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Enhancing Pace: Identifying and Validating the Cis-Regulatory Landscape of the Sinoatrial Node.

Since the publication of the human genome, it is clear that a far larger proportion of our genome is comprised of regulatory, noncoding information rather than coding sequences.1 One goal to understanding this regulatory information has been the identification of the cis-regulatory elements (CREs) found in the genome and the cell types in which they function.2 However, it has proven challenging to identify cell-type specific CREs from rare cell populations. This is an important goal because many rare cell populations play critical roles in human health. In this issue, 2 independent teams present their work illuminating the CRE landscape of the small, but extremely important, population of sinoatrial node (SAN) cardiomyocytes in the heart for the first time.3,4 Their combined efforts further our understanding of the complex gene regulatory networks during the development of the SAN and lay the groundwork for identifying disease causing mutations, which specifically affect SAN function, as a method for diagnostic screening and early treatment of patients.