1. During the cap stage of tooth development signaling for the cusp formation is largely controlled by which of the following

1. Inner enamel epithelial
2. Dental follicle
3. Dental papilla
4. Enamel knot

ANSWER d

The enamel knot is a reservoir of signaling pathway-related genes and signaling molecules that allow tooth morphogenesis to progress toward the bell stage and regulate the tooth's shape

• Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs.
• The enamel knot precursor cells can be detected first at the tip of the tooth buds by expression of the p21 gene, followed shortly after by Shh.
• By the cap stage, when the enamel knot is visible histologically, it expresses genes for many signaling molecules, including Bmp-2, Bmp-4, Bmp-7, Fgf-4, Fgf-9, Wnt-10b, Slit-1, and Shh.
• Three-dimensional reconstructions of the expression of these genes have revealed highly dynamic spatial and temporal nested patterns in the enamel knot.
• On the whole, receptors for the enamel knot signals are localized in the epithelial cells surrounding the enamel knot.
• Each tooth germ has a single primary enamel knot and secondary enamel knots at the tips of the future cusps in molars at the cap stage.
• Fgf-4 and Slit-1 may be the best molecular markers for enamel knot formation because these are the only two genes that have been observed in both primary and secondary knots.
• The exact physical role of the enamel knot is not yet established, but changes in its morphology in tooth germs of spontaneous mouse mutants with abnormal molar cusp formation, such as Tabby (Eda), downless (dl), and Crinkled (Edaar), have started to reveal some detail of this remarkable structure.
• The current view is that the enamel knot represents an organizational center that orchestrates cuspal morphogenesis.