ENHANCEMENT OF MOUSE CDC46 GENE EXPRESSION IN THE OSTEOBLAST BY LASER IRRADIATION

To identify any gene whose expression is enhanced by irradiation with low incident levels of laser energy, we previously constructed the cDNA library of the osteoblastic cell line MC3T3-E1, using a stepwise subtraction procedure between cells with and without laser irradiation. In the present study, we focused on one cDNA clone, designated as MCL-60. Our preliminary sequencing experiment indicated that this clone exhibited high homology with the gene coding for mouse CDC46 (cell division cycle 46 gene which is involved in the initiation of DNA replication of eukaryotic cells. To confirm the gene product, the DNA sequence of the cDNA clone MCL-60 was determined and assessed in the GenBank and EMBL nucleic acid databases. The transcription level of the cDNA clone MCL-60 wag examined by Northern blot analysis. The DNA sequence of clone MCL-60 exhibited 99.6% homology with that of CDC46 /MCM5 (minichromosome maintenance 5), and the deduced amino acid sequence exhibited 100% homology. Higher CDC46 mRNA levels were observed in laser irradiated cells compared to the levels in non-irradiated cells. Furthermore, DNA synthesis was increased by laser irradiation. These findings suggest that low incident levels of laser irradiation may play a principal role in stimulating proliferation of osteoblasts with enhancement of the gene expression of CDC46.