Apoptosis-inducing effect of ribosomal protein L4 during neurogenesis and aging

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The expression and distribution of rpL4 during rat brain development were examined by RT-PCR and in situ hybridization techniques. Marked expression of rpL4mRNA observed in the areas of high cellular proliferation in the brian of embryos and neonates (up to postnatal day 14). It is suggested that rpL4 would have certain roles involved in cell proliferation and cell death in the fetal and neonatal brain. Rat embryos were administered with 5-Azacytidine (5AzC) at day 13 and apoptosis and rpL4 mRNA expression in the brain were investigated. Brain cell apoptosis was observed at.9.to 24 hr after 5AzC administration. The level of rpL4 mRNA expression, however, did not change during this period.The expression of p53, P21, bax, cyclin G1, 'fas and gadd 45 in the 5AzC-treated rat embryonal brain was examined by immunohistochemistry and RT-PCR. Cell proliferation level was also examined by BrdU labeling. The number of TUNEL-positive apoptotic cells, p53-positive cells, and p21-positive cells were at the maximum level at 12 hr, 9 hr and 12 hr after 5 AzC-administration, respectively, and these cells were observed at the same areas. By RT-PCR, the expression of p21 (at 9 to 12 hr), bax (at 12 hr), cyclin G1 (at 9 to 24 hr), and fas (at 9 to 12 hr) was markedly increased compared with control. The number of BrdU-positive cells was markedly decreased at 12 hr after 5AzC-administration, indicating G1 arrest of the cell cycle.The results of the study clarified details of the rpL4 mRNA expression, and the mechanism of subsequent DNA damage and apoptosis, after 5AzC-administration. Same examination during the aging process is now going on.