Chemoattractant (PubMed:11859124). Activates the C-X-C chemokine receptor cxcr4 to induce a rapid and transient rise in the level of intracellular calcium ions, and chemotaxis (PubMed:11859124). Signaling with cxcr4 mediates the directional movement of mesodermal cells during gastrulation (Ref.2). Binds to the allosteric site (site 2) of integrins and activates them in a cxcr4-independent manner (By similarity). Monomer or homodimer; in equilibrium. Dimer formation is induced by non acidic pH and the presence of multivalent anions, and by binding to cxcr4 or heparin (By similarity). Isoform alpha is expressed throughout the inner deep cells of the blastocoel roof during gastrula stage embryos. Isoform beta is expressed in the developing central nervous system (CNS) of embryos; at stages 21-23, up-regulated in the anterior of the embryo where neural tube segregation occurs. At stages 32-34, expressed in the mid- and hindbrain, otic vesicles and eye, and the dorsal fin, and the embryonic heart at stage 32. At stages 39-40, isoform beta is highly expressed in the proctodeum in the posterior embryo. In the adult, isoform beta is highly expressed in the spleen, kidney, lung, stomach, testis and skeletal muscle. Lower levels are expressed in adult liver and heart. Expression is present at a very low level in adult brain and skin. Isoform alpha is expressed from the gastrula stage, whereas isoform beta is not expressed until the tailbud stage. Belongs to the intercrine alpha (chemokine CxC) family.