Changes in the activities of DNA polymerases in growing rat lungs

Abstract

We hypothesized that cellular proliferation and the capacity to repair DNA damage in the lung might differ during the pre- and postnatal periods, because the lung is exposed to higher oxygen concentrations and/or various mutagens after birth. In order to test this hypothesis, changes in DNA content and the activities of DNA polymerases α and β were studied in the lungs of 1-day prenatal to 42-day postnatal rats. Total DNA polymerase activity reached its highest level at 1 day prenatal and 1 day after birth. The activity decreased exponentially by 28% up to 14 days of age, a change inversely related to the change in DNA content. The change in total DNA polymerase activity agreed closely with the change in DNA polymerase α activity, but not the activity of the β form, although small elevations in both DNA polymerase α and β were observed on day 3, possibly reflecting the mechanical effect of delivery. The activity of DNA polymerase β remained relatively constant from 1 day before birth to 21 days after birth, varying by only about 5%. From these results, it is concluded that: (1) cellular proliferation in the lung is most active during the first 2 weeks after birth as supported by the increases in DNA polymerase α activity and DNA content, and (2) anticipating the oxygen enriched atmosphere after birth, the level of DNA polymerase β, involved in the DNA repair system, is already elevated during the prenatal period and remains constant throughout the postnatal period.

Key Words:

• lung growth and development
• DNA polymerase activity
• molecular forms of DNA polymerase
• DNA content