The in vitro morphogenesis of mouse molar tooth germs is inhibited by the anti-tumor antibiotic, hadacidin (N-formyl hydroxyaminoacetic acid). Organ cultures prepared from 15- and 16-day-old C57BL/6J embryos were maintained on agar-solidified medium. Treatment with hadacidin resulted in smaller than normal, morphologically aberrant tooth germs. Additionally, mitotic activity of tooth germs was inhibited in treated explants. Similarly, oral epithelium did not undergo its normal in vitro histogenesis when treated by this drug. Extended periods of treatment or treatment with high concentrations of hadacidin damaged the mesenchymal component of the tooth germs to a greater extent than it damaged the epithelium. Reversal of the developmental and mitotic inhibitions initiated by hadacidin was achieved by allowing the explants to recover on control medium. Hadacidin has been shown to be a competitive inhibitor of adenylo-succinate synthetase, which participates in the de novo synthesis of adenosine monophosphate (AMP). AMP can be synthesized by an alternative salvage pathway. Prevention of mitotic inhibition in hadacidin-treated explants was achieved by the simultaneous application of adenine and adenosine. These observations suggest that salvage purine biosynthetic pathways can function in developing tooth germs.

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The problem of the method of movement in vitro of a particular type of cell population (monolayers of epitheliocytes) form mouse kidney was investigated by means of time-lapse microcinemtograpy. It was found that within the daily enlarging cell sheet some cells move towards the explant. The possibility that the in vivo organization of these cells plays a role is suggested.

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Alanosine (2-amino-3-[hydroxynitrosoamino] propionic acid) an extracellular antitumor product of Streptomyces inhibits the in vitro morphogenesis of mouse molar tooth germs. Organ cultures prepared from 15- and 16-day-old C5 7BL/6J embryos were maintained on agar-solidified BME, supplemented with glutamine, gentamicin and fetal calf serum, in an incubation atmosphere of 5% CO₂ and 95% air. At a concentration of 16 µg/ml, alanosine severly inhibited growth of the explants and development of the tooth germs. Tooth germ inhibition was expressed as abnormal, or a lack of, folding of the dentino-enamel junction, disorientation of preameloblasts, negligible numbers of tooth germ cells in mitosis and failure of 2nd molar tooth germs to develop. These explants, after 4 days in culture, contrasted with larger explants, produced during the same culture period on control medium, exhibiting normally developing 1st and 2nd molar tooth germs with large numbers of cells in mitosis. The effects of the drug on the tooth germs were partially reversed by allowing the explants to recover on control media. Alanosine inhibits the conversion of inosine monophosphate to adenosine monophosphate, at the first step of a two-step conversion, in the de novo pathway of adenine nucleotide biosynthesis. The cytological and morphogenetic inhibition of tooth germ morphogenesis by alanosine can be partially prevented by the simultaneous application of adenine. These observations suggest that: (1) tooth germ development depends on adenine nucleotide synthesis, and (2) salvage as well as de novo adenine nucleotide biosynthetic enzymes function in normal tooth development.

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