Giardia lamblia: autoradiographic analysis of nuclear replication |
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Authors: | G P Wiesehahn E L Jarroll D G Lindmark E A Meyer L M Hallick |
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Affiliation: | 1. Department of Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201 USA;2. Department of Preventive Medicine, N.Y. State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA |
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Abstract: | Giardia lamblia trophozoites, grown in axenic culture, were labeled for various periods of time with [3H]thymidine. After autoradiography, grains were counted over each of the two nuclei in each trophozoite. Analysis of the fraction of trophozoites labeled for each time period resulted in an estimate of a generation time of 15 hr. The DNA synthetic or S phase for a trophozoite in culture was calculated to be 1.8 hr. G1 and G2 periods were determined to be 8.5 and 3 hr, respectively. A comparison of the labeling density between the two nuclei indicated that replication takes place simultaneously in both nuclei for at least 70% of S period. The fraction of asymmetrically labeled trophozoites is consistent with a model in which the nuclei replicate out of phase by 15-30 min, but, due to the small diameter of the nuclei relative to the grain size, the possibility that replication takes place simultaneously in both nuclei of a trophozoite throughout the S phase cannot be ruled out. |
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Keywords: | Protozoa parasitic Cell cycle Cultivation axenic Autoradiography Replication Nuclear division DNA synthetic period (S) Generation time (GT) Mitotic period (M) Interval between M and S (G1) Interval between S and M (G2) |
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