ULTRASTRUCTURE AND CYTOCHEMISTRY OF METABOLIC DNA IN TIPULA

Abstract

A DNA body is present in the females of the fly Tipula oleracea and is formed in contact with the sex chromosomes in the oogonial interphases. At each oogonial mitosis, the DNA body follows the chromosomes to one anaphase group and is included in one of the telophase nuclei. The body increases appreciably in size during the interphase of meiosis. All oocytes have the body, but only a few nurse cells possess it. The DNA body synthesizes its DNA at a different time than the chromosomes, as is shown by incorporation of tritiated thymidine, and contains 59 % of the DNA of the nucleus, as is disclosed by spectrophotometric measurements. At late diplotene the DNA body disintegrates, releasing its DNA into either the nucleus or the cytoplasm. When studied in the electron microscope, the DNA body appears composed of a tight mass of intertwined fibrils. Demonstration that the main mass of the body is composed of DNA is obtained from cytochemical tests which reveal that the DNA body is Feulgen positive, stains green with azure B, incorporates H3-thymidine, and after digestion with DNase is Feulgen negative. The DNA of the body is complexed with histone, like the DNA of the chromosomes, as is revealed by an intense alkaline fast green staining. Electron microscope examination of oocytes reveals that one side of the DNA body is in close contact with the nuclear envelope and that the other side possesses an outer shell composed mainly of particles 150 to 950 A in diameter. Between the outer shell and the chromosomes there is a band of low electron opacity, 4000 to 7000 A thick. In the light microscope, this light band together with the outer shell is Feulgen negative and stains violet with azure B, this is confirmation of the presence of RNA. In the oocytes the nucleoli are found inside the DNA body. These nucleoli have a nucleolonema composed mainly of particles 150 to 250 A. The nucleoli are Feulgen negative, alkaline fast green negative, stain violet with azure B, and do not stain with azure B after RNase digestion, thus confirming their RNA content. The presence of the nucleoli inside the DNA body and of a band of RNA between the body and the chromosomes is indicative of a high RNA synthetic activity. Since the DNA of the body is complexed with histone, as in the chromosomes, and the nucleoli are located inside the body, the simplest interpretation of the DNA body is that it represents hundreds of copies of the operons of the nucleolar organizing region or neighboring regions. The situation found in Tipula has several basic features in common with the polytene chromosomes of other Diptera and with the hundreds of nucleoli present in Triturus oocytes. In all three cases, genes seem to be copied hundreds of times but are kept in different types of packages. A DNA body like the one in Tipula oleracea is found in other species of Diptera and in the Coleoptera. There is no indication, from the present investigation, that the DNA body is in any way associated with a virus.

COMPARATIVE MORPHOLOGY OF NUCLEOLAR DNA IN DROSOPHILA

“…According to this suggestion, the DNA of some genetic loci may replicate considerably beyond the ploidy level of the nucleus as a whole (10,15,24,28). That such a phenomenon can occur phylogenetically, if not oatogenetically, has been demonstrated by Keyl (13).…”

A historical and evolutionary perspective on the biological significance of circulating DNA and extracellular vesicles

“…At late diplotene the DNA body disintegrates and its DNA is released into the nucleus or cytoplasm [142] similarly to the destruction of macronuclei in ciliated protozoa after micronuclei underwent division or meiosis [143][144][145].…”

“…At late diplotene the DNA body disintegrates and DNA is released into the nucleus or cytoplasm [142].…”

“…Lima-de-Faria and Moses studied DNA bodies in the females of the fly Tipula oleracea that formed in contact with the sex chromosomes in the oogonial interphases [142]. A DNA body synthesizes its DNA at a different time to that of the chromosomes, and its DNA forms complexes with histones, similar to the DNA of the chromosomes.…”

“…A DNA body synthesizes its DNA at a different time to that of the chromosomes, and its DNA forms complexes with histones, similar to the DNA of the chromosomes. At late diplotene, the DNA body disintegrates and its DNA is released into either the nucleus or the cytoplasm [142], similar to the destruction of macronuclei in ciliated protozoa (see ''Macronuclei and metabolic DNA'') after the micronuclei underwent division or meiosis [143][144][145]. The nucleoli of the Tipula oocytes are positioned within the DNA body and the presence of a band of RNA between the body and the chromosomes was detected, indicating that the DNA body has high RNA synthetic activity.…”