The development of the tectum in Xenopus laevis: an autoradiographic study

Development ◽  
1972 ◽  
Vol 28 (1) ◽  
pp. 87-115
Author(s):  
K. Straznicky ◽  
R. M. Gaze
Keyword(s):  
Xenopus Laevis ◽  
Dna Synthesis ◽  
Optic Tectum ◽  
Tritiated Thymidine ◽  
Dorsal Surface ◽  
Autoradiographic Study ◽  
Cell Type ◽  
Pole Cells ◽  
Serial Addition ◽  
The Times

The development of the optic tectum in Xenopus laevis has been studied by the use of autoradiography with tritiated thymidine. The first part of the adult tectum to form is the rostroventral pole; cells in this position undergo their final DNA synthesis between stages 35 and 45 or shortly thereafter. Next, the cells comprising the ventrolateral border of the tectum form. These cells undergo their final DNA synthesis at or shortly after stage 45. Finally the cells comprising the dorsal surface of the adult tectum form, mainly between stages 50–55. This part of the tectum originates from the serial addition of strips of cells medially, which displace the pre-existing tissue laterally and rostrally. The formation of the tectum is virtually complete by stage 58. The tectum in Xenopus thus forms in topographical order from rostroventral to caudo-medial. The distribution of labelled cells, several stages after the time of injection of isotope, indicates that, at any one time, a segment of tectum is forming which runs normal to the tectal surface and includes all layers from the ventricular layer out to the surface. In Xenopus, therefore, the times of origin of tectal cells appear to be related not to cell type or tectal layer but to the topographical position of the cells across the surface of the tectum.

Studies on the Autonomy of Pellicular DNA in Paramecium

1969 ◽  
Vol 5 (2) ◽  
pp. 365-372
Author(s):  
JOAN SMITH-SONNEBORN ◽  
W. PLAUT
Keyword(s):  
Dna Synthesis ◽  
Tritiated Thymidine ◽  
Autoradiographic Study ◽  
Sensitive Material ◽  
Selective Labelling ◽  
The Relationship

This autoradiographic study was designed to elucidate the relationship between the macronucleus and pellicular DNA in Paramecium. The capacity of the cell to synthesize pellicular DNA in the absence of the macronucleus was established by demonstrating the incorporation of tritiated thymidine into DNase-sensitive material in the pellicles of amacronucleate cells. Moreover, using a technique which leads to selective labelling of the macronucleus in normal paramecia, we have looked for evidence of transfer of labelled DNA from the macronucleus to the pellicle with time. Finding none, we conclude that labelled pellicular DNA is not of macronuclear origin, and that labelled pellicular DNA synthesis is not directly dependent on the presence of the macronucleus.

scholarly journals AUTORADIOGRAPHIC STUDY OF DNA SYNTHESIS AND THE CELL CYCLE IN SPERMATOGONIA AND SPERMATOCYTES OF MOUSE TESTIS USING TRITIATED THYMIDINE

1962 ◽  
Vol 14 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Valerio Monesi
Keyword(s):  
Dna Synthesis ◽  
Time Course ◽  
Average Duration ◽  
Tritiated Thymidine ◽  
Periodic Acid ◽  
Autoradiographic Study ◽  
Type B ◽  
Average Life ◽  
Periodic Acid Schiff ◽  
Average Life Span

Mice were injected intraperitoneally with 15 µc of H3-thymidine. The time course of the labeling in spermatogonia and spermatocytes was studied by using autoradiography on 5 µ sections stained by the periodic acid-Schiff method and hematoxylin over a period of 57 hours after injection. Four generations of type A (called AI, AII, AIII, and AIV), one of intermediate, and one of type B spermatogonia occur in one cycle of the seminiferous epithelium. The average life span is about the same in all spermatogonia, i.e., about 27 to 30.5 hours. The average pre-DNA synthetic time, including the mitotic stages from metaphase through telophase and the portion of interphase preceding DNA synthesis, is also not very different, ranging between 7.5 and 10.5 hours. A remarkable difference exists, however, in the duration of DNA synthesis and of the post-DNA synthetic period. The average DNA synthetic time is very long and is highly variable in type B (14.5 hours), a little shorter and less variable in intermediate (12.5 hours) and AIV (13 hours) spermatogonia, and much shorter and very constant in AIII (8 hours), AII and AI (7 to 7.5 hours) spermatogonia. Conversely, the average post-DNA synthetic time, corresponding essentially to the duration of the prophase, is short and very constant in type B (4.5 hours), longer and variable in intermediate (6 hours) and AIV (8 hours) spermatogonia, and much longer and much more variable in AIII (11 hours), AII and AI (14 hours) spermatogonia. The premeiotic synthesis of DNA takes place in primary spermatocytes during the resting phase and terminates just before the visible onset of the meiotic prophase. Its average duration is 14 hours. No further synthesis of DNA takes place in later stages of spermatogenesis.

scholarly journals THE TIMING OF MEIOSIS AND DNA SYNTHESIS DURING EARLY OOGENESIS IN THE TOAD, XENOPUS LAEVIS

1972 ◽  
Vol 52 (3) ◽  
pp. 569-576 ◽  
Author(s):  
Lesley Watson Coggins ◽  
Joseph G. Gall
Keyword(s):  
Xenopus Laevis ◽  
Dna Synthesis ◽  
Time Course ◽  
Tritiated Thymidine ◽  
Extrachromosomal Dna ◽  
Cell Nuclei ◽  
Chromosomal Dna ◽  
Late Pachytene ◽  
Before And After ◽  
Major Period

Recently metamorphosed female Xenopus laevis toads were injected with tritiated thymidine. Animals were kept at 20°C and were sacrificed 1–23 days after isotope injection. Radio-autographs of squash preparations of the ovaries were made. The progress of labeled germ cell nuclei was followed to obtain information on the time course of early meiosis and extra-chromosomal DNA synthesis. Premeiotic S was estimated to take not more than 7 days. Leptotene takes 4 days, zygotene takes 5 days, and pachytene was estimated to be completed in about 18 days. The major period of amplification of the extrachromosomal DNA occurs in pachytene and takes about 13 days. A low level of synthesis was observed before and after this period, in zygotene and late pachytene-early diplotene, extending the total time for extrachromosomal DNA synthesis during meiosis to about 18 days. These data allowed the calculation to be made that one round of replication of the amplified DNA takes between 1.2 and 3.0 days. It was also found that in both oogonial and premeiotic interphases, the nucleolus-associated DNA shows asynchronous (probably late) labeling with respect to the chromosomes.

The growth of the retina in Xenopus laevis: an autoradiographic study

Development ◽  
1971 ◽  
Vol 26 (1) ◽  
pp. 67-79
Author(s):  
K. Straznicky ◽  
R. M. Gaze
Keyword(s):  
Xenopus Laevis ◽  
Ganglion Cells ◽  
Tritiated Thymidine ◽  
Autoradiographic Study ◽  
Ciliary Margin

The growth of the retina has been studied in Xenopus by use of autoradiography with tritiated thymidine. At the time when retinal polarization first occurs (around stage 30) there are only some 20 ganglion cells across the retinal equator and the rest of the retina develops later, by annular addition of cells at the ciliary margin. This process continues beyond metamorphosis.

scholarly journals SYNTHESIS OF DEOXYRIBONUCLEIC ACID BY MICRO- AND MACRONUCLEI OF TETRAHYMENA PYRIFORMIS

1962 ◽  
Vol 13 (2) ◽  
pp. 193-203 ◽  
Author(s):  
Barbara B. McDonald
Keyword(s):  
Dna Synthesis ◽  
Generation Time ◽  
Deoxyribonucleic Acid ◽  
Tritiated Thymidine ◽  
Tetrahymena Pyriformis ◽  
Type Ii ◽  
Total Period ◽  
Daughter Cells ◽  
Generation Times ◽  
The Times

Evidence as to the times of DNA synthesis in micronucleate Tetrahymena pyriformis (mating type II, variety 1) has been obtained by briefly exposing individuals of different ages to tritiated thymidine, returning them to non-radioactive medium, fixing at division, and preparing autoradiographs. A variable length of interphase, ranging from a few minutes to about 2 hours, has been found to precede the initiation of macronuclear DNA synthesis. Once begun, however, the period of synthesis appears to be similar in all cells, regardless of generation time, and has been estimated at 1 to 1½ hours. Under the conditions of these experiments, the time elapsing between the end of synthesis and subsequent division into daughter cells ranges from approximately 1½ to 2½ hours in generation times long enough to allow such variability. Division of the micronucleus occurs shortly before the cell begins to divide; its DNA synthesis starts immediately and continues after cell division for a total period estimated at about an hour.

scholarly journals EVIDENCE FOR AN ESSENTIALLY CONSTANT DURATION OF DNA SYNTHESIS IN RENEWING EPITHELIA OF THE ADULT MOUSE

1963 ◽  
Vol 18 (1) ◽  
pp. 31-40 ◽  
Author(s):  
Ivan L. Cameron ◽  
Richard C. Greulich
Keyword(s):  
Dna Synthesis ◽  
Mammalian Cells ◽  
Adult Mouse ◽  
Tritiated Thymidine ◽  
Constant Duration ◽  
The Times ◽  
Time Required ◽  
Relationship Of

Tritiated thymidine autoradiography has been applied to several renewing epithelial tissues of the adult mouse in order to determine (a) the average time required for DNA synthesis; and (b) the temporal relationship of the synthesis period to the progenitor cycles of these populations. The average duration of DNA synthesis has been computed from curves describing the rates of appearance and disappearance of labeled metaphase figures in epithelia of colon, ileum, duodenum, esophagus, and oral cavity, in both normal and colchicine-treated animals. In general, application of colchicine does not significantly influence the derived values for DNA synthesis duration. The DNA synthetic time is remarkably similar in the tissues examined, despite wide differences in the times required for completion of the progenitor cycle (and for tissue renewal). Synthesis of DNA in these epithelial cells of the mouse requires approximately 7 hours. Agreement between this value and those derived by other investigators for mammalian cells in vivo and in vitro indicates that DNA synthetic time may be a temporal constant, of considerable potential utility to studies of cell proliferation. The advantages and shortcomings of this experimental approach to problems of cell population kinetics in vivo are discussed.

A STUDY OF BLASTOCYSTS DURING DELAY AND SUBSEQUENT IMPLANTATION IN LACTATING MICE

1968 ◽  
Vol 42 (3) ◽  
pp. 453-463 ◽  
Author(s):  
ANNE McLAREN
Keyword(s):  
Dna Synthesis ◽  
Thymidine Incorporation ◽  
Tritiated Thymidine ◽  
Uterine Horn ◽  
Uterine Epithelium ◽  
Serial Sections ◽  
Uterine Lumen ◽  
Fresh State

SUMMARY Blastocysts were studied on the 5th and 8th day of pregnancy in lactating mice, in the fresh state, flushed from the uterus, in squash preparations and in serial sections. At the earlier period some mitosis was observed. Tritiated thymidine incorporation studies gave some evidence of DNA synthesis on the 5th and 6th days of pregnancy. By the 8th day the blastocysts were longer, contained more cells, and mitosis had ceased. They were located at the anti-mesometrial end of the uterine lumen, closely apposed to the uterine epithelium, and with their long axes parallel to the long axis of the uterine horn. Implantation could be induced, either by the removal of the litter, or by the injection of an appropriate dose of oestrogen on the 5th or 7th (but not the 4th) day of pregnancy. Both treatments were followed by the appearance of W-bodies in the neighbourhood of the blastocysts, the disappearance of the shed zonae, and the appearance of Pontamine Blue reactivity, oedema of the uterine stroma and formation of the primary decidual zone, in that order.

Specification of retinotectal connexions during development of the toad Xenopus laevis

Development ◽  
1980 ◽  
Vol 55 (1) ◽  
pp. 77-92
Author(s):  
S. C. Sharma ◽  
J. G. Hollyfield
Keyword(s):  
Xenopus Laevis ◽  
Ganglion Cell ◽  
Retinal Ganglion Cells ◽  
Optic Tectum ◽  
Ganglion Cells ◽  
The Other ◽  
Retinal Ganglion ◽  
Visual Projection ◽  
Series Of Experiments ◽  
The Right

The specification of central connexions of retinal ganglion cells was studied in Xenopus laevis. In one series of experiments, the right eye primordium was rotated 180° at embryonic stages 24–32. In the other series, the left eye was transplanted into the right orbit, and vice versa, with either 0° or 180° rotation. After metamorphosis the visual projections from the operated eye to the contralateral optic tectum were mapped electrophysiologically and compared with the normal retinotectal map. In all cases the visual projection map was rotated through the same angle as was indicated by the position of the choroidal fissure. The left eye exchanged into the right orbit retained its original axes and projected to the contralateral tectum. These results suggest that retinal ganglion cell connexions are specified before stage 24.

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