Building bridges to the cortex

Innervation of the neocortex by the thalamus is dependent on the precise coordination of spatial and temporal guidance cues. In this issue of Cell, work by López-Bendito et al.(2006) reveals that tangentially migrating cells within the ventral telencephalon are essential for axonal navigation between the thalamus and the neocortex, a process apparently mediated by Neuregulin-1/ErbB4 short- and long-range signaling.     

Cell polarity: connecting to the cortex

A GTPase module controls growth-site selection in budding yeast cells. The GDP--GTP exchange factor of this module, Bud5, has now been localized to sites of cell division and shown to interact with a transmembrane protein that marks these sites.     

Anillin, a contractile ring protein that cycles from the nucleus to the cell cortex

We report the cDNA sequence and localization of a protein first identified by actin filament chromatography of Drosophila embryo extracts as ABP8 (Miller, K. G., C. M. Field, and B. M. Alberts. 1989. J. Cell Biol. 109:2963-2975). The cDNA encodes a 1201-amino acid protein which we name anillin. Anillin migrates at 190 kD on SDS-PAGE. Anillin is expressed throughout Drosophila development and in tissue culture cells. By immunofluorescence, anillin localizes to the nucleus of interphase cells, except in the syncytial embryo where it is always cytoplasmic. During metaphase, it is present in the cytoplasm and cortex, and during anaphase-telophase it becomes highly enriched in the cleavage furrow along with myosin II. In the syncytial embryo, anillin, along with myosin-II, is enriched in cortical areas undergoing cell cycle regulated invagination including metaphase furrows and the cellularization front. In contractile rings, metaphase furrows, and nascent ring canals, anillin remains bound to the invaginated cortex suggesting a stabilizing role. Anillin is not expressed in cells that have left the cell cycle. Anillin isolated from embryo extracts binds directly to actin filaments. The domain responsible for this binding has been mapped to a region of 244 amino acids by expression of protein fragments in bacteria. This domain, which is monomeric in solution, also bundles actin filaments. We speculate that anillin plays a role in organizing and/or stabilizing the cleavage furrow and other cell cycle regulated, contractile domains of the actin cytoskeleton.     

Perceiving time to collision activates the sensorimotor cortex

The survival of many animals hinges upon their ability to avoid collisions with other animals or objects, or to precisely control the timing of collisions. Optical expansion provides a compelling impression of object approach and in principle can provide the basis for judgments of time to collision (TTC) [1]. It has been demonstrated that pigeons [2] and houseflies [3] have neural systems that can initiate rapid coordinated actions on the basis of optical expansion. In the case of humans, the linkage between judgments of TTC and coordinated action has not been established at a cortical level. Using functional magnetic resonance imaging (fMRI), we identified superior-parietal and motor-cortex areas that are selectively active during perceptual TTC judgments, some of which are normally involved in producing reach-to-grasp responses. These activations could not be attributed to actual movement of participants. We demonstrate that networks involved in the computational problem of extracting TTC from expansion information have close correspondence with the sensorimotor systems that would be involved in preparing a timed motor response, such as catching a ball or avoiding collision.     

Interrelations between the sympathoadrenal system,adrenal cortex,and autonomic tone in seven- to nine-year-old children

Comprehensive study of the functional state of the sympathoadrenal system (SAS) and adrenal cortex (AC) and the specific features of the autonomic regulation of the cardiac rhythm revealed close correlations between the excretion of catecholamines (CAs) and androgens, on the one hand, and the initial autonomic tone (IAT) of the cardiovascular system of children, on the other hand. Most schoolchildren of both sexes with a predominant dependence of their cardiac rhythm on sympathetic influences were shown to excrete more noradrenaline (NA), 17-hydroxycorticosteroids, and 17-ketosteroids and less dopamine than their normotonic and vagotonic counterparts, which was accompanied by an increase in the NA-to-adrenaline ratio. In contrast, eight-and nine-year-old girls exhibited a relatively decreased activity of glucocorticoid functions of the AC associated with sympathicotonia. A local static effort performed as a functional test caused similarly directed changes in the functional states of the SAS and AC in a manner dependent on the child’s IAT, age, and sex. In the states of sympathicotonia or normotonia, nine-year-old girls exhibited a decrease in the excretion of CAs and DOPA or their insignificant increase accompanied by strengthening of the functional activity of the AC, especially of its androgen function. This may be interpreted as a manifestation of specific neuroendocrine interrelations in the adaptive mechanisms of nine-year-old girls and a higher stability of the pituitary-adrenal system, which controls metabolic processes in the growing body. In contrast, in normotonic and vagotonic seven-year-old boys (as well as in sympathicotonic eight-year-old boys), the local static effort revealed simultaneous decreases in the reserve potentials of the SAS and AC, probably caused by fatigue and asthenization of these children during their schoolwork.     

iASPP contributes to cell cortex rigidity,mitotic cell rounding,and spindle positioning

iASPP is a protein mostly known as an inhibitor of p53 pro-apoptotic activity and a predicted regulatory subunit of the PP1 phosphatase, which is often overexpressed in tumors. We report that iASPP associates with the microtubule plus-end binding protein EB1, a central regulator of microtubule dynamics, via an SxIP motif. iASPP silencing or mutation of the SxIP motif led to defective microtubule capture at the cortex of mitotic cells, leading to abnormal positioning of the mitotic spindle. These effects were recapitulated by the knockdown of the membrane-to-cortex linker Myosin-Ic (Myo1c), which we identified as a novel partner of iASPP. Moreover, iASPP or Myo1c knockdown cells failed to round up upon mitosis because of defective cortical stiffness. We propose that by increasing cortical rigidity, iASPP helps cancer cells maintain a spherical geometry suitable for proper mitotic spindle positioning and chromosome partitioning.     

From thought to action: the parietal cortex as a bridge between perception, action, and cognition

The lateral intraparietal area (LIP) is a subdivision of the inferior parietal lobe that has been implicated in the guidance of spatial attention. In a variety of tasks, LIP provides a "salience representation" of the external world-a topographic visual representation that encodes the locations of salient or behaviorally relevant objects. Recent neurophysiological experiments show that this salience representation incorporates information about multiple behavioral variables-such as a specific motor response, reward, or category membership-associated with the task-relevant object. This integration occurs in a wide variety of tasks, including those requiring eye or limb movements or goal-directed or nontargeting operant responses. Thus, LIP acts as a multifaceted behavioral integrator that binds visuospatial, motor, and cognitive information into a topographically organized signal of behavioral salience. By specifying attentional priority as a synthesis of multiple task demands, LIP operates at the interface of perception, action, and cognition.     

Analysis of conduction of visual,somatic, and audiovibratory sensory information to the hippocamapal cortex in lizards

Acute electrophysiological experiments on lizards (Ophisaurus apodus) showed that electrical stimulation of the anterior dorsolateral thalamic nucleus and medial forebrain bundle evokes short-latency responses in the hippocampal (mediodorsal) cortex which coincides in distribution and configuration with responses in the same cortical area to sensory stimulation. Extensive destruction of these structures inhibits, or even completely blocks, the conduction of sensory (visual, somatic, audiovibratory) and tactile impulses to the hippocampal cortex. It is concluded that the anterior dorsolateral thalamic nucleus and medial forebrain bundle constitutes, if not the only, at least the principal pathway for transmission of these sensory impulses to the hippocampal cortex in lizards.