The formation of polytene chromosomes during macronuclear development of the hypotrichous ciliate Stylonychia mytilus

Chromosoma ◽  
1981 ◽  
Vol 82 (2) ◽  
pp. 309-314 ◽  
Author(s):  
G. F. Meyer ◽  
H. J. Lipps
Keyword(s):  
Polytene Chromosomes ◽  
Macronuclear Development ◽  
Stylonychia Mytilus

Electron-Microscopic Observations on the Macronuclear Development of Stylonychia Mytilus and Tetrahymena Pyriformis (Ciliophora-Protozoa)

1973 ◽  
Vol 13 (2) ◽  
pp. 479-509 ◽  
Author(s):  
K. G. MURTI
Keyword(s):  
Dna Synthesis ◽  
Nuclear Membrane ◽  
Fibrous Material ◽  
Structural Changes ◽  
Degradation Products ◽  
Polytene Chromosomes ◽  
Tetrahymena Pyriformis ◽  
Nucleotide Sequences ◽  
Macronuclear Development ◽  
Stylonychia Mytilus

This report describes an ultrastructural investigation of macronuclear development following conjugation in Stylonychia mytilus (a spirotrichous ciliate) and Tetrahymena pyriformis (a holotrichous ciliate). In S. mytilus, polytene chromosomes are formed in the young macronucleus (macronuclear Anlage). They are subsequently broken between the bands by ‘membranous’ partitions; the assembly of the membranes appears to be concomitant with the formation of the polytene chromosomes. The membranes in the Anlage appear to originate from fibrous material seen in the early Anlage. This fibrous material in the earlier stages is seen concentrated at several points along the border of the inner nuclear membrane. In the later stages it is seen in the interior of the Anlage, outlining the developing polytene chromosomes. As the chromosomes reach the maximum degree of polyteny, the fibrous material condenses to acquire a membranous appearance and extends into the interband regions. The Anlage throughout this period shows a progressive increase in size. Subsequently, the membranes enclose individually each band plus portions of the 2 adjacent interband regions of the polytene chromosomes to form a large number of vesicles. After vesicle formation the Anlage shrinks, and the chromatin inside the vesicles shows degradative changes. Finally, the vesicles disappear, the membrane degradation products appear at the nuclear membrane, and the Anlage now contains nucleoli. The Anlage increases its DNA content by multiple rounds of replication to become a mature macronucleus. The ultra-structural changes observed in the Anlage support the idea of genetic diminution (i.e. extensive DNA synthesis, elimination of many DNA nucleotide sequences, and amplification of the remaining DNA nucleotide sequences in a second period of DNA synthesis) proposed earlier on the basis of cytochemical, biochemical, and limited electron-microscope studies. In T. pyriformis, the macronuclear development differs substantially from that of Stylonychia. Features such as the formation and degradation of polytene chromosomes are absent in the macronuclear development of Tetrahymena; the young macronucleus in this cell becomes a mature macronucleus by progressive increment in size and chromatin content with no apparent genetic diminution. These observations agree with cytochemical studies on the macronuclear development of Tetrahymena.

scholarly journals COMPARTMENTALIZATION OF THE DEVELOPING MACRONUCLEUS FOLLOWING CONJUGATION IN STYLONYCHIA AND EUPLOTES

1970 ◽  
Vol 47 (2) ◽  
pp. 395-407 ◽  
Author(s):  
John A. Kloetzel
Keyword(s):  
Electron Microscope ◽  
Fibrous Material ◽  
Polytene Chromosomes ◽  
Genetic Constitution ◽  
Thin Sections ◽  
Macronuclear Development ◽  
Individual Bands ◽  
Second Period ◽  
Replication Bands ◽  
Material Form

The development of the macronucleus following conjugation in the hypotrichous ciliates Euplotes and Stylonychia has been examined with the electron microscope. Banded polytene chromosomes can be seen in thin sections of the macronuclear anlagen during the early periods of exconjugant development. As the chromosomes reach their maximum state of polyteny, sheets of fibrous material appear between the chromosomes and transect the chromosomes in the interband regions. Individual bands of the polytene chromosomes thus appear to be isolated in separate compartments. Subsequently, during the stage when the bulk of the polytenic DNA is degraded (1), these compartments swell, resulting in a nucleus packed with thousands of separate spherical chambers. Individual chromosomes are no longer discernible. The anlagen retain this compartmentalized condition for several hours, at the end of which time aggregates of dense material form within many of the compartments. The partitioning layers disperse shortly before replication bands appear within the elongating anlagen, initiating the second period of DNA synthesis characteristic of macronuclear development in these hypotrichs. The evidence presented here suggests that the "chromatin granules" seen in the mature vegetative macronucleus represent the material of single bands of the polytene chromosomes seen during the earlier stages of macronuclear development. The possibility is also discussed that the degradation of DNA in the polytene chromosomes may be genetically selective, which would result in a somatic macronucleus with a different genetic constitution than that of the micronucleus from which it was derived.

scholarly journals DNA rearrangements in Euplotes crassus coincide with discrete periods of DNA replication during the polytene chromosome stage of macronuclear development.

1995 ◽  
Vol 15 (12) ◽  
pp. 6488-6495 ◽  
Author(s):  
J S Frels ◽  
C L Jahn
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Polytene Chromosome ◽  
Dna Sequences ◽  
Polytene Chromosomes ◽  
Single Locus ◽  
Dna Rearrangements ◽  
Macronuclear Development ◽  
Euplotes Crassus ◽  
Inhibition Of Dna Synthesis

Macronuclear development in Euplotes crassus begins with polytenization of micronuclear chromosomes and is accompanied by highly precise excision of DNA sequences known as internal eliminated sequences and transposon-like elements (Tecs). Quantitation of radiolabeled-precursor incorporation into DNA indicates that DNA synthesis during formation of polytene chromosomes is not continuous and occurs during two distinct periods. We demonstrate that the timing of Tec excision coincides with these replication periods and that excision can occur during both periods even at a single locus. We also show that Tec and internal eliminated sequence excisions are coincident in the second replication period, thus providing further evidence for similarity in their excision mechanism. Inhibition of DNA synthesis with hydroxyurea diminishes Tec element excision, indicating that replication is an important aspect of the excision process.

scholarly journals Large scale synchronous mating and the study of macronuclear development in Euplotes crassus.

1985 ◽  
Vol 101 (1) ◽  
pp. 79-84 ◽  
Author(s):  
M Roth ◽  
M Lin ◽  
D M Prescott
Keyword(s):  
Large Scale ◽  
Average Molecular Weight ◽  
Polytene Chromosomes ◽  
Dna Molecules ◽  
Chromosomal Dna ◽  
Base Pairs ◽  
Macronuclear Development ◽  
Euplotes Crassus ◽  
Large Populations ◽  
Small Size Group

After conjugation in hypotrichous ciliates, a new macronucleus is produced from a copy of the micronucleus. This transformation involves large-scale reorganization of DNA, with conversion of the chromosomal micronuclear genome into short, gene-sized DNA molecules in the macronucleus. To study directly the changes that occur during this process, we have developed techniques for synchronous mating of large populations of the hypotrichous ciliate Euplotes crassus. Electron microscope studies show that the micronuclear chromosomes are polytenized during the first 20 h of macronuclear development. The polytene chromosomes lack the band-interband organization observed in other hypotrichs and in the Diptera. Polytenization is followed by transectioning of the chromosomes. We isolated DNA at various times of macronuclear development and found that the average molecular weight of the DNA decreases at the time of chromosome transectioning. In addition, we have shown that a small size group of macronuclear DNA molecules (450-550 base pairs) is excised from the chromosomal DNA approximately 10 h later in macronuclear development.

Разработка интегративного критерия безопасности продуктов питания

2015 ◽  
pp. 14-21
Author(s):  
Валерий Васильевич Воробьев
Keyword(s):  
Tetrahymena Pyriformis ◽  
Stylonychia Mytilus

В статье рассматриваются ускоренные методы определения токсичности пищевого сырья и продуктов питания на основе использования инфузорий Tetrahymena pyriformis и Stylonychia mytilus. Показано, что применение экспресс-метода с использованием стилонихий по определению общей токсичности лососевой икры, пресервов из соленой кеты, горбуши и сельди с различными консервантами, по сравнению с методикой определения уровня токсичности с помощью тетрахимены, позволяет сократить продолжительность констатации в 5 – 16 раз.

scholarly journals Molecular Characterization of hobo-Mediated Inversions in Drosophila melanogaster

Genetics ◽  
1996 ◽  
Vol 144 (2) ◽  
pp. 647-656
Author(s):  
William B Eggleston ◽  
Nac R Rim ◽  
Johng K Lim
Keyword(s):  
X Chromosome ◽  
Polymerase Chain Reaction Amplification ◽  
Polytene Chromosomes ◽  
Chromosomal Inversions ◽  
Hobo Element ◽  
Reaction Amplification ◽  
Notch Locus ◽  
Polymerase Chain

Abstract The structure of chromosomal inversions mediated by hobo transposable elements in the Uc-1 X chromosome was investigated using cytogenetic and molecular methods. Uc-1 contains a phenotypically silent hobo element inserted in an intron of the Notch locus. Cytological screening identified six independent Notch mutations resulting from chromosomal inversions with one breakpoint at cytological position 3C7, the location of Notch. In situ hybridization to salivary gland polytene chromosomes determined that both ends of each inversion contained hobo and Notch sequences. Southern blot analyses showed that both breakpoints in each inversion had hobo-Notch junction fragments indistinguishable in structure from those present in the Uc-1 X chromosome prior to the rearrangements. Polymerase chain reaction amplification of the 12 hobo-Notch junction fragments in the six inversions, followed by DNA sequence analysis, determined that each was identical to one of the two hobo-Notch junctions present in Uc-1. These results are consistent with a model in which hobo-mediated inversions result from homologous pairing and recombination between a pair of hobo elements in reverse orientation.

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