COL1A2 and osteogenesis imperfecta: Osteoblasts isolated from OI and WT mice were used to confirm the cellular effects of the heterozygous Col1a2 mutation on osteoblast function.8 Osteoblasts had increased Ddit3 (Chop) mRNA expression (Figure S1A), increased apoptosis (Figure S1B), and showed a reduced capacity to deposit calcium in the extracellular matrix in vitro (Figure S1C).