Origin of INSL3-mediated testicular descent in therian mammals

R^B12H substitution in the B chain of RLN3 converts LGR7-specific RLN3 into an LGR8-specific ligand. (A) Identification of radical substitutions in the INSL3 B chain. Five radical substitutions in INSL3 (green letters). Three surface residues chosen for site-directed mutagenesis analyses (asterisks). Spatial positions of these critical residues are shown (right). In the structure model, residues in the B and A chains are indicated by blue and white space balls, respectively. (B) LGR7(RXFP1)- and LGR8 (RXFP2)-activation activity of human RLN3, INSL3, RLN3 R^B12H, RLN3 R^B12A, RLN3 F^B20R, and RLN3 S^B25P peptides (mean ± SEM, N = 4). (C) Competitive LGR7- and LGR8-binding analysis of RLN3, INSL3, RLN3 R^B12H, and RLN3 R^B12A peptides (mean ± SEM, N = 3). (D) Stimulation of cAMP production in cultured rat gubernaculum cells by INSL3 and RLN3 R^B12H peptides (mean ± SEM, N = 4). (*) Significantly different from controls (P < 0.01).