Modeling of mosaic patterns in chimeric liver and adrenal cortex: algorithmic organogenesis?

If organogenesis were a completely deterministic process, then the amount of information required to store the spatial position and fate of every cell in vertebrate organisms would be larger than the total information that could be contained in their genomes. This suggests that the instructions of developmental mechanisms involved in organogenesis, coded in DNA, must be at least in part procedural or algorithmically based. Chimeric mosaic patterns in rat livers have been shown to be isotropic and to have fractal profiles (D approximately 1.3) whereas adrenal gland mosaics show a less irregular radial pattern, with lower fractal dimension (D approximately 1.2) than in the liver. These findings suggested a possible model of parenchyma generation. We propose that during organogenesis in both liver and adrenal cortex, the same basic mechanism is directed to organ mass enlargement, whereas the differences observed in mosaic patterns between the organs could be due to the control of a single parameter, namely, a form of contact inhibition. Computer simulations in two dimensions returned comparable results in both the fractal dimension value of mosaic patches and appearance of the mosaic 'tissues', as observed histologically in chimeras. This suggests that position information and locomotion of cells would not be required to produce the mosaic pattern observed in chimeras.