The stable propagation of genetic material during cell division depends on the congression of chromosomes to the spindle equator before the cell initiates anaphase. bundles (K fibers) connect sister kinetochores of each chromosome to opposite spindle poles (1). Biorientation errors are linked to chromosome loss and cancers (2). Formation of sister K fibers occurs asynchronously (3) and once a kinetochore captures microtubules growing from a spindle pole the chromosome is usually transported toward this pole IKK-16 and becomes “monooriented” (4). Monooriented chromosomes remain near the spindle pole for variable times (3 4 until they suddenly “congress” to the spindle equator. Current models of mitotic spindle formation (5 6 postulate that chromosome congression occurs as the result of biorientation (7). We followed movements of individual chromosomes in mammalian cells by differential interference contrast (DIC) time-lapse microscopy (8). In addition to the chromosome oscillations that occur toward and away from spindle poles we frequently observed monooriented chromosomes making direct movements to the metaphase plate as if they were attempting to congress (fig. S1). Centromeres on these congressing chromosomes were frequently stretched which indicated force generation from the leading kinetochore (Film S1). Nevertheless these movements didn’t always create a steady alignment for the metaphase dish because chromosomes frequently returned towards the spindle pole after a 3- to 4-μm excursion. This chromosome behavior IKK-16 was seen in essentially every cell we imaged and in addition has been previously reported (9-12). To determine whether these chromosomes had been bioriented we adopted mitotic cells by DIC microscopy until among the chromosomes exhibited a protracted linear motion toward the metaphase dish and we set the cell when the chromosome got nearly reached the metaphase dish (~5 to 7 μm through the proximal spindle pole) (Fig. 1; Film S2). Three of five chromosomes examined by electron microscopy (EM) (8) had been already bioriented needlessly to say for congressing chromosomes (7). Yet in the additional two instances no microtubules emanated through the leading kinetochore dish for the congressing chromosome. Rather this kinetochore laterally interacted with microtubules of an adult K fiber mounted on a kinetochore of another bioriented chromosome added to the metaphase dish (Fig. 1D). The trailing kinetochore was mounted on the proximal spindle pole with a adult K fiber. This unexpected kind of kinetochore-microtubule interaction suggested that chromosomes may not have to be bioriented during congression. Fig. 1 Leading kinetochores aren’t mounted on microtubules throughout a IKK-16 chromosome’s try to congress IKK-16 properly. (A) Selected structures from a DIC time-lapse saving (also see Film S2). The cell was set as you chromosome (arrows) shifted toward the spindle IKK-16 … IKK-16 Because specific K materials are not solved by DIC microscopy we’re able to not really correlate the trajectory of a person chromosome shifting toward the spindle equator using the positions of encircling K materials. To overcome this restriction we imaged both microtubules and kinetochores by live-cell dual-channel fluorescence microscopy concurrently. Ace PtK1 epithelial cells produced from the marsupial rat kangaroo Online. 9 Skibbens RV Rieder CL Salmon ED. J Cell Biol. 1993;122:859. [PMC free of charge content] [PubMed] 10 Waters JC Skibbens RV Salmon ED. J Cell Sci. 1996;109:2823. [PubMed] 11 Khodjakov A Rieder CL. J Cell Biol. 1996;135:315. [PMC free of charge content] [PubMed] 12 Khodjakov A Cole RW McEwen BF Buttle KF Rieder CL. J Cell Biol. 1997;136:229. [PMC free of charge content] [PubMed] 13 Cimini D Cameron LA Salmon ED. Curr Biol. 2004;14:2149. [PubMed] 14 Rieder CL Salmon ED. J Cell Biol. 1994;124:223. [PMC free of charge content] [PubMed] 15 Rieder CL Schultz A Cole R Sluder G. J Cell Biol. 1994;127:1301. [PMC free of charge content] [PubMed] 16 Kapoor TM Mayer TU Coughlin ML Mitchison TJ. J Cell Biol. 2000;150:975. [PMC free of charge content] [PubMed] 17 Lampson MA Renduchitala K Khodjakov A Kapoor TM. Nat Cell Biol. 2004;6:232. [PubMed] 18 Euteneuer U McIntosh JR. J Cell Biol. 1981;89:338. [PMC free of charge content] [PubMed] 19 Real wood KW Sakowicz R Goldstein LSB Cleveland DW. Cell. 1997;91:357. [PubMed] 20 Yao X Anderson KL Cleveland DW. J Cell Biol. 1997;139:435. [PMC free of charge content] [PubMed] 21 Schaar BT Chan GKT Maddox P Salmon ED Yen TJ. J Cell Biol. 1997;139:1373. [PMC free of charge content] [PubMed] 22 McEwen BF et al. Mol Biol.