Submitted to: Biochemical Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2008
Publication Date: 12/1/2008
Citation: Carlson, B.A., Schweizer, U., Perella, C., Schrimali, R.K., Feigenbaum, L., Shen, L., Speransky, S., Floss, T., Jeong, S., Watts, J.J., Hoffman, V., Combs, G.F., Gladyshev, V.N., Hatfield, D.L. 2009. The Selenocysteine tRNA STAF-Binding Region is Essential for Adequate Selenocysteine tRNA Status, Selenoprotein Expression and Early Age Survival of Mice. Biochemical Journal. 418:61-71.
Interpretive Summary: Although selenium has been recognized as essential for life in mammals, recent efforts have focused on its role in health promotion and specifically in preventing cancer and heart disease, and boosting immune function. The beneficial actions of selenium occur at the molecular level through selenium-containing proteins called selenoproteins, of which there are 25 known in humans. The present research used complex molecular biological methods to obtain the gene necessary for the formation of a specific selenoprotein called selenocysteine. Mice that were developed without this gene (also known as transgenic) had unique physical characteristics. They had very reduced amounts of selenocysteine in key organs including liver, kidney, brain, lung, spleen, and muscle as compared to normal mice. In general, the mice without the necessary selenium-containing protein were larger than their normal siblings. However, they exhibited abnormal brain and nerve functions including a waddling gait and uncontrolled muscle trembling, and were very excitable and had seizures. The mice were unable to reproduce. These findings indicate that selenium plays important roles in regulating the function of the nervous system. This information will be useful to investigators seeking to further understand the biological means by which selenium exerts protective actions against viruses that can affect nerves.
Technical Abstract: STAF is a transcription activating factor for a number of RNA Pol III-and RNA Pol II-dependent genes including the selenocysteine (Sec) tRNA gene. Here, the role of STAF in regulating expression of Sec tRNA and selenoproteins was examined in an invivo model. Heterozygous inactivation of the Staf gene by a gene trapping approach resulted in chimeric mice that were larger in size. These mice manifested other phenotypic and pathological abnormalities, including preventing germline transmission of the mutant allele, but with apparent normal Sec tRNA gene (Trsp) expression. To further examine the role of STAF in Trsp expression, we generated transgenic mice in which the STAF binding site located upstream of Trsp was deleted. These mice were used to genetically complement Trsp-knokout mice. Levels of Sec tRNA were similar or slightly elevated in heart and testis, but reduced~60% in liver and kidney, ~70% in lung and spleen and ~80% in brain and muscle compared to the corresponding organs in control mice. Interestingly, the ratio of the two isoforms of Sec tRNA that differ from each other by a single Um34 was altered signficantly, and the Um34-containing form was substantially reduced in all tissues examined. Selenoprotein expression in these animal was most affected in tissues in which the Sec tRNA levels were most severely reduced. They had a neurological phenotype strikingly similar to that of mice in which the selenoprotein P gene had been removed and their lifespan was substantially reduced.