Fig. 1

The difference between mammalian and C. elegans skin. C. elegans attains a simple but tenacious body structure through evolution. During the embryonic stage, a group of epidermal cells undergo a series of fusions and to develop a large multinucleated syncytium hyp7. The syncytium will secrete the cuticle, an overlaid sheath of an extracellular matrix consisting of collagen, lipids, and glycoproteins. As a result, there are two layers within C. elegans skin: epidermis and cuticle. When the worm gets fully matured, the skin gets postmitotic and can only grow through polyploidization. On the other hand, the mammalian skin is a stratified epithelium made of keratinocytes in each layer. The basal layer contains stem cells that can proliferate and push daughter cells to migrate toward the surface. Due to the lack of oxygen and water around the outer layers, keratinocytes will die and cornify at the surface. These dead cells can compose the stratum corneum, which is the primary permeability barrier of the skin