Exploring the Wnt enhancer landscape in the mammary gland

The mammary gland is a complex and dynamic tissue. Its development and homeostasis require extensive and controlled communication between different cells. To regulate cell behavior, signaling molecules have to facilitate communication between cells at exactly the right time and place. WNT ligands are an example of such signaling molecules, and they are part of a conserved intercellular signaling pathway. Despite our knowledge of the WNT/CTNNB1 pathway, surprisingly little is known about how spatiotemporal expression of Wnt genes is regulated. To understand the basis of spatiotemporal specific cell-cell communication, we investigated how cell type specific Wnt expression is regulated in the mammary gland. An extensive transcriptomic analysis of the postnatal mammary gland showed specific expression patterns of Wnt genes in different cell populations. Generally speaking, specific gene expression patterns are thought to be established by regulatory elements that are scattered throughout the genome. We present a three-step plan on the identification of enhancers, which constitute a subcategory of regulatory elements that have the capacity to induce transcription of one or more genes. We used our workflow to find Wnt2 and Wnt4 enhancers that are active in the mammary gland. This resulted in the identification of an active enhancer hub upstream of the Wnt4 gene, and the identification of a Wnt2 enhancer, 15.4 kb upstream of the Wnt2 promoter. This has given us new insights into how cell type specific expression patterns of Wnt genes are established in the mammary gland