As you may already know, bone marrow contains cells that specialize in both bone as well as blood maintenance. Stem cells destined to become white blood cells, red blood cells and platelets are called hematopoietic stem cells (aka: HSCs). CXCL12 is a special ligand that helps keep HSCs in the bone marrow by acting as a chemical attractant for the chemokine receptor C-X-C (CXCR4) found on HSCs.
Some researchers are attempting to prevent CXCL12 from binding to the CXCR4 receptor to help mobilize HSCs to the blood where they might be effective for combating disease. Other researchers are exploring options involving HSC transplants.
A new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology argues that while most of the research in this area has examined mouse or zebrafish models, elasmobranchs (such as skates, sharks and rays) might be better models. The reason for their esteemed superiority is that these animals are cartilaginous, and thus lack bone marrow. Rather, blood cell production occurs in the epigonal organ (EO), which is located in a complex close to the gonads. In this new study, researchers show that little skates have the CXCR4 receptor and its ligand, CXCL12. The identification of this receptor/ligand pair in little skates shows that the immune function of CXCR4 and CXCL12 has been conserved throughout evolution and perhaps researchers should take a closer look at elasmobranchs for clues in how to understand this system.
Hersh TA, Dimond AL, Ruth BA, Lupica NV, Bruce JC, Kelley JM, King BL, Lutton BV. A role for the CXCR4-CXCL12 axis in the little skate, Leucoraja erinacea. American Journal of Physiology – Regulatorym Integrative and Comparative Physiology. 315(2): R218-R229, 2018.