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Published on: November 1, 2018
Laser microbeam-induced DNA damage inhibits cell division in fertilized eggs and early embryos
Zhong-Wei Wang1, Xue-Shan Ma, Jun-Yu Ma
1State Key Laboratory of Reproductive Biology; Institute of Zoology; Chinese Academy of Sciences; Beijing, China.
Abstract:
DNA double-strand breaks are caused by both intracellular physiological processes and environmental stress. In this study, we used laser microbeam cut (abbreviated microcut or cut), which allows specific DNA damage in the pronucleus of a fertilized egg and in individual blastomere(s) of an early embryo, to investigate the response of early embryos to DNA double-strand breaks. Line type γH2AX foci were detected in the cut region, while Chk2 phosphorylation staining was observed in the whole nuclear region of the cut pronuclei or blastomeres. Zygotes with cut male or female pronucleus showed poor developmental capability: the percentage of cleavage embryos was significantly decreased, and the embryos failed to complete further development to blastocysts. The cut blastomeres in 2-cell, 4-cell, and 8-cell embryos ceased cleavage, and they failed to incorporate into compacted morulae, but instead underwent apoptosis and cell death at the blastocyst stage; the uncut part of embryos could develop to blastocysts, with a reduced percentage or decreased cell number. When both blastomeres of the 2-cell embryos were cut by laser microbeam, cell death occurred 24 h earlier, suggesting important functions of the uncut blastomere in delaying cell death of the cut blastomere. Taken together, we conclude that microbeam-induced DNA damage in early embryos causes compromised development, and that embryos may have their own mechanisms to exclude DNA-damaged blastomeres from participating in further development.
Insights
Early embryos exposed to DNA double-strand breaks via laser microbeam cutting exhibit severely compromised development. Damaged cells undergo apoptosis, and embryos may possess mechanisms to eliminate these cells, impacting overall embryo viability.
Area of Science:
- Developmental Biology
- Genetics
- Cell Biology
Background:
- DNA double-strand breaks (DSBs) are critical DNA lesions.
- These breaks can arise from endogenous cellular processes or external environmental factors.
- Understanding the impact of DSBs on early embryonic development is crucial.
Purpose of the Study:
- To investigate the response of early mammalian embryos to precisely induced DNA double-strand breaks.
- To analyze the developmental consequences of DNA damage in zygotes and early blastomeres.
- To explore potential cellular mechanisms for handling DNA-damaged cells during embryogenesis.
Main Methods:
- Utilized laser microbeam cutting to induce specific DNA double-strand breaks in pronuclei and blastomeres of early embryos.
- Detected DNA damage response markers, including γH2AX foci and Chk2 phosphorylation.
- Monitored embryonic development, cleavage rates, blastocyst formation, and cell death.
Main Results:
- Laser microbeam-induced DNA damage in zygotes significantly reduced cleavage and blocked blastocyst development.
- Cut blastomeres in 2-cell, 4-cell, and 8-cell embryos ceased cleavage, underwent apoptosis, and were excluded from morula compaction.
- While uncut portions could develop to blastocysts, the overall percentage and cell number were reduced; simultaneous cutting of both blastomeres accelerated cell death.
Conclusions:
- Microbeam-induced DNA damage severely impairs early embryonic development.
- Early embryos possess mechanisms to cope with DNA damage, including apoptosis and potential exclusion of damaged blastomeres.
- The presence of intact blastomeres can influence the timing of cell death in damaged blastomeres.
