Cloning of the mouse sodium iodide symporter and its expression in the mammary gland and other tissues

Iodide concentration in milk by mammals is a necessary step for thyroid hor mone synthesis by the newborn. With the purpose of using the mouse as an an imal model to analyse the role of the sodium iodide symporter (NIS) in iodi de transport and its regulation in the mammary gland, mouse NIS (mNIS) cDNA was isolated from lactating mice. The cloned sequence shows an open readin g frame of 1854 nucleotides encoding a protein of 618 amino acids highly ho mologous to the rat and human NIS (95% and 81% identity respectively). Expr ession of mNIS in cultured mammalian cells induced cellular iodide accumula tion. This iodide uptake process is sodium dependent and inhibited by thioc yanate and perchlorate. Tissue distribution analysis revealed that mNIS mRN As are predominantly expressed in thyroid, stomach and in the lactating mam mary gland and are present to a lower extent in several other tissues. Our data show for the first time that the level of mNIS mRNA is upregulated in the mammary gland during lactation.