1Department of Biological Sciences, Wellesley College, 2Department of Developmental Biology, Harvard School of Dental Medicine, 3Department of Environmental Health, Harvard School of Public Health, 4Department of Human Evolutionary Biology, Harvard University, 5Institute of Dental Research and Department of Oral Pathology, Westmead Hospital
Friday All day, Clinch Concourse
Dentine- and enamel-forming cells secrete their respective tissues in rhythmic increments, resulting in the formation of successive growth lines. Experimental studies in primates and rodents have demonstrated that these lines are the result of daily secretory activity (circadian rhythms). In 2001, a Japanese team showed that the destruction of the master biological clock in mammals, the suprachiasmatic nucleus (SCN), resulted in the cessation of growth line formation in rats. Recently, researchers have hypothesized that melatonin (an endocrine hormone secreted with a circadian rhythm) may act as a messenger between the SCN and the developing teeth, and therefore may be a crucial component in the process of growth line formation. In order to test this hypothesis, we studied dental development in melatonin-deficient C57BL/6 mice. Six mice were given two (n=2), four (n=2), or five (n=2) injections of nitrilotriacetato lead (2 mg/kg Pb-NTA) at five day intervals from eight days of age to chronologically label the developing incisors. Following humane sacrifice, incisors were dissected, decalcified, sectioned, and stained in order to visualize the lead labels. Five growth lines were observed between consecutive lead labels, demonstrating clear daily incremental lines in C57BL/6 mice teeth, as in other rodents. These results suggest that melatonin may not have a principal role in the process of incremental line formation. Ultimately, further elucidation of circadian biology and its role in incremental feature formation will allow more accurate estimations of tooth formation time, an essential tool for reconstructing primate life history.
Funded by the Howard Hughes Medical Institute, Harvard University, and the Harvard School of Dental Medicine.