Involvement of a matrix metalloproteinase in MIS-induced cell death during urogenital development

Programmed cell death of the Mullerian duct eliminates the primitive female reproductive tract during normal male sexual differentiation. Mullerian inhibiting substance (MIS or AMH) triggers regression by propagating a BMP-like signaling pathway in the Mullerian mesenchyme that culminates in apoptosis of the Mullerian duct epithelium. Presently, the paracrine signal(s) used in this developmental event are undefined. We have identified a member of the matrix metalloproteinase gene family, Mmp2, as one of the first candidate target genes downstream of the MIS cascade to function as a paracrine death factor in Mullerian duct regression. Consistent with a role in regression, Mmp2 expression was significantly elevated in male but not female Mullerian duct mesenchyme. Furthermore, this sexually dimorphic expression of Mmp2 was extinguished in mice lacking the MIS ligand, suggesting strongly that Mmp2 expression is regulated by MIS signaling. Using rat organ genital ridge organ cultures, we found that inhibition of MMP2 activity prevented MIS-induced regression, whereas activation of MMP2 promoted ligand-independent Mullerian duct regression. Finally, MMP2 antisense experiments resulted in partial blockage of Mullerian duct regression. Based on our findings, we propose that similar to other developmental programs where selective elimination or remodeling of tissues occurs, localized induction of extracellular proteinases is critical for normal male urogenital development