Comparative biological responses to human Sonic, Indian, and Desert hedgehog

Abstract

A comprehensive comparison of Sonic (Shh), Indian (Ihh), and Desert (Dhh) hedgehog biological activities has not previously been undertaken. To test whether the three higher vertebrate Hh proteins have distinct biological properties, we compared recombinant forms of the N-terminal domains of human Shh, Ihh, and Dhh in a variety of cell-based and tissue explant assays in which their activities could be assessed at a range of concentrations. While we observed that the proteins were similar in their affinities for the Hh-binding proteins; Patched (Ptc) and Hedgehog-interacting protein (Hip), and were equipotent in their ability to induce Islet-1 in chick neural plate explant; there were dramatic differences in their potencies in several other assays. Most dramatic were the Hh-dependent responses of C3H10T1/2 cells, where relative potencies ranged from 80nM for Shh, to 500nM for Ihh, to >5microM for Dhh. Similar trends in potency were seen in the ability of the three Hh proteins to induce differentiation of chondrocytes in embryonic mouse limbs, and to induce the expression of nodal in the lateral plate mesoderm of early chick embryos. However, in a chick embryo digit duplication assay used to measure polarizing activity, Ihh was the least active, and Dhh was almost as potent as Shh. These findings suggest that a mechanism for fine-tuning the biological actions of Shh, Ihh, and Dhh, exists beyond the simple temporal and spatial control of their expression domains within the developing and adult organism.

Indian hedgehog gene transfer augments hematopoietic support of human stromal cells including NOD/SCID–ß2m–/– repopulating cells.

“…[32][33][34] Hedgehog family proteins have also been shown to function in distinct aspects of embryogenesis, and the tissue distribution of individual members is largely separated or else only partially overlapping. 21,22 Thus, it has been unclear which specific hedgehogs function in the BM microenvironment. In the present study, the expression of Ihh, but not Shh, was detected in bone marrow stromal cells and in stromal cells that express high levels of Ihh protein efficiently and that expand primitive hematopoietic cells.…”

“…In addition, although both share the receptor patched (Ptc) and use smoothened (Smo) as a signal-transduction molecule, hedgehog family members do not exhibit identical bioactivities. 21,22 Thus, it has been uncertain whether Ihh could be involved in regulation of HSCs.…”

Novel genes regulated by Sonic Hedgehog in pluripotent mesenchymal cells

“…A large proportion of Shh stimulated 10T1/2 cells enter the osteoblastic lineage, leading to a dramatic increase in alkaline phosphatase activity which can be readily assayed Nakamura et al, 1997;SpinellaJaegle et al, 2001). Studies in 10T1/2 cells have lead to a greater understanding of the functions of Shh (Pepinsky et al, 1998(Pepinsky et al, , 2000Williams et al, 1999;Saeki et al, 2000), Smo (Murone et al, 1999) and Gli family members (Ruiz i Altaba, 1999), as well as providing a means to investigate comparative effects of vertebrate Hh proteins (Pathi et al, 2001). In this study we have extended the use of 10T1/2 cells to provide a useful model system for the discovery of novel downstream target genes regulated by the Hh pathway.…”

Ihh/Gli2 Signaling Promotes Osteoblast Differentiation by Regulating Runx2 Expression and Function

“…Ihh, and its receptor components, patched (PTCH) and smoothened (Smo), are expressed in primary osteoblasts and its lineages (Murakami et al, 1997;Jemtland et al, 2003). In addition, Ihh stimulates osteoblast differentiation of the mesenchymal cell line C3H10T1/2 (Pathi et al, 2001). Mice deficient in the Ihh gene show reduced proliferation and maturation of chondrocytes and failure of osteoblast development in endochondral bones (St-Jacques et al, 1999;Hilton et al, 2005).…”