High order structure of Chironomus polytene chromosomes by scanning electron microscopy.

Abstract

Polytene chromosomes isolated from Chironomus salivary gland cells were processed with the Os04/TCH technique and examined by scanning electron microscopy (SEM) mainly using stereo techniques. When chromosomes were somewhat extended for preparation, band and interband regions became clearly visible. The bands appear to be dense masses of kinky fibers while the interband regions consist of the 30 nm chromatin fibers. On the other hand, in less extended chromosomes where band and interband regions were less distinctive, most of the component fibers appear to have coiled configurations and their diameters range 150 to more than 200 nm. We conclude, therefore, that the natural chromonemata of the polytene chromosomes are about 200 nm in diameter rather 30 nm even in the interband regions. The polytene chromosomes seem to have a cable-like structure.

Chromatin Structure in Bands and Interbands of Polytene Chromosomes Imaged by Atomic Force Microscopy

“…In contrast to the findings of Taniguchi and Takayama (1987), although those observations were done on Chironomus polytene chromosomes, 700-nm structures were found to exist in the chromosomes in the present study. The 700-nm-wide structures were generally present in all unstretched chromosomes investigated.…”

“…Chromatin fibrils of 25 nm width were reported in whole mount EM studies of Drosophila polytene chromosomes (DuPraw and Rae, 1966). With the same method it was observed that in Chironomus polytene chromosomes bands appeared to consist of dense masses of kinky fibers while interbands consist of 30-nm fibers (Taniguchi and Takayama, 1987). In less extended chromosomes, coiled fibers of 200-nm width were observed both in bands and interbands.…”

“…As a level of condensation above the 30-nm folded fiber, in general, an interphase fiber with an average width of 250 nm is observed (Manueledis and Chen, 1990, and references herein]. Two models describe the folding of the solenoid into the 250-nm fiber (Manueledis and Chen, 1990;Taniguchi and Takayama, 1987). They both assume a simple coiling of the solenoid into a thicker fiber with a cable like appearance.…”