Life Sciences Commons^™

Morphological Characterization Of The Immune Organs In Ostrich Chicks, Hui Song, Ke-Mei Peng, Sheng-He Li, Yan Wang, Lan Wei, Li Tang

Turkish Journal of Veterinary & Animal Sciences

This study describes the anatomical, light microscopic, and ultrastructural characterization of the immune organs in ostrich chicks. In this study 6 healthy 8-week-old ostrich chicks were processed for light and transmission electron microscopy. Hematoxylin and eosin as well as improved Weigert staining were used for light microscopy. The small thymus, which clustered caudally along both sides of the neck, contained Hassall's corpuscles in the medulla. The cloacal bursa, which formed the hanging and lateral walls of the cloaca, enveloped the cloaca but did not form a truly independent bursa. Inside the bursa convex papillae were densely distributed on the surface …

A Microscopic And Stereological Study Of The Renal Artery Transitional Zone Of The Adult Male Dog, Fatemah Ramezani Nowrozani

Turkish Journal of Veterinary & Animal Sciences

A transitional zone in the dog renal artery was documented and its parameters were recorded: length and volumes of the luminal wall, tunica intima, tunica media, and tunica adventitia-as well as these parameters in the non-transitional zone of artery. Twelve normal adult male dogs were studied. The specimens were processed in the routine manner for light and electron microscopy. After the determination of transitional zone length by light microscope, for the stereological study each renal artery was divided into transitional and non-transitional zones, and paraffin blocks were prepared. It was established that the transitional zone contains parallel and continuous elastic …

Transmission Electron Microscopic Study Of Renal Haemopoietic Tissues Of Channa Punctatus (Bloch) Experimentally Infected With Two Species Of Aeromonads, Rajarshi Ghosh, Sumit Homechaudhuri

Turkish Journal of Zoology

The ultrastructural pathological changes in the renal haemopoietic tissue of Channa punctatus (Bloch) experimentally infected with 2 species of aeromonads, Aeromonas hydrophila and Aeromonas salmonicida, were reported. Adult C. punctatus specimens were injected intramuscularly, once at a time, with a chosen sublethal dose (2 × 10^9 cfu mL^-^1) of aeromonads at 5 µL g^-^1 body weight of fish and were exposed to 72 h of duration. The leucocytes (especially macrophages and melanomacrophages) and other associated cells from the pronephric head kidney of aeromonad-infected C. punctatus were studied by fixed ultrathin sections for transmission electron microscopy. The sinusoidal cells, barrier cells, …

The Effect Of Shifts In Medium Types On The Growth And Morphology Of Spirulina Platensis (Arthrospira Platensis), Yean-Chang Chen

Journal of Marine Science and Technology

In order to reduce the cultural cost and increase the biomass of Spirulina platensis cultures, two basic culture media were used in the present study, the Zarrouk (Z9) and Provasoli's enriched seawater (PES) media. They were re-modified into five media by adding varied concentrations of NaCl, NaHCO3 and seawater (salinity). S. platensis could grow well in all of these media. The Z9 medium provided the best growth rate at the end of culture and the PES medium provided the best initial growth curve slope. After the media were shifted from PES to Z9, the long algal filaments fragmented to form …

Descriptive Characteristics Of Haemopoietic Cell Lineages In A Facultative Air Breathing Fish Clarias Batrachus (L.), Krishna Gangopadhyay, Sumit Homechaudhuri

Turkish Journal of Zoology

Haemopoietic tissues of the head kidney of Clarias batrachus were studied for morphometric analysis and ultrastructural descriptions of the erythropoietic and leucopoietic cell populations. Eight successive steps of developing erythrocytes from small lymphoid haemoblasts (SLHs) to mature erythrocytes (MEs) were distinguished. Progressive loss of RNA and synthesis of haemoglobin during haemopoiesis were coupled with denser nucleus and changes in cellular shapes. Transmission electron microscopy aided in clear distinction between cell lineages in the development of erythrocytes, granulocytes, and lymphocytes. Ultrastructural analysis of the pronephric stromal cells forming adherent multilayer of haemopoietic microenvironment was explicit in describing their ability to promote …

Morphological And Ultrastructural Changes In Tissues Of Intermediate And Definitive Hosts Infected By Protostrongylidae, Abdurakhim Ergashevich Kuchboev, Eric P. Hoberg

Turkish Journal of Zoology

Cellular and subcellular mechanisms involved in tissue responses to larval and adult lungworms (Protostrongylidae) were respectively explored through experimental and natural infections in molluscan intermediate (Xeropicta candacharica) and ruminant definitive hosts (Ovis aries). Reaction to developing larval stages in the gastropod is manifested as cellular infiltration involving lymphocytes and macrophages into the infected tissue, which restricts damage and may result in destruction and elimination of parasites from the intermediate host. Variations in the patterns of localization for infective third-stage larvae in the foot tissue of the intermediate host are described. In the definitive host, evaluation of lung tissue by histology …

The Effects Of Uv Radiation On Some Structural And Ultrastructural Parameters In Pepper (Capsicum Longum A.Dc.), Siavash Hosseini Sarghein, Jirair Carapetian, Jalil Khara

Turkish Journal of Biology

The objective of this study was to evaluate the effects on the structure and ultrastructure of pepper plants (Capsicum longum A.DC.) exposed to UV radiation under greenhouse conditions. The plants were grown in a growth chamber under uniform environmental conditions and after 35 days were exposed to UV-A and UV-C radiation for 15 and 8 days, respectively. Changes in root growth were not significant, but shoot growth decreased in UV-R-exposed plants and decreased significantly in UV-C-exposed plants. Leaf area also decreased in UV-R-exposed plants and decreased significantly in UV-C-exposed plants. Root thickness was not affected by UV treatment, but stem …

Role Of Flgt In Anchoring The Flagellum Of Vibrio Cholerae, Raquel M. Martinez, Brooke A. Jude, Thomas J. Kirn, Karen Skorupski, Ronald K. Taylor

Dartmouth Scholarship

Flagellar motility has long been regarded as an important virulence factor. In Vibrio cholerae, the single polar flagellum is essential for motility as well as for proper attachment and colonization. In this study, we demonstrate that the novel flagellar protein FlgT is involved in anchoring the flagellum to the V. cholerae cell. A screen for novel colonization factors by use of TnphoA mutagenesis identified flgT. An in-frame deletion of flgT established that FlgT is required for attachment, colonization, and motility. Transmission electron microscopy revealed that while the flgT mutant is capable of assembling a phenotypically normal flagellum, …

Ultrastructural Changes In Rat Liver By Methyleugenol And Evaluation Of Some Biochemical Parameters, Ayşegül Çerkezkayabeki̇r, Gülnur Kizilay, Fi̇gen Ertan

Turkish Journal of Biology

The present study investigated the effect of methyleugenol, a food flavoring and fragrance agent, on the livers of laboratory rats. Doses of 10 and 30 mg/kg/day of methyleugenol (in 0.5% methylcellulose) were administered intragastrically (IG) to 2 dose groups for 10 days alongside a control group (n = 10 for each group). Gains in body weight were not statistically significant for either dose. Lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) activities decreased (P < 0.05) for both dose groups, but AST (aspartate aminotransferase) activity decreased significantly (P < 0.05) only in the 30 mg/kg/day methyleugenol dose group. Alanine aminotransferase (ALT) activity did not change significantly in either group. The total amount of glucose remained unchanged, but glycogen in the liver decreased significantly (P < 0.05) in the 30 mg/kg/day methyleugenol dose group. There was also an increase of swelling in the smooth endoplasmic reticulum sacs (sER), electron dense accumulations in the sER, cytoplasmic vacuolization, a slight increase of mitochondria and lysosomes, and invaginations in the nucleus membranes of hepatocytes. Extensions in bile canaliculi and increasing microvilli of bile canaliculi in the liver were also observed. These findings indicate the ultrastructural toxic effect of methyleugenol on rat livers in 10 and 30 mg/kg/day doses. Therefore, we may speculate that the toxic effect of methyleugenol needs to be examined in detail.

Ceramide Kinase Regulates Phospholipase C And Phosphatidylinositol 4, 5, Bisphosphate In Phototransduction, Ujjaini Dasgupta, Takeshi Bamba, Salvatore Chiantia, Pusha Karim, Ahmad N. Abou Tayoun

Dartmouth Scholarship

Phosphoinositide-specific phospholipase C (PLC) is a central effector for many biological responses regulated by G-protein-coupled receptors including Drosophila phototransduction where light sensitive channels are activated downstream of NORPA, a PLCbeta homolog. Here we show that the sphingolipid biosynthetic enzyme, ceramide kinase, is a novel regulator of PLC signaling and photoreceptor homeostasis. A mutation in ceramide kinase specifically leads to proteolysis of NORPA, consequent loss of PLC activity, and failure in light signal transduction. The mutant photoreceptors also undergo activity-dependent degeneration. Furthermore, we show that a significant increase in ceramide, resulting from lack of ceramide kinase, perturbs the membrane microenvironment of …

Bub2 Regulation Of Cytokinesis And Septation In Budding Yeast, Su Young Park, Addie E. Cable, Jessica Blair, Katherine E. Stockstill, Katie Shannon

Biological Sciences Faculty Research & Creative Works

Background: The mitotic exit network (MEN) is required for events at the end of mitosis such as degradation of mitotic cyclins and cytokinesis. Bub2 and its binding partner Bfa1 act as a GTPase activating protein (GAP) to negatively regulate the MEN GTPase Tem1. The Bub2/Bfa1 checkpoint pathway is required to delay the cell cycle in response to mispositioned spindles. In addition to its role in mitotic exit, Tem1 is required for actomyosin ring contraction.

Results: To test the hypothesis that the Bub2 pathway prevents premature actin ring assembly, we compared the timing of actin ring formation in wild type, bub2Δ …

Ultrastructural And Histological Analysis Of Dark Spot Syndrome In Siderastrea Siderea And Agaricia Agaricites, Dorothy-Ellen A. Renegar, Patricia Blackwelder, J. D. Miller, D. J. Gochfeld, Alison L. Moulding

Marine & Environmental Sciences Faculty Proceedings, Presentations, Speeches, Lectures

Dark Spot Syndrome (DSS) typically manifests in scleractinian corals as lesions of varying color, size, shape and location that can result in skeletal changes and tissue death. A causative agent for DSS has not yet been identified. The objective of this study was histological and ultrastructural comparison of the cellular and skeletal characteristics of DSS-affected and healthy Siderastrea siderea and Agaricia agaricites. The greater resolution possible with transmission electron microscopy (TEM) revealed microbial activity and tissue changes not resolvable utilizing histology. DSS-affected tissue had less integrity, with increasing cellular degradation and vacuolization. A high concentration of electron dense inclusions, …

The Effect Of Febrile Temperature On Plasmodium Falciparum, Heidi Sue Porter

Theses and Dissertations

Previously it has been shown that cultures of Plasmodium falciparum died following exposure to a febrile temperature of 40°C, as demonstrated by a decrease in parasitemia of the following generation. In the current study, the effect of 40°C treatment on culture media, erythrocytes, and parasite glucose consumption, were ruled out as possible influences on parasite death, demonstrating that 40°C impacted the parasites directly. Metabolic profiling of DNA synthesis, protein synthesis, and glucose utilization during exposure to 40°C clearly indicated that febrile temperatures had direct effect on major metabolic pathways and parasite development, beginning 20-24 hr after erythrocyte invasion. The ring …

The Yeast Integral Membrane Protein Apq12 Potentially Links Membrane Dynamics To Assembly Of Nuclear Pore Complexes, John J. Scarcelli, Christin A. Hodge, Charles N. Cole

Dartmouth Scholarship

Although the structure and function of components of the nuclear pore complex (NPC) have been the focus of many studies, relatively little is known about NPC biogenesis. In this study, we report that Apq12 is required for efficient NPC biogenesis in Saccharomyces cerevisiae. Apq12 is an integral membrane protein of the nuclear envelope (NE) and endoplasmic reticulum. Cells lacking Apq12 are cold sensitive for growth, and a subset of their nucleoporins (Nups), those that are primarily components of the cytoplasmic fibrils of the NPC, mislocalize to the cytoplasm. APQ12 deletion also causes defects in NE morphology. In the absence of …

A Serratia Marcescens Oxyr Homolog Mediates Surface Attachment And Biofilm Formation, Robert M. Q. Shanks, Nicholas A. Stella, Eric J. Kalivoda, Megan R. Doe

Dartmouth Scholarship

OxyR is a conserved bacterial transcription factor with a regulatory role in oxidative stress response. From a genetic screen for genes that modulate biofilm formation in the opportunistic pathogen Serratia marcescens, mutations in an oxyR homolog and predicted fimbria structural genes were identified. S. marcescens oxyR mutants were severely impaired in biofilm formation, in contrast to the hyperbiofilm phenotype exhibited by oxyR mutants of Escherichia coli and Burkholderia pseudomallei. Further analysis revealed that OxyR plays a role in the primary attachment of cells to a surface. Similar to what is observed in other bacterial species, S. marcescens OxyR …

Regulation Of Meiotic Cohesion And Chromosome Core Morphogenesis During Pachytene In Drosophila Oocytes, Radhika S. Khetani, Sharon E. Bickel

Dartmouth Scholarship

During meiosis, cohesion between sister chromatids is required for normal levels of homologous recombination, maintenance of chiasmata and accurate chromosome segregation during both divisions. In Drosophila, null mutations in the ord gene abolish meiotic cohesion, although how ORD protein promotes cohesion has remained elusive. We show that SMC subunits of the cohesin complex colocalize with ORD at centromeres of ovarian germ-line cells. In addition, cohesin SMCs and ORD are visible along the length of meiotic chromosomes during pachytene and remain associated with chromosome cores following DNase I digestion. In flies lacking ORD activity, cohesin SMCs fail to accumulate at oocyte …

Inverse Regulation Of Biofilm Formation And Swarming Motility By Pseudomonas Aeruginosa Pa14, Nicky C. Caiazza, Judith H. Merritt, Kimberly M. Brothers, George A. O'Toole

Dartmouth Scholarship

We previously reported that SadB, a protein of unknown function, is required for an early step in biofilm formation by the opportunistic pathogen Pseudomonas aeruginosa. Here we report that a mutation in sadB also results in increased swarming compared to the wild-type strain. Our data are consistent with a model in which SadB inversely regulates biofilm formation and swarming motility via its ability both to modulate flagellar reversals in a viscosity-dependent fashion and to influence the production of the Pel exopolysaccharide. We also show that SadB is required to properly modulate flagellar reversal rates via chemotaxis cluster IV (CheIV cluster). …

An Essential Role For Endocytosis Of Rhodopsin Through Interaction Of Visual Arrestin With The Ap-2 Adaptor, Nicholas R. Orem, Luxi Xia, Patrick J. Dolph

Dartmouth Scholarship

Previously, we have identified a class of retinal degeneration mutants in Drosophila in which the normally transient interaction between arrestin2 (Arr2) and rhodopsin is stabilized and the complexes are rapidly internalized into the cell body by receptor-mediated endocytosis. The accumulation of protein complexes in the cytoplasm eventually results in photoreceptor cell death. We now show that the endocytic adapter protein AP-2 is essential for rhodopsin endocytosis through an Arr2-AP-2beta interaction, and mutations in Arr2 that disrupt its interaction with the beta subunit of AP-2 prevent endocytosis-induced retinal degeneration. We further demonstrate that if the interaction between Arr2 and AP-2 is …

Pollen Wall Ultrastructure Of Araceae And Lemnaceae In Relation To Molecular Classifications, Michael Hesse

Aliso: A Journal of Systematic and Floristic Botany

A comparative ultrastructural study of Araceae pollen walls was conducted for the first time. The results are based mainly on investigations by transmission electron microscopy of 101 species in 70 genera (out of a total of 105 genera), while pollen of 83 genera with 219 species were studied by scanning electron microscopy, generally without acetolysis. Special attention was given to Lemnaceae (including Limnobiophyllum) considered to be closely related to Araceae (especially to Pistia). The ultrastructural pollen wall characters are mostly in accordance with and strongly support the morphological classifications and the arrangement of genera within recent molecular trees. …

The Histochemical And Ultrastructural Effects Of Cadmium On Mouse Edl Muscle, Fati̇me Geyi̇koğlu, Aysel Temelli̇, Özgen Vuraler, Hasan Türkez

Turkish Journal of Zoology

The histochemical and ultrastructural effects of cadmium (Cd) on the extensor digitorum longus (EDL) muscles of male mice were investigated. Two doses of Cd (0.1 and 1.0 x 10^{-4} M) were injected into the mice. The animals were killed at the end of 48 h and their EDL muscles excised. Three types of fibers (I, IIA and IIB) were described by the succinic dehydrogenase (SDH) method in the control groups. The mitochondrial and sarcotubular contents of the fibers were different. The histochemical and ultrastructural characteristics of the EDL muscles in mice given Cd did not differ from those of the …

The Histochemical And Ultrastructural Structures Of Avian Latissimus Dorsi Muscle Fiber Types And Changes In Them Caused By Water Copper Level, Fati̇me Geyi̇koğlu, Özgen Vuraler, Aysel Temelli̇

Turkish Journal of Veterinary & Animal Sciences

The histochemical and ultrastructural effects of water Cu on the anterior latissimus dorsi (ALD) muscle of 120 newly hatched broilers were investigated in a 45-day experiment. Two doses of water Cu (250 mg Cu/kg water and 500 mg Cu/kg water) were given to the poults. Two distinct categories (IIIA and IIIB) of slow tonic fibers in the control groups were detected by enzyme reactions. The ultrastructure of the Z-line, mitochondrial content and sarcotubular content differed between the 2 fiber types. In the application of 250 mg Cu/kg water, the histochemical characteristics of the IIIB fibers were clearly different from those …

Ovarian Follicle Ultrastructure And Changes In Levels Of Ovarian Steroids During Oogenesis In Chalcalburnus Tarichi Pallas, 1811, Güler Ünal, Hati̇ce Karaki̇şi̇, Mahmut Elp

Turkish Journal of Veterinary & Animal Sciences

The ultrastructure of the ovarian follicle and the levels of the ovarian 11-dehydrocorticosterone (11-DHC), estradiol-17\beta (E_{2}), 17\alpha-hydroxyprogesterone (17\alpha-OHP), and progesterone (P) were studied during cortical alveoli, vitellogenesis and oocyte maturation in Chalcalburnus tarichi. The microvilli began to form on the oocyte surface during cortical alveoli phase and during vitellogenesis, came into contact in the pore canals of the zona radiata with microvilli formed from granulosa cells. While the special thecal cells posses specific organelles, which are characteristic of steroid-producing cells, namely, mitochondria with tubular cristae, smooth endoplasmic reticulum and lipid droplets, the granulosa cells contain organelles typical for protein-secreting cells. …

Ultrastructural Effects Of Retinyl Palmitate On Brown Adipocytes Of Fetal Mice, Candan Özoğul, Mete Köksal, Deni̇z Erdoğan

Turkish Journal of Veterinary & Animal Sciences

Brown adipose tissue (BAT) has a thermogenic function in animals. Mitochondrial uncoupling protein (UCP) is responsible for the thermogenic function in BAT cells. Vitamin A affects proliferation and differentiation in cells. Retinoic acid, a derivative of vitamin A, stimulates the expression of the UCP gene, which is found in BAT cells. Retinoic acid performs its function regardless of differentiation stage of BAT cells. It is known that vitamin A is teratogenic at therapeutic doses in pregnancy. In this study, effects of retinyl palmitate applied in a therapeutic dose were examined in mice fetal BAT cells. Tissue samples were subjected to …

The Kini Kinesin Kif2a Is Required For Bipolar Spindle Assembly Through A Functional Relationship With Mcak, Neil J. Ganem, Duane A. Compton

Dartmouth Scholarship

Although the microtubule-depolymerizing KinI motor Kif2a is abundantly expressed in neuronal cells, we now show it localizes to centrosomes and spindle poles during mitosis in cultured cells. RNAi-induced knockdown of Kif2a expression inhibited cell cycle progression because cells assembled monopolar spindles. Bipolar spindle assembly was restored in cells lacking Kif2a by treatments that altered microtubule assembly (nocodazole), eliminated kinetochore–microtubule attachment (loss of Nuf2), or stabilized microtubule plus ends at kinetochores (loss of MCAK). Thus, two KinI motors, MCAK and Kif2a, play distinct roles in mitosis, and MCAK activity at kinetochores must be balanced by Kif2a activity at poles for spindle …

Pf15p Is The Chlamydomonas Homologue Of The Katanin P80 Subunit And Is Required For Assembly Of Flagellar Central Microtubules, Erin E. Dymek, Paul A. Lefebvre, Elizabeth F. Smith

Dartmouth Scholarship

Numerous studies have indicated that the central apparatus plays a significant role in regulating flagellar motility, yet little is known about how the central pair of microtubules or their associated projections assemble. Several Chlamydomonas mutants are defective in central apparatus assembly. For example, mutant pf15 cells have paralyzed flagella that completely lack the central pair of microtubules. We have cloned the wild-type PF15 gene and confirmed its identity by rescuing the motility and ultrastructural defects in two pf15 alleles, the original pf15a mutant and a mutant generated by insertional mutagenesis. Database searches using the 798-amino-acid polypeptide predicted from the complete …

Pv1 Is A Key Structural Component For The Formation Of The Stomatal And Fenestral Diaphragms, Radu V. Stan, Eugene Tkachenko, Ingrid R. Niesman

Dartmouth Scholarship

PV1 is an endothelial-specific integral membrane glycoprotein associated with the stomatal diaphragms of caveolae, transendothelial channels, and vesiculo-vacuolar organelles and the diaphragms of endothelial fenestrae. Multiple PV1 homodimers are found within each stomatal and fenestral diaphragm. We investigated the function of PV1 within these diaphragms and their regulation and found that treatment of endothelial cells in culture with phorbol myristate acetate (PMA) led to upregulation of PV1. This correlated with de novo formation of stomatal diaphragms of caveolae and transendothelial channels as well as fenestrae upon PMA treatment. The newly formed diaphragms could be labeled with anti-PV1 antibodies. The upregulation …

Histological, Histochemical And Ultrastructural Investigations On The Esophagus Of Juvenile Rainbow Trout (Oncorhynchus Mykiss), Fati̇me Geyi̇koğlu, Özgen Vuraler, Aysel Temelli̇

Turkish Journal of Zoology

The histology of the esophagus of Oncorhynchus mykiss was studied. The structure of the esophagus exhibited differences as well as similarities when compared with previous studies. In this study, the histochemical and ultrastructural structure of the tunica muscularis externa in the esophagus of this fish is investigated. The muscle fibers are described as red and intermediate fibers according to the pH stability of their mATPase activities. The red fibers showed intense staining, while intermediate fibers showed moderate staining with succinic dehydrogenase (SDH) and toluidine blue. In addition, small diameter fibres were seen. These indicated to be the continuation of development …

Ultrastructure Of Mycobacterium Marinum Granuloma In Striped Bass Morone Saxatilis, D. T. Gauthier, W. K. Vogelbein, C. A. Ottinger

Biological Sciences Faculty Publications

An emerging epizootic of mycobacteriosis currently threatens striped bass Morone saxatilis populations in Chesapeake Bay, USA. Several species of mycobacteria, including Mycobacterium marinum, species resembling M. avium, M. gordonae, M. peregrinum, M. scrofulaceum and M. terrae, and the new species M. shottsii have been isolated from diseased and healthy bass. In this study, we describe the ultrastructure of developing M. marinum granulomas in experimentally infected bass over a period of 45 wk. The primary host response to injected mycobacteria was formation of large macrophage aggregations containing phagocytosed bacilli. M. marinum were always contained within phagosomes. Close …

A Role For Yip1p In Copii Vesicle Biogenesis, Matthew Heidtman, Catherine Z. Chen, Ruth N. Collins, Charles Barlowe

Dartmouth Scholarship

Yeast Ypt1p-interacting protein (Yip1p) belongs to a conserved family of transmembrane proteins that interact with Rab GTPases. We encountered Yip1p as a constituent of ER-derived transport vesicles, leading us to hypothesize a direct role for this protein in transport through the early secretory pathway. Using a cell-free assay that recapitulates protein transport from the ER to the Golgi complex, we find that affinity-purified antibodies directed against the hydrophilic amino terminus of Yip1p potently inhibit transport. Surprisingly, inhibition is specific to the COPII-dependent budding stage. In support of this in vitro observation, strains bearing the temperature-sensitive yip1-4 allele accumulate ER membranes …

Minus-End Capture Of Preformed Kinetochore Fibers Contributes To Spindle Morphogenesis, Alexey Khodjakov, Lily Copenagle, Michael B. Gordon, Duane A. Compton, Tarun M. Kapoor

Dartmouth Scholarship

Near-simultaneous three-dimensional fluorescence/differential interference contrast microscopy was used to follow the behavior of microtubules and chromosomes in living alpha-tubulin/GFP-expressing cells after inhibition of the mitotic kinesin Eg5 with monastrol. Kinetochore fibers (K-fibers) were frequently observed forming in association with chromosomes both during monastrol treatment and after monastrol removal. Surprisingly, these K-fibers were oriented away from, and not directly connected to, centrosomes and incorporated into the spindle by the sliding of their distal ends toward centrosomes via a NuMA-dependent mechanism. Similar preformed K-fibers were also observed during spindle formation in untreated cells. In addition, upon monastrol removal, centrosomes established a transient …