Dihydrotestosterone induction of EphB2 expression in the female genital tubercle mimics male pattern of expression during embryogenesis

Purpose: The Eph family constitutes the largest class of membrane bound tyrosine kinase receptors in higher vertebrates, being involved in complex cell-to-cell recognition events via their membrane anchored ligands, the ephrins. To uncover evidence for possible molecular involvement in genitourinary development, we evaluated the pattern of EphB2 expression in male and female genital tubercles (GTs) after culture with and without dihydrotestosterone (DHT). Materials and Methods: GTs of embryos from time pregnant CD1 mice heterozygous for the EphB2^lacz mutation were explanted at 12.5 to 14.5 days after conception. In these mutant mice the exons encoding the EphB2 tyrosine kinase and C-terminal domains were replaced with bacterial lacZ sequence encoding β-galactosidase to demonstrate EphB2 expression. The GTs were microdissected, cultured for 24 to 48 hours with or without addition of 10 nM DHT and then stained with X-gal to visualize the β-galactosidase reporter of EphB2 expression. Results: LacZ staining was detected along the borders of the urethral plate (UP) in males. Females expressed EphB2 at the GT base but DHT exposure induced EphB2 expression along the UP. Under culture conditions, progressive approximation of the UP borders was noted in male fetuses and androgen exposed females. UP approximation was not seen in the nonexposed female tubercles. Conclusions: EphB2 expression appears to be temporally and spatially regulated in the developing mouse GT and differs between sexes. Male pattern of expression can be induced in the female GT by DHT exposure. Given DHT exposure alters EphB2 expression, EphB2 is a candidate androgen regulated gene. These findings may give insight into UP closure in normal and pathological conditions.