DNA synthesis rate changes during the S phase in mouse epidermis.

Area of Science:

• Cell Biology
• Chronobiology
• Dermatology

Background:

• The cell cycle, particularly DNA synthesis during the S phase, is crucial for tissue maintenance and regeneration.
• Circadian rhythms influence various physiological processes, including cell proliferation in epidermal tissues.
• Understanding DNA synthesis patterns in epidermal cells is key to comprehending skin homeostasis and disease.

Purpose of the Study:

• To investigate the in vivo DNA synthesis rate throughout the S phase of mouse epidermal basal cells.
• To determine the influence of circadian timing on DNA replication patterns.
• To analyze the relationship between cell progression rate and DNA synthesis rate distribution within the S phase.

Main Methods:

• Isolation of mouse epidermal basal cells at different times of day.
• Analysis using DNA flow cytometry and cell sorting.
• Quantitative [3H]thymidine ([3H]TdR) autoradiography on sorted S-phase cell fractions.

Main Results:

• Circadian variation in the proportion of slowly replicating (unlabelled) cells within the S phase, with minima at midnight and early morning.
• A general trend of higher DNA synthesis rates in mid-S phase fractions, consistent across normal and perturbed epidermis.
• A bimodal DNA synthesis rate pattern in early morning, with maxima in early and late S phase, coinciding with maximum cell progression rate through S.

Conclusions:

• The proportion of slowly replicating cells in mouse epidermis is under circadian control.
• DNA synthesis rate distribution within the S phase exhibits a complex pattern influenced by circadian timing.
• Cell progression rate through S phase is related to the overall DNA synthesis rate and its distribution pattern.