Abstract
After conjugation in the ciliated protozoan, Oxytricha, polytene chromosomes are formed during the development of a macronucleus from a micronucleus. Here we report a microscopic study of these chromosomes and an analysis of their DNA. The polytene chromosomes of Oxytricha bear a strong morphological resemblance to the polytene chromosomes of the Dipteran salivary gland. The nucleus of a developing macronuclear anlage contains 120±2 polytene chromosomes and each chromosome has an average of 81 bands; a total of about 10,000 bands per nucleus. At a later stage in development, the number of bands per chromosome is reduced by a factor of four, presumably due to fusion of adjacent bands. The polytene chromosomes then break up into their constituent bands, each of which is encased in a vesicle. There are about 2,700 vesicles per nucleus. — During the growth of polytene chromosomes, there is a change in the relative proportion of sequences in the DNA. The DNA from polytene nuclei has a buoyant density of 1.695 g/cc, significantly lighter than the density of the original micronuclear DNA (1.698 g/cc to 1.702 g/cc). We interpret this buoyant density change to be the result of differential replication of DNA sequences during polytene chromosome growth. A second change in DNA composition occurs after the polytene stage of development, shown by a shift in buoyant density to 1.701 g/cc in the DNA of the mature macronucleus. During this second process, the molecular weight of the DNA is reduced from greater than 50×106 daltons to about 2×106 daltons.
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Alonso, P., Jareño, M. A.: Incorporacion de uridine-H3 en el esbozo macronuclear de Stylonyohia mytilus. Microbiol. España 27, 199–211 (1974)
Alonso, P., Perez-Silva, J.: Giant chromosomes in Protozoa. Nature (Lond.) 205, 313 (1965)
Ammermann, D.: Riesenchromosomen in der Macronukleusanlage der Ciliaten, Stylonychia spec. Naturwissenschaften 51, 249 (1964)
Ammermann, D.: Synthese und Abbau der Nucleinsäuren während der Entwicklung des Macronukleus von Stylonychia mytilus (Protozoa, Ciliata). Chromosoma (Berl.) 25, 107–120 (1968)
Ammermann, D.: Release of DNA breakdown products into the culture medium of Stylonychia mytilus exconjugants (Protozoa, Ciliata) during the destruction of the polytene chromosomes. J. Cell Biol. 40, 576–577 (1969)
Ammermann, D., Steinbruck, G., von Berger, L., Hennig, W.: The development of the macronucleus in the ciliated protozoan Stylonychia mytilus. Chromosoma (Berl.) 45, 401–429 (1974)
Birnstiel, M. L., Speirs, J., Purdom, I., Jones, K., Loening, U.: Properties and composition of the isolated ribosomal DNA satellite of Xenopus laevis. Nature (Lond.) 219, 454–463 (1968)
Bostock, C. J., Prescott, D. M.: Evidence of gene diminution during the formation of the macronucleus in the protozoan, Stylonychia. Proc. nat. Acad. Sci. Wash. 69, 139–142 (1972)
Borgi, E., Hersey, A. D.: Sedimentation rate as a measure of molecular weight of DNA. Biophys. J. 3, 309–321 (1963)
Cassagnau, P.: Les chromosomes salivaires polytènes chez Bilobella grassei (Denis) (Collemboles: Neanuridae). Chromosoma (Berl.) 35, 57–83 (1971)
Daneholt, B.: Transcription in polytene chromosomes. Cell 4, 1–9 (1975)
Dawid, I. B., Brown, D. D., Reeder, R. H.: Composition and structure of chromosomal and amplified ribosomal DNAs of Xenopus laevis. J. molec. Biol. 51, 341–360 (1970)
Dickson, E., Boyd, J. B., Laird, C. D.: Sequence diversity of polytene chromosome DNA from Drosophila hydei. J. molec. Biol. 61, 615–627 (1971)
Engberg, J., Nilsson, J. R., Pearlman, R. E., Leick, V.: Induction of nucleolar and mitochondrial DNA replication in Tetrahymena pyriformis. Proc. nat. Acad. Sci. (Wash.) 71, 894–898 (1974)
Flavell, R. A., Jones, I. G.: Mitochondrial deoxyribonucleic acid from Tetrahymena pyriformis and its kinetic complexity. Biochem. J. 116, 811–817 (1970)
Gall, J. G.: Free ribosomal RNA genes in the macronucleus of Tetrahymena. Proc. nat. Acad. Sci. (Wash.) 71, 3078–3081 (1974)
Gall, J. G., Cohen, E. H., Polan, M. L.: Repetitive DNA sequences in Drosophila. Chromosoma (Berl.) 33, 319–344 (1971)
Golikova, M. N.: Polytene chromosomes in the developing macronucleus of a ciliate. Citologija (USSR) 6, 250–253 (1964)
Hochman, B.: Analysis of a whole chromosome in Drosophila. Cold Spr. Harb. Symp. quant. Biol. 38, 581–589 (1974)
Jareño, M. A., Alonso, P., Perez-Silva, J.: Identification of some puffed regions in the polytene chromosomes of Stylonychia mytilus. Protistologica 8, 237–243 (1972)
Judd, B. H., Young, M. W.: An examination of the one cistron: one chromomere concept. Cold Spr. Harb. Symp. quant. Biol. 38, 573–579 (1974)
Kloetzel, J. A.: Compartmentalization of the developing macronucleus following conjugation in Stylonychia and Euplotes. J. Cell Biol. 47, 395–407 (1970)
Lauth, M. R., Spear, B. B., Heumann, J., Prescott, D. M.: DNA of ciliated Protozoa. V. DNA sequence diminution during macronuclear development of Oxytricha. Cell (in press, 1976)
Nagl, W.: Puffing of polytene chromosomes in a plant (Phaseolus vulgaris). Naturwissenschaften 56, 221–222 (1969)
Prescott, D. M., Bostock, C. J., Murti, K. G., Lauth, M. R., Gamow, E.: DNA of ciliated Protozoa. I. Electron microscopic and sedimentation analysis of macronuclear and micronuclear DNA of Stylonychia mytilus. Chromosoma (Berl.) 34, 355–366 (1971)
Prescott, D. M., Murti, K. G.: Chromosome structure in ciliated Protozoa. Cold Spr. Harb. Symp. quant. Biol. 38, 609–618 (1974)
Prescott, D. M., Murti, K. G., Bostock, C. J.: Genetic apparatus of Stylonychia sp. Nature (Lond.) 242, 597–600 (1973)
Rao, M. V. N., Ammermann, D.: Polytene chromosomes and nucleic acid metabolism during macronuclear development in Euplotes. Chromosoma (Berl.) 29, 246–254 (1970)
Wesley, R. D.: Inverted repetitious sequences in the macronuclear DNA of hypotrichous ciliates. Proc. nat. Acad. Sci. (Wash.) 72, 678–682 (1975)
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This paper is No. VI in the series, “DNA of Ciliated Protozoa.”
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Spear, B.B., Lauth, M.R. Polytene chromosomes of Oxytricha: Biochemical and morphological changes during macronuclear development in a ciliated protozoan. Chromosoma 54, 1–13 (1976). https://doi.org/10.1007/BF00331828
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DOI: https://doi.org/10.1007/BF00331828