The tau of MARK: a polarized view of the cytoskeleton

Microtubule-affinity regulating kinases (MARKs) were originally discovered by their ability to phosphorylate tau protein and related microtubule-associated proteins (MAPs), and thereby to regulate microtubule dynamics in neurons. Members of the MARK (also known as partition-defective [Par]-1 kinase) family were subsequently found to be highly conserved and to have key roles in cell processes such as determination of polarity, cell-cycle control, intracellular signal transduction, transport and cytoskeleton. This is important for neuronal differentiation, but is also prominent in neurodegenerative 'tauopathies' such as Alzheimer's disease. The identified functions of MARK/Par-1 are diverse and require accurate regulation. Recent discoveries including the x-ray structure of human MARKs contributed to an increased understanding of the mechanisms that control the kinase activity and, thus, the actin and microtubule cytoskeleton.