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Updated: Sep 23, 2026
Intranuclear Microinjection of DNA into Dissociated Adult Mammalian Neurons
Published on: December 10, 2009
Microinjection of deoxynucleotides into mouse cells. No evidence that precursors for DNA synthesis are channeled
1Institut für Molekularbiologie, Universität Wien, Austria.
Abstract:
The technique of microinjection was applied for the introduction of radioactive, phosphorylated precursors of DNA synthesis into living mouse cells in culture. Autoradiographs proved that DNA was well labeled by injected dTTP, dCTP, dATP, dGTP, and (to a minor extent) dTMP, but the efficiency was much lower when CDP, ADP, or GDP was used. For practical reasons, injections into nuclei were preferred, but injections into cytoplasm showed no principal difference with the autoradiographed nuclei. The kinetics of the uptake of the injected material agreed neatly with the calculation (from pool sizes and polymerization rate) that the intracellular deoxytriphosphates are sufficient for about 10 min of DNA synthesis. All this evidence strongly argues against the concept that precursors of DNA synthesis are channeled in vivo within a multienzyme complex and suggests a free diffusion of deoxynucleotides within the cell. Injected thymidine was less able to enter the deoxy nucleotide metabolism compared with thymidine from the culture medium. A mutant cell line deficient in thymidine kinase did not accumulate intracellular thymidine. These data indicate that thymidine kinase is a membrane associated enzyme and that uptake and phosphorylation of thymidine are coupled reactions.
Insights
Microinjection studies reveal that DNA synthesis precursors, deoxynucleotides, diffuse freely within mouse cells, challenging channeling theories. Thymidine kinase appears membrane-associated, coupling uptake and phosphorylation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Understanding DNA synthesis precursor availability is crucial for cell cycle regulation.
- Previous models proposed channeling of deoxynucleotides within multienzyme complexes.
- The role of thymidine kinase in nucleoside uptake and phosphorylation requires further elucidation.
Purpose of the Study:
- To investigate the intracellular fate and diffusion of radioactive DNA synthesis precursors.
- To examine the kinetics of deoxynucleotide incorporation into DNA.
- To determine the cellular localization and function of thymidine kinase.
Main Methods:
- Microinjection of radioactive deoxynucleotide triphosphates (dNTPs) and nucleosides into cultured mouse cells.
- Autoradiography to visualize and quantify the labeling of DNA.
- Kinetic analysis of precursor uptake and incorporation.
- Studies using a thymidine kinase-deficient mutant cell line.
Main Results:
- Microinjected dNTPs efficiently labeled DNA, with nuclear and cytoplasmic injections yielding similar results.
- Intracellular dNTP pools support approximately 10 minutes of DNA synthesis.
- Injected thymidine showed limited entry into deoxynucleotide metabolism compared to extracellular thymidine.
- A thymidine kinase-deficient mutant failed to accumulate intracellular thymidine, indicating coupled uptake and phosphorylation.
Conclusions:
- Evidence supports free diffusion of deoxynucleotides within the cell, refuting in vivo channeling models.
- Deoxynucleotide pools are sufficient for short-term DNA synthesis.
- Thymidine kinase is likely a membrane-associated enzyme, with its activity coupled to thymidine uptake.
