Melanosomes are large membranous organelles that synthesise and transport the pigment melanin. A complex comprising Rab27, melanophilin (MLPH) and myosin Va is involved in transporting melanosomes along actin filaments, and loss of this complex causes perinuclear clustering of these organelles. This can be reversed by mutations in the melanoregulin (MREG) gene, but the way in which MREG affects the movement of melanosomes has remained unclear. Mitsunori Fukuda and colleagues (p. ) now identify a function for MREG in microtubule-based melanosome transport. Reducing the expression MREG has no effect on melanosome trafficking. However, in melanocytes that lack functional Rab27A, shRNA-mediated knockdown of MREG results in redistribution of the organelles to the plasma membrane. A similar effect is observed when the function of the dynein–dynactin complex is impaired. This leads the authors to conclude that MREG is involved in retrograde melanosome transport along microtubules. Furthermore, they show that MREG mediates this function by associating with the Rab-interacting lysosomal protein (RILP), which binds to the dynactin subunit p150Glued and has a role in lysosomal trafficking. These findings suggest that a common mechanism involving RILP is involved in the regulation of lysosome and melanosome motility.
