Tissue Image of the Month - Hairs and follicles

A hair and hair follicle stained with H&E showing the different layers: a) external root sheath, b) internal root sheath, c) cuticle layer, d) medulla and e) cortex.
Immunohistochemical staining of a hair and hair follicle with an antibody towards human keratin 71. Strong staining (brown) is can be detected in the internal root sheath layer.

Hello everyone!

Tissue Atlas group is pleased to announce the launch of the Tissue Image of the Month. Previously, you have had the joy of experiencing interesting images of cellular organelles and proteins described by the Cell Atlas. Now we also hope that you will follow the blog posts and pictures of stained tissues with the same excitement and curiosity, as we dive into the world of histology, immunohistochemistry, cells and tissues.

First up - hairs and hair follicles.

Hair fibers consist of cells called trichocytes. The fibers vary in size, disposition and color due to factors such as age, sex, ethnicity and region of the body. The hairs on our bodies arise from the hair follicles, which are epidermal derivatives located in the connective tissue layer of skin, dermis. The hair follicles are composed of two distinct layers that wrap around the initial part of the hair fiber, the internal and external root sheath.

The hairs serve us several important functions, which include protection, regulation of body temperature and sensory functions. Histologically, hair can be divided into three layers, namely the medulla, cortex and cuticle layer, all originating from cells growing and dividing at the base of the hair, called the dermal papilla.

There are several important proteins expressed in hairs and hair follicles, among these are the keratins which are fundamental for the structural integrity of the hair shaft and hair follicle. The keratins can be divided into two types, acidic (type I) and basic (type II) keratins and many keratins are expressed exclusively in hairs and hair follicles. If you are eager to learn more about hair and hair follicle-specific proteins annotated in the Human Protein Atlas, you can access all of them here.

The brown-colored precipitate in the image is showing the localization of keratin 71, a type II keratin protein expressed in the inner root sheath of hair follicles. Keratin 71, encoded by the KRT71 gene, was first described in humans by Langbein and co-workers, and keratin 71 seems to play a crucial role in the formation of hair. In fact, in a study conducted by Fujimoto and co-workers, the authors showed that mutations in the KRT71 gene cause hypotrichosis, a condition of little or no hair growth.

Stay tuned for more interesting blog posts!

Feria Hikmet Noraddin