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, αV, 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 αVβ1 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 αVβ1 actively function on the surface of undifferentiated porcine SSCs, whereas α3, α5, α8, and α9 are present in inactive forms.
Keywords: functionality; integrins; pig; spermatogonial stem cells; undifferentiation.