Interaction between nucleosome assembly protein 1-like family members.

Mammals possess five nucleosome assembly protein 1-like (NAP1L) proteins, with three of them being expressed exclusively in the nervous system. The biological importance of the neuron-specific NAP1L2 protein is demonstrated by the neural tube defects occurring during the embryonic development of Nap1l2 mutant mice, which are associated with an overproliferation of neural stem cells and decreased neuronal differentiation. NAP1L2 controls the expression of its target genes, such as the cell cycle regulator Cdkn1c, at least in part via an effect on histone acetylation. Using a two-hybrid analysis, we have identified several proteins interacting with NAP1L2, including the ubiquitously expressed members of the nucleosome assembly protein family, NAP1L1 and NAP1L4. Structural studies further predict that all five NAP1-like proteins are able to interact directly via their highly conserved α-helices. These elements, in conjunction with the coexpression of all the NAP1-like proteins in neurons and the finding that deletion of Nap1l2 affects the cytoplasmic-nuclear distribution patterns of both NAP1L1 and NAP1L4 and their recruitment to target genes, suggest that combinatorial variation within the NAP family may ensure adaptation to the specific requirements for neuronal differentiation such as intercellular repartition, chromatin modification, transcriptional regulation, or the recruitment of specific transcription factors.