Journal Article

Laminin α3 forms a complex with β3 and γ3 chains that serves as the ligand for α 6β1-integrin at the apical ectoplasmic specialization in adult rat testes

Apical ectoplasmic specialization (ES) is a testis-specific hybrid cell/cell actin-based adherens junction and cell/matrix focal contact anchoring junction type restricted to the interface between Sertoli cells and developing spermatids. Recent studies have shown that laminin γ3, restricted to elongating spermatids, is a putative binding partner of α 6β 1-integrin localized in Sertoli cells at the apical ES. However, the identity of the α and β chains, which constitute a functional laminin ligand with the γ3 chain at the apical ES, is not known. Using reverse transcription-PCR and immunoblotting to survey all laminin chains in cells of the seminiferous epithelium, it was noted that α 2, α 3, β1, β2, β3, and γ3 chains were found in germ cells, whereas α 1, α 2, α 4, α 5, β1, β2, γ1, γ2, and γ3 chains were found in Sertoli cells, implying that α 3 and β3 are the plausible laminin chains restricted to germ cells that may be the bona fide partners of γ3. To verify this postulate, recombinant proteins based on domain G of α 3 and domain I of β3 and γ3 chains were produced and used to obtain the corresponding specific polyclonal antibodies. Additional studies have demonstrated that the laminin α 3, β3, and γ3 chains indeed are restricted to germ cells at the apical ES, co-localizing with each other and with β1-integrin. Furthermore, co-immunoprecipitation studies have confirmed the interactions among laminin α 3, β3, and γ3, as well as β1-integrin. When the functional laminin ligand at the apical ES was disrupted via blocking antibodies, such as using anti-laminin α 3 or γ3 IgG, this treatment perturbed adhesion between Sertoli and germ cells (mostly spermatids), leading to germ cell loss from the epithelium. More important, a transient disruption of the blood-testis barrier was also detected.