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PubMed1996

Spindle oscillation in cats: the role of corticothalamic feedback in a thalamically generated rhythm.

1. Spindles represent an oscillatory activity (7-14 Hz) of the electroencephalogram (EEG) originating in the thalamus and appearing during early stages of sleep. We investigated: (i) the phase relations between thalamic and cortical neurons during this rhythm; (ii) the patterns of spindles under different anaesthetics and their modifications at various levels of the membrane potential (Vm); and (iii) the potentiating role of the corticothalamic feedback in the genesis of spindles. Intra- and extracellular recordings were performed in cats from reticular and dorsal thalamic nuclei, as well as from various cortical areas. 2. In thalamic reticular neurons, spindles were sequences of waves at 7-14 Hz, riding on a prolonged depolarizing plateau and occurring in phase with depth-negative cortical EEG waves. In thalamocortical cells, spindles consisted of inhibitory postsynaptic potentials (IPSPs) in phase with depth-positive cortical EEG waves and occasionally leading to rebound spike bursts. In cortical cells, spindle waves were rhythmic (7-14 Hz) excitatory postsynaptic potentials (EPSPs) that sometimes gave rise to action potentials. Spindles occurred in phase among thalamic reticular, thalamocortical and neocortical neurons. 3. In thalamic reticular neurons, spindle waves and their depolarizing plateaux increased in amplitude with slight cellular hyperpolarization, but at a Vm more negative than -80 or -85 mV they decreased in amplitude. No frequency alterations were observed with these Vm changes. 4. The waxing-and-waning pattern of spontaneous spindles under barbiturate anaesthesia was distinct from the waning pattern under ketamine-xylazine anaesthesia. Under all anaesthetics, spindles had a waning pattern when elicited by cortical stimuli. The amplitude of cortical-evoked spindle waves diminished with the decrease in stimulation intensity. 5. Under urethane or ketamine-xylazine anaesthesia, spindle sequences were grouped by a cortically generated slow oscillation (< 1 Hz) and were preceded by a depth-positive EEG wave that corresponded to a prolonged hyperpolarization in all three investigated (cortical, thalamic reticular, and thalamocortical) cellular types. 6. We propose that the waxing pattern of spindle oscillation is due to a progressive entrainment of units into the oscillation until a maximum number is reached, depending on the background activity in the network. The phase relations between cortical, thalamic reticular and thalamocortical neurons are ascribed to distributed excitatory signals from thalamocortical neurons to both cortical and reticular neurons at each cycle of the oscillation. In turn, cortical neurons provide a powerful drive to potentiate the genesis of thalamic spindles.

Animals↗

PubMed1997

Cytochalasin J treatment significantly alters mitotic spindle microtubule organization and kinetochore structure in PtK1 cells.

It has previously been demonstrated that treatment of mitotic PtK1 cells with 10-20 microg/ml cytochalasin J (CJ) blocks or slows chromosome motion and has a significant effect on spindle architecture [Snyder and Cohen, 1995: Cell Motil. Cytoskeleton 32:245-257]. Spindle microtubules (MTs) were shown to reorganize within the spindle domain, with kinetochore MTs (kMTs) reduced in number and non-kinetochore MTs (nkMTs) shown to splay outside the original spindle domain. In some cases, bundles of MTs were shown to be refocused away from the original spindle poles, creating the appearance of a multi-polar spindle. In this paper we use serial section electron microscopy, coupled with computer-assisted reconstruction techniques, to determine the rearrangement of spindle MTs and chromosome position following brief treatments of mitotic cells with 10-20 microg/ml CJ at various stages of mitosis. CJ treatment of prometaphase cells reduces the number of kMTs and the size and organization of the kinetochore lamina. Instead of kinetochore bundles of MTs aligned parallel to one another and running from kinetochore to pole, this class of MTs is highly fragmented. Non-kinetochore MTs are also highly fragmented, usually less than 2 microm long, and remain relatively straight over short distances, with some MTs arranged at an oblique angle to the longitudinal spindle axis. In approximately 30% of cells treated with CJ, the failure of a small number of chromosomes to attach to spindle fibers can be documented. These chromosomes show a significant change in the organization of the kinetochore laminae. Light microscopic analysis of cells treated with CJ reveals loss of chromosome congression, with chromsomes usually located at the periphery of the spindle and some completely detached from the spindle. Cells treated with 10 microg/ml CJ for 10 min and released into tissue culture medium show a resumption of chromosome motion within a few minutes, both during congression and anaphase. Where kMTs are inserted into kinetochores, chromosome motion is seen; where chromosomes fail to attach to the spindle, no chromosome motion is observed. Cells treated in metaphase show a delayed entry into anaphase and a reduced rate of anaphase A, with the arms of some chromosomes remaining in the interzone region. Our results suggest that CJ-sensitive molecules play a role in the organization of spindle MTs, as well as their functional association to kinetochores.

Animals↗

PubMed1999

Influence of centriole behavior on the first spindle formation in zygotes of the brown alga Fucus distichus (Fucales, Phaeophyceae).

The influence of centrioles, derived from the sperm flagellar basal bodies, and the centrosomal material (MTOCs) on spindle formation in the brown alga Fucus distichus (oogamous) was studied by immunofluorescence microscopy using anti-centrin and anti-beta-tubulin antibodies. In contrast to a bipolar spindle, which is formed after normal fertilization, a multipolar spindle was formed in polyspermic zygote. The number of mitotic poles in polyspermic zygotes was double the number of sperm involved in fertilization. As an anti-centrin staining spot (centrioles) was located at these poles, the multipolar spindles in polyspermic zygotes were produced by the supplementary centrioles. When anucleate egg fragments were fertilized, chromosome condensation and mitosis did not occur in the sperm nucleus. Two anti-centrin staining spots could be detected, microtubules (MTs) radiated from nearby, but the mitotic spindle was never produced. When a single sperm fertilized multinucleate eggs (polygyny), abnormal spindles were also observed. In addition to two mitotic poles containing anti-centrin staining spots, extra mitotic poles without anti-centrin staining spots were also formed, and as a result multipolar spindles were formed. When karyogamy was blocked with colchicine, it became clear that the egg nucleus proceeded independently into mitosis accompanying chromosome condensation. A monoastral spindle could be frequently observed, and in rare cases a barrel-shaped spindle was formed. However, when a sperm nucleus was located near an egg nucleus, the two anti-centrin staining spots shifted to the egg nucleus from the sperm nucleus. In this case, a normal spindle was formed, the egg chromosomes arranged at the equator, and the associated MTs elongated from one pole of the egg spindle toward the sperm chromosomes which were scattered. From these results, it became clear that paternal centrioles derived from the sperm have a crucial role in spindle formation in the brown algae, such as they do during animal fertilization. However, paternal centrioles were not adequate for the functional centrosome during spindle formation. We speculated that centrosomal materials from the egg cytoplasm aggregate around the sperm centrioles and are needed for centrosomal activation.

Antibodies↗

PubMed1982

One-bag-fiber muscle spindles in tenuissimus muscles of the cat.

Over 150 complete and 139 incomplete single muscle spindles were examined in serial transverse sections of cat tenuissimus muscles in search for spindles lacking one of the two types of nuclear bag intrafusal fiber. Several histochemical reactions were used to type the intrafusal muscle fibers and assess the spindle motor and sensory innervation. One complete spindle lacked a bag1 fiber, and another spindle lacked a bag2 fiber. Several incomplete spindles also lacked bag1 fibers. In addition, ten double tandem spindles contained one capsular unit each that lacked the bag1 fiber, and one triple tandem spindle had two such capsules. All one-bag-fiber spindles had primary sensory innervation, but none had secondary sensory innervation. Their motor innervation was similar to that of the usual two-bag-fiber spindles in the number and disposition of intrafusal motor endings. It is unclear whether the one-bag fiber spindles, either single or tandem-linked, are products of an aberrant spindle development or represent a true anatomical and functional subcategory of the cat muscle spindle.

Adenosine Triphosphatases↗

PubMed2005

Noninvasive imaging of spindle dynamics during mammalian oocyte activation.

OBJECTIVE: To develop a method to evaluate spindle dynamics in living oocytes and in karyoplasts during the initial stages of activation and after pharmacological disruption of cytoskeleton. DESIGN: Morphological study using a novel microscope. SETTING: Translational research laboratory at marine biological laboratory. ANIMAL(S): Six-week-old CD-1 or B6C3F1 mice superovulated with pregnant mare's serum gonadotropin and human chorionic gonadotropin (hCG). INTERVENTION(S): Spindles of living oocytes and karyoplasts were imaged at 5-10 minute intervals using the Pol-Scope during the initial stages of oocyte activation and after pharmacological disruption of cytoskeleton. MAIN OUTCOME MEASURE(S): Assessment of spindle dynamics using Pol-Scope imaging. RESULT(S): During oocyte activation, spindle mid-region birefringence increased, followed by spindle rotation and second polar body extrusion in both intact oocytes and karyoplasts. Activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate failed to induce spindle activation in 60% of living oocytes and caused spindle disruption in some oocytes. Inhibition of PKC by a myristoylated PKC pseudosubstrate inhibited metaphase II release in most oocytes evaluated (86.7%). Cytochalasin D inhibited only spindle rotation and separation. Nocodazole disrupted spindles in less than 5 minutes after administration. CONCLUSION(S): Pol-Scope imaging allows investigation at near real time of spindle dynamics during activation of living oocytes. Spindles also showed evidence of activation even in karyoplasts. The procedure may be useful for detecting functional spindle aberrations in living oocytes. Further studies are needed to determine whether spindle dynamics predict clinical outcome.

Animals↗

PubMed2001

The spindle observation and its relationship with fertilization after intracytoplasmic sperm injection in living human oocytes.

OBJECTIVE: To image spindles in living human oocytes and to examine the relation between spindles and fertilization after ICSI. DESIGN: The LC polscope was used to examine spindles in an observational study of living oocytes. SETTING: Academic IVF clinic. PATIENT(S): Women being treated for infertility. INTERVENTION(S): Oocytes retrieved from patients for infertility treatment were examined before ICSI. Aged, unfertilized oocytes after IVF or ICSI were examined with polscope and confocal microscopes to compare the two methods. MAIN OUTCOME MEASURE(S): Spindle structure in living oocytes and fertilization after ICSI. RESULT(S): Spindles could be imaged in 61.4% of oocytes. More oocytes with spindles than oocytes without spindles fertilized normally after ICSI (61.8% vs. 44.2%). Spindles in most aged oocytes were partially or completely disassembled, and only a few microtubules around the chromosomes or dispersed microtubules in the cytoplasm were observed. Confocal images of immunostained spindles were almost identical to polscope images of spindle birefringence. CONCLUSION(S): Spindles in living human oocytes can be imaged by using the polscope. A birefringent spindle in human oocytes may clinically predict the quality and age of oocytes. This method also can be used to monitor spindle position during ICSI.

Cellular Senescence↗

PubMed2004

Spindle dynamics in living mouse oocytes during meiotic maturation, ageing, cooling and overheating: a study by polarized light microscopy.

A liquid crystal polarized light microscope (LC PolScope) was used to examine spindle dynamics in living mouse oocytes. Immature oocytes were cultured for 0-48 h and spindles were imaged with the PolScope at various time points of culture. Oocytes at metaphase I (M-I) and metaphase II (M-II) were also exposed to shifts of temperature from 25 to 41 degrees C to examine the effects of fluctuations of temperature on spindle dynamics. After examination with the PolScope, some oocytes were fixed and examined by immunocytochemical staining and confocal microscopy. After culturing for 6 h, 76% and 2% of the oocytes reached M-I and M-II stages and all oocytes had birefringent spindles. When the oocytes were cultured for 14-16 h, 88% and 6% of oocytes were at M-II and M-I stages respectively and all oocytes had birefringent spindles. However, when the oocytes were cultured for 22-48 h, the proportions of oocytes with birefringent spindles decreased as culture time was increased. Exposure of oocytes to 25 degrees C induced spindle disassembly within 10-20 min in both M-I and M-II oocytes. Most (93-100%) oocytes reassembled spindles after warming at 37 degrees C. Furthermore, exposure of oocytes at M-I stage but not at M-II stage, to 30 degrees C also induced significant microtubule disassembly. However, exposure of oocytes to 38-41 degrees C did not obviously change the quantity of microtubules in the spindles, which was measured by retardance. This study indicates that the PolScope can be used to examine spindle dynamics in living oocytes, and it has the advantage over the routine fluorescence microscope in that images can be obtained in the same individual oocyte and the quantity of microtubules can be measured by retardance in living oocytes. These results also indicate that the M-II spindle in mouse oocytes is sensitive to oocyte ageing and cooling, but not heating, and M-I spindle is more sensitive to temperature decline than M-II spindle.

Animals↗

PubMed1993

Inhibition of anaphase spindle elongation in vitro by a peptide antibody that recognizes kinesin motor domain.

Isolated central spindles or spindles in detergent-permeabilized cells from the diatom Cylindrotheca fusiformis can undergo ATP-dependent reactivation of spindle elongation in vitro. We have used a peptide antibody raised against a 10-amino acid portion common to the kinesin superfamily motor domain to look for kinesin-like motor activity during anaphase B of mitosis. The peptide antibody localizes to central spindles. Upon ATP reactivation of spindle elongation, antigens recognized by the antibody are associated exclusively with the central spindle midzone where antiparallel microtubules of each half-spindle overlap. The antibody recognizes several polypeptides by immunoblot using isolated spindle extracts. One of these polypeptides behaves like kinesin with respect to nucleotide-specific binding to and release from taxol-stabilized microtubules. Preincubation of the spindle model with the peptide antibody inhibits subsequent ATP reactivation of spindle elongation. Coincubation of the peptide antibody with peptide antigen rescues spindle function. These results support a role for kinesin-related protein(s) in spindle elongation (anaphase B) of mitosis and suggest that one or several polypeptides that we have identified in spindle extracts may fulfill this function.

Adenosine Triphosphate↗

PubMed1992

Role of astral microtubules and actin in spindle orientation and migration in the budding yeast, Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, before the onset of anaphase, the spindle apparatus is always positioned with one spindle pole at, or through, the neck between the mother cell and the growing bud. This spindle orientation enables proper chromosome segregation to occur during anaphase, allowing one replicated genome to be segregated into the bud and the other to remain in the mother cell. In this study, we synchronized a population of cells before the onset of anaphase such that > 90% of the cells in the population had spindles with the correct orientation, and then disrupted specific cytoskeletal elements using temperature-sensitive mutations. Disruption of either the astral microtubules or actin function resulted in improper spindle orientation in approximately 40-50% of the cells. When cells with disrupted astral microtubules or actin function entered into anaphase, there was a 100-200-fold increase in the frequency of binucleated cell bodies. Thus, the maintenance of proper spindle orientation by these cytoskeletal elements was essential for proper chromosome segregation. These data are consistent with the model that proper spindle orientation is maintained by directly or indirectly tethering the astral microtubules to the actin cytoskeleton. After nuclear migration, but before anaphase, bulk chromosome movement occurs within the nucleus apparently because the chromosomes are attached to a mobile spindle. The frequency and magnitude of bulk chromosome movement is greatly diminished by disruption of the astral microtubules but not by disruption of the nonkinetochore spindle microtubules. These results suggest that astral microtubules are not only important for spindle orientation before anaphase, but they also mediate force on the spindle, generating spindle displacement and in turn chromosome movement. Potential roles for this force in spindle assembly and orientation are discussed.

Actins↗

PubMed1993

Three-dimensional reconstruction and analysis of mitotic spindles from the yeast, Schizosaccharomyces pombe.

Mitotic spindles of Schizosaccharomyces pombe have been studied by EM, using serial cross sections to reconstruct 12 spindles from cells that were ultrarapidly frozen and fixed by freeze substitution. The resulting distributions of microtubules (MTs) have been analyzed by computer. Short spindles contain two kinds of MTs: continuous ones that run from pole to pole and MTs that originate at one pole and end in the body of the spindle. Among the latter there are three pairs of MT bundles that end on fibrous, darkly staining structures that we interpret as kinetochores. The number of MTs ending at each putative kinetochore ranges from two to four; all kinetochore-associated MTs disappear as the spindle elongates from 3-6 microns. At this and greater spindle lengths, there are no continuous MTs, only polar MTs that interdigitate at the spindle midzone, but the spindle continues to elongate. An analysis of the density of neighboring MTs at the midzone of long spindles shows that their most common spacing is approximately 40 nm, center to center, and that there is a preferred angular separation of 90 degrees. Only hints of such square-packing are found at the midzone of short spindles, and near the poles there is no apparent order at any mitotic stage. Our data suggest that the kinetochore MTs (KMTs) do not interact directly with nonkinetochore MTs, but that interdigitating MTs from the two spindle poles do interact to form a mechanically stable bundle that connects the poles. As the spindle elongates, the number of MTs decreases while the mean length of the MTs that remain increases. We conclude that the chromosomes of S. pombe become attached to the spindle by kinetochore MTs, that these MTs disappear as the chromosomes segregate, that increased separation of daughter nuclei is accompanied by a sliding apart of anti-parallel MTs, and that the mitotic processes of S. pombe are much like those in other eukaryotic cells.

Chromosomes, Fungal↗

PubMed1996

Role of gamma-tubulin in mitosis-specific microtubule nucleation from the Schizosaccharomyces pombe spindle pole body.

The ability of the Schizosacchromyces pombe spindle pole body to nucleate microtubules is activated at the onset of mitosis for forming a mitotic spindle, but it is inactivated during interphase. We have previously developed an in vitro assay for studying the molecular mechanism of spindle pole body activation using permeabilized interphase S. pombe cells and Xenopus mitotic extracts. We have shown that the interphase spindle pole body is activated indirectly by p34cdc2 protein kinase in Xenopus mitotic extracts. In this study we examined the role of gamma-tubulin, a component of both interphase and mitotic spindle pole body, in formation of the microtubule nucleating complex at the mitotic spindle pole body. A polyclonal antibody specific to S. pombe gamma-tubulin inhibited both activation of the interphase spindle pole body and microtubule nucleation from the mitotic spindle pole body. Addition of bacterially expressed S. pombe gamma-tubulin or its amino-terminal fragments to Xenopus mitotic extracts inhibited spindle pole body activation. Affinity chromatography of partially fractionated Xenopus mitotic extracts with the amino-terminal fragment of S. pombe gamma-tubulin showed that fractions bound to the fragment supported the activation. The fractions did not contain Xenopus gamma-tubulin, showing that activation of the spindle pole body is not due to recruitment of Xenopus gamma-tubulin to the spindle pole body. The spindle pole body activation occurred in extracts depleted of p34cdc2 protein kinase or MAP kinase. The activity of the fractions bound to the fragment was inhibited by a protein kinase inhibitor, staurosporine. These results suggest that S. pombe gamma-tubulin is a component of the microtubule nucleating complex, and that the function of proteins that interact with gamma-tubulin is required for activation of the spindle pole body. We present possible models for the activation that convert the immature microtubule nucleating complex at interphase into the mature microtubule nucleating complex at mitosis.

Amino Acid Sequence↗

PubMed1986

Comparison of spindle elongation in vivo and in vitro in Stephanopyxis turris.

The spindle in dividing cells of the diatom Stephanopyxis turris contains three distinct classes of microtubules: central spindle microtubules, which slide over each other and grow during anaphase spindle elongation; kinetochore-attached microtubules, which are located on the outer surface of the central spindle; and peripheral microtubules, which fan out from the spindle poles in astral-like arrays. The poles are multilayered structures, which remain attached to the spindle after isolation. In vitro, after addition of ATP, central spindles elongate and the two half-spindles slide completely apart with a concurrent decrease in the extent and magnitude of the zone of microtubule overlap. Spindle elongation takes place in spindles whose chromatin has been removed by enzymic digestion and the extent of elongation in vitro is increased by the addition of neurotubulin. After ATP addition the arrays of interdigitating microtubules in the zone of overlap become disordered and selectively depolymerize from the overlap zone polewards. In some reactivated spindles an unusual structure, a striated fibre, can be seen running from the pole plates part of the way towards the spindle midzone. The fibre has no precedent in mitotic ultrastructure and its function is unclear. These results demonstrate that we can duplicate the essential elements of anaphase B in vitro and that this system will be useful for further studies of the molecular basis of spindle elongation.

Anaphase↗

PubMed1985

Experimental analysis of the reproduction of spindle poles.

We have investigated the functional properties of the mechanisms that control the reproduction of spindle poles in fertilized sea-urchin eggs. By prolonging mitosis by three independent means, we show that a spindle pole can split during mitosis into two functional poles of normal appearance. However, these poles have only half the normal reproductive capacity; each daughter cell that receives a split pole, always forms a monopolar spindle at the next division. Each monopolar spindle appears to be exactly half of a spindle because two of them can come together to form a functional bipolar spindle of normal appearance. The poles of such spindles show normal reproduction in subsequent divisions. By following the development of individual cells with monopolar spindles, we show that such a cell can stay in mitosis longer than normal, and the single pole splits into two asters, which move apart to give a functional bipolar spindle. The poles of such a spindle have only half the normal reproductive capacity, because the two daughters of the cell always form monopolar spindles at the next mitosis. This novel cycle of development is often repeated. The occurrence of such phenomena does not depend upon the method used to induce monopolar spindles. These results show that each normal pole has two polar determinants. The results also demonstrate that the reproduction of spindle poles consists of three distinct events: splitting of the polar determinants, physical separation of the two determinants, and duplication of the determinants to return the pole to a duplex state. Splitting and duplication are distinct events because they can be experimentally put out of phase with each other for several cell cycles.

Animals↗

PubMed1976

The innervation of muscle spindles in the snake, Elaphe quadrivirgata.

The morphology and distribution of sensory endings in snake (Elaphe quadrivirgata) muscle spindles was studied in silver preparations. The sensory axon supplying long-capsule spindles often bifurcates before or after penetrating the capsule and runs for some distance along the intrafusal fibre. The sensory axon supplying short-capsule spindles penetrates the capsule at a sharp angle, and, without ramification, terminates abruptly on the intrafusal fibre. The sensory terminal is composed of terminal bulbs and small links. In long-capsule spindles the sensory ending is arranged longitudinally in one or two rows. The sensory ending in short-capsule spindles ramifies extensively, covering densely the intrafusal fibre. The area occupied by sensory bulbs was estimated to be slightly higher in short-capsule (15-17?) THAN IN LONG-CAPSULE SPINDLES (12-13). The functional significance of these findings is discussed. Motor innervation of muscle spindles in the snake Elaphe quadrivirgata was studied using AchE staining for light microscopy in conjection with electron microscopy. In the polar region of either type of spindle, the majority of the motor endings are of grape type. In long-capsule spindles plate endings may occur in the spindle pole as well as in the capsular region. Motor endings in the capsular region are mostly of plate type. Plate endings rarely occur in short-capsule spindles. Identified single motor endings were studied by electron microscopy. Intrafusal grape endings are characterized by a smooth post-synaptic membrane. Intrafusal plate endings in the polar region are characterized by junctional folds or gutterings; plate endings in the capsular region show less developed gutterings or indentations. The distribution of intrafusal motor endings was examined along the length of single intrafusal fibres. The long-capsule spindle often receives asymmetrical motor innervation around the capsular region, whereas motor endings in the short-capsule spindle distribute more symmetrically.

Acetylcholinesterase↗

PubMed1983

Incidence and prognostic value of spindles in post-traumatic coma.

One hundred and thirty-three EEGs were analysed from 80 comatose patients with signs of brain stem impairment due to head/brain injury. Seventy EEGs were taken in acute coma on day 1 or 2 after brain injury. Sixty-three EEGs were recorded in prolonged coma 3-12 days after brain injury. Brain stem involvement was divided by neurological signs and by CT scan into secondary lesions due to supratentorial mass displacement and primary lesions due do direct violence to the brain stem. Different EEG patterns were observed, but spindle activity was of special interest. Spindles were classified as typical (easily recognizable, well organized, 12-14 c/sec activity) or atypical (hardly recognizable, distorted form, 6-11 c/sec activity). Furthermore, asymmetries of spindles were noted. The spindles and their alterations were related to different stages of outcome. Spindles were seen in 91% of the EEGs in acute coma and in 30% in prolonged coma. In acute coma due to secondary brain stem involvement a good outcome was heralded by the occurrence of typical symmetrical spindles combined with early stages of secondary brain stem impairment at neurological examination. In cases of primary brain stem involvement typical spindles also suggested a good prognosis despite the observation of serious clinical signs (decerebrate posturing). The percentage of spindle activity decreased, and distortion and asymmetry of spindles increased with the worsening of outcome. Severe intracerebral lesions (confirmed by clinical and CT scan examinations) led to distortion, asymmetry and finally disappearance of spindles. In prolonged coma spindle activity was markedly reduced regardless of the final outcome. When spindles were present atypical and asymmetric forms significantly increased in patients with bad outcome. There were no significant differences in spindle activity in the different outcome categories, if primary and secondary brain stem lesions were compared.

Adolescent↗

PubMed2000

The Xenopus laevis aurora/Ip11p-related kinase pEg2 participates in the stability of the bipolar mitotic spindle.

The Xenopus laevis aurora/Ip11p-related kinase pEg2 is required for centrosome separation, which is a prerequisite for bipolar mitotic spindle formation. Here, we report that the inhibition of pEg2 by addition of either an inactive kinase or a monoclonal antibody destabilizes bipolar spindles previously assembled in Xenopus egg extracts. The bipolar spindles collapse to form structures such as microtubule asters with chromosome rosettes, monopolar spindles, and multipolar spindles. In collapsed spindles, chromosomes remain attached to the microtubules plus ends. The destabilization of the bipolar spindle is reminiscent of the destabilization observed after inhibition of cross-linking activities which maintain parallel and anti-parallel microtubules linked together. We have previously reported that pEg2 phosphorylates the kinesin-related protein XlEg5 which is involved in centrosome separation but which was also reported to be involved in spindle stability. The collapse of the bipolar spindle observed after inhibition of pEg2 suggests that the kinase might regulate the cross-linking activity of XlEg5. We do not exclude the possibility that pEg2 also regulates other microtubule-based motor proteins involved in bipolar spindle stability. To our knowledge, this is the first evidence that aurora/Ip11p-related kinase activity actually participates not only in mitotic spindle formation by regulating centrosome separation but also in mitotic spindle stabilization.

Animals↗

PubMed1981

Formation of muscle spindles in regenerated avian muscle grafts.

Pigeon muscles lacking muscle spindles were grafted into sites which normally have a muscle containing spindles. The reciprocal transplantations were also made. After two to eight months, the graft of the donor muscle without spindles had regenerated into a muscle containing muscle spindles. The reciprocal grafts, muscles containing spindles transplanted to a site lacking spindle innervation, had neither muscle spindles nor remnants of the spindles. These experiments demonstrate that 1) the innervation is required for formation of the spindle; 2) the original spindles do not survive transplantation; and 3) parts of the original spindle are not required for spindle regeneration.

Animals↗

PubMed1999

Vibration sensitivity of cat muscle spindles at short muscle lengths.

Experiments are described in which the vibration sensitivity was tested for primary and secondary endings of soleus muscle spindles of the anaesthetised cat. The vibratory stimulus was applied longitudinally to the muscle tendon and, after locating the site of the spindle in the muscle, applied transversely to muscle fibres directly overlying the spindle. All measurements were made with the muscle slack, at 20 mm shorter than its maximum physiological length (Lm-20 mm). Spindles were separated into two groups: spontaneous spindles, which maintained background activity at this length, and silent spindles, which did not. Two forms of muscle conditioning were used: hold-long, in which the muscle was stretched by 5 mm, contracted and then returned to the test length, and hold-test, in which a conditioning contraction was given at the test length. After hold-test, most spindles responded to longitudinal vibration; after hold-long, most did not. This difference in responsiveness was attributed to the presence or absence of slack in intrafusal and extrafusal fibres, due to the muscle's thixotropic property. When the vibration was applied transversely, at a site directly overlying the spindle, responses of silent spindles continued to show thixotropic behaviour, whereas responses of spontaneous spindles were almost independent of the form of muscle conditioning. It is proposed that the ability of spontaneous spindles to maintain background activity at short muscle lengths is due to connective tissue or elastic fibre links between the sensory ending and the spindle capsule. The vibratory stimulus, applied transversely, reaches the sensory ending via these strands which, as non-muscle tissue, do not alter their mechanical state as a result of muscle conditioning.

Animals↗