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Updated: Dec 12, 2025
In Vitro and In Vivo Detection of Mitophagy in Human Cells, C. Elegans, and Mice
Published on: November 22, 2017
Evidence of Selection Against Damaged Mitochondria During Early Embryogenesis in the Mouse
Thiago S Machado1,2, Carolina H Macabelli1, Maite Del Collado3
1Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, Brazil.
Abstract:
There is evidence of a purifying filter acting in the female germline to prevent the expansion of deleterious mutations in the mitochondrial DNA (mtDNA). Given our poor understanding of this filter, here we investigate the competence of the mouse embryo to eliminate dysfunctional mitochondria. Toward that, mitochondria were damaged by photoirradiation of NZB/BINJ zygotes loaded with chloromethyl-X-rosamine (CMXRos). The resultant cytoplasm was then injected into C57BL/6J zygotes to track the levels of NZB/BINJ mtDNA during the preimplantation development. About 30% of NZB/BINJ mtDNA was present after injection, regardless of using photoirradiated or non-photoirradiated cytoplasmic donors. Moreover, injection of photoirradiated-derived cytoplasm did not impact development into blastocysts. However, lower levels of NZB/BINJ mtDNA were present in blastocysts when comparing injection of photoirradiated (24.7% ± 1.43) versus non-photoirradiated (31.4% ± 1.43) cytoplasm. Given that total mtDNA content remained stable between stages (zygotes vs. blastocysts) and treatments (photoirradiated vs. non-photoirradiated), these results indicate that the photoirradiated-derived mtDNA was replaced by recipient mtDNA in blastocysts. Unexpectedly, treatment with rapamycin prevented the drop in NZB/BINJ mtDNA levels associated with injection of photoirradiated cytoplasm. Additionally, analysis of mitochondria-autophagosome colocalization provided no evidence that photoirradiated mitochondria were eliminated by autophagy. In conclusion, our findings give evidence that the mouse embryo is competent to mitigate the levels of damaged mitochondria, which might have implications to the transmission of mtDNA-encoded disease.
Insights
Mouse embryos can reduce damaged mitochondrial DNA (mtDNA) levels. This process, crucial for preventing mtDNA-encoded diseases, involves replacing faulty mitochondria rather than autophagy.
Area of Science:
- Reproductive Biology
- Cellular Biology
- Genetics
Background:
- Mitochondrial DNA (mtDNA) mutations can accumulate and cause disease.
- A purifying filter in the female germline is thought to limit deleterious mtDNA mutations.
- The mechanisms by which early embryos handle dysfunctional mitochondria are poorly understood.
Purpose of the Study:
- To investigate the mouse embryo's capacity to eliminate damaged mitochondria.
- To understand the role of early embryonic development in mitigating mitochondrial dysfunction.
- To explore potential therapeutic interventions for mtDNA-related disorders.
Main Methods:
- Mitochondria were damaged in mouse zygotes using photoirradiation and a fluorescent dye (CMXRos).
- Cytoplasm containing damaged or normal mitochondria was injected into recipient zygotes.
- Levels of donor mtDNA were tracked throughout preimplantation development using quantitative analysis.
- Mitochondria-autophagosome colocalization was assessed to investigate elimination pathways.
- The effect of rapamycin treatment on mtDNA levels was evaluated.
Main Results:
- Injected zygotes developed into blastocysts, irrespective of mitochondrial damage.
- Blastocysts showed reduced levels of damaged donor mtDNA compared to normal donor mtDNA.
- This reduction indicates replacement of damaged mitochondria by the recipient's own mitochondria.
- Rapamycin treatment unexpectedly prevented the decrease in damaged mtDNA levels.
- Autophagy was not identified as a mechanism for removing photo-damaged mitochondria.
Conclusions:
- Mouse embryos possess a mechanism to mitigate damaged mitochondrial DNA levels.
- This embryonic competence may play a role in preventing the transmission of mtDNA-encoded diseases.
- The findings suggest a non-autophagic pathway for managing mitochondrial quality control in early embryos.
- Rapamycin's effect warrants further investigation regarding mitochondrial regulation.
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