Figure 5. Comparison of epithelium renewal dynamics in different species.

(A) The transit amplifying-to-stem cell ratio is the highest in teleost but the lowest in human during normal homeostasis. (B) The differentiated-to-transit amplifying cell ratio is the lowest in teleost but the highest in human during normal homeostasis. (C) As a strategy of efficient tissue restitution, there will be a transient expansion of the transit amplifying population by 10–15% in these species. This value does not vary much as long as the lesion ranges below ∼95% of the epithelium tissue. (D) Recovery time varies in these species. In teleost, epithelium can be restituted in a shorter period of time, but this is achieved by allowing a bigger transient expansion in the transit amplifying population. In human, it takes longer time to complete epithelium restitution, but this is achieved with a tighter mediation over the expansion of the transit amplifying population. These data suggest that these species employ different strategies in maintenance of homeostasis. Compared with intestines of other species, human intestine harbors minimum number of stem cells to support a larger villus size and restitutes epithelium through tightly mediated proliferation to maintain genome integrity and minimize the possibility of carcinogenic transformations.