INDUCTION OF DNA SYNTHESIS OR APOPTOSIS IN MAMMALIAN NUCLEI BY XENOPUS EGG EXTRACTS THAT FAIL TO SUPPORT THE REPLICATION OF SPERM CHROMATIN

Abstract

Cell-free extracts of Xenopus eggs are widely used to study DNA replication in higher eukaryotes. However, with Xenopus sperm chromatin as template, it is a common experience that the efficiency of replication varies from extract to extract, for reasons that are unclear. Here we show that the majority of extracts unable to support sperm replication are nevertheless able to induce DNA synthesis in intact mammalian nuclei. Those that do not, induce apoptosis.

Heterogeneity in nuclear transport does not affect the timing of DNA synthesis in quiescent mammalian nuclei induced to replicate in Xenopus egg extracts

“…In order to gain insight into the nature of the factors regulating entry into S phase and the onset of DNA synthesis, we have been exploiting the ability of Xenopus egg extracts to support the initiation and completion of chromosomal DNA replication in vitro (Leno & Laskey 1991a; Hutchison 1993). Although it has been reported that G 0 nuclei do not replicate in this system unless first permeabilized (Leno & Munshi 1994, 1997; Wu & Gilbert 1997), we have found that intact nuclei from quiescent Swiss 3T3 cells can be induced to undergo significant levels of DNA replication in Xenopus egg extracts (Hola et al 1994, 1996; Logothetou‐Rella, Sun & Brooks 2000; Sun et al 2000), though the capacity for replication declines with the duration of quiescence (Sun et al 2000). Those nuclei that initiate DNA synthesis do so asynchronously, despite exposure to a common level of replication factors (Hola et al 1994, 1996).…”