2cChIP-seq and 2cMeDIP-seq: The Carrier-Assisted Methods for Epigenomic Profiling of Small Cell Numbers or Single Cells.

Chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) can profile genome-wide epigenetic marks associated with regulatory genomic elements. However, conventional ChIP-seq is challenging when examining limited numbers of cells. Here, we developed a new technique by supplementing carrier materials of both chemically modified mimics with epigenetic marks and dUTP-containing DNA fragments during conventional ChIP procedures (hereafter referred to as 2cChIP-seq), thus dramatically improving immunoprecipitation efficiency and reducing DNA loss of low-input ChIP-seq samples. Using this strategy, we generated high-quality epigenomic profiles of histone modifications or DNA methylation in 10-1000 cells. By introducing Tn5 transposase-assisted fragmentation, 2cChIP-seq reliably captured genomic regions with histone modification at the single-cell level in about 100 cells. Moreover, we characterized the methylome of 100 differentiated female germline stem cells (FGSCs) and observed a particular DNA methylation signature potentially involved in the differentiation of mouse germline stem cells. Hence, we provided a reliable and robust epigenomic profiling approach for small cell numbers and single cells.

Tracking Histone Modifications in Embryos and Low-Input Samples Using Ultrasensitive STAR ChIP-Seq.

ChIP-seq is a powerful technique that allows the detection of chromatin localization for proteins and epigenetic modifications. However, conventional ChIP-seq usually requires millions of cells. This becomes a daunting task for applications in which only limited experimental materials are available. For example, during mammalian embryo development, the epigenomes undergo drastic reprogramming which endows a fertilized egg with the potential to develop into the whole body. Low-input ChIP-seq methods would be instrumental to help decipher molecular mechanisms underlying such epigenetic reprogramming. Here we describe an optimized ChIP-seq method-STAR (Small-scale TELP-Assisted Rapid) ChIP-seq-that allows the detection of histone modifications using only a few hundred cells. This method is proven to be robust in epigenomic profiling in both embryos and cultured cells.

ChIP-Seq from Limited Starting Material of K562 Cells and Drosophila Neuroblasts Using Tagmentation Assisted Fragmentation Approach.

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.