title: Targeted gene deletion demonstrates that the cell adhesion molecule ICAM-4 is critical for erythroblastic island formation.
abstract: Erythroid progenitors differentiate in erythroblastic islands, bone marrow niches composed of erythroblasts surrounding a central macrophage. Evidence suggests that within islands adhesive interactions regulate erythropoiesis and apoptosis. We are exploring whether erythroid intercellular adhesion molecule 4 (ICAM-4), an immunoglobulin superfamily member, participates in island formation. Earlier, we identified alpha(V) integrins as ICAM-4 counterreceptors. Because macrophages express alpha(V), ICAM-4 potentially mediates island attachments. To test this, we generated ICAM-4 knock-out mice and developed quantitative, live cell techniques for harvesting intact islands and for re-forming islands in vitro. We observed a 47% decrease in islands reconstituted from ICAM-4 null marrow compared to wild-type marrow. We also found a striking decrease in islands formed in vivo in knock-out mice. Further, peptides that block ICAM-4/alpha(V) adhesion produced a 53% to 57% decrease in reconstituted islands, strongly suggesting that ICAM-4 binding to macrophage alpha(V) functions in island integrity. Importantly, we documented that alpha(V) integrin is expressed in macrophages isolated from erythroblastic islands. Collectively, these data provide convincing evidence that ICAM-4 is critical in erythroblastic island formation via ICAM-4/alpha(V) adhesion and also demonstrate that the novel experimental strategies we developed will be valuable in exploring molecular mechanisms of erythroblastic island formation and their functional role in regulating erythropoiesis.
authors.affiliation: Life Sciences Division, University of California, Lawrence Berkeley National Laboratory, Bldg 74, 1 Cyclotron Road, Berkeley, CA 94720, USA.
authors.forename: Gloria
authors.initials: G
authors.lastname: Lee
authors.forename: Annie
authors.initials: A
authors.lastname: Lo
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Short
authors.forename: Tosti J
authors.initials: TJ
authors.lastname: Mankelow
authors.forename: Frances
authors.initials: F
authors.lastname: Spring
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Parsons
authors.forename: Karina
authors.initials: K
authors.lastname: Yazdanbakhsh
authors.forename: Narla
authors.initials: N
authors.lastname: Mohandas
authors.forename: David J
authors.initials: DJ
authors.lastname: Anstee
authors.forename: Joel Anne
authors.initials: JA
authors.lastname: Chasis
mesh_terms: D000818:Animals; D001483:Base Sequence; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D004247:DNA / Q000235:genetics; D004900:Erythroblasts / Q000166:cytology* / Q000378:metabolism*; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000378:metabolism; D004920:Erythropoiesis / Q000235:genetics / Q000502:physiology*; D018390:Gene Targeting; D039564:Integrin alphaV / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008958:Models, Molecular; D017434:Protein Structure, Tertiary
chemical_list: D015815:Cell Adhesion Molecules; D039564:Integrin alphaV; D004247:DNA