Cord-like mosaic patches in the adrenal cortex are fractal: implications for growth and development.

Organogenesis proceeds rapidly and faithfully during fetal development. The process includes generation of parenchyma, followed by organization into functional tissues. The method by which the growth of organ parenchyma is regulated is not known, but insight into this regulation has been obtained by studying mosaic tissues of experimental chimeras and transgenic mosaics. The patterns revealed by this procedure offer an indication of how the parenchyma was generated. In the liver, the pattern appears as islands of one cell type in a sea of the other cell type, while in the adrenal cortex the pattern is one of alternating cords of one cell type adjacent to the other cell type. We have established previously that mosaic patches in the liver are fractal. The fractal dimensions of patches in the liver are consistent with an iterative, recursive growth model with simple stereotypical division rules. Here we report that the patches in mosaic adrenal cortex of the mouse and rat are also fractal and that the fractal dimension of the surface of the patches is lower than that in the liver. Fetal development and fractal dimensions of adrenal cortical mosaic patches are consistent with an algorithmic cell division model in which parenchymal growth is constrained to edges of growth centers forcing cord structures to form. Fractal analysis of the geometry of mosaic patches in tissues of experimental chimeras is helpful in constructing hypotheses of organ growth.