Culturing skin from eight day chicken embryos: the development of feather buds

Erin Betters, Katy Lewis, Katie Crawford







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Within chick embryos, interactions between the epidermis and dermis of the skin result in the formation of preliminary feather buds, and later, specific feather types or cutaneous structures (Gilbert, 2003). The outer layer of skin, the epidermis, is formed from the ectoderm of the developing embryo; it covers the embryo following the development of the neural tube (Gilbert, 2003). After neurulation, the preliminary epidermis undergoes a series of cell divisions and dif-ferentiations to form the skin. The final product consists of the basal layer, or germinal epithelium, the spinous layer, the granular layer, and cells known as keratinocytes (Gilbert, 2003).

Altogether, the cells of the epidermis are connected and form an epithelium, or sheet of cells (Gilbert, 2003). Under the epidermis lies the dermis, which has its origins from the meso-derm and is a mesenchymal layer of “loosely” associated cells (Gilbert, 2003). The epidermis signals to the dermis through the production of sonic hedgehog and transforming growth factor-beta (SHH, TGF-beta) proteins. Once the dermis receives these factors its cells aggregate, and in turn signal back to the epidermis, causing certain genes to be activated (Gilbert, 2003). As a re-sult, different cutaneous structures are formed, based on the location of the dermis (Gilbert, 2003). Of particular note, such interactions between the epidermis and dermis layers lead to the initial development of feather buds. In the early stages, parts of the epidermis thicken and form epidermal palcodes, under which the dermal cells aggregate to form dermal papilla – a small projection of tissue at the base of the feather (Bellairs et al., 1998). In time, feather buds appear as these structures elongate, forming the basis from which feathers will be formed (Bellairs et al., 1998)(figure 2C).

Understanding that the development of the skin can occur autonomously from the rest of the organism, specifically in culture, has proven vital to the development of techniques to treat burn injuries, as well as factored into the creation of artificial skin such as Apligraf (OI, 2003; Scott, 2000). Apligraf, composed of a collagen matrix, fibroblast cells (which contribute to the dermis), and keratinocytes, has been used to treat both diabetic and venous ulcers. (OI, 2003; Cebra-Thomas, 2004). If the complexities of skin formation can be understood, strides could be made in the development of skin grafts, allowing for greater availability to patients. In addition, greater understanding of the chemical signals between the dermal and epidermal layers could be used to design treatments for burn patients whose skin layers have been damaged, helping the patient’s own skin regenerate rather than depending on whole skin grafts.

This experiment seeks to demonstrate that the skin of eight-day-old chick embryos, if re-moved, can continue to develop to the feather bud stage in culture(figure 2C). We expect that, as in past experiments, this development will be successful to the point of late feather bud development, but will arrest before any actual feather development takes place (as it would in-ovo) (Cebra-Thomas, 2004).