Appearance of a functional insulin receptor during rabbit embryogenesis

The domain structure of the insulin receptor was investigated in liver and brown adipose tissue of developing rabbits. The structure of the binding domain (α-subunit) was analysed after covalent labelling with a 125I photo-reactive insulin analogue. The structure of the tyrosine kinase domain (β-subunit) and the transmission of the hormonal signal from the α-to the β-subunit were analysed by stimulating with insulin the autophosphorylation of the β-subunit. Finally, the immunoreactivity of the receptor in developing tissues was assessed with anti-receptor antibodies. The results show that a functional insulin receptor can be detected at the early stages of fetal development in both tissues and is conserved throughout ontogenesis to adulthood.