DNA Replication Licensing and Paternal DNA Degradation in Mammalian Embryo

다국어 초록 (Multilingual Abstract)

Mammalian DNA replication occurs only at the fixed place, termed the origin of replication, origin of replication is not recognized by the DNA sequence. It is recognized by the DNA licensing, which indicate that DNA replication is prepared. Furthermore, in the case of mammalian one-cell embryo is separated into paternal and maternal pronuclei, and DNA licensing and DNA replication takes place each in a separate pronuclei. Based on the characteristics of these mammalian one-cell embryo, we tested whether paternal DNA that was destined for degradation was properly licensed, by testing for the presence of MCM7 and ORC2, two licensing proteins, in the paternal pronuclei. We also tested whether the zygote recognized the TOP2B mediated DNA fragmentation in epididymal spermatozoa or the nuclease degradation in vas deferens spermatozoa, by testing for the presence of gamma-H2AX. Sperm DNA fragmentation does not prevent licensing of DNA replication origins. The embryo recognizes DNA that is damaged by nucleases, but not by TOP2B because H2AX is phosphorylated in paternal pronuclei resulting from spermatozoa with fragmented DNA from vas deferens spermatozoa treated with divalent cations, but not from epididymal spermatozoa treated the same way. Our data indicate that the one-cell embryo does harbor a mechanism to prevent the replication of severely damaged DNA from spermatozoa, even though the embryos do not undergo classical apoptosis.