Ontogeny of the skin and the transition from scar-free to scarring phenotype during wound healing in the pouch young of a marsupial, Monodelphis domestica.

The marsupial Monodelphis domestica provides a versatile model for the study of "fetal" wound healing. The pouch young of this species have been used to perform a systematic histological study of wound healing and skin development throughout pouch life; from Pouch Day 0 to Pouch Day 30 with comparisons drawn against adults. We have demonstrated that pouch young heal without macroscopic scars if wounded before Pouch Day 9 and that a transition into a scarring healing phenotype occurs around the ninth pouch day. The inflammatory reaction of wounds and aspects of skin differentiation such as dermal collagen organisation, adipose layer development, hair follicle growth, and epithelial maturation have been documented using simple ranking scales to highlight trends through pouch life. Inflammation was noted to become prominent after Pouch Day 9. There was also a general temporal correlation between the other aspects of differentiation and the transition into a scarring phenotype. It is concluded that although fetal wounds may have different cytokine profiles due to the differences of inflammatory reaction compared to adults, other aspects of skin development play a role in determining the healing phenotype.