Phosphorylation controls spatial and temporal activities of motor-PRC1 complexes to complete mitosis

During mitosis, spindle architecture alters as chromosomes segregate into daughter cells. The microtubule crosslinker protein regulator of cytokinesis 1 (PRC1) is essential for spindle stability, chromosome segregation and completion of cytokinesis, but how it recruits motors to the central spindle to coordinate the segregation of chromosomes is unknown. Here, we combine structural and cell biology approaches to show that the human CENP-E motor, which is essential for chromosome capture and alignment by microtubules, binds to PRC1 through a conserved hydrophobic motif. This binding mechanism is also used by Kinesin-4 Kif4A:PRC1. Using in vitro reconstitution, we demonstrate that CENP-E slides antiparallel PRC1-crosslinked microtubules. We find that the regulation of CENP-E -PRC1 interaction is spatially and temporally coupled with relocalization to overlapping microtubules in anaphase. Finally, we demonstrate that the PRC1-microtubule motor interaction is essential in anaphase to control chromosome partitioning, retain central spindle integrity and ensure cytokinesis. Taken together our findings reveal the molecular basis for the cell cycle regulation of motor-PRC1 complexes to couple chromosome segregation and cytokinesis.

Reconstitution of an active human CENP-E motor

CENP-E is a large kinesin motor protein which plays pivotal roles in mitosis by facilitating chromosome capture and alignment, and promoting microtubule flux in the spindle. So far, it has not been possible to obtain active human CENP-E to study its molecular properties. Xenopus CENP-E motor has been characterized in vitro and is used as a model motor; however, its protein sequence differs significantly from human CENP-E. Here, we characterize human CENP-E motility in vitro. Full-length CENP-E exhibits an increase in run length and longer residency times on microtubules when compared to CENP-E motor truncations, indicating that the C-terminal microtubule-binding site enhances the processivity when the full-length motor is active. In contrast with constitutively active human CENP-E truncations, full-length human CENP-E has a reduced microtubule landing rate in vitro, suggesting that the non-motor coiled-coil regions self-regulate motor activity. Together, we demonstrate that human CENP-E is a processive motor, providing a useful tool to study the mechanistic basis for how human CENP-E drives chromosome congression and spindle organization during human cell division.

Perceiving tongue position

Two experiments on perceiving the tongue position were conducted in which naive human subjects pointed to gingival targets, or to extensions of their fingertip, with their tongue. The aim in experiment 1 was to inquire about the existence and accuracy of the perception of the horizontal position of the tongue inside and outside the mouth, and whether kinesthetic elements other than the skin might contribute to perceiving tongue position. Vertical positioning and the calibration of the sensory map that can be presumed to underlie position sense in the tongue were examined in experiment 2. It was found that position sense is equally good in the presence and absence of anesthesia of the mucosa, suggesting that the muscles, tendons, and corollary discharge contribute to position sense in the tongue. Perception of the tongue position both inside and outside the mouth is accurate, with the error in tongue positioning being about 2 degrees. Feedback improved naive subjects' accuracy very little.

Contribution of joint and muscle afferents to position sense at the human proximal interphalangeal joint

Experiments were carried out to examine the perceived position of the human index finger about the proximal interphalangeal joint. In protocol I, the finger was moved from an intermediate position at velocities ranging from 200 deg/min to 2 deg/min, then held still at one of three positions. The subject's task was visually to align a finger silhouette that was coaxial with the joint to the kinaesthetically perceived position of the unseen finger. Judgements of position were found to be quite accurate, and unaffected by previous velocity. Protocol II showed that although the direction of joint displacements of 0.01 and 0.1 deg could not be detected at any velocity, 1 deg could be detected at 200 deg/min and 10 deg at 20 and 2 deg/min. In protocol III the finger was moved at 2 deg/min and maintained at either 105 or 175 deg. It was found that the position of the unanaesthetized finger was quite accurately known, but with digital nerve block, subjects clearly perceived the finger to be at the mid-position (approximately 130-150 deg). This suggests that the absence of joint and cutaneous afference is interpreted by the CNS as indicating mid-position. The slight bias of the sensed position towards the objective position shown by the results also indicates that muscle afferents can provide a crude signal related to joint position. This finding was further supported by the observation that splinting the distal interphalangeal joint into flexion resulted in flexion bias in the perceived angle of the proximal interphalangeal joint. Anaesthesia of the middle finger, thumb and distal portion of the index finger (leaving proximal joint unaffected), had little effect on position matching performance, suggesting that the large error in position sense during anaesthesia of the whole finger is due to loss of afference specifically related to the proximal interphalangeal joint, and not due to loss of non-specific facilitatory influences from cutaneous and joint afferents. The results argue for an important proprioceptive role for joint afferents at finger joints.

The effect of loading on position sense in the tongue

The position sense of the tongue and aftereffects on the position sense subsequent to loading were directly investigated. Nine subjects judged the straightahead with the tongue before and after straining laterally with the tongue against the horizontal force induced by a 29.5-g weight. Two of these subjects also participated in the experiment after the surface of the tongue had been anesthetized. Prior loading of the tongue biased the subjects' subsequent judgment of the straight-ahead; following loading, the tongue was placed farther in the direction of the previous effort. The results are discussed with reference to postcontraction effects from experiments on loading the limb and eye.

Oscillator Mechanisms in the Human Motor System

It is proposed that the human motor system is organized to use hardware and/or software non-linear oscillator mechanisms, the output of these oscillators being responsible for driving the limbs via signals to muscle groups. Following earlier theoretical development, it is argued that these muscle groupings act as a unit and themselves are likely to behave as a non-linear system. The attributes of non-linear oscillators are many, and they are potentially significant for the explanation of motor behavior. This paper reviews and presents recent experiments that investigated the properties of muscular aftercontraction. The basic finding shows that subsequent to a period of moderate strain against a fixed surface the treated limb exhibits prolonged involuntary molar oscillations in the plane of the treatment. These results provide for the presence of driving oscillator mechanisms in the human motor apparatus. The mechanisms show generality of action in that directed attention can lead to oscillation of untreated limbs. Overall, the experiments showed that the movements exhibited the mutual interaction, synchronization, and preservation of phase relationships that are fundamental properties of non-linear oscillators. the picture that emerges is that these mechanisms can drive involuntary movements that are richly patterned: like slow versions of voluntary movements. The aftercontraction phenomenon proves to be an excellent tool for research on the oscillatory substrate of human motor organization.

Modifying an underlying component of perceived arm length: adaptation of tactile location induced by spatial discordance

In four experiments we examined the adaptation and aftereffect that resulted from a treatment yielding tactile/kinesthetic length discordance between the arms. Perceived discordance diminished with trials and tended to zero. Subsequent visual/tactile cross-modal judgments of distance showed the aftereffect to be a change in the perceived location of an unseen probed spot on each hand with respect to the location of a truly coincident visual marker. This occurred toward the body for the probed spot on one arm and away from the body on the other. There were three other main findings: (a) Arm movement was not a necessary condition for adaptation or aftereffect; (b) with intrinsic length information about the right arm present, but touch information from the right index finger absent during treatment, adaptation and aftereffect were abolished; (c) aftereffects of tactile location that were manifest at the hand and wrist tended to zero when a point close to the elbow was tested with a cross-modal procedure. The experiments provide evidence that the mapping of the tactile sheet onto an internal length domain had been modified by the treatment. The sensory consequences of the treatment led many subjects to report spontaneously that their arms felt to be of different lengths.

Modifying an underlying component of perceived arm length: adaptation of tactile location induced by spatial discordance

In four experiments we examined the adaptation and aftereffect that resulted from a treatment yielding tactile/kinesthetic length discordance between the arms. Perceived discordance diminished with trials and tended to zero. Subsequent visual/tactile cross-modal judgments of distance showed the aftereffect to be a change in the perceived location of an unseen probed spot on each hand with respect to the location of a truly coincident visual marker. This occurred toward the body for the probed spot on one arm and away from the body on the other. There were three other main findings: (a) Arm movement was not a necessary condition for adaptation or aftereffect; (b) with intrinsic length information about the right arm present, but touch information from the right index finger absent during treatment, adaptation and aftereffect were abolished; (c) aftereffects of tactile location that were manifest at the hand and wrist tended to zero when a point close to the elbow was tested with a cross-modal procedure. The experiments provide evidence that the mapping of the tactile sheet onto an internal length domain had been modified by the treatment. The sensory consequences of the treatment led many subjects to report spontaneously that their arms felt to be of different lengths.

Perception of impossible limb positions induced by tendon vibration

When the wrist flexor muscle is vibrated and the wrist is passively extended to a position close to its anatomical limit, the hand is felt to be bent to a position about 29 degrees beyond its maximum operating range. The mechanism of position sense must in this case be operating on the basis of extrapolation. Ambiguity of sensed position can occur in this situation. Some subjects, when opposing the vibration-induced contraction of bicepts, report experiencing multiple forearms.

Differential effects on test stress on the heart rates of extraverts and introverts

A mental arithmetic task was administered to 39 subjects under conditions which imposed social stress. Using the relaxed state to provide a baseline, changes in heart rate and finger blood volume pulse were recorded. The subjects were divided to obtain groups with extreme scores on Eysenck's PEN scales, and the groups were compared on the two psychophysiological measures. Contrary to Eysenck's theory of Autonomic Lability as the neurological basis of N, the high N scoring group was not differentiated from the low N group by change in level of sympathetic activity as indicated by blood volume pulse, while, on the heart-rate measure, introverts showed a large increase and extraverts considerably less: there was no overlap between groups (p less than 0.001). It was concluded that extraverts exhibit greater parasympathetic activity relative to sympathetic arousal under this stress condition.

Oculomotor adaptation to prisms: complete transfer between eyes

It is argued that previous experiments investigating interocular transfer of adaptation have been concerned with an adaptation of the registered position of the limb used to indicate direction. Thus the question of interocular transfer of adaptation sited at the eye remains open. Two experiments are reported. The first showed that there was complete transfer between exposed and unexposed eyes. The conditions were such that the adaptation could be explained only as a change in the registered position of the eye in the head, or of the head on the shoulders. The second experiment showed that changes of this latter kind did not occur.

A relationship between Eysenck's P scale and change in muscle action potentials with attention to perceptual tasks

An experiment is described in which an index of change in muscle tension produced by perceptual discrimination tasks, and scores on Eysenck's PEN scales, were measured on 39 university students. It was hypothesized that if P is an index of psychoticism, as has been claimed (Eysenck & Eysenck, 1968) then an index of one central feature of so called 'psychotics', namely attention difficulty while decision making, should correlate positively with P. P was found to correlate significantly with a measure of increase of EMG on the perceptual discrimination tasks (r = 0-54, P less than 0-001). Correlations of this index with N and E were zero. The results are considered to be particularly significant, since scores on P, E and N gave almost zero intercorrelations in the sample tested, and L scores were exceedingly low. Further evidence is provided which suggests that both P and muscle tension increase are directly related to the degree of endorsement of paranoid ideas.

Disturbance of the oculomotor system due to lateral fixation

Three experiments are reported on the effects of previous lateral deviation of the eyes. There is a large effect on their subsequent resting position, and a smaller instantaneous effect on voluntary eye centring. Both are in the direction of previous fixation. The latter effect becomes insignificant within 30 s. The treatment produces errors in visually guided reaching away from the previous direction of fixation. The effects are consistent with a change in registered eye position, an effect also produced by exposure to prisms. Despite this similarity, the disturbance to the oculomotor system caused by these two treatments is sharply differentiated by the resting position. Prisms cause subsequent low frequency, high amplitude oscillations of the eyes (Craske and Templeton, 1968), whereas following lateral deviation the mean resting position returns gradually towards the pre-treatment position.

Shifts in kinesthesis through time and after active and passive movement

The position sense of a stationary arm was investigated subsequent to an horizontally adductive movement with axis the shoulder joint. The right arm was the treated arm: it reached a test position actively, using minimal voluntary effort, or passively from each of 10 starting positons. The blind-folded S localized the index finger of the treated arm by attempting to touch it with the index finger of his left hand. The results indicate that subsequent to active movement the final position of a limb is more accurately known than a position resulting from passive movement. A second finding is that concomitant with both forms of limb placement there is a unidirectional drift of perceived limb position over trials.

Adaptive changes of opposite sign in the oculomotor systems of the two eyes

Subjects inspected their feet via base-out prisms for 3 min. Using binocular vision, subsequent reaching without prisms showed significant overestimation of distance. Monocular testing showed a lateral shift in pointing to targets in opposite directions for each eye. This indicates that registered, as opposed to actual, convergence is a factor in near distance perception, and that opposite adaptation occurs within the motor control system for each eye.