Summary
When embryonic cells in vitro are exposed to bromodeoxyuridine (BUdR) the duration of exposure can be made to last for several cell generation times. Such exposure is known to prevent embryonic cells undergoing terminal differentiation while leaving cell division and basic cell function unaffected. When BUdR is injected into pregnant mammals, it remains available for incorporation in the DNA for only a fraction of one S phase and causes foetal anomalies that are apparently the result of cell death and a transient slowing of the cell generation time but not of failure of cell lines to differentiate.
The objectives of our experiments were to ascertain the availability time of BUdR in the chicken embryo in ovo, to assess its teratogenicity and to examine its effects on the growth of the embryo.
When 3H-BUdR (0.02 mg) was injected into the albumen space on day 3 of incubation, subsequent scintillation spectrometry and autoradiography showed that the drug was incorporated into the DNA of the embryo for more than 8 h or more than one cell generation time at this stage of development. On the other hand, a trace amount of tritiated thymidine (3H-TdR) was available for only one hour, the difference being probably due to an expansion of the nucleotide precursor pool in the case of BUdR.
The injection of 0.02 mg BUdR on day 3 caused growth retardation as manifested by differences in weight and in DNA content between BUdR and saline treated embryos. The difference in DNA content was evident 24 h after treatment and was probably due in part of the cell necrosis in the developing CNS that began 10 h after injection. Differences in weight did not become apparent until 4 days after treatment and were thus thought to be due to factors other than cell necrosis.
On day 11 of incubation, the mortality of BUdR treated embryos became significantly greater than that of controls and many survivors after this time had ventral body wall defects. When treatment was delayed until days 4 or 6, the subsequent development of BUdR and saline treated embryos was indistinguishable. The sensitivity of day 3 was thought to be due to the fact that embryo DNA content quadrupled between days 3 and 4 whereas it only doubled per 24 h period thereafter.
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Bannigan, J., Langman, J. & van Breda, A. The uptake of 5-bromodeoxyuridine by the chicken embryo and its effects upon growth. Anat Embryol 162, 425–434 (1981). https://doi.org/10.1007/BF00301868
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DOI: https://doi.org/10.1007/BF00301868