Polarized expression of members of the solute carrier SLC19A gene family of water-soluble multivitamin transporters: Implications for physiological function

Humans lack biochemical pathways for the synthesis of the micronutrients thiamine and folate. Cellular requirements are met through membrane transport activity, which is mediated by proteins of the SLC19A gene family. By using live-cell confocal imaging methods to resolve the localization of all SLC19A family members, we show that the two human thiamine transporters are differentially targeted in polarized cells, establishing a vectorial transport system. Such polarization decreases functional redundancy between transporter isoforms and allows for independent regulation of thiamine import and export pathways in cells.