A new p63-deficient mouse model or a fresh look at an old one?

Abstract

The p53-related transcription factor p63 gene encodes six isoforms by the use of two promoters -TA and DN -and alternative splicing at the 3 0 -terminus, resulting in a, b, and g variants. Its critical importance in development has been illustrated by the discovery that dominantly inherited mutations in the p63 gene are found in a number of human ectodermal dysplasias with defects in limb and skin development, 1 and by the generation of mouse models lacking p63 by two independent laboratories. Although the strategies for generating these models were different, the phenotypes were very similar: the mice die soon after birth with severe defects in limbs, craniofacial development, and absence of skin. 2,3The phenotypes of the different p63-deficient models -three generated by the Bradley laboratory (p63 Brdm1, p63 Brdm2, and p63 Brdm3) as well as the one generated by the McKeon laboratory -were essentially identical in their more evident manifestations. However, differences in the interpretation of the phenotypes of these models have led to different views regarding the role of p63 in epidermal morphogenesis and tumor susceptibility. This is far from unprecedented, especially as different mouse strains (129Sv/B57BL/6 in Bradley's and B57BL/6/BALB/c in McKeon's) and KO strategies were used. McKeon's model was generated in a 'traditional' way, by deleting exons 6-8, coding for the DNA-binding domain (DBD). On the other hand, Mills et al.2 generated two mouse strains -Brdm1 and Brdm2 -with targeting vectors that used a gap-repair-dependent mechanism to generate ES cells harboring disrupted p63 alleles; the Brdm1 allele is disrupted within exon 6 of the DBD; the Brdm2 allele is disrupted within intron 10, involving the 3 0 -region of the gene: the transcript would be devoid of exons 11-14, which are incorporated in the a-and b-isoforms. The same laboratory has reported another mouse strain -Brdm3 -in which a conventional floxed LoxP insertion hits the DBD coding exons 5-7, encoding the majority of the DBD in the case of the p63 Brdm3 allele. The three Brdm mice are phenotypically identical.In this issue of Cell Death Differentiation, Wolff et al. 4performed a set of experiments leading to the conclusion that the Brdm2 mouse model is a partial KO: 4 they detected a truncated p63 transcript, reminiscent, but not identical of the endogenous p63 transcript that encodes the p63g-isoform.The truncated transcript is entirely consistent with the genomic organization of Brdm2 originally reported by Mills et al.2 Wolff et al. expressed this transcript in transfections and found that the resulting protein was similar to p63g in its ability to transactivate an Mdm2 luciferase reporter. Immunohistochemical analysis using the 4A4 and H137 antibodies showed that p63 is clearly present, although the amount of p63g produced in utero, as determined by western blotting, was barely detectable. Analyses of embryonic sections of McKeon's mice were negative. The g-isoforms lack the SAM domain, a protein-protein interaction module present in ...

Delineating Molecular Mechanisms of Squamous Tissue Homeostasis and Neoplasia: Focus on p63

“…Based on further studies in embryos, the authors proposed these patches to be remnants of a more developed E15 epidermis 3–5 layers thick containing terminally differentiated epithelium that was transient in nature due to mechanical stress at birth, and suggested that the Brdm2 mice were equivalent to p63 α / β knockout mice [29]. This observation and ensuing studies generated much controversy, as to whether the recharacterized mice were the same as those used by others or if perhaps a spontaneous genetic event might be at play [29–33], which to date remains unresolved.…”

Treasure or artifact: a decade of p63 research speaks for itself

“…3). In addition to reversion events, other types of novel genetic changes could have occurred in the p63 Brdm2/Brdm2 mice, which may account for the phenotypic differences that were observed by Wolff et al (Reviewed by Aberdam and Mantovani (20)).…”

MicroRNA-203 contributes to skin re-epithelialization

“…25 It has an antiproliferative role, fundamental for skin development and differentiation, targeting the 3′-UTR of the transcription factor p63. 22, 26 Indeed, p63, a member of the p53 family, has an important role in maintaining basal keratinocyte proliferative potential in adult normal epidermis, 27, 28, 29, 30, 31, 32, 33 during development 34, 35, 36, 37 and in pathological conditions. 23, 24, 38, 39 MiR-203 downregulation, as described in several cancers, 42, 43, 44, 45, 46 promotes EMT transition and enables tumor cells to acquire invasive metastatic features.…”