A functional analysis of p53 during early development of xenopus laevis

Abstract

p53 is a nuclear protein that acts like a tumor suppressor and is involved in regulation of cellular growth. In Xenopus, the p53 protein is highly expressed during oogenesis and is strictly cytoplasmic in the oocyte. We have analysed its participation in DNA replication and transcription during early development, using the egg and oocyte as model-systems. The injection of sperm nuclei into Xenopus eggs is followed by DNA replication and mitotic events. We show that the endogenous p53 enters the nuclei and moves through a series of discrete subnuclear loci whose distribution is S-phase speci®c. A speci®c peripheral nuclear localization of p53 is observed before entry into S-phase, followed by an internal localization which is strictly dependent on ongoing DNA synthesis. At no stage in the cell cycle, however, did we observe any co-localization with RPA or PCNA, which were used as initiation or elongation markers for DNA replication. We also show that injection into the nucleus of the oocyte of small amounts of either Xenopus or human p53 ± less than 10% of the cytoplasmic storage ± is su cient to block RNA polymerase IIdependent transcription from a coinjected TATA-boxcontaining reporter plasmid. Transcription is rescued by microinjection of the TATA-box binding protein (TBP), suggesting that nuclear exclusion of p53 during oogenesis may be necessary for transcription of maternal genes. These characteristics are discussed in relation to the regulation of nuclear activities during early embryogenesis.

Phosphorylation of p53 Is Regulated by TPX2-Aurora A in Xenopus Oocytes

“…In oocytes, all p53 appears to be cytoplasmic and therefore unlikely to be involved in transcription (30). During the postfertilization cleavage divisions, a small fraction of p53 translocates into the nucleus at each division (31), but since transcription is largely absent from embryos until the midblastula transition (12th cleavage), it is unlikely that p53 is involved in transcription-dependent processes. Instead, in early embryos, it has been suggested to play a role in S phase regulation and in DNA repair, to prevent reinitiation of DNA replication during S phase, and to block premature entry from S phase into mitosis (50).…”

“…Recently, our group showed that Xenopus p53 is able to inhibit Aurora A kinase activity in vitro, but this inhibitory effect can be suppressed by prior binding of Aurora A to TPX2 (9). Contrary to somatic cells, where p53 is nuclear, unstable, and expressed at a very low level, p53 is highly expressed in the cytoplasm of Xenopus oocytes and stable until later stages of development (30,31). The high concentration of both p53 and Aurora A in the oocyte provided a suitable basis for investigating p53-Aurora A interaction and also evaluating Xenopus p53 as a substrate of Aurora A.…”

Bcr-Abl protein tyrosine kinase activity induces a loss of p53 protein that mediates a delay in myeloid differentiation

“…p53 has a key role in sensing DNA damage and cell cycle regulation (for review see Levine, 1997) whilst also being involved in the regulation of di erentiation (Amariglio et al, 1997;Sabapathy et al, 1997;Shounan et al, 1996;Soddu et al, 1996). Alterations in p53 expression are heavily implicated in CML disease progression (see Introduction).…”

Regulation of the cell cycle by p53 after DNA damage in an amphibian cell line

“…Treatment of this cell line with various DNA damaging agents led to phenotypes indistinguishable from those observed in mammalian cells, including both cell cycle arrest and apoptosis. It has been previously shown that Xp53 is stored in the cytoplasm of oocytes and migrates to the nucleus after fertilization (Amariglio et al, 1997;Tchang and Mechali, 1999). Such delocalization could act by supplying the p53 necessary for the protection of the embryo during the development.…”