CDKN1A and colitis: Both PC Clusters 1 and 2 are characterized by increased expression of two markers of radio-resistant and secretory progenitors with self-renewal capacity during regeneration, namely Krt1925 and Atoh126, while increased expression of Reg3b, known for its protective role in the development of colitis and ileitis27, and Cdkn1a (p21), a marker of terminal differentiation in the intestine28, was observed in Cluster 2 compared to 1.