Pushing for answers: is myosin V directly involved in moving mitochondria?

Abstract

In budding yeast, the actin-based class V myosin motors, Myo2 and Myo4, transport virtually all organelles from mother to bud during cell division. Until recently, it appeared that mitochondria may be an exception, with studies showing that the Arp2/3 complex is required for their movement. However, several recent studies have proposed that Myo2 has a direct involvement in mitochondria inheritance. In this issue, Altmann et al. (Altmann, K., M. Frank, D. Neumann, S. Jakobs, and B. Westermann. 2008. J. Cell Biol. 181:119-130) provide the strongest support yet that Myo2 and its associated light chain Mlc1 function directly and significantly in both mitochondria-actin interactions and in the movement of mitochondria from mother to bud. The conflicting functions of Arp 2/3 and Myo2 may be reconciled by the existence of multiple pathways involved in mitochondrial transport.

Figure 1.

Structure of the Myo2 globular cargo binding domain (Pashkova et al., 2006), PDB ID: 2F6H, displayed using PyMOL. Helices H4 and H6 contain the surface residues D1297, L1301, N1304, N1307, and Q1233 (shown in blue) that are important for vacuole movement as well as mitochondria morphology and distribution (Pashkova et al., 2006). Mutations in L1301 and Q1233 display the most severe mitochondrial defects. Residues shown in magenta are important for the movement of secretory vesicles but not the vacuole or mitochondria.

Figure 2.

Model showing mitochondria movement during cell division in budding yeast. Mitochondria may use Arp2/3- and/or Myo2-based mechanisms for anterograde movement (i). Retrograde movement (ii) requires mechanisms that link mitochondria to actin cables but does not require force generation. Yellow arrows indicate the direction of retrograde actin flow and black arrows indicate the direction of mitochondria movement.