Cxcl12 (chemokine (C-X-C motif) ligand 12), expressed by perivascular stromal cells, endothelial cells and osteoblasts, is a chemokine required for hematopoietic stem cell (HSC) maintenance and retention in the bone marrow. It also promotes the proliferation and maintenance of B-lineage progenitors, and common lymphoid progenitors.
Exon 2 of the Cxcl12 gene is flanked by loxP sites in this allele, making it possible to conditionally inactivate the gene in cells that express Cre recombinase. Homozyous floxed animals are viable and fertile, born at predicted Mendelian ratios, and show no overt defects in their hematopoietic system. Excision of the floxed segment creates a frameshift mutation that is believed to block protein expression. Cre-mediated recombination in the hematopoietic system leads to defects in hematopoiesis, including hematopoietic stem cell and lymphoid progenitor depletion.
Homozygous null mice created through crosses with CMV-cre (see Stock No. 006054) are not viable, but heterozygotes are born at predicted ratios, have normal cellularity, B-cell frequency and HSC frequency in the bone marrow and spleen. Widespread tamoxifen-induced knockout of the gene in adult mice derived from crosses with UBC-cre/ERT2 mice (see Stock No. 007001) depletes HSCs from adult bone marrow.
Conditional deletion of Cxcl12 from haematopoietic cells using Vav1-cre (see Stock No. 008610) or Nes-cre (see Stock No. 003771) has little or no effect on HSCs or restricted progenitors. Deletion from endothelial cells using Tie2/Tek-cre (see Stock No. 004128) depletes HSCs but not myeloerythroid or lymphoid progenitors. Deletion from perivascular stromal cells through crosses with Lepr-cre (see Stock No. 008320) depletes HSCs and certain restricted progenitors and mobilizes these cells into circulation. Deletion from osteoblasts using Col1a1 (Col2.3)-cre depletes certain early lymphoid progenitors but not HSCs or myeloerythroid progenitors, and does not mobilize these cells into circulation. Depletion of Cxcl12 in perivascular stromal cells and osteoblasts achieved through crosses with Prx1-cre (see Stock No. 005584) produces mice that exhibit a depletion of lymphoid progenitors and show significant reductions in bone marrow cellularity as well as the frequencies of HSCs.
