EXPRESSION OF P21(WAF1 CIP1) DURING MOUSE ODONTOGENESIS/

p21(WAF1/CIP1) is a cyclin-dependent kinase (Cdk) inhibitor. This prot ein may function during development as an inducible growth inhibitor t hat contributes to cell cycle exit and differentiation. The expression pattern of p21 during mouse embryogenesis was correlated with termina l differentiation of multiple cell lineages including skeletal muscles , cartilage, skin and nasal epithelium. p21 expression was analyzed by in situ hybridization during odontogenesis as well as during in vitro tooth development in chemically defined medium with or without retino ic acid. p21 transcripts were detected in the restricted area of inner dental epithelium during late cap and initial bell stages and then co nfined to the post-mitotic odontoblasts and ameloblasts. The replicati ng cells were devoid of any signal. The distribution of p21 mRNA in vi tro, whatever the culture conditions, was similar to the in vivo patte rn. p21 protein immunolocalization was superimposed on the transcripts distribution but more restricted in ameloblasts. TGF beta 1 is known to induce p21 expression. During dental cytodifferentiations, TGF beta 1 and p21 expressions overlap. Growth inhibition by TGF beta 1 may be associated with p21 induction.