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DNA SYNTHESIS IN RANA PIPIENS TADPOLE LIVER DURING TRIIODOTHYRONINE‐INDUCED METAMORPHOSIS 1
Author(s) -
SMITHGILL SANDRA J.
Publication year - 1979
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.1979.00291.x
Subject(s) - tadpole (physics) , rana , triiodothyronine , dna , medicine , chemistry , biology , endocrinology , biochemistry , thyroid , physics , particle physics
The relationship of DNA synthesis and cellular turnover to biochemical differentiation during Ts‐induced metamorphosis of R. pipiens liver was investigated. Rates of DNA synthesis were estimated by rates of 3 H‐thymidine incorporation into the acid‐precipitable fractions, corrected for both precursor uptake into the acid‐soluble pool, and for endogenous thymine pool size. During T 3 ‐induced metamorphosis, periods of DNA synthesis and fluctuations in DNA content preceded expression of biochemical differentiation as measured by the enzyme arginase, and fluctuations in synthesis rates preceded corresponding fluctuations in content. The earliest response to T 3‐ , was a 50% decrease in liver DNA, followed by increases in thymidine incorporation at 16 hr, 2 days, and 5‐8 days. The size of the endogenous thymine pool was not significantly altered by T 3 These results indicate that both DNA synthesis and cellular turnover play a significant role in determining net DNA synthetic rates and content during metamorphosis. Expression of thyroxin‐induced development of the tadpole liver appears to be associated with both proliferation and cellular death, and metamorphosis of the liver cannot be occurring in a “fixed population of cells.”