Mitosis, microtubule dynamics and the evolution of kinesins

All living organisms must transmit genetic information through successive generations, and all six eukaryotic supergroups utilize a mitotic spindle to accomplish this task. The mitotic spindle is the cellular machinery responsible for chromosome segregation during mitosis, and it is comprised of hundreds of proteins. During evolution, eukaryotic cells have developed different mechanisms and different kinds of mitotic spindles to segregate the chromosomes (Drechsler and McAinsh, 2012). Regardless of the differences, the common characteristic of all these different mitotic spindles is the utilization of microtubules and kinesins, as all known eukaryotes studied to this date possess kinesins (Wickstead et al., 2010). The mitotic spindle is a bipolar array of microtubules of varied lengths that continuously grow and shrink. These highly dynamic microtubules are nucleated by centrosomes and contact the chromosomes in the centromeric region to facilitate chromosome attachment and segregation. Although chromosome movement is powered in part by changes in microtubule assembly (Shelden and Wadsworth, 1992), kinesins associated with microtubules and other spindle structures refine the movement of chromosomes in the spindle. Kinesins participate in chromosome attachment, influence microtubule dynamics and contribute to anaphase spindle elongation (reviewed in (Cross and McAinsh, 2014)). Thus, kinesins, in conjunction with dynamic microtubules, ensure the proper distribution of genetic material between the two daughter cells to avoid aneuploidy. Kinesins are a class of molecular motors that use the energy from hydrolysis of ATP to translocate along the microtubule or control microtubule end dynamics (Vale et al., 1985, 1996; Desai et al., 1999). They have been identified in members of all six eukaryotic supergroups including extremely deep-rooted members (Fig. 1). Processive kinesins are able to perform successive work-producing cycles of ATP hydrolysis without detaching from the substrate microtubule whereas non-processive kinesins readily detach from microtubules but can be quite effective working in ensembles. There are 14 families of kinesins, and most members possess two distinct functional domains: an ATP-hydrolyzing motor domain and a tail domain that can associate with cellular structures or cargo (Lawrence et al., 2004; Miki et al., 2005). The motor domain is very well conserved among the different kinesins families while the tail domains are more divergent. Most kinesins translocate to the plus ends of the microtubule and possess an N-terminal motor domain. There are kinesins with the motor at the C-terminus that translocate to the minus end of the microtubule. Besides this hand over hand “walking” activity (Yildiz et al., 2004), there are some kinesins that are able to control microtubule dynamics through promoting polymerization, promoting depolymerization or pausing polymerization activity (Desai et al., 1999; Bringmann et al., 2004; Cui et al., 2005). Figure 1 Six eukaryotic supergroups including, in each case, a few members in which kinesins have been unambiguously identified. Organisms thought to be more deeply rooted are indicated (*). In Opisthokont metazoans there appear to be Kinesins involved in every step of mitosis, belonging to the families 4, 5, 6, 7, 8, 10, 12, 13, 14 (reviewed in (Cross and McAinsh, 2014)). Here we are going to review the kinesins involved in each phase of mitosis with an emphasis on the stages of mammalian cell division. Additionally, we will consider the role of kinesins in deep-rooted eukaryotes.