427. MDM2 maintains the latency of expression of TRP53 in the mouse preimplantation embryo

Abstract

TRP53 is a tumour suppressor that causes cell-cycle arrest or cell death in response to a range of stressors. Normal preimplantation embryo development requires that TRP53 is maintained in a labile state¹. Culture of mouse C57BL6 preimplantation embryos causes this latency to be breached and this is a cause of the low embryo viability following culture. MDM2 is an ubiquitin ligase that targets TRP53 for degradation by the proteosome. MDM2 is activated by Serine 166 phosphorylation (pMDM2). This is commonly catalysed by the phosphatidylinositol-3 kinase (PI3K) and AKT signalling pathway. A range of embryotrophins activate the PI3K and AKT pathway. This study tested the hypothesis that TRP53 is maintained in a latent state in the normal embryo by the activation of MDM2 by the actions of embryotrophins via a PI3K and AKT signalling pathway. Genetic deletion of Mdm2 prevents normal preimplantation development in a Trp53 dependent manner². Addition of an MDM2 inhibitor (Nutlin-3) to culture medium caused a dose-dependent inhibition of zygote development (P < 0.001) that did not occur in Trp53^−/−embryos. Immunofluorescence and western blot analysis detected pMDM2 throughout mouse preimplantation development. Zygote culture reduced the levels of pMDM2 formation. Furthermore, blocking the actions of Paf, PI3K or AKT in vitro reduced in the expression of pMDM2, and also resulted in higher levels of TRP53 expression in embryos. The embryopathy resulting from increased TRP53 could be partially ameliorated by the addition of the TRP53 antagonist α-pifithrin to media (P < 0.05). The results show MDM2 was activated by an embryotrophin (Paf), PI3K and AKT signalling pathway and was required for the latency of TRP53 expression in the preimplantation embryos.

(1) Li A, Chandrakanthan V, Chami O, O’Neill C. (2007) Biology of Reproduction 76: 362–367.

(2) Montes de Oca Luna R, Wagner DS, Lozano G. (1995) Nature 378: 203–205.