Developmental expression of APEX nuclease, a multifunctional DNA repair enzyme, in mouse brains

Expression of the mammalian major apurinic/apyrimidinic (AP) endonuclease (designated as APEX nuclease, or HAP1, APE or Ref-1 gene product) during mouse brain development was investigated by in situ and northern blot hybridizations. The enzyme is known to be a redox factor (Ref-1) stimulating DNA binding activity of AP-1 binding proteins such as Fos and Jun as well as a multifunctional DNA repair enzyme having 5' AP endonuclease, DNA 3' repair diesterase, 3'-5' exonuclease and DNA 3'-phosphatase activities. In the embryonic and postnatal development, APEX mRNA was expressed at high levels in the proliferative zone of various brain regions, with showing temporal and spatial changes. Its expression decreased in association with brain development to the basal expression level which was observed even in adulthood, with the exception of its expression in the hippocampal formation. The growth-dependent expression of APEX gene suggests that it has some roles on cell proliferation and/or differentiation in developmental brain. Its expression on the hippocampal formation became significant from postnatal day 7 and then increased. The pyramidal and granule cell layers expressed it at a higher level than most other brain regions at postnatal day 21. The developmental change of APEX gene expression was not necessarily associated with the changes of expression of c-fos and c-jun genes measured by northern blot hybridization. However, the present results suggested that APEX/Ref-1 gene product can interact with AP-1 binding proteins in brain, especially in the hippocampal formation, to regulate some brain functions by redox-activation.