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Mice deficient for cytosolic thymidine kinase gene develop fatal kidney disease
Vasily N Dobrovolsky1, Thomas Bucci, Robert H Heflich
1National Center for Toxicological Research, Food and Drug Administration, Jefferson, AR, USA. vdobrovolsky@nctr.fda.gov
Abstract:
The thymidine kinase (Tk) gene codes for a cytosolic protein involved in the pyrimidine nucleotide salvage pathway. A functional Tk gene is not necessary for cells in culture, and a naturally occurring Tk deficient phenotype has not been described in humans or animal models. In order to determine the biological significance of the Tk gene, we created Tk(-/-) knockout (KO) mice through homologous recombination in mouse embryonic stem cells. Tk KO mice have shortened life spans compared with their wild-type or Tk heterozygous (HET) siblings. All Tk KO mice develop sclerosis of kidney glomeruli and die before one year of age of kidney failure. Among other changes in KO animals, the most consistent is a switch from exclusively mucous secretion to predominantly serous secretion in the sublingual salivary gland. HET parents can produce KO mice at a frequency approaching Mendelian inheritance. Other observations in KO animals include an elevated level of serum thymidine, a significant decrease in the cloning efficiency of splenic lymphocytes, an increase in the frequency of hypoxanthine guanine phosphoribosyl transferase gene mutant lymphocytes, and histological alteration in the lymphoid structure of the spleen. In addition, KO animals sporadically exhibit inflammation of the arteries, which taken together with the lymphocyte and spleen abnormalities, suggest an abnormal immune system. Alterations in Tk KO mice indicate that the pyrimidine nucleotide salvage pathway is indispensable in vivo.
Insights
The thymidine kinase (Tk) gene is essential for life, as Tk knockout mice exhibit kidney failure and shortened lifespans. This study reveals the pyrimidine salvage pathway
Area of Science:
- Biochemistry
- Genetics
- Immunology
Background:
- The thymidine kinase (Tk) gene encodes a crucial enzyme in the pyrimidine nucleotide salvage pathway.
- A functional Tk gene is dispensable for cells in culture, and Tk deficiency has not been previously observed in vivo.
- The biological significance of Tk in a whole organism remained largely undetermined.
Purpose of the Study:
- To investigate the in vivo biological significance of the thymidine kinase (Tk) gene.
- To characterize the phenotype of Tk-deficient mice created through homologous recombination.
Main Methods:
- Generation of Tk knockout (KO) mice using homologous recombination in mouse embryonic stem cells.
- Phenotypic analysis of Tk KO mice, including lifespan, organ histology, and immune cell function.
- Biochemical analysis of serum thymidine levels and lymphocyte gene mutation frequencies.
Main Results:
- Tk KO mice exhibited significantly shortened life spans and died before one year of age due to kidney failure (sclerosis of glomeruli).
- Consistent alterations observed in KO mice included a switch in sublingual salivary gland secretion from mucous to serous.
- KO animals displayed elevated serum thymidine, decreased splenic lymphocyte cloning efficiency, increased hypoxanthine guanine phosphoribosyl transferase (HPRT) gene mutant lymphocytes, and spleen histological abnormalities.
- Sporadic arterial inflammation in KO animals suggested potential immune system dysregulation.
Conclusions:
- The pyrimidine nucleotide salvage pathway, mediated by thymidine kinase, is indispensable for mammalian survival in vivo.
- Tk deficiency leads to severe multi-organ pathology, including kidney failure and immune system alterations.
- Tk KO mice provide a valuable model for studying the in vivo functions of the pyrimidine salvage pathway and its impact on health and immunity.