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Publisher Summary This chapter deals with the paradigm of cell signaling. It uses the nomenclature to annotate the classes of molecules involved in cell signaling. It also lists signaling pathways and explains their role in tissue homeostasis and tissue engineering. The molecular mechanism by which cells communicate, referred to as cellular signaling are discussed. Cellular signaling is initiated by generation of a ligand; i.e. a molecular entity generated by a sending a cell to bring about a change in the physiology of a responding cell. A central paradigm can be recognized in most events of cellular signaling, which consists of three distinct steps: signal initiation, signal transduction, and gene activation. The chapter defines that signaling pathways are regulated at many different levels, i.e. extracellularly, in the cytoplasm and in the nucleus. This provides engineers multiple means to manipulate the cell appropriately.

Recessive epidermolysis bullosa simplex (REBS) is characterized by generalized cutaneous blistering in response to mechanical trauma. This results from fragility of the basal keratinocytes that lack keratin tonofilaments because of homozygote null mutation in the keratin 14 gene. REBS patients display in addition focal dyskeratotic skin lesions with histology of epidermolytic hyperkeratosis (EHK) and tonofilament clumping in the suprabasal layers of the epidermis. in this study we examined whether it is possible to mimic in vitro the bullous and dyskeratotic cellular phenotype. For this purpose, fibroblasts from non-dyskeratotic (K14-/-) and dyskeratotic (K14-/-) skin of a REBS patient and fibroblasts from a healthy donor (K14+/+) were isolated and incorporated into collagen matrices. Subsequently, fresh biopsies originating from the nondyskeratotic and dyskeratotic skin of the patient and from a healthy donor were placed onto the collagen matrices and cultured at the air-liquid interface. Epidermal morphogenesis was evaluated on the basis of tissue morphology and the expression of a series of keratins. The results of the present study indicate that basal cell vacuolization in REBS can be mimicked in vitro but not the EHK. Fibroblasts seem to play an important regulatory role in establishing the REBS phenotype. These findings suggest that wild-type fibroblasts may enhance the stability of K14-/- keratinocytes in vitro.