Molecular mechanisms controlling skin heterogeneity

This project summary pertains to the Supplement. Different regions of the skin vary in their characteristics such as thickness, pigmentation, innervation, and presence, size and density of hair follicles and sweat glands, that are reflected in differential responses to injury and disease. While regional

characteristics of the skin are established during fetal development, positional information must be retained in the skin throughout life to allow for maintenance of regional characteristics and their re-establishment in wound healing. Positional information resides in the skin dermis, but its molecular basis is poorly understood.

In the parent grant, we proposed to address these questions by identifying candidate factors and areas of chromatin involved in establishing skin heterogeneity in embryogenesis through single cell RNA-seq and single cell ATAC-seq experiments on different regions of developing mouse skin (Aim 1). To determine

which of these candidate factors and chromatin areas may also be responsible for maintaining regional skin heterogeneity in adult life, we are performing the same analyses on the corresponding areas of adult skin. We hypothesize that epigenetic mechanisms contribute to maintenance of regional skin characteristics. To test

this, we will first identify patterns of DNA methylation and histone modifications that characterize developing dermis in specific skin regions by carrying out Bisulfite-seq to reveal sites of DNA methylation and CUT&RUN for histone modifications that mark enhancers and active, repressed, or poised genes. We will then ask which

of these patterns are maintained in adult dermal cells from the same regions (Aim 2). To test the functions of candidate regulators in directing and maintaining region-specific differentiation programs, we will use inducible genetic tools to delete the corresponding genes in developing or adult mouse dermis in vivo. Initial analyses

have been focused on DKK2, SOSTDC1, IGFBP4, and TWIST1, that were identified in preliminary studies as showing regional differential expression in developing mouse and human skin and influence molecular pathways important in skin development and/or hair growth (Aim 3). The Diversity Supplement application is based on our subsequent studies that identified the IGFBP

family member IGFBP7 as being more highly expressed in hairless and less hairy compared with more hairy developing skin. Unexpectedly, in adult dorsal skin IGFBP7 localizes to the arrector pili muscle (APM), an essential niche for peripheral sympathetic nerves that innervate bulge stem cells in the adult hair follicle and

are required for their activation. Preliminary data from Igfbp7-null mice show that in the absence of IGFBP7 the APM is disorganized and thicker than in control mice and shows abnormal branching. Based on these data, we will test two hypotheses in the Supplement: (i) in embryonic skin, IGFBP7 contributes to suppression of hair

follicle development in hairless and less hairy skin regions; and (ii) IGFBP7 plays a separate role in dorsal hairy skin to control development and/or maintenance of the APM.