Characterization of the cellular origin of a tissue-engineered human phalanx model by in situ hybridization

Tissue-engineered models of human phalanges have previously been fabricated from a combination of bovine periosteum, cartilage, tendon, and biodegradable polyglycolic acid and poly-L-lactic acid scaffolds. Resulting constructs implanted in athymic mice for more than 40 weeks developed new bone, cartilage, and tendon and became vascularized, but cell types comprising the constructs were unidentified. The origin of cells in middle phalanx models implanted for 20 weeks in nude mice has been studied by in situ hybridization analyzing species-specific gene expression. Oligonucleotide probes homologous to species-specific gene sequences of bovine type II and X collagen, aggrecan, bone sialoprotein, biglycan, and osteopontin, and mouse decorin were labeled with ³⁵S and hybridized to respective serial sections of bovine tissue, mouse tissue, and phalanx constructs. In situ hybridization showed positive message and tissue-specific localization for all bovine-specific probes examined within cartilaginous and midshaft portions of constructs and negative message for the mouse-specific decorin probe. These data show that osteoblasts and chondrocytes comprising constructs are derived exclusively from their original bovine sources over 20 weeks of implantation. Defining the cellular origin of the models lends insight into their biological, chemical, and physical nature and their growth and development. Maintenance of their initial genotype is crucial for future application of the models in augmenting impaired human phalanges and related tissues.