Genetic Regulation of Amelogenesis and Implications for Hominin Ancestors

Growth and development of the third permanent molar in Paranthropus robustus from Swartkrans, South Africa

“…When comparing such data sets, much depends on how close to the EDJ cross striation spacing measurements have been possible and on the different definitions of inner cuspal enamel. These new results for SK 835 do however suggest it may be premature to use summary differences in rates of enamel formation rather than gradients through time to support taxonomic differences 55,92 . www.nature.com/scientificreports/ Ramirez Rozzi 79 has calculated that secretory ameloblasts in thick enamelled molars attributed to P. boisei continue to form cuspal enamel for a greater proportion of the total crown formation time (53.8%, range in n = 14 M3s, 43-73%) than, for example, in thinner enamelled gorillas (15-23%, n = 8 molars).…”

“…There is now good evidence that circadian clocks operate in ameloblasts and odontoblasts [51][52][53][54] and that they regulate amelogenin secretion and other ameloblast activities 55 as enamel prism formation cycles through alternating fast and slow phases [56][57][58][59][60][61] . How exactly this circadian rhythm manifests as a fine dark cross striation across the narrow slowly formed constriction of a prism body is however less clear 55,56 .…”

“…There is now good evidence that circadian clocks operate in ameloblasts and odontoblasts [51][52][53][54] and that they regulate amelogenin secretion and other ameloblast activities 55 as enamel prism formation cycles through alternating fast and slow phases [56][57][58][59][60][61] . How exactly this circadian rhythm manifests as a fine dark cross striation across the narrow slowly formed constriction of a prism body is however less clear 55,56 . Cross striations are more porous 62 and show a compositional contrast in back-scattered electrons-based (BSE) microscopic images that has been attributed to increased carbonate content 56 , or perhaps to an alternating dominance of matrix over mineral deposition during the day 55 .…”

“…How exactly this circadian rhythm manifests as a fine dark cross striation across the narrow slowly formed constriction of a prism body is however less clear 55,56 . Cross striations are more porous 62 and show a compositional contrast in back-scattered electrons-based (BSE) microscopic images that has been attributed to increased carbonate content 56 , or perhaps to an alternating dominance of matrix over mineral deposition during the day 55 . It is also likely that abrupt changes in enamel crystallite orientation and/or continuity contribute to the appearance of cross striations in TLM and in polarised light microscopy (PLM) 63,64 .…”

Measures of maturation in early fossil hominins: events at the first transition from australopiths to earlyHomo

“…This has become possible in a few cases by studying the incremental structure of tooth enamel and dentine [53][54][55][56]. The evidence that growth markings in enamel and dentine have a daily periodicity [57][58][59] has recently strengthened with new studies documenting the control of enamel matrix protein secretion by various clock-genes [60][61][62]. The ages at death cited in this study and the ages for defined stages of tooth development used here have all previously been published [34,35,[63][64][65][66][67][68][69][70] and are based on the daily incremental record preserved within fossil tooth enamel and dentine.…”