title: The tale of early hematopoietic cell seeding in the bone marrow niche.
abstract: Since introduction of the notion of a "niche" that hosts engraftment and activity of hematopoietic cells, there is a massive effort to discover its structure and decipher its function. Our understanding of the niche is continuously changing with reinterpretation of traditional concepts and apprehension of new insights into the biology of hematopoietic cell homing, seeding, and engraftment. Here we discuss some of the early events in hematopoietic stem cell seeding and engraftment and propose a perspective based on visualization of labeled bone marrow cells in real time in vivo. Primary seeding of hematopoietic cells in the bone marrow niches evolves as a complex and dynamic process; however, it follows discrete topological and chronological patterns. Initial seeding occurs on the endosteal surface of the marrow, which includes heterogeneous niches for primary seeding. Several days after transplantation the endosteal niches become more restrictive, hosting primarily mitotically quiescent cells, and gradual centripetal migration is accompanied by engagement in proliferation and differentiation. The hematopoietic niches evolve as heterogeneous three-dimensional microenvironments that are continuously changing over time.
authors.affiliation: Frankel Laboratory of Experimental Bone Marrow Transplantation, Center for Stem Cell Research, Department of Pediatric Hematology-Oncology, Schneider Children's Medical Center of Israel, Petach Tikva, Israel 49202.
authors.forename: Isaac
authors.initials: I
authors.lastname: Yaniv
authors.forename: Jerry
authors.initials: J
authors.lastname: Stein
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Farkas
authors.forename: Nadir
authors.initials: N
authors.lastname: Askenasy
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000502:physiology*; D002448:Cell Adhesion; D002465:Cell Movement; D005269:Femur / Q000502:physiology / Q000637:transplantation*; D006085:Graft Survival; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D008954:Models, Biological