BIVALENT FORMING RACE OF MESOCYCLOPS EDAX (COPEPODA, CRUSTACEA)

1980 ◽  
Vol 22 (3) ◽  
pp. 427-431 ◽  
Author(s):  
C. C. Chinnappa
Keyword(s):  
Chromosome Morphology ◽  
Chromatin Diminution ◽  
Cleavage Division ◽  
Large Rings ◽  
Bivalent Formation ◽  
Cleavage Stages ◽  
Mesocyclops Edax

Meiosis and chromosome morphology in females of a bivalent forming race of Mesocyclops edax (S. A. Forbes) are described. Meiosis is achiasmate and exhibits regular bivalent formation (2n = 14). Chromosome analyses of other populations of M. edax revealed that the females are heterozygous for several interchanges leading to the formation of large rings. Chromatin diminution during cleavage stages suggests that the elimination of H-segments occurs at the fourth cleavage division.

Analysis of DNA Levels During Gonomery in Early Cleavage Divisions of the Freshwater Copepod Mesocyclops Edax

1997 ◽  
Vol 3 (S2) ◽  
pp. 191-192 ◽  
Author(s):  
E.M. Rasch ◽  
G.A. Wyngaard
Keyword(s):  
Acetic Acid ◽  
Early Cleavage ◽  
Chromatin Diminution ◽  
Cleavage Division ◽  
Relative Contribution ◽  
Male Genome ◽  
Egg Carrying ◽  
Mesocyclops Edax ◽  
Chromosome Regions ◽  
Absolute Etoh

Gonomery, the separate grouping of maternal and paternal chromosomes during the first few mitoses following fertilization (Fig. 1) and chromatin diminution, the fragmentation and elimination of whole chromosome regions during specific stages of early cleavage in all primordial cells of the soma, occur in several species of copepods, ascarid nematodes, ciliated protozoa, Japanese hagfish 9 and a few other invertebrates. Because of the marked loss of DNA from all presumptive somatic cells by selective chromatin diminution during the 4th cleavage division in M. edax, it was of interest to determine DNA levels in chromosomes during gonomery in anaphases preceding diminution (Fig. 1). It was also important to estimate the DNA content of sperm as an index of the relative contribution by the male genome at fertilization in this species.Mature males and egg-carrying females were fixed in 3:1 methanol/acetic acid for 3-5 mins, swollen in 45% acetic acid for 2-3 mins, squashed, frozen in liquid N2 for coverslip removal, thawed in 2 changes of absolute ETOH and air dried.

DNA levels in somatic and germ line cells of a freshwater crustacean, Mesocyclops edax

1995 ◽  
Vol 53 ◽  
pp. 924-925
Author(s):  
E. M. Rasch ◽  
G.A. Wyngaard
Keyword(s):  
Acetic Acid ◽  
Somatic Cell ◽  
Nuclear Dna ◽  
Germ Line ◽  
Internal Reference ◽  
Chromatin Diminution ◽  
Internal Reference Standard ◽  
Freshwater Crustacean ◽  
Mesocyclops Edax ◽  
Chromosome Regions

Chromatin diminution--the fragmentation and elimination of chromosome Regions--provides an unusual opportunity to study genomic reorganization during development. Some species of copepods regularly excise and discard large amounts of nuclear DNA from presumptive somatic cell lines during early cleavage stages . To study this phenomenon in M. edax we determined DNA-Feulgen levels for more than 5,600 individual nuclei from squash preparations of 30 female and 25 male adults collected from lakes in Nova Scotia, Virginia and Florida. Fixation in 3:1 methanol/acetic acid was followed by squashing individual specimens in 45% acetic acid, freezing each slide in liquid N2 and thawing in absolute ethanol before air drying. Each series of slides was stained with the feulgen reaction for DNA and measured with a Vickers M86 scanning and integrating microdensitometer at 560 nm, using chicken RBC nuclei as an internal reference standard of 2.5 pg DNA per cell. This allowed us to ask several questions: are there differences in genome size (1) among specimens from different collecting localities, (2) between females and males at any single locality, and (3) between cells of germ line and somatic cell lineages?

Chromatin diminution in the copepod Mesocyclops edax: diminution of tandemly repeated DNA families from somatic cells

Genome ◽  
2006 ◽  
Vol 49 (6) ◽  
pp. 657-665 ◽  
Author(s):  
Guy Drouin
Keyword(s):  
Dna Sequences ◽  
Germ Line ◽  
Somatic Cells ◽  
Repeated Sequences ◽  
Cyclopoid Copepod ◽  
Embryonic Cells ◽  
Repeated Dna ◽  
Chromatin Diminution ◽  
Mesocyclops Edax ◽  
Tandemly Repeated Dna

Chromatin diminution, i.e., the loss of selected chromosomal regions during the differentiation of early embryonic cells into somatic cells, has been described in taxa as varied as ciliates, copepods, insects, nematodes, and hagfish. The nature of the eliminated DNA has been extensively studied in ciliate, nematode, and hagfish species. However, the small size of copepods, which makes it difficult to obtain enough DNA from early embryonic cells for cloning and sequencing, has limited such studies. Here, to identify the sequences eliminated from the somatic cells of a copepod species that undergoes chromatin diminution, we randomly amplified DNA fragments from germ line and somatic line cells of Mesocyclops edax, a freshwater cyclopoid copepod. Of 47 randomly amplified germ line clones, 45 (96%) contained short, tandemly repeated sequences composed of either 2 bp CA-repeats, 8 bp CAAATAGA-repeats, or 9 bp CAAATTAAA-repeats. In contrast, of 83 randomly amplified somatic line clones, only 47 (57%) contained such short, tandemly repeated sequences. As previously observed in some nematode species, our results therefore show that there is partial elimination of chromosomal regions containing (CAAATAGA and CAAATTAAA) repeated sequences during the chromatin diminution observed in the somatic cells of M. edax. We speculate that chromatin diminution might have evolved repeatedly by recruitment of RNAi-related mechanisms to eliminate nonfunctional tandemly repeated DNA sequences from the somatic genome of some species.Key words: chromatin diminution, Mesocyclops edax, copepod, satellite DNA, hetorochromatin.

Chromatin diminution in the copepod Mesocyclops edax: elimination of both highly repetitive and nonhighly repetitive DNA

Genome ◽  
2013 ◽  
Vol 56 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Christian McKinnon ◽  
Guy Drouin
Keyword(s):  
Repetitive Dna ◽  
Tandem Repeats ◽  
Repetitive Sequences ◽  
Embryonic Cells ◽  
Chromatin Diminution ◽  
Developmentally Regulated ◽  
Dna Elimination ◽  
Eukaryotic Species ◽  
Cyclops Kolensis ◽  
Mesocyclops Edax

Chromatin diminution, a developmentally regulated process of DNA elimination, is found in numerous eukaryotic species. In the copepod Mesocyclops edax, some 90% of its genomic DNA is eliminated during the differentiation of embryonic cells into somatic cells. Previous studies have shown that the eliminated DNA contains highly repetitive sequences. Here, we sequenced DNA fragments from pre- and postdiminution cells to determine whether nonhighly repetitive sequences are also eliminated during the process of chromatin diminution. Comparative analyses of these sequences, as well as the sequences eliminated from the genome of the copepod Cyclops kolensis, show that they all share similar abundances of tandem repeats, dispersed repeats, transposable elements, and various coding and noncoding sequences. This suggests that, in the chromatin diminution observed in M. edax, both highly repetitive and nonhighly repetitive sequences are eliminated and that there is no bias in the type of nonhighly repetitive DNA being eliminated.

On cyclical alterations in the Feulgen staining of nuclei during the development of nematodes

Parasitology ◽  
1963 ◽  
Vol 53 (1-2) ◽  
pp. 273-283 ◽  
Author(s):  
L. Monné
Keyword(s):  
Germ Cells ◽  
Technical Assistance ◽  
Somatic Cells ◽  
Germinal Vesicle ◽  
Subsequent Development ◽  
The Other ◽  
Feulgen Staining ◽  
Chromatin Diminution ◽  
Cleavage Stages ◽  
Forms Of Life

In the Ascaroidea the germinal vesicle, the pronuclei and the nuclei of all the blastomeres prior to chromatin diminution are strongly Feulgen positive. The nuclei of the somatic cells, which become suddenly Feulgen negative upon chromatin diminution, gradually become strongly Feulgen positive again during subsequent development. The nuclei of the germ track cells which are not subjected to chromatin diminution remain strongly Feulgen positive during the whole development. In all the other metazoa, including the nematodes where chromatin diminution does not occur, the germinal vesicle, the synkaryon and the nuclei of the blastomeres during the earliest cleavage stages are Feulgen negative. The latter, however, become gradually strongly Feulgen positive again during the subsequent development. The nuclei of the female germ cells and the synkaryon of protozoa and plants have also been reported to be Feulgen negative. Thus, the Feulgen-positive nuclei of the definitive somatic cells always originate from Feulgen-negative nuclei, in the Ascaroidea from the Feulgen-negative nuclei of the blastomeres and in all other forms of life from the Feulgen-negative nuclei of the eggs. The Feulgen-positive nuclei of the germ cells also originate from Feulgen-negative nuclei except in the Ascaroidea, where they originate from Feulgen-positive nuclei. In the somatic track the sequence of Feulgen-positive nuclei is interrupted in all forms of life and during the germ track it is also interrupted in all forms of life except the Ascaroidea, where it is uninterrupted. These biologically important phenomena are discussed.These investigations have been supported by a grant from the Knut and Alice Wallenberg stiftelse. The author is indebted to Mrs. M. Wahlström and E. Nowak for their valuable technical assistance.

On an Application of the Metallurgical Stage to Chromosome Morphology

1967 ◽  
Vol 25 ◽  
pp. 28-29
Author(s):  
Godfrey C. Hoskins
Keyword(s):  
Human Chromosome ◽  
Electron Micrographs ◽  
Chromosome Morphology ◽  
Electron Optics ◽  
Electron Micrograph ◽  
Photographic Evidence ◽  
Sophisticated Equipment ◽  
Periodic Arrangement

The first serious electron microscooic studies of chromosomes accompanied by pictures were by I. Elvers in 1941 and 1943. His prodigious study, from the manufacture of micronets to the development of procedures for interpreting electron micrographs has gone all but unnoticed. The application of todays sophisticated equipment confirms many of the findings he gleaned from interpretation of images distorted by the electron optics of that time. In his figure 18 he notes periodic arrangement of pepsin sensitive “prickles” now called secondary fibers. In his figure 66 precise regularity of arrangement of these fibers can be seen. In his figure 22 he reproduces Siegbahn's first stereoscopic electron micrograph of chromosomes.The two stereoscopic pairs of electron micrographs of a human chromosome presented here were taken with a metallurgical stage on a Phillips EM200. These views are interpreted as providing photographic evidence that primary fibers (1°F) about 1,200Å thick are surrounded by secondary fibers (2°F) arranged in regular intervals of about 2,800Å in this metanhase human chromosome. At the telomere the primary fibers bend back on themselves and entwine through the center of each of each chromatid. The secondary fibers are seen to continue to surround primary fibers at telomeres. Thus at telomeres, secondary fibers present a surface not unlike that of the side of the chromosome, and no more susceptible to the addition of broken elements from other chromosomes.

Laser Scanning Confocal Microscopy and Three-Dimesnsional Reconstruction of the Mitotic Spindles of Unequally Dividing Embryonic Cells

1990 ◽  
Vol 48 (3) ◽  
pp. 166-167
Author(s):  
J. Holy ◽  
G. Schatten
Keyword(s):  
Confocal Microscopy ◽  
Mitotic Spindle ◽  
Laser Scanning ◽  
Three Dimensional ◽  
Laser Scanning Confocal Microscopy ◽  
Two Dimensions ◽  
Embryonic Cells ◽  
Mitotic Spindles ◽  
Cleavage Division ◽  
Scanning Confocal Microscopy

One of the classic limitations of light microscopy has been the fact that three dimensional biological events could only be visualized in two dimensions. Recently, this shortcoming has been overcome by combining the technologies of laser scanning confocal microscopy (LSCM) and computer processing of microscopical data by volume rendering methods. We have employed these techniques to examine morphogenetic events characterizing early development of sea urchin embryos. Specifically, the fourth cleavage division was examined because it is at this point that the first morphological signs of cell differentiation appear, manifested in the production of macromeres and micromeres by unequally dividing vegetal blastomeres.The mitotic spindle within vegetal blastomeres undergoing unequal cleavage are highly polarized and develop specialized, flattened asters toward the micromere pole. In order to reconstruct the three-dimensional features of these spindles, both isolated spindles and intact, extracted embryos were fluorescently labeled with antibodies directed against either centrosomes or tubulin.

Sign in / Sign up

Export Citation Format

Share Document