LARVAL AGE AND THE PATTERN OF DNA SYNTHESIS IN POLYTENE CHROMOSOMES

1968 ◽  
Vol 10 (1) ◽  
pp. 82-90 ◽  
Author(s):  
David Nash ◽  
John Bell
Keyword(s):  
Drosophila Melanogaster ◽  
Salivary Gland ◽  
Dna Synthesis ◽  
Polytene Chromosomes ◽  
Larval Life ◽  
Gland Cells ◽  
Salivary Gland Cells ◽  
Puparium Formation ◽  
Chromosome Ii ◽  
Replicative Cycle

It has been shown, by autoradiography using H3-thymidine, that the frequency of salivary gland cells where DNA synthesis covers the entire length of a specific polytene chromosomal segment (Chromosome II, 56F-60A, Drosophila melanogaster) drops off some time during the last day of larval life. The frequency of highly discontinuous DNA synthesis over the same region remains at about the same level until a stage closer to puparium formation, when all DNA synthesis stops.If a cycle of DNA synthesis, once initiated, goes to completion, then this finding indicates that the patterns of spatially continuous synthesis tend to occur early in the replicative cycle and that the terminal phases of the cycle involve highly discontinuous patterns of synthesis.

WHOLE MOUNT ELECTRON MICROSCOPY OF THE NUCLEOLUS IN SALIVARY GLAND CELLS OF DROSOPHILA MELANOGASTER

1977 ◽  
Vol 19 (1) ◽  
pp. 21-29 ◽  
Author(s):  
Gary D. Burkholder
Keyword(s):  
Electron Microscopy ◽  
Drosophila Melanogaster ◽  
Salivary Gland ◽  
Peripheral Region ◽  
Core Region ◽  
28S Rrna ◽  
The Core ◽  
Gland Cells ◽  
Salivary Gland Cells ◽  
Whole Mount

The nucleolus of Drosophila melanogaster salivary gland cells, examined by whole mount electron microscopy, consists of a fibrillar core region and a peripheral region containing both fibres and granules. These regions appear to correspond to the fibrillar and granular components, respectively, seen in thin sections. Most of the nucleoli were attached to the chromocenter region of the polytene chromosomes, containing the nucleolar organizer. Bundles of relatively straight chromatin fibres, 13 nm in diameter, extended from the chromocenter into the core region of the nucleolus, however it was not possible to trace the path of these chromatin fibres through the nucleolus since they were obscured within the mass of nucleolar fibres. The nucleolar fibres in both the core and peripheral regions were irregular and knobby, with a diameter of about 15 nm. In the core region, the fibres appeared to be of considerable length and were characteristically clustered together to form small interconnected masses. The fibres in the peripheral region were relatively short and some appeared to blend with amorphous, poorly-defined pools of material. Electron dense granules 15-20 nm in diameter were also associated with this amorphous substance. It is hypothesized that the formation and subsequent packaging of the 28s rRNA may be represented by a morphological transition of the peripheral fibres, via an amorphous pool-like intermediate stage, into the nucleolar granules. The results of this study indicate that whole mount electron microscopy may be a useful alternative to thin sectioning in high resolution studies of the nucleolus.

scholarly journals CHROMOSOME-NUCLEAR MEMBRANE-CYTOPLASMIC INTERRELATIONS IN DROSOPHILA

1956 ◽  
Vol 2 (4) ◽  
pp. 407-414 ◽  
Author(s):  
Helen Gay
Keyword(s):  
Drosophila Melanogaster ◽  
Salivary Gland ◽  
Larval Development ◽  
Electron Micrographs ◽  
Nuclear Membrane ◽  
Membrane Structure ◽  
Deoxyribonucleic Acid ◽  
Cellular Function ◽  
Gland Cells ◽  
Salivary Gland Cells

The structural evidence for nucleocytoplasmic interrelationships observed in electron micrographs of salivary-gland cells of third instar larvae of Drosophila melanogaster has been reviewed. It has been found that the characteristic nuclear membrane outpocketings with their adjacent highly differentiated chromosomal materials occur at one stage of larval development at a time when a new cellular function is being initiated. Preliminary cytochemical studies to characterize the materials transferred from nucleus to cytoplasm indicate that deoxyribonucleic acid occurs within the blebs. Observations on chromosome and nuclear membrane structure are also presented.

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