Cellular events and the pattern of p53 protein expression following cyclophosphamide-initiated cell death in various organs of developing embryo

This study was aimed at characterizing the temporal patterns of cell respon ses and p53 protein expression in the limbs, head, and liver of embryos res ponding to cyclophosphamide (CP)-induced teratogenic insult. ICR murine emb ryos were examined 24, 48, or 72 h after injection of 40 mg/kg CP on day 12 of pregnancy. The cellular events and temporal pattern of p53 protein expr ession were determined by FACS analysis and by TUNEL (apoptosis) in the hea d, limbs, and liver of the embryos. All tested organs showed apoptosis and a significantly decreased proportion of live cells after 24 h. Subsequent e vents were organ-dependent. In the liver, there were no dysmorphic events a t any time and excessive cell death had been almost compensated for by 48 h . Compensation was preceded by G(1) arrest and accompanied by an increased level of p53 protein in surviving cells. Excessive cell death in the head a nd the limbs resulted in structural anomalies. In the head, there was an in creased level of p53 protein and G(1) arrest after 24 h and the number of l ive cells at 48 h was equal to that seen in earlier samples, despite apopto sis. In the limbs, however, only isolated viable cells were seen by 48 h, b ut there was no increased level of p53 protein or G(1) arrest. Results of t his study suggest that the differential sensitivity of tested organ systems to CP may be associated with differences in cellular events following CP-i nitiated cell death. They also suggest that the input of p53 in determining the response of these organ systems to CP-induced teratogenic insult may b e different. Teratogenesis Carcinog. Mutagen. 19:353-367, 1999. (C) 1999 Wi ley-Liss, Inc.