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 hormone synthesis by the newborn. With the purpose of using the mouse as an animal model to analyse the role of the sodium iodide symporter (NIS) in iodide transport and its regulation in the mammary gland, mouse NIS (mNIS) cDNA was isolated from lactating mice. The cloned sequence shows an open reading frame of 1854 nucleotides encoding a protein of 618 amino acids highly homologous to the rat and human NIS (95% and 81% identity respectively). Expression of mNIS in cultured mammalian cells induced cellular iodide accumulation. This iodide uptake process is sodium dependent and inhibited by thiocyanate and perchlorate. Tissue distribution analysis revealed that mNIS mRNAs are predominantly expressed in thyroid, stomach and in the lactating mammary 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.