The role of p53 in normal development and teratogen-induced apoptosis and birth defects in mouse embryos

摘要

In the studies described in this dissertation, we investigated the roles of p53 innormal development, teratogen-induced apoptosis, and birth defects. In the first study,the activation of p53 and its target genes, p21, NOXA, and PUMA, were examinedduring neural tube closure in mouse embryos exposed to hyperthermia (HS) or 4-peroxycyclophosphamide (4CP), teratogens known to induce neural tube defects(NTDs). In the second study, using p53-deficient mice, we examined the expression ofmRNAs and microRNAs (miRNAs) during neural tube closure. In the third study, theincidence of NTDs was investigated in p53- and p21-deficient mouse embryos exposedto HS. Finally, we examined the induction of apoptosis in p53-deficient mouse embryosexposed to HS.HS and 4CP induced the activation of p53 by phosphorylation and accumulationof the protein, leading to an increase in p21 proteins and mRNAs. Although HS and4CP also induced the expression of Noxa and Puma mRNAs, no significant increases inNOXA and PUMA proteins were observed, suggesting a possible role of transcriptionindependentapoptosis. In the second study, we showed that the expression of 388 genesand 5 miRNAs were significantly altered in p53 -/- compared to p53 +/+ embryos.Finally, we showed that 10% of p53 -/- pups exhibit exencephaly, spina bifida, and/orpreaxial polydactyly, whereas no malformations were observed among p21 -/- offspringin the absence of HS. HS resulted in an increased incidence of exencephaly in both p53and p21 null mice indicating that these two proteins act as teratogen suppressors. Our preliminary data additionally showed that a decreased level of apoptosis was observed inHS-treated embryos lacking a p53 allele, suggesting that too little apoptosis may becausally linked to NTDs observed in embryos exposed to HS. Taken together, thesestudies suggest that precise control of apoptosis and cell cycle arrest pathways arecritical for neural tube development and the prevention of teratogen-induced NTDs.