The role of histone modification in epigenetic regulation of gene expression and cell specification.

During development and differentiation, each cell of multicellular organisms acquires properties fundamental for its specific functions; this happens in the absence of modifications of the DNA nucleotide sequence, and is thus "epigenetic" in nature. The sequential restriction of transcriptional activity to the genes involved in metabolic processes and in cell-specific functions depends on modifications of the structural organization of the DNA-protein complex known as chromatin. Importantly, chromatin structure can change in differentiated cells in response to different stimuli, among which hormonal stimulation, and neurotransmission. The main proteins involved in chromatin structure organization are histones, which can be modified in many ways, and that also exist as isoforms (histone variants), with different structural and functional effects on chromatin. Thanks to sequential epigenetic modifications, cells acquire a memory of their past, stored in their chromatin organization. These processes are even more important in the nervous system, responsible for storing the memory of the entire organism. In this chapter, we will discuss the different types of histone modifications, as well as their effects on chromatin structure and function, with a particular focus on nerve cells as well as on the possible relationships among exercise and diet, and histone modifications.