Fig. 5. Radioactive in situ hybridisation analysis of mandibular explants after 2 days in culture in the absence or presence of soluble human activin receptors IIA and IIB. Adjacent serial frontal sections through tooth buds were analysed using bright field illumination to show histology (A,E,I), using Msx1 expression to determine the viability of the explants and to assist with orientation of the tooth germs within the explants (B,F,J), using Irx1 (C,G,K) and follistatin (Fst) expression (D,H,L) in the dental epithelia of the explants to assess the efficiency of repression of the activin signalling pathway. Explants treated with 0 mg/ml (A-D), 12.5 mg/ml (E-H) and 25 mg/ml (I-L) soluble receptors are shown. Fst expression is faint but detectable in the control explants and those treated with 12.5 mg/ml soluble receptors. It is missing from explants cultured in the presence of 25 mg/ml or higher concentrations of soluble receptors. Irx1 expression, however, appears to require less activin signalling, as it is maintained using concentrations of up to 25 mg/ml, and is lost at higher concentrations of soluble receptors. The hybridisation signal seen close to the non-oral surface of the explants corresponds to Irx1 expression in the superficial dermis in G and Fst expression in the tongue in L. Orange asterisks indicate the position of tooth germs.
