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Published on: October 11, 2012
Apaf-1-independent programmed cell death in mouse development
A Nagasaka1, K Kawane, H Yoshida
1Department of Medical Chemistry, Kyoto University, Yoshida-Konoe, Sakyo-ku, Japan.
Abstract:
Many cells die during mammalian development and are engulfed by macrophages. In DNase II(-/-) embryos, the TUNEL-positive DNA of apoptotic cells is left undigested in macrophages, providing a system for studying programmed cell death during mouse development. Here, we showed that an Apaf-1-null mutation in the DNase II(-/-) embryos greatly reduced the number of macrophages carrying DNA at E11.5. However, at later stages of the embryogenesis, a significant number of macrophages carrying undigested DNA were present in Apaf-1(-/-) embryos, indicating that cells died and were engulfed in an Apaf-1-independent manner. In most tissues of the Apaf-1(-/-) embryos, no processed caspase-3 was detected, and the DNA of dead cells accumulated in the macrophages appeared intact. Many nonapoptotic dead cells were found in the tail of the Apaf-1(-/-) embryos, suggesting that the Apaf-1-independent programmed cell death occurred, and these dead cells were engulfed by macrophages. In contrast, active caspase-3 was detected in E14.5 thymus of Apaf-1(-/-) embryos. Treatment of fetal thymocytes with staurosporine, but not etoposide, induced processing of procaspases 3 and 9, indicating that the E14.5 thymocytes have the ability to undergo caspase-dependent apoptosis in an Apaf-1-independent manner. Thus, programmed cell death in mouse development, which normally proceeds in an efficient Apaf-1-depenent mechanism, appears to be backed up by Apaf-1-independent death systems.
Insights
Apoptotic cell engulfment in mouse development relies on Apaf-1 (Apoptotic protease activating factor 1). However, an Apaf-1-independent cell death system backs up this process, ensuring developmental cell death continues.
Area of Science:
- Developmental Biology
- Cell Death Mechanisms
- Immunology
Background:
- Mammalian development involves significant cellular death, with macrophages engulfing apoptotic cells.
- DNase II-deficient (DNase II(-/-)) embryos provide a model for studying programmed cell death, as undigested DNA accumulates in macrophages.
Purpose of the Study:
- To investigate the role of Apaf-1 (Apoptotic protease activating factor 1) in programmed cell death and macrophage engulfment during mouse embryogenesis.
- To identify alternative pathways for programmed cell death when the Apaf-1-dependent mechanism is absent.
Main Methods:
- Analysis of Apaf-1-null mutations in DNase II(-/-) mouse embryos.
- Assessment of DNA-containing macrophages at various embryonic stages (E11.5 and later).
- Detection of processed caspase-3 and caspase-9 in embryonic tissues and fetal thymocytes.
- Induction of apoptosis in fetal thymocytes using staurosporine and etoposide.
Main Results:
- Apaf-1 deficiency significantly reduced DNA-containing macrophages at E11.5 but not at later embryonic stages, indicating Apaf-1-independent engulfment.
- Non-apoptotic dead cells were observed in Apaf-1(-/-) embryos, suggesting an alternative cell death pathway.
- While most tissues in Apaf-1(-/-) embryos lacked processed caspase-3, E14.5 thymocytes showed active caspase-3 and could undergo caspase-dependent apoptosis independently of Apaf-1.
Conclusions:
- Programmed cell death during mouse development primarily utilizes an Apaf-1-dependent mechanism.
- An Apaf-1-independent programmed cell death system exists and can compensate for the absence of Apaf-1, particularly in later developmental stages and specific tissues like the thymus.
- This backup system ensures the efficient removal of dead cells, crucial for normal embryonic development.
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