Fig. 2

Unified current view for the structure and properties of the niche in model organisms. This illustration presents the most significant basic structures assumed to define a stem cell niche, as derived from studies of vertebrates’ hematopoietic systems (and of other SCNs in various organs) and the germ cell niches of the non-ecdysozoan model invertebrates Drosophila melanogaster and Caenorhabditis elegans. At the top, we list the four physiological properties associated with niche functionality (derived from [69]). The different cellular, signaling, and matrix components affiliated with SCN activities are further depicted (based on [70]). Variations in the presence of the different components occur in different animal systems (and may also be explained by a current lack of knowledge)