Serotonin can regulate gene expression inside neurons -- ScienceDailyThe study revolves around DNA and how it works to form each person's individual biological map. Each cell in the body contains two meters of DNA, the blueprint for all functions of all cells in the body. This DNA is wound around spools of histone proteins (proteins that package DNA in the nucleus of cells, and are heavily prone to chemical modifications that aid in the regulation of gene expression) into structures referred to as nucleosomes. When DNA encoding a specific gene is wound tightly within the spool, that gene is less likely to be expressed. When the gene is not wound as tightly, it is more likely to be expressed. This can affect many functions of a given cell. Serotonin is a chemical that can transmit signals between neurons in the brain and is involved in the regulation of mood. Selective serotonin reuptake inhibitors, known as SSRIs, alter the amounts of serotonin in the brain, which enables mood changes. When small packages of serotonin are released from a neuron, the resulting signals set up a chain reaction of communication between different parts of the brain. The research team discovered that a protein called tissue transglutaminase 2 can directly attach serotonin molecules to histone proteins (a process called histone serotonylation), which in turn loosens the spool to enable more robust gene expression. Specifically, they found that in developing rodent brains and human neurons, genes near the part of the spool loosened by the serotonin are more likely to be expressed. They also showed that a specific binding complex enables this process.