Chromosomes micromanipulation

Chromosome micromanipulation. II. Induced reorientation and the experimental control of segregation in meiosis. Chromosoma, 21 17-50. 

Houchmandzadeh, B., Marko, J.F., Chatenay, D., and Libchaber, A. (1997) Elasticity and structure of eukaryote chromosomes studied by micromanipulation and micropipette aspiration. J. Cell. Biol. 139, 1-12. 

Spindle Mechanical Properties. How does the spindle respond to the mitotic forces so that force directionality is controlled and orderly chromosome motion results Artificial forces have been used to study chromosome attachment to the spindle. Especially informative are the centrifugation studies of Schrader (1934), Shimamura (1940), and Yamamoto (1964), and the micromanipulation experiments of Carlson (1952). Recent micromanipulation results (Nicklas and Staehly, 1967) add some details to the earlier observations and confirm them during normal prometaphase and anaphase motion. Artificial forces sufficient to stretch the chromosome cause little or no increase in the distance from the pole to the kinetochore, but there is much less resistance to lateral or poleward displacement. The spindle as a whole behaves in micromanipulation and during isolation as a single body it is a mechanical unit independent of the rest of the cell (reviewed by Mazia, 1961). The simplest, and the classic, interpretation attributes these mechanical properties to individual spindle fibers in order to account for the... 

Fig. 9. A living crane fly Nephrotoma suturalis) spermatocyte in anaphase I, showing the consequences of displacing a chromosome across the interzonal region. The arrows indicate the kinetochores of the displaced chromosome just before the micromanipulation experiment (0.0-minute print), just after displacement and removal of the needle (1.9 minutes), and during the subsequent steady motion back to the lower pole (4.5 to 17.0 minutes the two sister chromatids are visible throughout). The average velocity was 0.93 p per minute, typical of normal anaphase motion in this material. XI,000. (From unpublished experiments of Forer and Koch.)...

Fig. 14. Stable unipolar malorientation of two interlocked bivalents in a living grasshopper Melanoplus differentialis) spermatocyte. The kinetochoric ends of the two bivalents are labeled "a,b" and c,d/ respectively, and the time in minutes is indicated on each print. The interlocking was produced by micromanipulation already completed by the 0-minute print the chromosome configuration produced is most readily seen on the 137-and 155-minute prints. Double nondisjunction occurred in anaphase (175 to 289-minute prints). XI,000. (From Henderson and Koch. 1970. Chromosoma, 29 207-216. Modified by omission of four prints.)...

Exactly this is observed in studies on fixed cells (reviewed by John and Lewis, 1965, pp. 52ff.) and following experimental destruction of the linkage by micromanipulation of living cells (Nicklas, unpublished). A more exact prediction is possible from the postulated role of bipolar tension in reorientation unpaired meiotic chromosomes that retain the meiotic synorientation of both sister kinetochores to the same pole should be unstable and frequently reorient. If, however, they achieve amphiorientation, as do mitotic chromosomes, a stable bipolar orientation should result. Both conditions occur in nature and with the expected result (living cells with unpaired sex chromosomes, Dietz, 1956 Bauer et al., 1961 Nicklas, 1961 fixed cells, reviewed by John and Lewis, 1965). 

The oocytes of the newt Triturus veridens mature for months and grow to 2 mm in diameter with nuclei 1 mm in diameter. By micromanipulation, the chromosomes and nucleoli can be extracted. After appropriate treatment of the nucleoli, it can be shown under the electron microscope that their core is made of an axial fiber of deoxyribonucleoprotein from which ribonu-cleoprotein fibrils emerge in clusters of 80-100. Between the clusters are portions of nontranscribed DNA referred to as spacer DNA. A distinct granule 125 A in diameter links the DNP to the RNP fibers. The granule is believed to be RNA polymerase. Somewhat similar pictures were obtained when portions of the lampbrush chromosomes were examined. 

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