The differentiation of the columella in avian embryos treated with hadacidin with some observations on other skeletal abnormalities.

Single doses of N-formyl hydroxyaminoacetic acid (hadacidin) were injected into chick embryos HH stages 5-30. Embryos surviving for 8+ days total incubation time were recovered and examined for gross and microscopically observable defects. Particular attention was paid to the development of the columella. Survival was only 20%, but a high incidence of cranio-facial and hind limb defects was observed in most age groups. While three categories of columella defect were observed, reflecting some degree of age dependency, this chondrogenic tissue is less susceptible to teratogenic action than other skeletal tissues. The types of columella defect observed are interpreted in the light of a model of cellular interactions in fenestra vestibularis differentiation presented previously. It is concluded that hadacidin produces abnormalities of skeletal differentiation by disrupting morphogenetic, rather than the initiative phases of development of particular elements.