Genetic modification of ER-Hoxb8 osteoclast precursors using CRISPR/Cas9 as a novel way to allow studies on osteoclast biology.

Osteoclasts are cells specialized in bone resorption. Currently, studies on murine osteoclasts are primarily performed on bone marrow-derived cells with the use of many animals and limited cells available. ER-Hoxb8 cells are conditionally immortalized monocyte/macrophage murine progenitor cells, recently described to be able to differentiate toward functional osteoclasts. Here, we produced an ER-Hoxb8 clonal cell line from C57BL/6 bone marrow cells that strongly resembles phenotype and function of the conventional bone marrow-derived osteoclasts. We then used CRISPR/Cas9 technology to specifically inactivate genes by biallelic mutation. The CRISPR/Cas9 system is an adaptive immune system in Bacteria and Archaea and uses small RNAs and Cas nucleases to degrade foreign nucleic acids. Through specific-guide RNAs, the nuclease Cas9 can be redirected toward any genomic location to genetically modify eukaryotic cells. We genetically modified ER-Hoxb8 cells with success, generating NFATc1-/- and DC-STAMP-/- ER-Hoxb8 cells that lack the ability to differentiate into osteoclasts or to fuse into multinucleated osteoclasts, respectively. In conclusion, this method represents a markedly easy highly specific and efficient system for generating potentially unlimited numbers of genetically modified osteoclast precursors.