Development of Hair Fibres

Abstract

The growth of hairs occurs during the anagen phase of the follicle cycle. Hair growth begins with basement membrane-bound stem cells (mother cells) around the dermal papilla neck which continuously bud off daughter cells which further divide as a transient amplifying population. Division ceases as cell line differentiation begins, which entails changes in cell junctions, cell shape and position, and cell-line specific cytoplasmic expression of keratin and trichohyalin. As the differentiating cells migrate up the bulb, nuclear function ceases in cortex, cuticle and inner root sheath (IRS) layers. Past the top of the bulb, cell shape/position changes cease, and there is a period of keratin and keratin-associated protein (KAP) synthesis in fibre cell lines, with increases, in particular of KAP species. A gradual keratinization process begins in the cortex at this point and then non-keratin cell components are increasingly broken down. Terminal cornification, or hardening, is associated with water loss and precipitation of keratin. In the upper follicle, the hair, now in its mature form, detaches from the IRS, which is then extracted of material and becomes fragmented to release the fibre. Finally, the sebaceous and sudoriferous (if present) glands coat the fibre in lipid-rich material and the fibre emerges from the skin. This chapter follows the origin of the hair growth in the lower bulb and traces the development of the various cell lines.

Integrated Analysis of Methylome and Transcriptome Changes Reveals the Underlying Regulatory Signatures Driving Curly Wool Transformation in Chinese Zhongwei Goats

“…The GO functional analysis in our study demonstrated that these DMGs were mainly enriched in the classifications of cell structure (e.g., cell projection and plasma membrane) and cell communication (e.g., cytoskeletal protein binding, channel activity and ion channel activity) (Supplementary Figure S4). Cell junctions (GO: 0030054) and cytoskeletal protein binding (GO: 0008092) have been reported to regulate cortex cell movement and reshaping in certain areas of the HF (Morioka et al, 2006;Harland and Plowman, 2018). These results were in agreement with previous reports and verified the importance of intercellular communication during cell reshaping of the HF bulb (Runswick et al, 2001;Arita et al, 2004).…”

Can plant‐derived phytochemicals provide symptom relief for hair loss? A critical review

“…During the active hair growth periods, HMK proliferate and cells are ‘pushed’ upwards, whilst undergoing lineage specific differentiation and keratinization. This results in the formation of the three structural compartments of the hair fibre, medulla, cortex and cuticle, the follicle inner root sheath (IRS) that plays a role in the shaping of the hair fibre , and the companion layer . The follicle is encased by the outer root sheath (ORS), which contains stem cells that play an active role in the initiation of the hair growth cycles .…”

High‐pressure freezing followed by freeze substitution of a complex and variable density miniorgan: the wool follicle

“…Follicles contain both mesenchymal and epithelial compartments. Hair growth and cornification occurs within the proximal 1-2 mm, a process extensively described in previous studies (Rogers, 2006;Harland, 2018b;Harland & Plowman, 2018;Harland et al, 2019). Briefly, cells from a proximally located and rapidly dividing transient amplifying population migrate distally, then (Auber's line) stop dividing and differentiate into seven phenotypically distinct lineages of keratinocyte, arranged in cylindrical layers, which form the hair shaft and the inner root sheath (IRS) that supports the developing hair ( Fig.…”

“…Buried deep under the epidermis, active follicles are elongated cylindrical structures that are approximately 200 µm in diameter and 3-4 mm long with a bulb-like protuberance at their proximal end. They are surrounded by a thick network of collagen fibrils within which are embedded blood vessels, fibroblasts, neurons and adipocytes (Harland, 2018a;Harland & Plowman, 2018). Follicles contain both mesenchymal and epithelial compartments.…”