PARP1 and necrotizing enterocolitis: We further used two protein markers, namely Lgr5, an epithelial stem cell marker, and E-cadherin, an epithelial cell marker, and found that the upregulated expression of PARP1 and PAR was predominantly distributed at the top and base of the villi, as marked by Lgr5, in intestinal tissues of NEC mice; meanwhile, the structure of intestinal villi was damaged and destroyed, as evidenced by the impaired expression and localization of E-cadherin in NEC mice (Fig. 3A–D).