Cutaneous structure development
Encyclopedia
Cutaneous structures arise from the epidermis and include a variety of features such as hair, feathers, claws and nails.
During embryogenesis, the epidermis splits into two layers: the periderm (which is lost) and the basal layer
. The basal layer is a stem cell
layer and through asymmetrical divisions, becomes the source of skin cells throughout life. It is maintained as a stem cell layer through an autocrine signal, TGF-a
, and through paracrine signal FGF7 aka keratinocyte growth factor
(KGF) produced by the dermis below the basal cells. In mice, over-expression of these factors leads to an overproduction of granule cells and thick skin.
Hair and feathers are formed in a regular pattern and it is believed to be the result of a reaction-diffusion system. This reaction-diffusion system combines an activator, Sonic hedgehog
, with an inhibitor, BMP4 or BMP2, to form clusters of cells in a regular pattern. Sonic hedgehog-expressing epidermal cells induce the condensation of cells in the mesoderm. The clusters of mesodermal cells signal back to the epidermis to form the appropriate structure for that position. BMP signals from the epidermis inhibit the formation of placodes in nearby ectoderm.
It is believed that the mesoderm defines the pattern. The epidermis instructs the mesodermal cells to condense and then the mesoderm instructs the epidermis of what structure to make through a series of reciprocal inductions. Transplantation experiments involving frog and newt epidermis indicated that the mesodermal signals are conserved between species but the epidermal response is species-specific meaning that the mesoderm instructs the epidermis of its position and the epidermis uses this information to make a specific structure.
During embryogenesis, the epidermis splits into two layers: the periderm (which is lost) and the basal layer
Stratum germinativum
The stratum basale is the deepest layer of the five layers of the epidermis, which is the outer covering of skin in mammals. The stratum basale is a continuous layer of cells...
. The basal layer is a stem cell
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
layer and through asymmetrical divisions, becomes the source of skin cells throughout life. It is maintained as a stem cell layer through an autocrine signal, TGF-a
Transforming growth factor
Transforming growth factor is used to describe two classes of polypeptide growth factors, TGFα and TGFβ....
, and through paracrine signal FGF7 aka keratinocyte growth factor
Keratinocyte Growth Factor
The Keratinocyte Growth Factor , also known as FGF7, is a growth factor present in the epithelialization-phase of wound healing. In this phase, keratinocytes are covering the wound, forming the epithelium....
(KGF) produced by the dermis below the basal cells. In mice, over-expression of these factors leads to an overproduction of granule cells and thick skin.
Hair and feathers are formed in a regular pattern and it is believed to be the result of a reaction-diffusion system. This reaction-diffusion system combines an activator, Sonic hedgehog
Sonic hedgehog
Sonic hedgehog homolog is one of three proteins in the mammalian signaling pathway family called hedgehog, the others being desert hedgehog and Indian hedgehog . SHH is the best studied ligand of the hedgehog signaling pathway. It plays a key role in regulating vertebrate organogenesis, such as...
, with an inhibitor, BMP4 or BMP2, to form clusters of cells in a regular pattern. Sonic hedgehog-expressing epidermal cells induce the condensation of cells in the mesoderm. The clusters of mesodermal cells signal back to the epidermis to form the appropriate structure for that position. BMP signals from the epidermis inhibit the formation of placodes in nearby ectoderm.
It is believed that the mesoderm defines the pattern. The epidermis instructs the mesodermal cells to condense and then the mesoderm instructs the epidermis of what structure to make through a series of reciprocal inductions. Transplantation experiments involving frog and newt epidermis indicated that the mesodermal signals are conserved between species but the epidermal response is species-specific meaning that the mesoderm instructs the epidermis of its position and the epidermis uses this information to make a specific structure.