DNA SYNTHESIS AND CELL TURNOVER IN RANA PIPIENS TADPOLE LIVER DURING SPONTANEOUS METAMORPHOSIS

Area of Science:

• Developmental Biology
• Cell Biology
• Biochemistry

Background:

• Liver metamorphosis in *Rana pipiens* involves complex cellular changes.
• Understanding DNA synthesis and cellular turnover is key to deciphering liver development during amphibian metamorphosis.

Purpose of the Study:

• To investigate the relationship between DNA synthesis, cellular turnover, and biochemical differentiation in the *Rana pipiens* liver during metamorphosis.
• To determine the role of cell proliferation and death in the metamorphic liver.

Main Methods:

• Quantified DNA content per cell and total DNA content throughout metamorphic stages.
• Measured rates of DNA synthesis using 3H-thymidine incorporation, corrected for precursor uptake and endogenous thymine pools.
• Assessed changes in cell number and population dynamics during liver metamorphosis.

Main Results:

• Average DNA per cell remained constant until juvenile growth, then fluctuated during metamorphosis.
• DNA content showed decreases at preclimax stages, preceded by fluctuations in DNA synthesis rates.
• DNA synthesis peaked at stages XVI and XVIII, dropped significantly during climax, and then recovered.

Conclusions:

• Both DNA synthesis and cellular turnover are critical for regulating net DNA synthesis and content in the metamorphic liver.
• Liver metamorphosis involves cell proliferation and death, suggesting a replacement of larval cells by adult cells.
• The metamorphic liver does not consist of a fixed cell population; rather, it undergoes dynamic population changes.