Expression and regulation of FAAP in the mouse epididymis.

The focal adhesion-associated protein (FAAP), encoded by the murine D10Wsu52e gene, is named as involved in modulating cell adhesion dynamics. It is a highly conserved and ubiquitously expressed protein, and its human homologue HSPC117 has been identified in many protein complexes. However, the expression and regulation of the FAAP gene have not yet been well characterized. Herein, we demonstrate that FAAP mRNA and protein expression are highly regionalized in the mouse epididymis with predominant enrichment in the initial segment. During sexual maturation, FAAP mRNA is always expressed in the caput epididymides. Castration causes rapid and significant decrease of FAAP mRNA abundance within the initial segment, whereas testosterone replacement fails to reverse the regression. Unilateral orchidectomy and efferent duct ligation studies further validate that expression of the FAAP mRNA is highly dependent on the presence of luminal testicular factors rather than testosterone. Furthermore, FAAP expression in the initial segment is not affected by cryptorchism.