Images were acquired using an Olympus IX81 microscope. == MicroCT analysis == Femurs and lumbar vertebrae were dissected, fixed overnight in 4% paraformaldehyde and stored in 70% ethanol at 4C. propose to call this factor Osteolectin. DOI: http://dx.doi.org/10.7554/eLife.18782.001 Research Organism: Mouse == Introduction == Fate mapping studies in vivo show there are multiple distinct waves of mesenchymal progenitors that form skeletal tissues during development and then maintain the skeleton throughout adulthood (Liu et al., 2013; Maes et al., 2010; Mizoguchi et al., 2014; Park et al., 2012; Takashima et al., 2007; Worthley et al., 2015; Lycopodine Zhou et al., 2014a). These include Osterix+cells that give rise to osteoblasts, osteocytes, and stromal cells in developing bones (Liu et al., 2013; Maes et al., 2010; Mizoguchi et al., 2014), Nestin-CreER-expressing cells that transiently form osteoblasts and bone marrow Lycopodine stromal cells in the early postnatal period (Mndez-Ferrer et al., 2010; Ono et al., 2014a; Takashima et al., 2007), Grem1-expressing cells that form osteoblasts, chondrocytes, and stromal cells postnatally (Worthley et al., 2015) and Leptin Receptor (LepR)-expressing stromal cells that are the major source of bone and adipocytes in adult mouse bone marrow (Mizoguchi et al., 2014; Zhou et al., 2014a). Osterix+osteogenic progenitors also persist periosteally, on the outer surface of adult bones, where they help to repair bone injuries (Maes et al., 2010). Bone marrow stromal cells include skeletal stem Lycopodine cells (SSCs) as well as multiple other populations of mesenchymal progenitors (Chan et al., 2015). SSCs are multipotent progenitors that form fibroblast colonies in culture (CFU-F) with the potential to differentiate into osteoblasts, chondrocytes, and adipocytes (Bianco and Robey, 2015; Friedenstein et al., 1970). Bone marrow CFU-F can be identified based on the expression of CD146, CD271, VCAM-1, and Thy-1 in humans, or LepR, PDGFR, CD51, and/or CD105 in mice, as well as the lack of expression of hematopoietic and endothelial markers (Chan et al., 2009, 2015; James et al., 2015; Mabuchi et al., 2013; Morikawa et al., 2009; Omatsu et al., 2010; Park et al., 2012; Sacchetti et al., 2007; Zhou et al., 2014a). CFU-F are enriched among bone marrow stromal cells that express high levels of the hematopoietic growth factorsScf(Zhou et al., 2014a) andCxcl12(Ding and Morrison, 2013; Omatsu et al., 2014; Sugiyama et al., 2006). Multiple growth factor families promote osteogenesis Lycopodine including Wnts (Cui et al., 2011; Krishnan et al., 2006), Bone Morphogenetic Proteins (BMPs) (Nakamura et al., 2007; Rahman et al., 2015), and Insulin-like Growth Factors (Yakar and Rosen, 2003). However , these factors have broad effects on Lycopodine many tissues, precluding their systemic administration to promote osteogenesis. Sclerostin, a Wnt signaling inhibitor that is locally produced by osteocytes, negatively regulates bone formation (Li et al., 2005). Sclerostin inhibitors can be administered systemically to promote bone formation (McClung et al., 2014). Factors secreted by bone marrow stromal cells promote osteogenesis (Chan et al., 2015), though the full repertoire of such factors remains to be identified. Osteoporosis is a progressive bone disease characterized by decreased bone mass and increased fracture risk (Harada and Rodan, 2003). Aging, estrogen insufficiency, long-term glucocorticoid use, and mechanical unloading all contribute to the development of osteoporosis (Harada and Rodan, 2003). Most existing osteoporosis therapies involve antiresorptive agents, such as bisphosphonates (Black et al., 1996; Liberman et al., 1995) and estrogens (Michaelsson et al., 1998), which reduce the rate of bone loss but do not promote new bone formation. Teriparatide, a small peptide derived from human parathyroid hormone (PTH; amino acids 134) is used clinically to promote the formation of new bone (Neer et al., 2001). Nonetheless, some patients cannot take Teriparatide (Kraenzlin and Meier, 2011) and its use is limited to two years because of a potential risk of osteosarcoma (Neer et al., 2001). Clec11a (C-type lectin domain family 11, member A) is a secreted sulfated glycoprotein that is expressed in the bone marrow and can promote colony formation by human hematopoietic progenitors in culture (Bannwarth et al., 1998, 1999; Hiraoka et al., 1997; Mio et al., 1998). The plasma level of human Clec11a correlates with hemoglobin level Rabbit polyclonal to ZNF471.ZNF471 may be involved in transcriptional regulation (Keller et al., 2009; Ouma et al., 2010) and increases in patients after bone marrow transplantation (Ito et al., 2003). As a result, Clec11a has been considered a hematopoietic growth factor. However , Clec11is also expressed in skeletal tissues (Hiraoka et al., 2001) and the physiological function of Clec11a in vivo has not yet been tested. == Results == == Clec11ais expressed by subsets of bone marrow stromal cells, osteoblasts, osteocytes and hypertrophic chondrocytes == Reanalysis of our published microarray data (Ding et al., 2012) revealed that among enzymatically dissociated bone marrow cells, Clec11awas significantly more highly expressed byScf-GFP+CD45-Ter119-CD31-stromal cells (more than 90%.