Deficiency in the Actin Nucleator Cordon Bleu (Cobl) Causes Hypoplastic Enamel in Murine Mandibular Molars

The protein Cordon Bleu (Cobl) belongs to the group of actin nucleators. Through the formation of trimeric actin nuclei, Cobl authorizes the genesis of filamentous actin structures. Cobl has been detected by our group in secretory active and mature ameloblasts. Nevertheless, most aspects of its role in amelogenesis is still unclear. In this study, mandibular molars of 8-13 week old Cobl knock-out (KO) mice (n=6) were collected and enamel samples (n=132) subjected to histomorphometric analysis (quantitative analysis). Enamel composition was investigated by Fourier Transform Infrared spectroscopy (FTIR) and Raman Spectroscopy (qualitative analysis). Results were compared to samples obtained from wild-type mice (WT, n=5). In Cobl KO, reduced absolute (p<0.01) and relative histomorphometric enamel areas (p=0.02) were detected. Cobl KO also showed an increase in enamel-free areas in the molar cusps region. Compared to WT, those defects occurred by an increased probability of 1.323 (p=0.004). FTIR and Raman Spectroscopy revealed no differences in the enamel composition. In summary, Cobl deficency results in hypoplastic enamel and causes an increase in enamel-free areas. It is assumed that Cobl has a transient influence during the secretory stage of amelogenesis. Further investigations are needed to gain more detailed information on the function of Cobl in these processes.