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Fine structure of kinetochore in Indian muntjac

Experimental Cell Research
Publication Date
DOI: 10.1016/0014-4827(71)90625-2


Abstract The large size of Indian muntjac (miniature deer) chromosomes and the presence of an unusually long centromere region on an X-autosome fusion chromosome provided an ideal subject for the study of the fine structure of the kinetochore. Whole mount electron microscopy demonstrated a marked restriction in the lateral looping of chromatin fibers in the region of the centromere. By thin section electron microscopy it was possible to distinguish longitudinal from transverse sections of the kinetochore. In longitudinal sections the outer layer was long (up to 1.45 μm) and straight and subcomponents consisting of two parallel or seemingly intertwined 90 Å lines were frequently seen. In transverse sections the outer layer was shorter, averaging 0.45 μm. It curved in a semicircle around part of the chromosome, and the subcomponents frequently appeared as a series of tubule-like structures. The inner layer of the kinetochore was intimately associated with and was probably composed of chromatin fibers. Transverse and serial longitudinal sections showed that the outer layer was an oval plate-like structure and was not composed of two kinetochore filaments. The structural features of the outer layer suggested that it does not contain chromatin fibers. The spindle fibers pass through the outer layer and usually disappear from view in the middle layer. In some sections they can be seen to pass through the middle and inner layer, and in other sections they appear to turn within the body of the chromosome and re-emerge through the inner and outer layer.

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