Chromatin Immunoprecipitation Assay of Brain Tissues Using Percoll Gradient-Purified Nuclei

Protein–DNA interactions are critical to maintain genome stability, DNA replication, chromosome �segregation and to regulate gene expression. Chromatin immunoprecipitation (ChIP) is a powerful technique to study these interactions within living neurons and nervous tissue. In particular, ChIP analysis of chromatin in which protein–DNA interactions are first fixed in situ provides a valuable approach to identify specific transcription factor–DNA interactions and their regulation in the developing nervous system. Here we describe a procedure utilizing Percoll gradient purification of nuclei from fresh brain tissue pre-fixed with formaldehyde for ChIP analysis. This purification protocol provides an enrichment of neuronal nuclei in high yield. We also illustrate the suitability of chromatin prepared from Percoll-purified brain nuclei for ChIP analysis of regulated transcription factor interactions with neuronal gene promoters.