Aberrant activation of p53 due to loss of MDM2 or MDMX causes early lens dysmorphogenesis

Abstract

Although forming a heterodimer or heterooligomer is essential for MDM2 and MDMX to fully control p53 during early embryogenesis, deletion of either MDM2 or MDMX in specific tissues using the loxp-Cre system reveals phenotypic diversity during organ morphogenesis, which can be completely rescued by loss of p53, suggesting the spatiotemporal independence and specificity of the regulation of p53 by MDM2 and MDMX. In this study, we investigated the role of the MDM2-MDMX-p53 pathway in the developing lens that is a relatively independent region integrating cell proliferation, differentiation and apoptosis. Using the mice expressing Cre recombinase specifically in the lens epithelial cells (LECs) beginning at E9.5, we demonstrated that deletion of either MDM2 or MDMX induces apoptosis of LEC and reduces cell proliferation, resulting in lens developmental defect that finally progresses into aphakia. Specifically, the lens defect caused by MDM2 deletion was evident at E10, occurring earlier than that caused by MDMX deletion. These lens defects were completely rescued by loss of two alleles of p53, but not one allele of p53. These results demonstrate that both MDM2 and MDMX are required for monitoring p53 activity during lens development, and they may function independently or synergistically to control p53 and maintain normal lens morphogenesis.

Monitoring p53 by MDM2 and MDMX is required for endocrine pancreas development and function in a spatio-temporal manner

“…To obtain mice with MDM2 deletion specifically in developing endocrine pancreas, we first crossed Le-Cre; MDM2 f/+ with MDM2 f/f mice as described in the Methods section, and the genotypes of their offspring were determined by PCR analysis as shown in our previous study (Zhang et al, 2014). Four genetic types of pups including Le-Cre; MDM2 f/f , Le-Cre; MDM2 f/+ , MDM2 f/f and MDM2 f/+ , were obtained with a normal Mendelian ratio as shown in Fig.…”

“…1A, indicating that the deletion of MDM2 in developing pancreas does not cause embryonic lethality. However, all the Le-Cre; MDM2 f/f pups were eyeless (Zhang et al, 2014), developed hyperglycemia with random blood glucose level higher than 400 mg/dl (Fig. 1B), and died within one week after birth (Fig.…”

“…1A). In this study, we only focused on pancreatic organogenesis, as the lens phenotypes have been reported previously (Zhang et al, 2014). Through fluorescence immunostaining we confirmed the deletion of MDM2 specifically in embryonic pancreatic endocrine by concomitantly expressing LE-Cre (Fig.…”

“…5), we next investigated if p53 activation might also be the cause for the developmental defects of pancreas and diabetic phenotypes in the MDM2- and MDMX-deleted mice, by introducing p53 floxed alleles into MDM2 or MDMX conditional knockout mice and deleting p53 gene by Le-Cre. The genotype of p53 floxed allele was identified by PCR as shown in our previous study (Zhang et al, 2014). As expected, the defects of endocrine pancreas caused by knocking out either MDM2 or MDMX were rescued by TP53 deletion.…”

“…It has been indicated that MDM2 forms a complex with MDMX through their C-terminal RING domains to inhibit p53 during early embryogenesis (Huang et al, 2011; Pant et al, 2011). However, during later developmental stages of organogenesis and adult life, MDM2 and MDMX may independently or cooperatively regulate p53 to delicately control cell proliferation, differentiation, and death so that each organ maintains unique shape and function, which is supported by the more severe phenotypes observed with conditional deletion of MDM2 in lens epithelium (Zhang et al, 2014), cardiomyocytes (Xiong et al, 2007), central nervous system (Xiong et al, 2006), smooth muscle cells (Boesten et al, 2006), and erythroid progenitor cells (Maetens et al, 2007), compared to those with loss of MDMX. Considering the participation of cell proliferation, differentiation, and apoptosis in the pancreatic development and the potential involvement of p53 in pancreas-related diseases as described above, we hypothesized that MDM2 and MDMX could also be critical for controlling these p53-dependent events during pancreatic development and diabetes initiation and progression.…”