Mouse models targeting selenocysteine tRNA expression for elucidating the role of selenoproteins in health and development

Abstract

Selenium (Se) deficiency has been known for many years to be associated with disease, impaired growth and a variety of other metabolic disorders in mammals. Only recently has the major role that Se-containing proteins, designated selenoproteins, play in many aspects of health and development begun to emerge. Se is incorporated into protein by way of the Se-containing amino acid, selenocysteine (Sec). The synthesis of selenoproteins is dependent on Sec tRNA for insertion of Sec, the 21st amino acid in the genetic code, into protein. We have taken advantage of this dependency to modulate the expression of Sec tRNA that in turn modulates the expression of selenoproteins by generating transgenic, conditional knockout, transgenic/standard knockout and transgenic/conditional knockout mouse models, all of which involve the Sec tRNA gene, to elucidate the intracellular roles of this protein class.

Figure 1

Primary structures of bovine liver (A) selenocysteyl-tRNA^[Ser]Sec_mcm⁵_U and (B) selenocysteyl-tRNA^[Ser]Sec_mcm⁵_Um shown in a cloverleaf model. Mammalian Sec tRNA^[Ser]Sec’s are 90 nucleotides in length and have modified bases at positions 34 (mcm⁵U), 37 (mcm⁵Um; and although the modification at position 37 is often referred to as a modified base, Um34 is a methyl group addition to the 2’-position of the ribose and thus the modification results in a modified nucleoside), 55 (pseudouridine; ψ) and 58 (N1-methyladenosine, m¹A). The structures of the two highly modified bases at positions 34 and 37, mcm⁵U and mcm⁵Um, respectively, are shown in the figure and Sec tRNA^[Ser]Sec_mcm⁵_U is responsible for synthesis of housekeeping selenoproteins and Sec tRNA^[Ser]Sec_mcm⁵_Um for stress-related selenoproteins. The bases at positions 34 and 37 have been mutated, T34A34 and A37G37, and the consequences of these mutations are that neither mutant tRNA can form Um34 resulting in a virtual loss in stress-related selenoprotein expression (see text for details.).