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PubMed1978

Receptor potential and spike initiation in two varieties of snake muscle spindles.

1. Receptor potentials, in response to ramp-and-hold stretch, have been recorded from two varieties of snake muscle spindles. 2. The two types of spindles have a similar sensitivity of impulse discharge to amplitude of receptor potential during the static phase of stretch. 3. Receptor potentials from short-capsule spindles show a high dynamic sensitivity to velocity of stretch. Amplitude of dynamic receptor potentials is well related to frequency of dynamic discharge except beyond a certain velocity of stretch where the frequency deviates progressively more than expected from linearity. 4. Receptor potentials from long-capsule spindles show a low dynamic sensitivity to velocity of stretch and amplitude of dynamic receptor potentials is well correlated with dynamic firing frequency. 5. The threshold level of receptor potential for initiating spike discharge varies with the velocity of stretch, the relation being similar for the two types of spindles. 6. It is concluded that the basis for functional differentiation of snake spindles may lie in the mechanism by which deformation of sensory endings is transformed into receptor potential. 7. Late adaptation of impulse discharge, a characteristic feature of the response of the short-capsule spindle to maintained stretch, has been related to length changes of the sensory region measured directly with Nomarski optics. The linear relation found between the slow adaptive fall of impulse discharge and the simultaneous shortening of the sensory region strongly suggests a mechanical basis for the late adaptation.

Action Potentials↗

PubMed1979

Activity patterns in individual hindlimb primary and secondary muscle spindle afferents during normal movements in unrestrained cats.

1. Chronically implanted microelectrode wires in the L7 and S1 dorsal root ganglia were used to record unit activity from cat hindlimb primary and secondary muscle spindle afferents. Units could be reliably recorded for several days, permitting comparison of their activity with homonymous muscle EMG and length during a variety of normal, unrestrained movements. 2. The general observation was that among both primary and secondary endings there was a broad range of different patterns of activity depending on the type of muscle involved and the type of movement performed. 3. During walking, the activity of a given spindle primary was usually consistent among similar step cycles. However, the activity was usually poorly correlated with absolute muscle length, apparently unrealted to velocity of muscle stretch, and could change markedly for similar movements performed under different conditions. 4. Spindle activity modulation not apparently related to muscle length changes was assumed to be influenced by fusimotor activity. In certain muscles, this presumption leads to the conclusion that gamma-motoneurons may be activated out of phase with homonymous alpha-motoneurons as well as by more conventional alpha-gamma-motoneuron coactivation. 5. Simultaneous recordings of two spindle primary afferents from extensor digitorum longus indicated that spindles within the same muscle may differ considerably with respect to this presumed gamma-motoneuron drive. 6. Spindle secondary endings appeared to be predominantly passive indicators of muscle length during walking, but could demonstrate apparently strong fusimotor modulation during other motor activities such as postural changes and paw shaking. 7. Both primary and secondary endings were observed to undergo very rapid modulation of firing rates in response to presumed reflexly induced intrafusal contractions. 8. It is suggested that the pattern of fusimotor control of spindles may be tailored to the specific muscle and task being performed, rather than necessarily dominated by rigid alpha-gamma coactivation.

Animals↗

PubMed1984

Active force and sensory response of single isolated cat muscle spindles in vitro.

Active tetanic tension developed by stimulation of a nerve innervating single isolated muscle spindles of the cat was measured. The maximum tetanic force varied among spindles, ranging from 2.3 to 8.5 mg. For four spindles, the maximum tetanic force was converted into the force per unit cross-sectional area of nuclear chain and nuclear bag fibers. The results are discussed in terms of structural and functional complexities of the intrafusal fibers. The length-tension diagram of single isolated spindles showed maximum tetanic tension occurring at a spindle length longer than 1o, which was defined as the length beyond which passive tension starts to develop. This result, which appears to be different from the corresponding diagram for extrafusal muscle, is discussed in relation to the existing reports on the mechanical properties of intrafusal fibers. Spindle sensory response vs. tetanic tension was analyzed for single isolated spindles with two independent nerve supplies, one containing sensory and the other containing fusimotor axons. The results suggest that the static discharge rate of sensory endings may be linearly related, within the range examined, to the tetanic plateau tension of intrafusal fibers.

Afferent Pathways↗

PubMed1985

Activity of spindle afferents from cat anterior thigh muscles. II. Effects of fusimotor blockade.

Chronically implanted electrodes and nerve cuff catheters were used to record the activity of individual muscle spindle afferents during treadmill walking as low doses of lidocaine were infused around the femoral nerve to progressively block gamma motoneuron activity. Both primary and secondary endings from both the monarticular knee extensors and the biarticular hip/knee muscles of the anterior thigh showed large decreases in afferent activity, usually well before changes in the electromyographic activity, force output, or length and velocity were seen in the parent muscles. This decline in the proprioceptive signal feeding back onto the spinal cord, which we presume to have involved most of the spindles supplied by the femoral nerve, did not cause noticeable irregularities or instability of the walking gait. At the peak of the fusimotor blockade, spindle afferents from knee extensor muscles lost about half of their usually brisk activity during the near-isometric contraction of the stance phase. Significant decreases in the response to passive stretch during the flexion phase also occurred. At the peak of the fusimotor blockade, spindle afferents from the biarticular muscles lost all of their activity during the rapidly shortening swing phase and about half of their activity during the rapidly lengthening stance phase. For both monarticular and biarticular muscle spindles, the activity decreases in stance and swing phase often occurred at distinctly different stages of the progressive fusimotor blockade, indicating several different sources of fusimotor control. From these data, we infer that the sensitivity of most spindle afferents is substantially influenced by fusimotor activity during phases of both extrafusal activity and extrafusal silence. At least some of this influence appears to come from fusimotor neurons whose recruitment is independent of the extrafusal recruitment. The extent and type of fusimotor effects on spindle afferent sensitivity (dynamic or static) appear to be specialized for the mechanical events that tend to occur during those phases.

Afferent Pathways↗

PubMed1987

Dynamics and directional sensitivity of neck muscle spindle responses to head rotation.

With the use of floating electrodes we recorded from the C2 dorsal root ganglion of decerebrate cats during sinusoidal and trapezoidal head rotation. Fifty-one spontaneously firing afferents were identified as muscle spindle endings. Some were identified by their excitatory response to injection of succinylcholine, others by the similarity of their behavior to that of endings excited by the drug. Because afferent input to the ganglion was restricted by sectioning most nerve trunks, most spindle endings were presumably located in ventral and ventrolateral perivertebral muscles. The firing of each spindle afferent was modulated most effectively by tilting the head in a specific direction; this direction was termed its response vector. Responses to sine waves and trapezoids were then studied with stimuli oriented as closely as possible to the vertical plane of this vector. Most spindle afferents could be classified in one of two categories. Those with high gain, pronounced nonlinearity, and high dynamic index were called type A. Those classified as type B had low gain, a fairly linear response, and low dynamic index. In response to small (0.5 degrees) stimuli, type A endings had phase leads of approximately 40 degrees at frequencies of sinusoidal stimulation of 0.02-0.1 Hz, increasing to approximately 80 degrees at 4 Hz; with larger (2.5 degrees) stimuli, phase was advanced by an additional 10-20 degrees at all frequencies. Phase of type B responses was less advanced than that of type A responses. Gain slopes of the two types of endings were similar. Bode plots of spindle afferents strongly resembled those of upper cervical neurons whose activity is modulated by head rotation. Each spindle afferent had a response vector whose direction remained stable with time, different frequencies of stimulation, and different stimulus amplitudes. The distribution of response vectors covered approximately 270 degrees, with a gap near nose down pitch. Changing initial head position usually had little effect on the direction of an afferent's response vector or on response dynamics. However, stimulation far from the best plane could transform a type A into a type B response. This raises the possibility that type B receptors could be type A receptors best stimulated by yaw and with only low sensitivity to stimulation in vertical planes. Type A receptors have all the properties of spindle primaries. The identification of type B receptors remains uncertain, because they may include secondary afferents as well as primaries stimulated far from their best three-dimensional vector.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1996

Impulse initiation in the mammalian muscle spindle during combined fusimotor stimulation and succinyl choline infusion.

1. This is a report of observations on the responses of the primary and secondary endings of soleus muscle spindles of the anesthetized cat to the combined effects of the depolarizing neuromuscular blocker succinyl choline (SCh), given intravenously, and fusimotor stimulation. The findings were interpreted in terms of a dual pacemaker model for activity generated in the bag1 intrafusal fiber interacting with activity coming from bag2 and chain fibers. 2. In preliminary experiments it was found, using whole ventral root stimulation at fusimotor strength, that spindle responses to fusimotor stimulation were not blocked by SCh, whereas extrafusal junctions blocked rapidly. In the presence of SCh, fusimotor responses of spindle secondary endings were, on average, slightly larger than their control values before SCh was given, whereas fusimotor responses of primary endings were slightly smaller. 3. A study of the responses of spindle primary endings to stimulation of single dynamic (gamma D) and static (gamma S) axons in the presence of SCh revealed a fundamental difference in behavior. None of the responses to stimulation of gamma D axons (9 gamma D axons with 8 primary endings) showed significant summation with the responses to SCh. By contrast, the 20 gamma S axons studied showed varying degrees of summation with the responses to SCh. The responses of secondary endings to gamma S stimulation in the presence of SCh resembled those of primary endings and gamma S stimulation. 4. To explain these differences it is proposed that the primary ending has two separate sites of impulse initiation, one close to terminals on the bag1 intrafusal fiber (innervated by gamma D axons) and a second close to terminals on the bag2 and chain fibers (innervated by gamma S axons). It is proposed that the maintained increase in spindle firing observed during SCh infusion is the result of a bag2 contracture. The response to gamma S stimulation, contracting bag2 and chain fibers, adds to the SCh response. The degree of summation varies depending on whether the gamma S activates bag2 fibers, chain fibers, or both. The bag1 contracture, together with the effects of gamma D stimulation, acts through a separate pacemaker and therefore does not sum with the steady increase in spindle firing in the presence of SCh. There may be pacemaker switching between the bag1 generator and the bag2 and chain generator. 5. If the model is representative of most spindles containing the three kinds of intrafusal fibers, and the contractions of bag2 and chain fibers generate activity through a common impulse generator, then this bears on the question of the functional independence of the bag2 and chain fiber systems.

Animals↗

PubMed1998

Representation of wrist joint kinematics by the ensemble of muscle spindles from synergistic muscles.

Proprioceptive information about movement is transmitted to the central nervous system by a variety of receptor types, which are widely distributed among the muscles, joints, and skin. Muscle spindles are known to be an important and reliable source of information for the perception of movement kinematics. Previous studies that focused on the characteristics of single muscle spindle firing patterns have left the impression that each receptor fires in relation to a number of kinematic variables, leaving the following question unanswered: what role is played by the ensemble of muscle spindles within the same muscle or within synergistic muscles? The study described in this paper addressed whether the perception of joint position and velocity is based on the net input of muscle spindles residing in all synergistic muscles crossing a joint. Normal human adults performed a motor coordination task that required perception of joint velocity and dynamic position at the wrist. The task was to open the left hand briskly as the right wrist was passively rotated in the flexion direction through a prescribed target angle. In randomly occurring trials, the tendons to three muscles [extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), and extensor digitorum (ED)] were vibrated either individually or in different combinations during the performance of the motor task. Tendon vibration is known to distort muscle spindle firing patterns, and consequently, kinesthesia. By comparing performance errors with and without tendon vibration, the relative influences of muscle spindles residing in ECR, ECU, and ED were quantified. Vibration of the individual ECR, ECU, or ED tendons produced systematic undershoot errors in performance, consistent with the misperception of wrist velocity and dynamic position. Performance errors were larger when combinations of, rather than individual, muscle tendons were vibrated. The error resulting from simultaneous vibration of ECR and ECU was roughly equal to the sum of the errors produced by vibration of the individual tendons. These effects of vibrating synergistic tendons at the wrist suggest that kinesthesia is derived from the integrated input of muscle spindles from all synergistic muscles.

Adult↗

PubMed2006

Induction of apoptosis by monastrol, an inhibitor of the mitotic kinesin Eg5, is independent of the spindle checkpoint.

Spindle poisons such as paclitaxel are widely used as cancer therapeutics. By interfering with microtubule dynamics, paclitaxel induces mitotic arrest and apoptosis. Targeting the kinesin Eg5, which is required for the formation of a bipolar spindle, is a promising therapeutic alternative to drugs that interfere with microtubule dynamics. Recent data suggest that the spindle checkpoint can determine the response of tumor cells to microtubule poisons. The relationship between checkpoint function and Eg5 inhibition, however, has not yet been fully investigated. Here, we used time-lapse video microscopy and biochemical analysis to study the effect of spindle checkpoint abrogation on the response of HeLa cells to monastrol, a selective Eg5 inhibitor. In HeLa cells, monastrol activated the spindle checkpoint, leading to mitotic arrest and apoptosis. Small interfering RNA-mediated depletion of the spindle checkpoint proteins BubR1 or Mad2 significantly shortened drug-induced arrest, causing premature mitotic exit without cell division. Time-lapse microscopy as well as analysis of caspase activation shows that these checkpoint-deficient cells initiate apoptosis after mitotic exit in response to monastrol. Checkpoint-deficient cells treated with paclitaxel, on the other hand, yielded a higher frequency of cells with >4N DNA content and a decreased incidence of apoptotic events, particularly in Mad2-depleted cells. These results indicate that the immediate fate of postmitotic cells is influenced by both the nature of the checkpoint defect and the type of drug used. Furthermore, these results show that inactivation of the kinesin Eg5 can induce apoptosis in tumor cells in the absence of critical spindle checkpoint components.

Calcium-Binding Proteins↗

PubMed2000

Muscle spindle reinnervation following phenol block.

Infusion of phenol into peripheral nerves is used clinically to manage spasticity. It produces relief of symptoms by chemical denervation. We simulated the clinical procedure by bathing the lateral plantar nerve of rats in 7% phenol solution for 20 min. We studied the innervation of muscle spindles in the plantar lumbrical muscles of untreated rats and in rats 4 and 6 weeks after a single phenol block. Spindles were identified by the immunoreactivity of nuclear bag(1) fibers to slow tonic myosin (antibody ALD 19). The integrity of the sensory and motor reinnervation of spindles was evaluated using a monoclonal antibody specific for a high molecular weight neurofilament protein. Four weeks after phenol block, muscle spindles were difficult to find, as their immunoreactivity to antibody ALD 19 was reduced. In those spindles studied, most (>80%) were completely denervated. The remainder of which were innervated by afferents only. None received efferent (gamma) innervation. After 6 weeks, spindles were readily identified and nearly all (>90%) received recognizable afferent innervation. A much smaller number (38%) received gamma innervation. Phenol block thus results in a complete denervation of muscle spindles, followed by a fairly rapid sensory reinnervation. Reinnervation by gamma motor neurons is either incomplete or significantly delayed.

Animals↗

PubMed2001

Muscle spindles in extraocular muscles of human infants.

The capacity of muscle spindles in adult human extraocular muscles (EOM) to provide effective proprioception was questioned on the grounds of their peculiar morphology. Their appearance could be attributable to ageing and to test this possibility examples of infant muscle spindles have been examined. Forty encapsulated structures from five extraocular muscles removed post mortem from 4 infant patients aged 6 days, 5, 23 and 30 months were examined by means of light microscopy using serial transverse sections. Seven of them were identified as false spindles. The remaining 33 structures, identified as spindles, contained a total of 175 intrafusal fibres varying from 2 to 12 (mean: 6) in each. 130 of these fibres (74.3%) were of nuclear chain type. Unequivocal evidence of bag fibres was not found. Spindles lacked or had a limited equatorial expansion, and the inner capsule was incomplete and irregularly shaped. 45 (25.7%) of the intrafusal fibres had extrafusal features with large diameters, peripherally placed nuclei, no equatorial modification and without associated sensory nerve terminals. Serial sections revealed that a majority of the nuclear chain fibres were interrupted, fragmented or terminated abruptly, and most spindles contained at least one incomplete fibre. These observations show that the atypical features observed in adult human EOM spindles are also present in infants and are therefore not attributable to ageing.

Child, Preschool↗

PubMed2005

Role of occlusal vertical dimension in spindle function.

Several studies have suggested the jaw-muscle spindle as the receptor responsible for regulating and maintaining the occlusal vertical dimension (OVD). However, to challenge this assumption, we hypothesized that long-term changes in OVD could affect the sensory inputs from jaw-muscle spindles. In this study, we investigated changes in masseter muscle spindle function under an increased OVD (iOVD) condition. Responses of primary and secondary endings of masseter muscle spindles to cyclic sinusoidal stretches were investigated. Twenty barbiturate-anesthetized female Wistar rats were divided into control and iOVD groups. Rats in the iOVD group received a 2.0-mm composite resin build-up to the maxillary molars. After iOVD, masseter muscle spindle sensitivity gradually decreased. Primary and secondary spindle endings were affected differently. We conclude that iOVD caused reduction in masseter muscle spindle sensitivity. This result suggests that peripheral sensory plasticity may occur following changes in OVD. Such changes may provide a basis for physiological adaptation to clinical occlusal adjustments.

Acrylic Resins↗

PubMed2006

Kinesin-5 motors are required for organization of spindle microtubules in Silvetia compressa zygotes.

BACKGROUND: Monastrol, a chemical inhibitor specific to the Kinesin-5 family of motor proteins, was used to examine the functional roles of Kinesin-5 proteins during the first, asymmetric cell division cycle in the brown alga Silvetia compressa. RESULTS: Monastrol treatment had no effect on developing zygotes prior to entry into mitosis. After mitosis entry, monastrol treatment led to formation of monasters and cell cycle arrest in a dose dependent fashion. These findings indicate that Kinesin-5 motors maintain spindle bipolarity, and are consistent with reports in animal cells. At low drug concentrations that permitted cell division, spindle position was highly displaced from normal, resulting in abnormal division planes. Strikingly, application of monastrol also led to formation of numerous cytasters throughout the cytoplasm and multipolar spindles, uncovering a novel effect of monastrol treatment not observed in animal cells. CONCLUSION: We postulate that monastrol treatment causes spindle poles to break apart forming cytasters, some of which capture chromosomes and become supernumerary spindle poles. Thus, in addition to maintaining spindle bipolarity, Kinesin-5 members in S. compressa likely organize microtubules at spindle poles. To our knowledge, this is the first functional characterization of the Kinesin-5 family in stramenopiles.

Cell Polarity↗

PubMed2006

A default mechanism of spindle orientation based on cell shape is sufficient to generate cell fate diversity in polarised Xenopus blastomeres.

The process of oriented divisions of polarised cells is a recurrent mechanism of cell fate diversification in development. It is commonly assumed that a specialised mechanism of spindle alignment into the axis of polarity is a prerequisite for such systems to generate cell fate diversity. Oriented divisions also take place in the frog blastula, where orientation of the spindle into the apicobasal axis of polarised blastomeres generates inner and outer cells with different fates. Here, we show that, in this system, the spindle orients according to the shape of the cells, a mechanism often thought to be a default. We show that in the embryo, fatedifferentiative, perpendicular divisions correlate with a perpendicular long axis and a small apical surface, but the long axis rather then the size of the apical domain defines the division orientation. Mitotic spindles in rounded, yet polarised, isolated Xenopus blastula cells orient randomly, but align into an experimentally introduced long axis when cells are deformed early in the cell cycle. Unlike other systems of oriented divisions, the spindle aligns at prophase, rotation behaviour is rare and restricted to small angle adjustments. Disruption of astral microtubules leads to misalignment of the spindle. These results show that a mechanism of spindle orientation that depends on cell shape rather than cortical polarity can nevertheless generate cell fate diversity from a population of polarised cells.

Animals↗

PubMed1990

Treatment with beta bungarotoxin blocks muscle spindle formation in fetal rats.

Sensory and motor fibers of peripheral nerves were irreversibly destroyed in fetal rats by administering beta bungarotoxin (BTX) on embryonic day 16 or 17, after assembly of primary myotubes, but before the formation of muscle spindles. Soleus muscles of toxin-treated fetuses and their untreated littermates were removed just prior to birth and were examined by light microscopy of serial transverse sections for the presence of spindles and immunocytochemical expression of several isoforms of myosin heavy chains (MHC). Untreated muscles exhibited numerous spindles that were innervated by branches of intramuscular nerves and contained muscle fibers expressing a slow-tonic MHC isoform characteristic of the intrafusal but not extrafusal fibers. Toxin-treated muscles were devoid of intramuscular nerve bundles and perineurial structures. Encapsulations of muscle fibers resembling spindles were absent and no myotubes expressed the slow-tonic MHC isoform associated with intrafusal fibers in beta BTX-treated muscles. Thus, the assembly of muscle spindles, formation of the spindle capsule, and transformation of undifferentiated myotubes into the intrafusal fibers that contain spindle-specific myosin isoforms all depend on the presence of innervation in prenatal rat muscles.

Animals↗

PubMed2004

Elongation of centriolar microtubule triplets contributes to the formation of the mitotic spindle in gamma-tubulin-depleted cells.

The assembly of the mitotic spindle after depletion of the major gamma-tubulin isotype by RNA-mediated interference was assessed in the Drosophila S2 cell line. Depletion of gamma-tubulin had no significant effect on the cytoskeletal microtubules during interphase. However, it promoted an increase in the mitotic index, resulting mainly in monopolar and, to a lesser extent, asymmetrical bipolar prometaphases lacking astral microtubules. This mitotic accumulation coincided with the activation of the mitotic checkpoint. Immunostaining with an anti-Asp antibody revealed that the spindle poles, which were always devoid of gamma-tubulin, were unfocused and organized into sub-spindles. Despite the marked depletion of gamma-tubulin, the pericentriolar proteins CP190 and centrosomin were recruited to the spindle pole(s), where they formed three or four dots, suggesting the presence of several centrioles. Electron microscopic reconstructions demonstrated that most of the monopolar spindles exhibited three or four centrioles, indicating centriole duplication with a failure in the separation process. Most of the centrioles were shortened, suggesting a role for gamma-tubulin in centriole morphogenesis. Moreover, in contrast to metaphases observed in control cells, in which the spindle microtubules radiated from the pericentriolar material, in gamma-tubulin-depleted cells, microtubule assembly still occurred at the poles but involved the elongation of centriolar microtubule triplets. Our results demonstrate that, after depletion of gamma-tubulin, the pericentriolar material is unable to promote efficient microtubule nucleation. They point to an alternative mechanism of centrosomal microtubule assembly that contributes to the formation of abnormal, albeit partially functional, mitotic spindles.

Animals↗

PubMed1992

Mutants of the microtubule motor protein, nonclaret disjunctional, affect spindle structure and chromosome movement in meiosis and mitosis.

The Drosophila microtubule motor protein, nonclaret disjunctional (ncd), is required for proper chromosome distribution in meiosis and mitosis. We have examined the meiotic and mitotic divisions in wild-type Drosophila oocytes and early embryos, and the effects of three ncd mutants (cand, ncd and ncdD) on spindle structure and chromosome movement. The ncd mutants cause abnormalities in spindle structure early in meiosis I, and abnormal chromosome configurations throughout meiosis I and II. Defective divisions continue in early embryos of the motor null mutant, cand, with abnormal early mitotic spindles. The effects of mutants on spindle structure suggest that ncd is required for proper meiotic spindle assembly, and may play a role in forming or maintaining spindle poles in meiosis. The disruption of normal meiotic and mitotic chromosome distribution by ncd mutants can be attributed to its role as a spindle motor, although a role for ncd as a chromosome-associated motor protein is not excluded. The ncd motor protein functions not only in meiosis, but also performs an active role in the early mitotic divisions of the embryo.

Animals↗

PubMed1993

Ultraviolet microbeam irradiation of chromosomal spindle fibres in Haemanthus katherinae endosperm. I. Behaviour of the irradiated region.

We used an ultraviolet microbeam to irradiate chromosomal spindle fibres in metaphase Haemanthus endosperm cells. An area of reduced birefringence (ARB) was formed at the position of the focussed ultraviolet light with all wavelengths we used (260, 270, 280, and 290 nm). The chromosomal spindle fibre regions (kinetochore microtubules) poleward from the ARBs were unstable: they shortened (from the ARB to the pole) either too fast for us to measure or at rates of about 40 microns per minute. The chromosomal spindle fibre regions (kinetochore microtubules) kinetochore-ward from the ARBs were stable: they did not change length for about 80 seconds, and then they increased in length at rates of about 0.7 microns per minute. The lengthening chromosomal spindle fibres sometimes grew in a direction different from that of the original chromosomal spindle fibre. The chromosome associated with the irradiated spindle fibre sometimes moved off the equator a few micrometers, towards the non-irradiated half-spindle. We discuss our results in relation to other results in the literature and conclude that kinetochores and poles influence the behaviour of kinetochore microtubules.

Animal Population Groups↗

PubMed1993

Kinesin-like molecules involved in spindle formation.

To study the possible involvement of kinesin-like molecules in mitosis a polyclonal antibody against the head domain of Drosophila kinesin heavy chain (HD antibody) was microinjected into PtK1 cells at the prophase-prometaphase transition. Progress of the cell through mitosis was recorded for subsequent detailed analysis. Cells injected with pre-immune IgG progressed through mitosis at rates similar to those for noninjected cells. After HD antibody injections, chromosomes failed to congress to an equatorial plane and cells failed to form a bipolar spindle. Rather, the spindle poles came together, resulting in a monopolar-like configuration with chromosomes arranged about the poles in a rosette. Sometimes the monopolar array moved to the margin of the cell in a way similar to anaphase B movement in normal cells. Antibody-injected cells progressed into the next cell cycle as evidenced by chromosome decondensation and nuclear envelope reformation. Anti-tubulin immunofluorescence confirmed the presence of a radial monopolar array of microtubules in injected cells. HD antibody stained in a punctate pattern in interphase and the spindle region in mitotic PtK1 cells. The antibody also reacted with spindle fibers of isolated mitotic CHO spindles and with kinetochores of isolated CHO chromosomes. Immunoblotting indicated that the major component recognized by the antibody is the 120 kDa kinesin heavy chain. At higher protein loads the antibody recognized also a 34 kDa polypeptide in PtK1 cell extracts, a 135 kDa polypeptide in a preparation of CHO spindles and a 300 kDa polypeptide in a preparation of CHO mitotic chromosomes. We conclude that a kinesin-like molecule is important for the formation and/or maintenance of the structure of mitotic spindle.

Animals↗