Last week, Valerie Horsley and her colleagues at Yale University in New Haven, Connecticut, reported that cellular signaling capable of regenerating dormant follicles comes from a transcription factor which regulates precursor cells that form the skin's fatty layer beneath the epidermis.
During the body's early development, stem cells in the skin develop along three different pathways, differentiating into hair follicles, into sebaceous glands for secreting fat to lubricate and waterproof the skin, and into the epidermis itself.
The walls of the epidermis are thinner.
The epidermis lies outside of this skeleton.
Unlike thorns, prickles are actually pointed protuberances from a plant's epidermis.
Instead, blocks of tough, fibrous cells associated with the xylem (water-conducting tissue), some lignification of the most common type of cells (parenchyma) in the stem, and silicification of the epidermis (outermost layer of cells) provide the structural rigidity of bamboo stems.
The amphibian epidermis has five to seven layers of cells formed from a basal stratum germinativum.
The colours of reptiles are produced by both melanocytes in the epidermis and three types of chromatophores in the dermis: melanophores, which contain melanin; xanthophores, which contain yellow pigments; and iridophores, which contain reflecting platelets of colourless guanine.
They also possess many other horny derivatives of the epidermis, including nails, claws, hooves, quills, and horns.
As well as the clear horizontal stratification of the epidermis, a vertical organization is also apparent, at least in nonglabrous skin, in the sense that the ascending keratinizing cells appear to form regular columns.
Whether covered with leaf armour or not, the surface of the fern stem is protected by an epidermis, or "skin," a single layer of epidermal cells, which are more or less flat cells with thick outer walls.
