Ancestry. Potential. Where do cells in adult animals come from in the embryo? Do all cells in the embryo can give rise to all cells in the adult animal? By labeling and then following the lineage of embryonic cells into the adult organism, scientist can determine to what extent cells contribute to one, two or multiple organs. By repeating the experiment at different times during embryonic development, scientist can determine when cells that contributed to multiple organs start losing this capacity, contributing to less and less tissues. By projecting the identities of adult cells into embryonic tissues, scientist generate a map of cellular fates; the potential of embryonic cells to give rise to adult tissues. This is a fate map.
Fate maps are the one of the oldest, least intrusive, and most valuable experimental approaches in developmental biology, as they provide information on the potential cells to contribute to tissues, organs, and systems of the body of an organism. The earliest fate maps were done over 100 years ago by following the distribution of black and yellow pigments naturally present in the fertilized eggs of several marine species (mollusks and echinoderms). Subsequently, methods were developed to follow the fate of cells in embryos lacking pigments. One of these first experiments was done in amphibian embryos using the vital dye markers (e. g., Carbon particles, Nile blue, Carmine red). More information on fate maps can be found here.
Modern fate-mapping techniques utilize genetic tricks to permanently label cells. Because of their permanent nature, genetic labeling approaches are far superior than labeling cells with vital dyes that bleach, bleed, or get diluted and lost as cells divide. The brainbow method to label cells with different fluorescent proteins not only allows labeling multiple cells with different colors simultaneously, but it is also esthetically pleasing.
The fate map simulation for the 32-cell stage of African clawed frog Xenopus laevis is based on results published by Jonathan Slack’s group in 1987 (Dale and Slack 1987). Since then, numerous other fate maps have been generated, each one mapping with greater detail the contribution of each embryonic cell to the frog larvae (e.g., Lane and Smith, 1999). To further explore Xenopus fate maps, please visit Xenbase.
The fate map simulation of the 64-cell stage tunicate embryo, Holocynthia roretzi, is based on the pioneering work of Hiroki Nishida (Nishida, 1987). Since then, numerous other fate maps of tunicate embryos have been published (Hirano and Nishida, 1997; Hotta et al., 2007; Nishida and Stach, 2014). In 2007, the group of Kohji Hotta published a detailed analysis of the early development of a second tunicate species, Ciona intestinalis (Hotta et al., 2007). This work has an associated Four-dimensional Ascidian Body Atlas (FABA) website that is excellent and worth exploring.
The fate map simulation of gastrula stage zebrafish embryo was generated using the pioneering work of Charles Kimmel group (Kimmel et al, 1990). Since then, advances in transgenesis, microscopy and computing has allowed the analysis of cell fates and movements in real time, in live specimens. One incredible example of this work was published in 2019 (Shah, et al. 2019). When checking out this work, don’t forget to go to the supplemental information section and look at the incredible movies achieved there.