The rapid increase of genome-wide datasets on gene expression, chromatin states, and transcription factor (TF) binding locations offers an exciting opportunity to interpret the information encoded in genomes and epigenomes. This task can be challenging as it requires joint modeling of context-specific activation of cis-regulatory elements (REs) and the effects on transcription of associated regulatory factors. To meet this challenge, we propose a statistical approach based on paired expression and chromatin accessibility (PECA) data across diverse cellular contexts. In our approach, we model (i) the localization to REs of chromatin regulators (CRs) based on their interaction with sequence-specific TFs, (ii) the activation of REs due to CRs that are localized to them, and (iii) the effect of TFs bound to activated REs on the transcription of target genes (TGs). The transcriptional regulatory network inferred by PECA provides a detailed view of how trans-and cis-regulatory elements work together to affect gene expression in a context-specific manner. We illustrate the feasibility of this approach by analyzing paired expression and accessibility data from the mouse Encyclopedia of DNA Elements (ENCODE) and explore various applications of the resulting model. gene regulation | transcription factor | regulatory element | chromatin regulator | chromatin activity E ver since the emergence of high-throughput gene expression experiments (1), computational biologists have been interested in the inference of gene regulatory relationships from gene expression data across diverse cellular contexts corresponding to diverse cell types and experimental conditions ( Fig. 1, red boxes). However, progress has been hindered by the fact that gene expression measurements provide little information on underlying regulatory mechanisms such as transcription factor binding and chromatin modification. To fill this gap, chromatin immunoprecipitationbased methods (2, 3) have been developed for the genome-wide mapping of transcriptional regulator binding locations and the detection of epigenetic marks characteristic of specific chromatin states. For example, by performing thousands of ChIP-seq experiments, the Encyclopedia of DNA Elements (ENCODE) consortium has generated such data for many chromatin marks and transcriptional regulators on a small number of cell lines (Fig. 1, green boxes). However, because a large number of transcriptional regulators and chromatin marks have to be analyzed one by one, it is unlikely that such comprehensive data will become available for many other cell lines. For most cellular contexts, the desired data will remain missing in the foreseeable future (Fig. 1, gray boxes).On the other hand, it is known that many of the protein-DNA interactions important for gene regulation occur in regulatory elements (REs) such as enhancers and insulators, which compose only a small portion of the noncoding sequences in a genome. The REs active in gene regulation in a given cellular state tend to have an open chromatin struc...