造血干细胞存在于骨髓中一个专门的调控环境中。现在，这一小环境的精确位置和特点因两项尖端的成像研究而变得更清楚了。
Lo Celso等人在动物活体中对各个造血干细胞进行了跟踪，发现成骨细胞陷入在由微血管构成的网中，不同造血干细胞群根据它们分化阶段的不同而位于不同地方。Xie等人利用新开发的“间接体内疗法”（ex vivo）实时成像技术和免疫测定对荧光标记的造血干细胞因响应辐照而发生的“寻的”（homing）行为进行了跟踪研究。他们报告说，骨髓腔里的薄膜形成一个特殊区域，在正常情况下会维持造血干细胞，但在发生骨髓损伤时会促使它们增加数量。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 92-96 (1 January 2009) | doi:10.1038/nature07434
Live-animal tracking of individual haematopoietic stem/progenitor cells in their niche
Cristina Lo Celso1,4, Heather E. Fleming1,4, Juwell W. Wu3,4, Cher X. Zhao1,4, Sam Miake-Lye1, Joji Fujisaki3,4, Daniel C?té3,7, David W. Rowe5, Charles P. Lin3,4 & David T. Scadden1,2,4,6
1 Center for Regenerative Medicine and,
2 Cancer Center,
3 Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, 185 Cambridge Street, Boston, Massachusetts 02114, USA
4 Harvard Stem Cell Institute, 42 Church Street, Cambridge, Massachusetts 02138, USA
5 University of Connecticut Health Center, 663 Farmington Avenue, Farmington, Connecticut 06030, USA
6 Department of Stem Cell and Regenerative Biology, Harvard University, 42 Church Street, Cambridge, Massachusetts 02138, USA
7 Present address: Centre de Recherche Université Laval Robert-Giffard, Département de Physique, Université Laval, Québec, Québec G1J 2G3, Canada.
Stem cells reside in a specialized, regulatory environment termed the niche that dictates how they generate, maintain and repair tissues1, 2. We have previously documented that transplanted haematopoietic stem and progenitor cell populations localize to subdomains of bone-marrow microvessels where the chemokine CXCL12 is particularly abundant3. Using a combination of high-resolution confocal microscopy and two-photon video imaging of individual haematopoietic cells in the calvarium bone marrow of living mice over time, we examine the relationship of haematopoietic stem and progenitor cells to blood vessels, osteoblasts and endosteal surface as they home and engraft in irradiated and c-Kit-receptor-deficient recipient mice. Osteoblasts were enmeshed in microvessels and relative positioning of stem/progenitor cells within this complex tissue was nonrandom and dynamic. Both cell autonomous and non-autonomous factors influenced primitive cell localization. Different haematopoietic cell subsets localized to distinct locations according to the stage of differentiation. When physiological challenges drove either engraftment or expansion, bone-marrow stem/progenitor cells assumed positions in close proximity to bone and osteoblasts. Our analysis permits observing in real time, at a single cell level, processes that previously have been studied only by their long-term outcome at the organismal level.
