In this chapter, we have seen that cells have intricate mechanisms for the regulated spatial and temporal assembly and turnover of microfilaments to perform their many functions. Biochemical analyses of actin-
The protein inventories provided by genomic sequences have also documented a large number of myosin families, yet the biochemical properties of many of these motors, or their biological functions, remain to be elucidated. Again, recent technical developments, including the ability to tag motors with fluorescent tracers such as GFP, or to knock out relevant genes with the CRISPR technology, or to knock down their expression with RNAi, are providing very powerful avenues to help reveal motor functions. However, some important aspects of motors remain largely unexplored. For example, a motor that transports an organelle down a filament first has to bind the organelle, then transport it, and then release it at the destination. However, little is known about how these different events are coordinated or how these types of myosin-
Twenty years ago it was believed that all actin assembly was driven by activation of the Arp2/3 complex. Then the nucleating and capping activities of formins were discovered, and more recently, additional actin nucleators, with colorful names such as Spire, Cordon-
Finally, although we have generally discussed microfilaments without regard to tissue type—