Identification of EphrinB1 expression in prostatic mesenchyme and a role for EphB-EphrinB signalling in prostate development.

Paracrine signalling from mesenchyme to epithelium plays a key role in regulating prostate organogenesis and it is important to identify the mesenchymally expressed molecules that regulate organ growth, though currently few such molecules are known. Tyrosine kinase signalling via EphB receptors has been characterised in many developmental processes, and EphB3 mRNA expression was detected in prostate inductive mesenchyme in previous gene profiling studies. This led us to examine the expression and function of EphrinB signalling in prostate development, to determine if EphrinB ligands might function as mesenchymal paracrine regulators of prostate growth. Using PCR, wholemount in situ hybridisation, and immunohistochemistry we examined the expression of EphB receptors and EphrinB ligands in rat prostate during development to determine which showed mesenchymal expression. EphB3 and EphrinB1 transcripts and proteins were expressed in the mesenchyme of developing prostate and in female urogenital mesenchyme and smooth muscle. The function of EphrinB signalling was examined using in vitro organ culture assays of ventral prostate (VP), which were treated with EphB3-Fc and EphrinB1-Fc proteins to inhibit or augment Ephrin signalling. Addition of recombinant EphB3-Fc resulted in a significant decrease in VP organ size, while recombinant EphrinB1-Fc resulted in a significant increase in VP organ size and epithelial proliferation. Additionally, EphrinB1-Fc reduced the degree of epithelial branching in VP organs and increased ductal tip size, though without disrupting normal differentiation. We have identified expression of EphrinB1 in prostatic mesenchyme and suggest that the EphrinB signalling system acts as a regulator of prostate growth. EphrinB-EphB signalling may function as an autocrine regulator of mesenchyme and/or as a paracrine regulator of epithelia.