Polo-like kinases (Plks) were first reported to have a role in meiosis and mitosis in Drosophila melanogaster nearly 20 years ago. Now, we recognize that Plks are crucial regulators of cell division that are broadly conserved from yeast to humans, absent only from plants. Emerging evidence also shows that Plks link cell division to various developmental processes. Yet, despite their conservation and biological importance, Plks have different functions and regulatory processes in different organisms and tissues, as reviewed by Vincent Archambault and David M. Glover on page 265. The authors argue that we will only be able to unravel the biology of Plks by continuing to study these proteins in various model systems, so that we can identify further differences.
Even in the same model system, one can stumble upon a diversity of functions, for example, in the case of endosomes. In an Opinion on page 287, Gwyn W. Gould and Jennifer Lippincott-Schwartz describe recent observations that show that endosomes have roles in a diverse array of processes, including cytokinesis, polarization and migration. These functions are distinct from those classically associated with endosomes. The authors speculate that endosomes are multifunctional platforms on which unique sets of molecular machines can be assembled to suit different cellular roles.
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