Apoptosis in the cortex of the developing mouse kidney.

Area of Science:

• Developmental Biology
• Cell Biology
• Histology

Background:

• Published apoptosis levels in developing rat kidneys (approx. 2.5%) appear high for a tissue without apparent need for continuous cell death.
• Investigating apoptosis and mitosis in developing mammalian kidneys is crucial for understanding organogenesis.

Purpose of the Study:

• To quantify and characterize apoptosis and mitosis in the developing mouse kidney cortex.
• To compare apoptosis levels in wholemount versus cryosectioned embryonic kidney tissues.
• To determine if apoptosis levels in the embryonic kidney are typical of other developing mammalian tissues.

Main Methods:

• Confocal microscopy of wholemount embryonic mouse kidneys stained with propidium iodide.
• Analysis of nuclear morphology to count mitotic, apoptotic, and interphase nuclei.
• Comparison of apoptosis and mitotic indices in wholemount kidneys, tails, and lungs.

Main Results:

• The mean apoptotic index in wholemount embryonic mouse kidneys was 0.28%, approximately 10% of levels reported in cryosectioned rat kidneys.
• Mitotic index peaked at E14.5 (around 2-3%) and decreased to 0.5% by P14.
• Cryosectioning may artifactually inflate apoptosis measurements due to nuclear fragmentation.

Conclusions:

• Apoptosis levels in wholemount embryonic mouse kidney cortex are substantially lower than previously reported.
• The observed low level of apoptosis is typical for embryonic mouse tissues not requiring extensive cell death during development.
• Cryosectioning artifacts may account for discrepancies in previously reported apoptosis rates.