Multivalent DNA and nucleosome acidic patch interactions specify VRK1 mitotic localization and activity

A key role of chromatin kinases is to phosphorylate histone tails during mitosis to spatiotemporally regulate cell division. Vaccinia-related kinase 1 (VRK1) is a serine-threonine kinase that phosphorylates histone H3 threonine 3 (H3T3) along with other chromatin-based targets. While structural studies have defined how several classes of histone-modifying enzymes bind to and function on nucleosomes, the mechanism of chromatin engagement by kinases is largely unclear. Here, we paired cryo-electron microscopy with biochemical and cellular assays to demonstrate that VRK1 interacts with both linker DNA and the nucleosome acidic patch to phosphorylate H3T3. Acidic patch binding by VRK1 is mediated by an arginine-rich flexible C-terminal tail. Homozygous missense and nonsense mutations of this acidic patch recognition motif in VRK1 are causative in rare adult-onset distal spinal muscular atrophy. We show that these VRK1 mutations interfere with nucleosome acidic patch binding, leading to mislocalization of VRK1 during mitosis, thus providing a potential new molecular mechanism for pathogenesis.

Effects of vitamin A on the behaviour of migratory neural crest cells in vitro

It has been proposed elsewhere that the teratogenic effects of retinoids on craniofacial morphogenesis are caused by a disturbance of the migration of cranial neural crest cells. The effects of 3.5 X 10(−5) M and 3.5 X 10(−6) M-retinol on the migration of avian neural crest cells in vitro have been investigated by monitoring cell morphology, locomotory behaviour, fibronectin distribution and actin-microfilament organization. Retinol retards migration by affecting cell-to-substratum adhesiveness. Cells exposed to medium containing retinol are less adherent to the substratum, and although the cell surface is very mobile, are unable to extend or maintain lamellipodia. As a consequence the cells do not actively translocate. Fibronectin distribution at the cell surface is sparse, possibly as a result of shedding, and actin distribution remains diffuse. At the retinol molarities used all these effects are reversible. Thus cells allowed to recover in normal medium flatten out, display lamellipodia and commence active translocation. Fibronectin becomes organized into a fibrillar array and actin microfilaments become organized into cables. The period needed for this recovery is directly related to the molarity of retinol during the initial exposure; after recovery the retinol-treated cells are virtually indistinguishable from control cells. We propose that in vivo the effects of retinoids might be to impair cell-extracellular matrix interaction, thus impeding a cell's ability to migrate through that matrix. Contrary to previous suggestions, the in vivo effects are probably not in any way ‘specific’ to neural crest cells but are more accurately considered as ‘selective’, in that any cell undergoing migration would be similarly affected.