RRM2 and intervertebral disk degenerative disorder: Interestingly, Ubiquitin-conjugating enzyme e2c (UBE2C), Ribonucleoside-diphosphate reductase subunit M2 (RRM2), and Cell division cycle 20 homologue (CDC20), holding important role in the regulation of cell cycle process (39–41), were firstly found in IDD and needed further study.