ABSTRACT
During development of the central nervous system, the transition from progenitor maintenance to differentiation is directly triggered by a lengthening of the cell cycle that occurs as development progresses. However, the mechanistic basis of this regulation is unknown. The proneural transcription factor Neurogenin 2 (Ngn2) acts as a master regulator of neuronal differentiation. Here, we demonstrate that Ngn2 is phosphorylated on multiple serine-proline sites in response to rising cyclin-dependent kinase (cdk) levels. This multi-site phosphorylation results in quantitative inhibition of the ability of Ngn2 to induce neurogenesis in vivo and in vitro. Mechanistically, multi-site phosphorylation inhibits binding of Ngn2 to E box DNA, and inhibition of DNA binding depends on the number of phosphorylation sites available, quantitatively controlling promoter occupancy in a rheostat-like manner. Neuronal differentiation driven by a mutant of Ngn2 that cannot be phosphorylated by cdks is no longer inhibited by elevated cdk kinase levels. Additionally, phosphomutant Ngn2-driven neuronal differentiation shows a reduced requirement for the presence of cdk inhibitors. From these results, we propose a model whereby multi-site cdk-dependent phosphorylation of Ngn2 interprets cdk levels to control neuronal differentiation in response to cell cycle lengthening during development.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/metabolism , Gene Expression Regulation, Developmental , Nerve Tissue Proteins/metabolism , Neurogenesis , Xenopus Proteins/metabolism , Animals , Cell Cycle , Cell Differentiation , HeLa Cells , Humans , Mice , Models, Biological , Mutation , Neurons/cytology , Phosphorylation , Xenopus laevisABSTRACT
Forty years on, a group of midwives who joined forces in Liverpool as nursing students are now contemplating retirement. Their working lives have been revolutionised in the interim.
