Melanin's backups

Sports teams and melanin-making cells follow the same strategy: they have substitutes in case a regular can't perform. The cells rely on redundant proteins to deliver enzymes for pigment production, as Wasmeier et al. report on page 271. The results might clarify researchers' understanding of an enigmatic class of cell organelles that participate in everything from immunity to blood clotting.

The melanosomes that manufacture melanin are lysosome-related organelles (LROs), which store and synthesize molecules in many cell types. In platelets, for example, LROs house coagulation factors. Researchers are still working out the details of LRO formation. One mystery is how melanosomes stock up on the enzymes tyrosinase and tyrosinase-related protein-1 (Tyrp1), which are essential for making melanin. Wasmeier et al. investigated one protein that might have a role in the process, Rab38.

Mice with a faulty version of...