The increasing knowledge on how protein tau is organized in live cells has shown that the protein forms nanometer-sized hotspots which are different from tau microtubules. These hotspots, essential for aggregation, include (306)VQIVYK(311) and (275)VQIINK(280) aggregation-promoting hotspots, the first found in all tau isoforms and the latter included mainly in 4R isoforms.