Abstract
Mature cerebellar granule cells in culture die by a process that requires new RNA and protein synthesis when deprived of depolarizing concentrations of potassium. We investigated gene expression during the early phase of the cell death program evoked by potassium deprivation. Using a differential gene display technique, we isolated a cDNA that was increased by potassium deprivation. This cDNA was homologous to the 3' mRNA end of neuronal pentraxin 1 (NP1), a gene encoding a secreted glycoprotein whose expression is restricted to the nervous system. Reverse-Northern and Northern blot analyses confirmed that treatment with low potassium induces overexpression of NP1 mRNA, with a subsequent increase in NP1 protein levels. Time-course studies indicated that overexpression of NP1 protein reaches a maximum after 4 h of exposure to potassium deprivation and 4 h before significant cell death. Incubation of cerebellar granule cells with an antisense oligodeoxyribonucleotide directed against NP1 mRNA reduced low potassium-evoked NP1 protein levels by 60% and attenuated neuronal death by 50%, whereas incubation with the corresponding sense oligodeoxyribonucleotide was ineffective. Furthermore, acute treatment with lithium significantly inhibited both overexpression of NP1 and cell death evoked by low potassium. These results indicate that NP1 is part of the gene expression program of apoptotic cell death activated by nondepolarizing culture conditions in cerebellar granule cells.
Highlights
In the central nervous system, during normal embryonic development, the number of neurons is adjusted by activation of a built-in gene expression program that kills unnecessary cells in a process described as programmed cell death [1]
This cDNA was homologous to the 3 mRNA end of neuronal pentraxin 1 (NP1), a gene encoding a secreted glycoprotein whose expression is restricted to the nervous system
Exposure to Low Potassium Induces Cell Death in Mature Cerebellar Granule Cells—Treatment of mature cerebellar granule cells with low potassium resulted in a time-dependent increase in neuronal death, measured with propidium iodide fluorescence (Fig. 1)
Summary
In the central nervous system, during normal embryonic development, the number of neurons is adjusted by activation of a built-in gene expression program that kills unnecessary cells in a process described as programmed cell death [1]. These results indicate that NP1 is part of the gene expression program of apoptotic cell death activated by nondepolarizing culture conditions in cerebellar granule cells. This result indicates that these clones correspond to the gene whose overexpression was induced by treatment with low potassium and, the gene that confers the high intensity signal to the AP21G1 band (Fig. 2).
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