CLONING AND CHARACTERIZATION OF A NEW-TYPE OF MOUSE CHEMOKINE

We report here the identification and characterization of the mouse ho mologue of a human CX3C chemokine described by F. Bazan et al. (1997, Nature 385, 640-644). Termed fractalkine, this molecule constitutes a fourth or delta chemokine structural type that displays a novel CX3C s equence fingerprint. Distinct from the alpha, beta, or gamma chemokine families, the polypeptide chain of CX3C predicts a 373-amino-acid typ e I transmembrane glycoprotein with the chemokine domain resting on to p of an extended mucin-like stalk. Comparison of the mouse and human p rotein chains shows a high degree of conservation in all the globular segments with the exception of the stalk portion. The striking identit y of an amino acid stretch encompassing a putative juxtamembrane cleav age site suggests the evolutionary conservation of both membrane-bound and processed CX3C forms. Northern analysis reveals the presence of m ouse CX3C mRNA in heart, brain, lung, kidney, skeletal muscle, and tes tis tissues. The mouse CX3C gene was further localized to the central region of chromosome 8 by interspecific backcross mapping; a related l ocus was detected on chromosome 11. The novel location of this gene fr om other chemokine gene clusters adds to the notion that CX3C is a fun damentally new class of chemokine. (C) 1998 Academic Press.