of cell survival induced by 22 s microgravity. The ABL2 gene was significantly up-regulated after P1 and P31, TUBB was slightly induced, but ACTA2 and VIM mRNAs were not changed. β-Tubulin immunofluorescence revealed a cytoplasmic rearrangement. Vibration had no effect. Hypergravity reduced CARD8, NOS3, VASH1, SERPINH1 (all P1), CAV2, ADAM19, TNFRSF12A, CD40, and ITGA6 (P31) mRNAs. These data suggest that microgravity alters the gene expression patterns and the cytoskeleton of ECs very early. Several gravisensitive signaling elements, such as AMPKα1 and integrins, are involved in the reaction of ECs to altered gravity.     

Oxidation of HRas cysteine thiols by metabolic stress prevents palmitoylation in vivo and contributes to endothelial cell apoptosis

Here we demonstrate a new paradigm in redox signaling, whereby oxidants resulting from metabolic stress directly alter protein palmitoylation by oxidizing reactive cysteine thiolates. In mice fed a high-fat, high-sucrose diet and in cultured endothelial cells (ECs) treated with high palmitate and high glucose (HPHG), there was decreased HRas palmitoylation on Cys181/184 (61±24% decrease for cardiac tissue and 38±7.0% in ECs). This was due to oxidation of Cys181/184, detected using matrix-assisted laser desorption/ionization time of flight (MALDI TOF)-TOF. Decrease in HRas palmitoylation affected its compartmentalization and Ras binding domain binding activity, with a shift from plasma membrane tethering to Golgi localization. Loss of plasma membrane-bound HRas decreased growth factor-stimulated ERK phosphorylation (84±8.6% decrease) and increased apoptotic signaling (24±6.5-fold increase) after HPHG treatment that was prevented by overexpressing wild-type but not C181/184S HRas. The essential role of HRas in metabolic stress was made evident by the similar effects of expressing an inactive dominant negative N17-HRas or a MEK inhibitor. Furthermore, the relevance of thiol oxidation was demonstrated by overexpressing manganese superoxide dismutase, which improved HRas palmitoylation and ERK phosphorylation, while lessening apoptosis in HPHG treated ECs.     

The CDK5 repressor CDK5RAP1 is a methylthiotransferase acting on nuclear and mitochondrial RNA

The unusual cyclin-dependent protein kinase 5 (CDK5) was discovered based on its sequence homology to cell cycle regulating CDKs. CDK5 was found to be active in brain tissues, where it is not involved in cell cycle regulation but in the regulation of neuronal cell differentiation and neurocytoskeleton dynamics. An aberrant regulation of CDK5 leads to the development of various neurodegenerative diseases including Alzheimer's disease. Although CDK5 is not regulated by cyclins, its activity does depend on the association with a protein activator and the presence or absence of further inhibitory factors. Recently, CDK5RAP1 was discovered to inhibit the active CDK5 kinase. Here, we show that CDK5RAP1 is a radical SAM enzyme, which postsynthetically converts the RNA modification N6-isopentenyladenosine (i(6)A) into 2-methylthio-N6-isopentenyladenosine (ms(2)i(6)A). This conversion is surprisingly not limited to mitochondrial tRNA, where the modification was known to exist. Instead, CDK5RAP1 introduces the modification also into nuclear RNA species establishing a link between postsynthetic kinase-based protein modification and postsynthetic RNA modification.