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De novo synthesis of DNA in human platelets
Abstract:
Platelets, incubated with radiolabeled thymidine and purified free of contaminating nucleated cells, were analyzed for their ability to synthesize DNA. The only DNA species isolated from these purified platelets was mitochondrial DNA. The CsCl gradient-purified platelet DNA was treated with the restriction endonucleases EcoRI, HindIII and HpaI yielding the expected pattern for human mitochondrial DNA. Nitrocellulose blots of the electrophoresed, restriction endonuclease-treated DNA were fluorographed. All of the DNA fragments generated by the restriction enzymes were labeled, indicating de novo synthesis. This was further substantiated by inhibition of DNA synthesis by ethidium bromide and 2',3'-dideoxythymidine. Platelet DNA appeared to become greatly fragmented after 4 to 7 days storage while all of the thymidine incorporated was observed in intact mitochondrial DNA. These results indicate a continuous degradation of platelet mitochondrial DNA with no apparent repair mechanism. The ability of platelets to synthesize DNA may be associated with the protein synthetic capacity of platelets previously described.
Insights
Platelets can synthesize mitochondrial DNA, but it continuously degrades without repair. This DNA synthesis ability may link to platelet protein synthesis capabilities.
Area of Science:
- Molecular Biology
- Hematology
Background:
- Platelets are anucleated cell fragments crucial for hemostasis.
- Their capacity for synthesizing DNA has been a subject of investigation.
Purpose of the Study:
- To investigate the de novo DNA synthesis in purified human platelets.
- To characterize the type and fate of synthesized DNA within platelets.
Main Methods:
- Platelets were incubated with radiolabeled thymidine.
- DNA was isolated and analyzed using CsCl density gradients and restriction endonuclease digestion (EcoRI, HindIII, HpaI).
- DNA synthesis was assessed via fluorography and inhibition studies with ethidium bromide and 2',3'-dideoxythymidine.
Main Results:
- Purified platelets synthesized only mitochondrial DNA.
- Restriction enzyme analysis confirmed the identity of platelet DNA as human mitochondrial DNA.
- Synthesized DNA fragments were labeled, indicating de novo synthesis, and this process was inhibited by specific agents.
- Platelet mitochondrial DNA showed significant fragmentation after 4-7 days of storage, with no evidence of repair.
Conclusions:
- Human platelets possess the capability for de novo mitochondrial DNA synthesis.
- Platelet mitochondrial DNA undergoes continuous degradation without an apparent repair mechanism.
- This DNA synthesis function may be linked to the protein synthesis machinery within platelets.