Oral morphogenesis

Fig. 1. Diagrammatic representation of the build-up of structures postulated to be essential for cell division and oral morphogenesis in Tetrahymena. The heavy arrows between 1 and 2, and 2 and 4 indicate the path of assembly while the thin arrows denote that proteins already built into more complex units can be in continuous exchange with proteins in the intracellular environment. A heat shock is postulated to open or greatly stimulate the reaction from 2 to 3. (From Zeuthen and Williams. 1969. In Nucleic Acid Metabolism, Cell Differentiation and Cancer Growth, Pergamon Press.)...

In conclusion, heat shocks (1) block cell division and (2) synchronize oral morphogenesis and division in that order. Subsequently, the first synchronous division (3) triggers most of the cells into a synchronous replication phase. As far as morphologic and many other criteria can tell us, oral morphogenesis (Frankel, 1962) and the synchronized cell cycle that begins with the first and second synchronous division (Holz, 1960) are essentially normal. 

Chapin RE, Morgan KT, Bus JS. 1983. The morphogenesis of testicular degeneration induced in rats by orally administered 2,5-hexanedione. Exp. Mol. Pathol. 38 149-69... 

Most of these ultrastructural investigations were performed on enamel slabs carried in the buccal sulcus or mounted on the buccal sites of the teeth. However, within the oral cavity, saliva provides a series of distinctly different fluid environments [74], and secretions from different salivary glands vary considerably and have a specific protein composition [75], Consequently, more recently published electron microscopic and CLSM studies have focussed on site-dependent differences in the formation (morphogenesis) of the in vivo pellicle [17,28]. 

These findings provide evidence for regional, site-dependent differences in the morphogenesis of the in vivo-formed salivary pellicle. It is suggested that factors acting locally in the oral cavity, shearing forces and the differing supply... 

Hannig M Ultrastructural investigation of pellicle morphogenesis at two different intraoral sites during a 24-h period. Clin Oral Invest 1999 3 88-95. 

Donoghue et al. 2000), thus independently corroborating homology between conodont and vertebrate hard tissues. Conodont hard tissues therefore reflect the plesiomorphic state for the vertebrate skeleton. From this, it follows that odontodes are the plesiomorphic patterning unit in the morphogenesis of the vertebrate skeleton and that an oral skeleton (i.e. dentition) is plesiomorphic relative to external armour. 

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