To determine if Spp1 is required for this Sox9-mediated process, heart valve explants and cultured rib chondrocytes isolated from post natal Sox9fl/fl mice were subject to infection with AdV-Cre, and/or an adenovirus containing a short hairpin (sh) RNA sequence to target Spp1 knockdown (AdV-shSpp1). This evidence concerns the gene SPP1 and infection.