Molecular Aspects of Sebaceous Differentiation

Abstract

Epidermal progenitor cells give rise to multiple skin lineages: hair follicle, sebaceous gland, and the overlying interfollicular epidermis [30, 39]. The multipotent stem cells reside in the bulge region of the hair follicle. These cells transform into the epidermis (epidermal keratinocytes) as well as its associated structures, sebaceous gland (sebocytes), and cells of the hair follicle (follicular keratinocytes). Sebocytes are the major cells within sebaceous glands (SG) [43]. The human SG is a multiacinar, holocrine-secreting tissue present in all areas of the skin except for the palms and soles. Its development is closely related to the differentiation of the hair follicle and the epidermis. SG develops in the 13–16th weeks of gestation in humans, arising in a cephalocaudal sequence from the hair follicle. In the skin, most sebaceous glands are associated with the upper portion of a hair follicle, forming the pilosebaceous unit. They are located as an outgrowth of the hair follicle outer root sheath, at the level of the middle dermis [54]. Development of the pilosebaceous unit involves an ordered set of developmental processes [26]. During late embryogenesis, developing hair follicles (hair peg stage) display several bulges of which one will give rise to the sebaceous gland and is located just above the hair follicle stem cell bulge and below the infundibulum of the developing follicle [26].