WHOAS : Browsing Visiting Investigators by Issue Date

Article

The role of sulfhydryl and disulfide groups of membrane proteins in electrical conduction and chemical transmission

(University of Puerto Rico Medical Sciences Campus, 1984-09) Zuazaga, Conchita ; Steinacker, Antoinette ; del Castillo, Jose

The chemical reactions of sulfhydryl and disulfide groups in proteins are discussed and the use of reagents specific for these groups as a tool in electrophysiology is reviewed. The drastic and specific changes seen when these group-specific reagents are used demonstrate the critical role of sulfhydryl and disulfide groups in electrical excitability, synaptic transmission and, particularly, postsynaptic receptor function. Sulfhydryl groups have been shown to be involved in the slow inactivation process of the voltage-dependent sodium channel, in the activation of voltage-dependent calcium channels and in sodium channel conductance. Sulfhydryl and disulfide groups have been shown to Intervene in the function of the acetylcholine receptor at the vertebrate neuromuscular junction and in invertebrate glutaminergic recepton. The release of neurotransmitter from the presynaptic termInals of these neuromuscular junctions Is also sensitive to sulfhydryl and disulfide group modification. Although in most instances the site of action of the reagents has not been resolved, their use has produced a clearer picture of receptor and channel structure-function relationships.

Preprint

Representation of odorants by receptor neuron input to the mouse olfactory bulb

( 2001-04-13) Wachowiak, Matt ; Cohen, Lawrence B.

To visualize odorant representations by receptor neuron input to the mouse olfactory bulb, we loaded receptor neurons with calcium-sensitive dye and imaged odorant-evoked responses from their axon terminals. Fluorescence increases reflected activation of receptor neuron populations converging onto individual glomeruli. We report several findings. First, five glomeruli were identifiable across animals based on their location and odorant responsiveness; all five showed complex response specificities. Second, maps of input were chemotopically organized at near-threshold concentrations but, at moderate concentrations, involved many widely distributed glomeruli. Third, the dynamic range of input to a glomerulus was greater than that reported for individual receptor neurons. Finally, odorant activation slopes could differ across glomeruli, and for different odorants activating the same glomerulus. These results imply a high degree of complexity in odorant representations at the level of olfactory bulb input.

Preprint

Odorant specificity of three oscillations and the DC signal in the turtle olfactory bulb

( 2002-11-16) Lam, Ying-Wan ; Cohen, Lawrence B. ; Zochowski, Michal R.

The odour-induced population response in the in vivo turtle (Terepene sp.) olfactory bulb consists of three oscillatory components (rostral, middle and caudal) that ride on top of a DC signal. In an initial step to determine the functional role of these four signals, we compared the signals elicited by different odorants. Most experiments compared isoamyl acetate and cineole, odorants which have very different maps of input to olfactory bulb glomeruli in the turtle and a different perceptual quality for humans. We found substantial differences in the response to the two odours in the rise-time of the DC signal and in the latency of the middle oscillation. The rate of rise for cineole was twice as fast as that for isoamyl acetate. Similarly, the latency for the middle oscillation was about twice as long for isoamyl acetate as it was for cineole. On the other hand, a number of characteristics of the signals were not substantially different for the two odorants. These included the latency of the rostral and caudal oscillation, the frequency and envelope of all three oscillations and their locations and spatial extents. A smaller number of experiments were carried out with hexanone and hexanal; the oscillations elicited by these odorants did not appear to be different from those elicited by isoamyl acetate and cineole. Qualitative differences between the oscillations in the turtle and those in two invertebrate phyla suggest that different odour processing strategies may be used.

Article

Identification of juvenile hormone-active alkylphenols in the lobster Homarus americanus and in marine sediments

(Marine Biological Laboratory, 2004-02) Biggers, William J. ; Laufer, Hans

We have identified, by gas chromatography/mass spectrometry, four alkylphenols that are present in the hemolymph and tissues of the American lobster Homarus americanus and in marine sediments. These alkylphenols are used industrially in antioxidant formulations for plastic and rubber polymer manufacturing, and are similar in structure to a known endocrine disruptor, bisphenol A. The compound 2-t-butyl-4-(dimethylbenzyl)phenol was present at concentrations of 0.02 to 1.15 µg/ml in hemolymph and 8.95 to 21.58 µg/g in sediments. A second compound, 2,4-bis-(dimethylbenzyl)phenol, was present at concentrations between 0.07 and 19.78 µg/ml in hemolymph and 138.94 to 224.89 µg/g in sediment, while a third compound, 2,6-bis-(t-butyl)-4-(dimethylbenzyl)phenol, was found at concentrations between 0.01 and 13.00 µg/ml in hemolymph, 2.55 and 6.11 µg/g in hepatopancreas, and 47.85 and 74.66 µg/g in sediment. A fourth compound, 2,4-bis-(dimethylbenzyl)-6-t-butylphenol, was found at concentrations of 0.20 to 70.71 µg/ml in hemolymph, 23.56 to 26.89 µg/g in hepatopancreas, and 90.68 to 125.58 µg/g in sediment. These compounds, along with bisphenol A, 4-dimethylbenzylphenol, and nonylphenol, display high juvenile hormone activity in bioassays. Alkylphenols at high concentrations are toxic to crustaceans and may contribute significantly to lobster mortality; at lower concentrations, they are likely to have endocrine-disrupting effects.

Article

Carbohydrate–carbohydrate interaction provides adhesion force and specificity for cellular recognition

(Rockefeller University Press, 2004-05-17) Bucior, Iwona ; Scheuring, Simon ; Engel, Andreas ; Burger, Max M.

The adhesion force and specificity in the first experimental evidence for cell–cell recognition in the animal kingdom were assigned to marine sponge cell surface proteoglycans. However, the question whether the specificity resided in a protein or carbohydrate moiety could not yet be resolved. Here, the strength and species specificity of cell–cell recognition could be assigned to a direct carbohydrate–carbohydrate interaction. Atomic force microscopy measurements revealed equally strong adhesion forces between glycan molecules (190–310 piconewtons) as between proteins in antibody–antigen interactions (244 piconewtons). Quantitative measurements of adhesion forces between glycans from identical species versus glycans from different species confirmed the species specificity of the interaction. Glycan-coated beads aggregated according to their species of origin, i.e., the same way as live sponge cells did. Live cells also demonstrated species selective binding to glycans coated on surfaces. These findings confirm for the first time the existence of relatively strong and species-specific recognition between surface glycans, a process that may have significant implications in cellular recognition.

Article

Regulation of a formin complex by the microtubule plus end protein tea1p

(Rockefeller University Press, 2004-06-07) Feierbach, Becket ; Verde, Fulvia ; Chang, Fred

The plus ends of microtubules have been speculated to regulate the actin cytoskeleton for the proper positioning of sites of cell polarization and cytokinesis. In the fission yeast Schizosaccharomyces pombe, interphase microtubules and the kelch repeat protein tea1p regulate polarized cell growth. Here, we show that tea1p is directly deposited at cell tips by microtubule plus ends. Tea1p associates in large "polarisome" complexes with bud6p and for3p, a formin that assembles actin cables. Tea1p also interacts in a separate complex with the CLIP-170 protein tip1p, a microtubule plus end–binding protein that anchors tea1p to the microtubule plus end. Localization experiments suggest that tea1p and bud6p regulate formin distribution and actin cable assembly. Although single mutants still polarize, for3{Delta}bud6{Delta}tea1{Delta} triple-mutant cells lack polarity, indicating that these proteins contribute overlapping functions in cell polarization. Thus, these experiments begin to elucidate how microtubules contribute to the proper spatial regulation of actin assembly and polarized cell growth.

Article

Revisiting the role of H+ in chemotactic signaling of sperm

(Rockefeller University Press, 2004-07-26) Solzin, Johannes ; Helbig, Annika ; Van, Qui ; Brown, Joel E. ; Hildebrand, Eilo ; Weyand, Ingo ; Kaupp, U. Benjamin

Chemotaxis of sperm is an important step toward fertilization. During chemotaxis, sperm change their swimming behavior in a gradient of the chemoattractant that is released by the eggs, and finally sperm accumulate near the eggs. A well established model to study chemotaxis is the sea urchin Arbacia punctulata. Resact, the chemoattractant of Arbacia, is a peptide that binds to a receptor guanylyl cyclase. The signaling pathway underlying chemotaxis is still poorly understood. Stimulation of sperm with resact induces a variety of cellular events, including a rise in intracellular pH (pHi) and an influx of Ca2+; the Ca2+ entry is essential for the chemotactic behavior. Previous studies proposed that the influx of Ca2+ is initiated by the rise in pHi. According to this proposal, a cGMP-induced hyperpolarization activates a voltage-dependent Na+/H+ exchanger that expels H+ from the cell. Because some aspects of the proposed signaling pathway are inconsistent with recent results (Kaupp, U.B., J. Solzin, J.E. Brown, A. Helbig, V. Hagen, M. Beyermann, E. Hildebrand, and I. Weyand. 2003. Nat. Cell Biol. 5:109–117), we reexamined the role of protons in chemotaxis of sperm using kinetic measurements of the changes in pHi and intracellular Ca2+ concentration. We show that for physiological concentrations of resact (<25 pM), the influx of Ca2+ precedes the rise in pHi. Moreover, buffering of pHi completely abolishes the resact-induced pHi signal, but leaves the Ca2+ signal and the chemotactic motor response unaffected. We conclude that an elevation of pHi is required neither to open Ca2+-permeable channels nor to control the chemotactic behavior. Intracellular release of cGMP from a caged compound does not cause an increase in pHi, indicating that the rise in pHi is induced by cellular events unrelated to cGMP itself, but probably triggered by the consumption and subsequent replenishment of GTP. These results show that the resact-induced rise in pHi is not an obligatory step in sperm chemotactic signaling. A rise in pHi is also not required for peptide-induced Ca2+ entry into sperm of the sea urchin Strongylocentrotus purpuratus. Speract, a peptide of S. purpuratus may act as a chemoattractant as well or may serve functions other than chemotaxis.

Article

Voltage imaging from dendrites of mitral cells : EPSP attenuation and spike trigger zones

(Society for Neuroscience, 2004-07-28) Djurisic, Maja ; Antic, Srdjan ; Chen, Wei R. ; Zecevic, Dejan

To obtain a more complete description of individual neurons, it is necessary to complement the electrical patch pipette measurements with technologies that permit a massive parallel recording from many sites on neuronal processes. This can be achieved by using voltage imaging with intracellular dyes. With this approach, we investigated the functional structure of a mitral cell, the principal output neuron in the rat olfactory bulb. The most significant finding concerns the characteristics of EPSPs at the synaptic sites and surprisingly small attenuation along the trunk of the primary dendrite. Also, the experiments were performed to determine the number, location, and stability of spike trigger zones, the excitability of terminal dendritic branches, and the pattern and nature of spike initiation and propagation in the primary and secondary dendrites. The results show that optical data can be used to deduce the amplitude and shape of the EPSPs evoked by olfactory nerve stimulation at the site of origin (glomerular tuft) and to determine its attenuation along the entire length of the primary dendrite. This attenuation corresponds to an unusually large mean apparent "length constant" of the primary dendrite. Furthermore, the images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. Finally, secondary dendrites clearly support the active propagation of action potentials

Article

Exposure to hypoxia rapidly induces mitochondrial channel activity within a living synapse

(American Society for Biochemistry and Molecular Biology, 2004-11-23) Jonas, Elizabeth A. ; Hickman, John A. ; Hardwick, J. Marie ; Kaczmarek, Leonard K.

One of the earliest effects of hypoxia on neuronal function is to produce a run-down of synaptic transmission, and more prolonged hypoxia results in neuronal death. An increase in the permeability of the outer mitochondrial membrane, controlled by BCL-2 family proteins, occurs in response to stimuli that trigger cell death. By patch clamping mitochondrial membranes inside the presynaptic terminal of a squid giant synapse, we have now found that several minutes of hypoxia trigger the opening of large multiconductance channels. The channel activity is induced concurrently with the attenuation of synaptic responses that occurs under hypoxic conditions. Hypoxia-induced channels are inhibited by NADH, an agent that inhibits large conductance channels produced by a pro-apoptotic fragment of BCL-xL in these synaptic mitochondria. The appearance of hypoxia-induced channels was also prevented by the caspase/cysteine protease inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone (Z-VAD-fmk), which inhibits proteolysis of BCL-xL during hypoxia. Both NADH and Z-VAD-fmk reduced significantly the rate of decline of synaptic responses during hypoxia. Our results indicate that an increase in outer mitochondrial channel activity is a very early event in the response of neurons to hypoxia and suggest that this increase in activity may contribute to the decline in synaptic function during hypoxia.

Article

Potassium currents distinguish the two subtypes of morphologically distinct skate bipolar cells

(Marine Biological Laboratory, 2004-12) Qian, Haohua ; Chappell, Richard L. ; Redenti, Stephen ; Ripps, Harris

Bipolar cells in the vertebrate retina are second-order neurons that convey visual information from photoreceptors to ganglion cells, the neurons that relay the message to the brain. Bipolar cells consist typically of multiple subtypes that differ in their morphology, synaptic connections, and response properties. The individual subtypes are thought to carry different aspects of the visual signal through the retina, and they often exhibit unique membrane properties and neurotransmitter receptors. In the all-rod skate retina, only two morphologically and pharmacologically distinct subtypes of bipolar cell have been identified thus far. The large-field bipolar cells, with extensive dendritic arbors, are glycine-insensitive, whereas the small-field bipolar cells, which have only one or two dendritic branches, are sensitive to glycine. In the present study, we explored further the membrane properties of these two subtypes of skate bipolar cell with emphasis on the voltage-sensitive potassium currents. Our results show that the cells exhibit different voltage-activated current profiles, suggesting that the signals they transmit contain different features of the visual scene.

Article

Histidine suppresses zinc modulation of connexin hemichannels

(Marine Biological Laboratory, 2004-12) Chappell, Richard L. ; Qian, Haohua ; Zakevicius, Jane ; Ripps, Harris

Zinc has been shown to modulate hemichannel currents of connexins Cx35 and Cx38 in Xenopus oocytes. In both cases the effects were biphasic; i.e., low concentrations of zinc enhanced, whereas higher concentrations decreased, the magnitudes of the voltage-activated hemichannel currents. The present study was designed to determine the effects of zinc on hemichannels formed by Cx26, a connexin reportedly expressed on dendrites of carp horizontal cells and implicated in a mechanism for photoreceptor feedback. In addition, we examined whether histidine, a zinc chelator, would block the action of zinc on Cx26 hemichannel currents, or would exert a direct effect on those currents.

Article

Constitutively active G-protein-gated inwardly rectifying K+ channels in dendrites of hippocampal CA1 pyramidal neurons

(Society for Neuroscience, 2005-04-13) Chen, Xixi ; Johnston, Daniel

A diversity of ion channels contributes to the active properties of neuronal dendrites. From the apical dendrites of hippocampal CA1 pyramidal neurons, we recorded inwardly rectifying K+ channels with a single-channel conductance of 33 pS. The inwardly rectifying K+ channels were constitutively active at the resting membrane potential. The amount of constitutive channel activity was significantly larger in the apical dendrites than in the soma. Activities of these inwardly rectifying K+ channels were inhibited by Ba2+ (200 µM) and tertiapin (10 nM), both of which are believed to block G-protein-coupled inwardly rectifying K+ (GIRK) channels. Intracellularly applied GTP{gamma}S (20 µM) during dual dendritic recordings significantly increased constitutive channel activity. Baclofen (20 µM), an agonist for the G-protein-coupled GABAB receptor, also significantly increased the level of channel activity. Therefore, these channels are GIRK channels, which are constitutively active at rest in the apical dendrites of CA1 pyramidal neurons and can be further activated via G-protein-coupled neurotransmitter receptors.

Preprint

Imaging the division process in living tissue culture cells

( 2005-07-29) Khodjakov, Alexey ; Rieder, Conly L.

We detail some of the pitfalls encountered when following live cultured somatic cells by light microscopy during mitosis. Principle difficulties in this methodology arise from the necessity to compromise between maintaining the health of the cell while achieving the appropriate temporal and spatial resolutions required for the study. Although the quality of the data collected from fixed cells is restricted only by the quality of the imaging system and the optical properties of the specimen, the major limiting factor when viewing live cells is radiation damage induced during illumination. We discuss practical considerations for minimizing this damage, and for maintaining the general health of the cell, while it is being followed by multi-mode or multi-dimensional light microscopy.

Article

Polar body formation in Spisula oocytes : function of the peripheral aster

(Marine Biological Laboratory, 2005-08) Pielak, Rafal M. ; Hawkins, Christopher ; Pyie, Aung ; Bautista, Jennifer ; Lee, Kyeng-Gea ; Cohen, William D.

Activated Spisula oocytes proceed through meiotic stages rapidly and in near synchrony, providing an excellent system for analyzing polar body formation. Our previous studies suggested that cortical spreading of the metaphase peripheral aster determines spatial features of the cortical F-actin ring that is generated prior to extrusion of the polar body. We tested this hypothesis by experimentally altering the number and cortical contact patterns of peripheral asters. Such alteration was achieved by (a) lovastatin-induced arrest at metaphase I, with and without hexylene glycol modification, followed by washout; and (b) cytochalasin-D inhibition of extrusion of the first polar body, with washout before extrusion of the second polar body. Both methods induced simultaneous formation of two or more cortically spreading asters, correlated with subsequent formation of double, or even triple, overlapping F-actin rings during anaphase. Regardless of pattern, ring F-actin was deposited near regions of greatest astral microtubule density, indicating that microtubules provided a positive stimulus to which the cortex responded indiscriminately. These results strongly support the proposed causal relationship between peripheral aster spreading and biogenesis of the F-actin ring involved in polar body formation.

Preprint

Kinetochore fiber formation in animal somatic cells : dueling mechanisms come to a draw

( 2005-09-12) Rieder, Conly L.

The attachment to and movement of a chromosome on the mitotic spindle is mediated by the formation of a bundle of microtubules (MTs) that tethers the kinetochore on the chromosome to a spindle pole. The origin of these “kinetochore fibers” (K-fibers) has been investigated for over 125 years. As noted in 1944 by Schrader, there are only three possible ways to form a K-fiber: either it a) grows from the pole until it contacts the kinetochore; b) grows directly from the kinetochore; or c) it forms as a result of an interaction between the pole and the chromosome. Since Schrader’s time it has been firmly established that K-fibers in centrosome-containing animal somatic cells form as kinetochores capture MTs growing from the spindle pole (route a). It is now similarly clear that in cells lacking centrosomes, including plants and many animal oocytes, K-fibers “self-assemble” from MTs generated by the chromosomes (route b). Can animal somatic cells form K-fibers in the absence of centrosomes by the “self-assembly” pathway? In 2000 the answer to this question was shown to be a resounding “yes”. With this result, the next question became whether the presence of a centrosome normally suppresses K-fiber self-assembly, or if this route works concurrently with centrosome-mediated K-fiber formation. This question, too, has recently been answered: observations on untreated live animal cells expressing GFP-tagged tubulin clearly show that kinetochores can nucleate the formation of their associated MTs in the presence of functional centrosomes. The concurrent operation of these two “dueling” routes for forming K-fibers in animals helps explain why the attachment of kinetochores and the maturation of K-fibers occur as quickly as it does on all chromosomes within a cell.

Article

Response of the American lobster to the stress of shell disease

(National Shellfisheries Association, 2005-10) Laufer, Hans ; Demir, Neslihan ; Biggers, William J.

Shell disease is a problem affecting lobsters in eastern Long Island Sound causing disfiguration of the shell, decreasing the lobsters' value, and whereas mild and medium levels of the disease are not lethal, ultimately, severe cases result in mortality. Levels of the molting hormone, ecdysone, were quantitated, using a radioimmunoassay (RIA), in hemolymph of animals exhibiting shell disease. Our results indicate that levels of ecdysone were increased in the hemolymph of shell-diseased lobsters, with a medium level of expression of the disease to 89 ± 32 ng/mL (n = 76), whereas unaffected, presumably healthy ones had 57 ± 16 ng/mL (n = 210). In 7 of 10 months of the year shell-diseased animals had higher ecdysone levels in their hemolymph than unaffected animals. In addition, ecdysone levels were abnormally high, 165 ± 53 ng/mL (n = 5), in shell-diseased ovigerous lobsters, whereas normal unaffected ovigerous ones had low levels of this hormone, 13 ± 4 ng/mL (n = 7). These results indicate that shell disease may induce lobsters to alter the systemic levels of ecdysone, possibly serving as a defensive measure, allowing the animals to ward off the effects of shell disease through induced molting.

Preprint

Optical recording from respiratory pattern generator of fetal mouse brainstem reveals a distributed network

( 2005-10-17) Eugenin, Jaime ; Nicholls, John G. ; Cohen, Lawrence B. ; Muller, Kenneth J.

Unfailing respiration depends on neural mechanisms already present in mammals before birth. Experiments were made to determine how inspiratory and expiratory neurons are grouped in the brainstem of fetal mice. A further aim was to assess whether rhythmicity arises from a single pacemaker or is generated by multiple sites in the brainstem. To measure neuronal firing, a fluorescent calcium indicator dye was applied to embryonic central nervous systems isolated from mice. While respiratory commands were monitored electrically from third to fifth cervical ventral roots, activity was measured optically over areas containing groups of respiratory neurones, or single neurones, along the medulla from the facial nucleus to the pre-Bötzinger complex. Large optical signals allowed recordings to be made during individual respiratory cycles. Inspiratory and expiratory neurones were intermingled. A novel finding was that bursts of activity arose in a discrete area intermittently, occurring during some breaths, but failing in others. Raised CO2 partial pressure or lowered pH increased the frequency of respiration; neurons then fired reliably with every cycle. Movies of activity revealed patterns of activation of inspiratory and expiratory neurones during successive respiratory cycles; there was no evidence for waves spreading systematically from region to region. Our results suggest that firing of neurons in immature respiratory circuits is a stochastic process, and that the rhythm does not depend on a single pacemaker. Respiratory circuits in fetal mouse brainstem appear to possess a high safety factor for generating rhythmicity, which may or may not persist as development proceeds.

Article

Design and function of superfast muscles : new insights into the physiology of skeletal muscle

(Annual Reviews, 2005-10-24) Rome, Lawrence C.

Superfast muscles of vertebrates power sound production. The fastest, the swimbladder muscle of toadfish, generates mechanical power at frequencies in excess of 200 Hz. To operate at these frequencies, the speed of relaxation has had to increase approximately 50-fold. This increase is accomplished by modifications of three kinetic traits: (a) a fast calcium transient due to extremely high concentration of sarcoplasmic reticulum (SR)-Ca2+ pumps and parvalbumin, (b) fast off-rate of Ca2+ from troponin C due to an alteration in troponin, and (c) fast cross-bridge detachment rate constant (g, 50 times faster than that in rabbit fast-twitch muscle) due to an alteration in myosin. Although these three modifications permit swimbladder muscle to generate mechanical work at high frequencies (where locomotor muscles cannot), it comes with a cost: The high g causes a large reduction in attached force-generating cross-bridges, making the swimbladder incapable of powering low-frequency locomotory movements. Hence the locomotory and sound-producing muscles have mutually exclusive designs.

Preprint

Endoplasmic reticulum targeted GFP reveals ER organization in tobacco NT-1 cells during cell division

( 2005-11-07) Gupton, S. L. ; Collings, D. A. ; Allen, N. S.

The endoplasmic reticulum (ER) of plant cells undergoes a drastic reorganization during cell division. In tobacco NT-1 cells that stably express a GFP construct targeted to the ER, we have mapped the reorganization of ER that occurs during mitosis and cytokinesis with confocal laser scanning microscopy. During division, the ER and nuclear envelope do not vesiculate. Instead, tubules of ER accumulate around the chromosomes after the nuclear envelope breaks down, with these tubules aligning parallel to the microtubules of the mitotic spindle. In cytokinesis, the phragmoplast is particularly rich in ER, and the transnuclear channels and invaginations present in many interphase cells appear to develop from ER tubules trapped in the developing phragmoplast. Drug studies, using oryzalin and latrunculin to disrupt the microtubules and actin microfilaments respectively, demonstrate that during division, the arrangement of ER is controlled by microtubules and not by actin, which is the reverse of the situation in interphase cells.

Preprint

Chromosomes can congress to the metaphase plate before biorientation

( 2005-12-09) Kapoor, Tarun M. ; Lampson, Michael A. ; Hergert, Polla ; Cameron, Lisa ; Cimini, Daniela ; Salmon, Edward D. ; McEwen, Bruce F. ; Khodjakov, Alexey

The stable propagation of genetic material during cell division depends on the congression of chromosomes to the spindle equator before the cell initiates anaphase. It is generally assumed that congression requires that chromosomes are connected to the opposite poles of the bipolar spindle (i.e., “bi-oriented”). We found that chromosomes can congress before becoming bioriented. By combining the use of reversible chemical inhibitors, live-cell light microscopy and correlative electron microscopy, we found that mono-oriented chromosomes could glide towards the spindle equator alongside kinetochore fibers attached to other already bi-oriented chromosomes. This congression mechanism depended on the kinetochore-associated plus enddirected microtubule motor CENP-E (kinesin-7).

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