Integrin Heterodimers Expressed on the Surface of Porcine Spermatogonial Stem Cells

To date, in vitro culture systems able to sufficiently expand the small population of spermatogonial stem cells (SSCs), a tool for the development of sperm-mediated gene transfer techniques in transgenic pigs, in the porcine seminiferous tubule have not been reported. Therefore, as a step toward engineering a noncellular niche to support the in vitro maintenance of porcine SSC self-renewal, we investigated the types of integrin heterodimers that are expressed and functional on their membrane. The α and β integrin subunit protein expressions were analyzed using immunocytochemistry and fluorescence immunoassay, and the function of integrin heterodimers was confirmed by attachment and antibody inhibition assays. The integrin subunits, α₃, α₄, α₅, α₆, α₈, α₉, α_V, and β₁, were identified on the surface of them. Moreover, they showed significantly increased adhesion to fibronectin, laminin, and vitronectin, and functional blocking of integrin α₄β₁, α₆β₁, or α_Vβ₁ significantly inhibited adhesion to these molecules. They showed significantly decreased adhesion to tenascin C and functional blocking of integrin α₅β₁ did not significantly inhibit adhesion to fibronectin. Accordingly, we confirmed that the integrin heterodimers α₄β₁, α₆β₁, and α_Vβ₁ actively function on the surface of undifferentiated porcine SSCs, whereas α₃, α₅, α₈, and α₉ are present in inactive forms.