How complex, three-dimensional structures emerge from single sheets of cells is a fundamental question in developmental biology. The dispensability of hair follicles makes them the perfect model system for studying this question—specifically, how structures and organs develop from buds. In a new study, Elaine Fuchs and colleagues use a three-pronged approach—involving gene expression analysis, transgenic mice, and cell cultures—to study how epithelial buds, the precursors of hair follicles, form. Their experiments point to two key actors in a signaling pathway that molds a targeted cluster of cells into a hair bud.
During the budding process, overlapping signaling pathways from two adjacent embryonic cell layers—the epithelium and the mesenchyme—direct morphogenesis. The mesenchymal cells initiate the cell-to-cell “crosstalk?that controls bud formation by first directing a small cluster of epithelial cells to form a placode, the pouch that forms hair plugs. The placode in turn directs underlying mesenchymal cells to form the base of the hair follicle, called the dermal papilla, and both structures contribute to the mature hair follicle. During development, cells are constantly bombarded with external signals. The trick is figuring out which signals trigger the transcriptional and behavioral properties in cells that spur bud formation.
In previous experiments, Fuchs and colleagues show