Cross-fostering of the tammar wallaby ( Macropus eugenii) pouch young accelerates fore-stomach maturation

There are two phases of fore-stomach development during the first 200 days of pouch life in tammar wallaby. For the first 170 days, the mucosa displays an immature gastric glandular phenotype that changes to a cardia glandular phenotype, which remains for the rest of the animal’s life. During this 200-day period after birth, the pouch young (PY) is dependent on maternal milk, which progressively changes in composition. We showed previously that PY cross-fostered to host mothers at a later stage of lactation accelerated development. In this study, we investigated whether cross-fostering and exposure to late lactation stage milk affected the transition to cardia glandular phenotype. In fostered PY fore-stomach, there was increased apoptosis, but no change in cell proliferation. The parietal cell population was significantly reduced, and expression of gastric glandular phenotype marker genes ( ATP4A, GKN2, GHRL and NDRG2) was down-regulated, suggesting down-regulation of gastric phenotype in fostered PY fore-stomach. The expression of cardia glandular phenotype genes ( MUC4, KRT20, CSTB, ITLN2 and LPLUNC1) was not changed in fostered PY. These data suggest that fore-stomach maturation proceeds via two temporally distinct processes: down-regulation of gastric glandular phenotype and initiation of cardia glandular phenotype. In fostered PY, these two processes appear uncoupled, as gastric glandular phenotype was down-regulated but cardia glandular phenotype was not initiated. We propose that milk from later stages of lactation and/or herbage consumed by the PY may play independent roles in regulating these two processes.