Systems Biology

Chromatin immunoprecipitation is extensively used to investigate the epigenetic profile and transcription factor binding sites in the genome. However, when the starting material is limited, the conventional ChIP-Seq approach cannot be implemented. This protocol describes a method that can be used to generate the chromatin profiles from as low as 100 human or 1,000 Drosophila cells. The method employs tagmentation to fragment the chromatin with concomitant addition of sequencing adaptors. The method generates datasets with high signal to noise ratio and can be subjected to standard tools for ChIP-Seq analysis

Systems biology approaches can be used to study the regulatory interactions occurring between many components of the biological system at the whole-genome level and decipher the circuitries implicated in the regulation of cellular processes, including those imparting virulence to opportunistic fungi. Candida albicans (C. albicans) is a leading human fungal pathogen. It undergoes morphological switching between a budding yeast form and an elongated multicellular hyphal form. This transition is required for C. albicans’ ability to cause disease and is regulated through highly interconnected regulatory interactions between transcription factors (TFs) and target genes. The chromatin immunoprecipitation (ChIP)-High-throughput sequencing (Seq) technology (ChIP-Seq) is a powerful approach for decoding transcriptional regulatory networks. This protocol was optimized for the preparation of ChIP DNA from filamenting C. albicans cells followed by high-throughput sequencing to identify the targets of TFs that regulate the yeast-to-hyphae transition.

The Illumina sequencing platform is very popular among next-generation sequencing platforms. However, the DNA sequencing library construction kit provided by Illumina is considerably expensive. The protocol described here can be used to construct high-quality sequencing libraries from chromatin immunoprecipitated DNA. It uses key reagents from third-party vendors and greatly reduces the cost in library construction for Illumina sequencing.