Investigations into Cell Differentiation Using Cells in Culture

Abstract

Almost every multicellular organism is a clone of cells descended from a single original cell, the fertilized egg. This cell is the ultimate totipotent stem cell, having the potential to form a complex organism through proliferation, differentiation and organization of the differentiated tissue. Cellular differentiation may be defined as the process by which “a cell acquires or displays a new stable phenotype without changing its genotype” (Ham and Veomett 1980), and embryonic development involves the progressive production of generations of stem cells, each with greater restriction of potential for differentiation. In this way, a single fertilized egg cell gives rise to three germ layers, the ectoderm, mesoderm and endoderm, each of which, in turn, gives rise to the specific tissue types of an adult organism, all the cells of which possess identical genomes. Thus, the ectoderm gives rise to the epidermis and the nervous system, the mesoderm gives rise to the vertebral column, connective tissue, cartilage, bone, fibrous tissue, muscle cells and the vascular system, and the endoderm gives rise to the digestive tract, the trachea and the lungs. Once established, the cells of the germ layers are no longer totipotent but are determined stem cells and so, for example, a mesodermal stem cell will only give rise to mesodermal tissue and generally will not differentiate into ectodermal or endodermal tissue types.