Scientists create 4D molecular map of hair follicle development using new imaging tool

Researchers at Johns Hopkins Medicine have developed a molecular imaging technology called 3D DNase-Enhanced Expression Profiling (3DEEP) that captures three-dimensional gene expression data from tissue sections 100–400 micrometers thick. The method removes genomic DNA that can interfere with the detection of messenger RNA, allowing precise spatial mapping of millions of RNA molecules within intact tissue samples.

The team applied 3DEEP to skin from newborn mice, collecting 3D snapshots of hundreds of hair follicles at different developmental stages. By computationally classifying cell types and estimating the molecular age of each follicle, they aligned the static images into a chronological sequence, effectively creating a stop-motion animation of organ formation. An interactive online interface was built to explore this four-dimensional dataset.

Analysis of the 4D map identified three distinct phases in hair follicle development. First, precursor cells organize spatially to establish the organ's axis perpendicular to the skin surface. Next, these precursors differentiate into the multiple cell types required for the follicle. Finally, the new cell types grow and remodel into a mature follicle capable of producing a hair strand.

To test the tool's ability to reveal developmental defects, the researchers compared follicles from normal mice with those from hairless mice lacking the Foxn1 gene, which is critical for hair growth. The comparison showed that follicles in hairless mice experienced delayed development: cells proliferated at a higher rate but had a reduced capacity to mature and assume specialized roles at the correct time.

The Foxn1 mutation led to a breakdown in cellular communication and timing, causing the follicular structure to collapse before a hair strand could form. Luis Garza, a professor of dermatology and co-author, noted that the hair follicle serves as a model for understanding broader principles of organ development because it forms through processes similar to those of other organs.

The study, published in Cell, demonstrates that 3DEEP can visualize complex, coordinated multicellular processes that have been difficult to observe. Soichiro Asami, the first author and a Ph.D. candidate, said the technology tackles the long-standing challenge of visualizing organ development over time, which could eventually aid earlier diagnosis of developmental conditions and tumors.

Garza suggested that if the technique can be applied to human tissue, it may help researchers understand the causes of specific hair loss conditions in individual patients and support personalized treatment approaches. The work was a collaboration between biomedical engineers Reza Kalhor and Jean Fan, dermatologist Luis Garza, and their teams.