The Hedgehog signalling pathway in bone formation

Abstract

Embryonic bone development and bone remodeling throughout life both rely critically on the Hedgehog signaling pathway. A team led by Ling Ye from Sichuan University in China and Ying-Zi Yang from the National Human Genome Research Institute in Maryland, USA, review how this key regulatory pathway of animal development affects bone health and disease. During early limb development in vertebrates, for example, one protein in the pathway, Sonic Hedgehog, acts to regulate patterning and growth. Another protein, Indian Hedgehog, later helps convert cartilage into bone in the developing skeleton. The authors discuss how the disruption of Hedgehog signaling can cause severe bone disorders, while enhancing Hedgehog activity can help repair fractured bones. A better understanding of Hedgehog signaling should improve bone disease prevention, diagnosis and treatment.

Keywords

bone development / bone disease / endochondral ossification / hedgehog / homeostasis / joint formation / patterning

References

[1] Zhang Y, Kalderon D. Hedgehog acts as a somatic stem cell factor in the Drosophila ovary. Nature, 2001, 410(6828): 599-604.

[2] Hui CC, Joyner AL. A mouse model of greig cephalopolysyndactyly syndrome: the extra-toesJ mutation contains an intragenic deletion of the Gli3 gene. Nat Genet, 1993, 3(3): 241-246.

[3] Thayer SP, di Magliano MP, Heiser PW. Hedgehog is an early and late mediator of pancreatic cancer tumorigenesis. Nature, 2003, 425(6960): 851-856.

[4] Watkins DN, Berman DM, Burkholder SG. Hedgehog signalling within airway epithelial progenitors and in small-cell lung cancer. Nature, 2003, 422(6929): 313-317.

[5] Reya T, Morrison SJ, Clarke MF. Stem cells, cancer, and cancer stem cells. Nature, 2001, 414(6859): 105-111.

[6] Nüsslein-Volhard C, Wieschaus E. Mutations affecting segment number and polarity in Drosophila. Nature, 1980, 287(5785): 795-801.

[7] Steinhauer J, Treisman JE. Lipid-modified morphogens: functions of fats. Curr Opin Genet Dev, 2009, 19(4): 308-314.

[8] Farrero E, Prats E, Manresa F. Outcome of non-invasive domiciliary ventilation in elderly patients. Respir Med, 2007, 101(6): 1068-1073.

[9] Chen X, Tukachinsky H, Huang CH. Processing and turnover of the Hedgehog protein in the endoplasmic reticulum. J Cell Biol, 2011, 192(5): 825-838.

[10] Ma Y, Erkner A, Gong R. Hedgehog-mediated patterning of the mammalian embryo requires transporter-like function of dispatched. Cell, 2002, 111(1): 63-75.

[11] Burke R, Nellen D, Bellotto M. Dispatched, a novel sterol-sensing domain protein dedicated to the release of cholesterol-modified hedgehog from signaling cells. Cell, 1999, 99(7): 803-815.

[12] Gradilla AC, Guerrero I. Hedgehog on the move: a precise spatial control of Hedgehog dispersion shapes the gradient. Curr Opin Genet Dev, 2013, 23(4): 363-373.

[13] Nakano Y, Guerrero I, Hidalgo A. A protein with several possible membrane-spanning domains encoded by the Drosophila segment polarity gene patched. Nature, 1989, 341(6242): 508-513.

[14] Hooper JE, Scott MP. The Drosophila patched gene encodes a putative membrane protein required for segmental patterning. Cell, 1989, 59(4): 751-765.

[15] Ingham PW. Localized hedgehog activity controls spatial limits of wingless transcription in the Drosophila embryo. Nature, 1993, 366(6455): 560-562.

[16] Alcedo J, Ayzenzon M, Von Ohlen T. The Drosophila smoothened gene encodes a seven-pass membrane protein, a putative receptor for the hedgehog signal. Cell, 1996, 86(2): 221-232.

[17] Hooper JE. Distinct pathways for autocrine and paracrine Wingless signalling in Drosophila embryos. Nature, 1994, 372(6505): 461-464.

[18] van den Heuvel M, Ingham PW. Smoothened encodes a receptor-like serpentine protein required for hedgehog signalling. Nature, 1996, 382(6591): 547-551.

[19] Chen CH, von Kessler DP, Park W. Nuclear trafficking of Cubitus interruptus in the transcriptional regulation of Hedgehog target gene expression. Cell, 1999, 98(3): 305-316.

[20] Wang G, Amanai K, Wang B. Interactions with Costal2 and suppressor of fused regulate nuclear translocation and activity of cubitus interruptus. Genes Dev, 2000, 14(22): 2893-2905.

[21] Méthot N, Basler K. Suppressor of fused opposes hedgehog signal transduction by impeding nuclear accumulation of the activator form of Cubitus interruptus. Development, 2000, 127(18): 4001-4010.

[22] Price MA, Kalderon D. Proteolysis of the Hedgehog signaling effector Cubitus interruptus requires phosphorylation by glycogen synthase kinase 3 and casein kinase 1. Cell, 2002, 108(6): 823-835.

[23] Jia J, Amanai K, Wang G. Shaggy/GSK3 antagonizes Hedgehog signalling by regulating Cubitus interruptus. Nature, 2002, 416(6880): 548-552.

[24] Lum L, Yao S, Mozer B. Identification of Hedgehog pathway components by RNAi in Drosophila cultured cells. Science, 2003, 299(5615): 2039-2045.

[25] Robbins DJ, Nybakken KE, Kobayashi R. Hedgehog elicits signal transduction by means of a large complex containing the kinesin-related protein costal2. Cell, 1997, 90(2): 225-234.

[26] Hooper JE. Smoothened translates Hedgehog levels into distinct responses. Development, 2003, 130(17): 3951-3963.

[27] Huangfu D, Liu A, Rakeman AS. Hedgehog signalling in the mouse requires intraflagellar transport proteins. Nature, 2003, 426(6962): 83-87.

[28] Christensen ST, Clement CA, Satir P. Primary cilia and coordination of receptor tyrosine kinase (RTK) signalling. J Pathol, 2012, 226(2): 172-184.

[29] Nozawa YI, Lin C, Chuang PT. Hedgehog signaling from the primary cilium to the nucleus: an emerging picture of ciliary localization, trafficking and transduction. Curr Opin Genet Dev, 2013, 23(4): 429-437.

[30] Gherman A, Davis EE, Katsanis N. The ciliary proteome database: an integrated community resource for the genetic and functional dissection of cilia. Nat Genet, 2006, 38(9): 961-962.

[31] Ishikawa H, Thompson J, Yates JR. Proteomic analysis of mammalian primary cilia. Curr Biol, 2012, 22(5): 414-419.

[32] Berbari NF, O'Connor AK, Haycraft CJ. The primary cilium as a complex signaling center. Curr Biol, 2009, 19(13): R526-R535.

[33] Ingham PW, McMahon AP. Hedgehog signaling in animal development: paradigms and principles. Genes Dev, 2001, 15(23): 3059-3087.

[34] Echelard Y, Epstein DJ, St-Jacques B. Sonic hedgehog, a member of a family of putative signaling molecules, is implicated in the regulation of CNS polarity. Cell, 1993, 75(7): 1417-1430.

[35] Riddle RD, Johnson RL, Laufer E. Sonic hedgehog mediates the polarizing activity of the ZPA. Cell, 1993, 75(7): 1401-1416.

[36] Rohatgi R, Milenkovic L, Scott MP. Patched1 regulates hedgehog signaling at the primary cilium. Science, 2007, 317(5836): 372-376.

[37] Corbit KC, Aanstad P, Singla V. Vertebrate Smoothened functions at the primary cilium. Nature, 2005, 437(7061): 1018-1021.

[38] Incardona JP, Lee JH, Robertson CP. Receptor-mediated endocytosis of soluble and membrane-tethered Sonic hedgehog by Patched-1. Proc Natl Acad Sci U S A, 2000, 97(22): 12044-12049.

[39] Briscoe J, Thérond PP. The mechanisms of Hedgehog signalling and its roles in development and disease. Nat Rev Mol Cell Biol, 2013, 14(7): 416-429.

[40] Ribes V, Briscoe J. Establishing and interpreting graded Sonic Hedgehog signaling during vertebrate neural tube patterning: the role of negative feedback. Cold Spring Harb Perspect Biol, 2009, 1(2): a002014.

[41] Haycraft CJ, Banizs B, Aydin-Son Y. Gli2 and Gli3 localize to cilia and require the intraflagellar transport protein Polaris for processing and function. PLoS Genet, 2005, 1(4): e53.

[42] Endoh-Yamagami S, Evangelista M, Wilson D. The mammalian Cos2 homolog Kif7 plays an essential role in modulating Hh signal transduction during development. Curr Biol, 2009, 19(15): 1320-1326.

[43] Cheung HO, Zhang X, Ribeiro A. The kinesin protein Kif7 is a critical regulator of Gli transcription factors in mammalian hedgehog signaling. Sci Signal, 2009, 2(76): ra29.

[44] Liem KF Jr, He M, Ocbina PJ. Mouse Kif7/Costal2 is a cilia-associated protein that regulates Sonic hedgehog signaling. Proc Natl Acad Sci U S A, 2009, 106(32): 13377-13382.

[45] Svärd J, Heby-Henricson K, Henricson KH. Genetic elimination of Suppressor of fused reveals an essential repressor function in the mammalian Hedgehog signaling pathway. Dev Cell, 2006, 10(2): 187-197.

[46] Cooper AF, Yu KP, Brueckner M. Cardiac and CNS defects in a mouse with targeted disruption of suppressor of fused. Development, 2005, 132(19): 4407-4417.

[47] Kim J, Kato M, Beachy PA. Gli2 trafficking links Hedgehog-dependent activation of Smoothened in the primary cilium to transcriptional activation in the nucleus. Proc Natl Acad Sci U S A, 2009, 106(51): 21666-21671.

[48] Humke EW, Dorn KV, Milenkovic L. The output of Hedgehog signaling is controlled by the dynamic association between Suppressor of Fused and the Gli proteins. Genes Dev, 2010, 24(7): 670-682.

[49] Tukachinsky H, Lopez LV, Salic A. A mechanism for vertebrate Hedgehog signaling: recruitment to cilia and dissociation of SuFu-Gli protein complexes. J Cell Biol, 2010, 191(2): 415-428.

[50] Li ZJ, Nieuwenhuis E, Nien W. Kif7 regulates Gli2 through Sufu-dependent and independent functions during skin development and tumorigenesis. Development, 2012, 139(22): 4152-4161.

[51] Barnfield PC, Zhang X, Thanabalasingham V. Negative regulation of Gli1 and Gli2 activator function by Suppressor of fused through multiple mechanisms. Differentiation, 2005, 73(8): 397-405.

[52] Wilson CW, Nguyen CT, Chen MH. Fused has evolved divergent roles in vertebrate Hedgehog signalling and motile ciliogenesis. Nature, 2009, 459(7243): 98-102.

[53] Brennan D, Chen X, Cheng L. Noncanonical Hedgehog signaling. Vitam Horm, 2012, 88: 55-72.

[54] Jenkins D. Hedgehog signalling: emerging evidence for non-canonical pathways. Cell Signal, 2009, 21(7): 1023-1034.

[55] Thorogood PV, Hinchliffe JR. An analysis of the condensation process during chondrogenesis in the embryonic chick hind limb. J Embryol Exp Morphol, 1975, 33(3): 581-606.

[56] Zhu J, Nakamura E, Nguyen MT. Uncoupling Sonic hedgehog control of pattern and expansion of the developing limb bud. Dev Cell, 2008, 14(4): 624-632.

[57] Kronenberg HM. Developmental regulation of the growth plate. Nature, 2003, 423(6937): 332-336.

[58] Wang B, Fallon JF, Beachy PA. Hedgehog-regulated processing of Gli3 produces an anterior/posterior repressor gradient in the developing vertebrate limb. Cell, 2000, 100(4): 423-434.

[59] Kicheva A, Cohen M, Briscoe J. Developmental pattern formation: insights from physics and biology. Science, 2012, 338(6104): 210-212.

[60] Wada N, Kawakami Y, Nohno T. Sonic hedgehog signaling during digit pattern duplication after application of recombinant protein and expressing cells. Dev Growth Differ, 1999, 41(5): 567-574.

[61] te Welscher P, Fernandez-Teran M, Ros MA. Mutual genetic antagonism involving GLI3 and dHAND prepatterns the vertebrate limb bud mesenchyme prior to SHH signaling. Genes Dev, 2002, 16(4): 421-426.

[62] Suzuki T. How is digit identity determined during limb development?. Dev Growth Differ, 2013, 55(1): 130-138.

[63] Towers M, Mahood R, Yin Y. Integration of growth and specification in chick wing digit-patterning. Nature, 2008, 452(7189): 882-886.

[64] Day TF, Yang Y. Wnt and hedgehog signaling pathways in bone development. J Bone Joint Surg Am, 2008, 90(Suppl 1): 19-24.

[65] Chinnaiya K, Tickle C, Towers M. Sonic hedgehog-expressing cells in the developing limb measure time by an intrinsic cell cycle clock. Nat Commun, 2014, 5: 4230.

[66] Bitgood MJ, McMahon AP. Hedgehog and Bmp genes are coexpressed at many diverse sites of cell-cell interaction in the mouse embryo. Dev Biol, 1995, 172(1): 126-138.

[67] St-Jacques B, Hammerschmidt M, McMahon AP. Indian hedgehog signaling regulates proliferation and differentiation of chondrocytes and is essential for bone formation. Genes Dev, 1999, 13(16): 2072-2086.

[68] Kindblom JM, Nilsson O, Hurme T. Expression and localization of Indian hedgehog (Ihh) and parathyroid hormone related protein (PTHrP) in the human growth plate during pubertal development. J Endocrinol, 2002, 174(2): R1-R6.

[69] Vortkamp A, Lee K, Lanske B. Regulation of rate of cartilage differentiation by Indian hedgehog and PTH-related protein. Science, 1996, 273(5275): 613-622.

[70] Zhao Q, Brauer PR, Xiao L. Expression of parathyroid hormone-related peptide (PthrP) and its receptor (PTH1R) during the histogenesis of cartilage and bone in the chicken mandibular process. J Anat, 2002, 201(2): 137-151.

[71] Karperien M, Lanser P, de Laat SW. Parathyroid hormone related peptide mRNA expression during murine postimplantation development: evidence for involvement in multiple differentiation processes. Int J Dev Biol, 1996, 40(3): 599-608.

[72] Long F, Linsenmayer TF. Regulation of growth region cartilage proliferation and differentiation by perichondrium. Development, 1998, 125(6): 1067-1073.

[73] Long F, Ornitz DM. Development of the endochondral skeleton. Cold Spring Harb Perspect Biol, 2013, 5(1): a008334.

[74] Murakami S, Noda M. Expression of Indian hedgehog during fracture healing in adult rat femora. Calcif Tissue Int, 2000, 66(4): 272-276.

[75] Jemtland R, Divieti P, Lee K. Hedgehog promotes primary osteoblast differentiation and increases PTHrP mRNA expression and iPTHrP secretion. Bone, 2003, 32(6): 611-620.

[76] Mo R, Freer AM, Zinyk DL. Specific and redundant functions of Gli2 and Gli3 zinc finger genes in skeletal patterning and development. Development, 1997, 124(1): 113-123.

[77] Park HL, Bai C, Platt KA. Mouse Gli1 mutants are viable but have defects in SHH signaling in combination with a Gli2 mutation. Development, 2000, 127(8): 1593-1605.

[78] Hojo H, Ohba S, Yano F. Gli1 protein participates in Hedgehog-mediated specification of osteoblast lineage during endochondral ossification. J Biol Chem, 2012, 287(21): 17860-17869.

[79] Litingtung Y, Dahn RD, Li Y. Shh and Gli3 are dispensable for limb skeleton formation but regulate digit number and identity. Nature, 2002, 418(6901): 979-983.

[80] Hilton MJ, Tu X, Cook J. Ihh controls cartilage development by antagonizing Gli3, but requires additional effectors to regulate osteoblast and vascular development. Development, 2005, 132(19): 4339-4351.

[81] Joeng KS, Schumacher CA, Zylstra-Diegel CR. Lrp5 and Lrp6 redundantly control skeletal development in the mouse embryo. Dev Biol, 2011, 359(2): 222-229.

[82] Mak KK, Chen MH, Day TF. Wnt/beta-catenin signaling interacts differentially with Ihh signaling in controlling endochondral bone and synovial joint formation. Development, 2006, 133(18): 3695-3707.

[83] Amano K, Densmore M, Nishimura R. Indian hedgehog signaling regulates transcription and expression of collagen type X via Runx2/Smads interactions. J Biol Chem, 2014, 289(36): 24898-24910.

[84] Hojo H, Ohba S, Taniguchi K. Hedgehog-Gli activators direct osteo-chondrogenic function of bone morphogenetic protein toward osteogenesis in the perichondrium. J Biol Chem, 2013, 288(14): 9924-9932.

[85] Abzhanov A, Rodda SJ, McMahon AP. Regulation of skeletogenic differentiation in cranial dermal bone. Development, 2007, 134(17): 3133-3144.

[86] Lenton K, James AW, Manu A. Indian hedgehog positively regulates calvarial ossification and modulates bone morphogenetic protein signaling. Genesis, 2011, 49(10): 784-796.

[87] Rice DP, Connor EC, Veltmaat JM. Gli3Xt-J/Xt-J mice exhibit lambdoid suture craniosynostosis which results from altered osteoprogenitor proliferation and differentiation. Hum Mol Genet, 2010, 19(17): 3457-3467.

[88] Jenkins D, Seelow D, Jehee FS. RAB23 mutations in Carpenter syndrome imply an unexpected role for hedgehog signaling in cranial-suture development and obesity. Am J Hum Genet, 2007, 80(6): 1162-1170.

[89] Huycke TR, Eames BF, Kimmel CB. Hedgehog-dependent proliferation drives modular growth during morphogenesis of a dermal bone. Development, 2012, 139(13): 2371-2380.

[90] Kim HJ, Rice DP, Kettunen PJ. FGF-, BMP- and Shh-mediated signalling pathways in the regulation of cranial suture morphogenesis and calvarial bone development. Development, 1998, 125(7): 1241-1251.

[91] Tavella S, Biticchi R, Schito A. Targeted expression of SHH affects chondrocyte differentiation, growth plate organization, and Sox9 expression. J Bone Miner Res, 2004, 19(10): 1678-1688.

[92] Regard JB, Malhotra D, Gvozdenovic-Jeremic J. Activation of Hedgehog signaling by loss of GNAS causes heterotopic ossification. Nat Med, 2013, 19(11): 1505-1512.

[93] Murakami S, Nifuji A, Noda M. Expression of Indian hedgehog in osteoblasts and its posttranscriptional regulation by transforming growth factor-beta. Endocrinology, 1997, 138(5): 1972-1978.

[94] Zhong M, Carney DH, Boyan BD. 17β-Estradiol regulates rat growth plate chondrocyte apoptosis through a mitochondrial pathway not involving nitric oxide or MAPKs. Endocrinology, 2011, 152(1): 82-92.

[95] Ohba S, Kawaguchi H, Kugimiya F. Patched1 haploinsufficiency increases adult bone mass and modulates Gli3 repressor activity. Dev Cell, 2008, 14(5): 689-699.

[96] Kitaura Y, Hojo H, Komiyama Y. Gli1 haploinsufficiency leads to decreased bone mass with an uncoupling of bone metabolism in adult mice. PLoS One, 2014, 9(10): e109597.

[97] Mak KK, Bi Y, Wan C. Hedgehog signaling in mature osteoblasts regulates bone formation and resorption by controlling PTHrP and RANKL expression. Dev Cell, 2008, 14(5): 674-688.

[98] Tian Y, Xu Y, Fu Q. Osterix is required for Sonic hedgehog-induced osteoblastic MC3T3-E1 cell differentiation. Cell Biochem Biophys, 2012, 64(3): 169-176.

[99] Kiuru M, Solomon J, Ghali B. Transient overexpression of sonic hedgehog alters the architecture and mechanical properties of trabecular bone. J Bone Miner Res, 2009, 24(9): 1598-1607.

[100] Ito H, Akiyama H, Shigeno C. Hedgehog signaling molecules in bone marrow cells at the initial stage of fracture repair. Biochem Biophys Res Commun, 1999, 262(2): 443-451.

[101] Miyaji T, Nakase T, Iwasaki M. Expression and distribution of transcripts for sonic hedgehog in the early phase of fracture repair. Histochem Cell Biol, 2003, 119(3): 233-237.

[102] Wang Q, Huang C, Zeng F. Activation of the Hh pathway in periosteum-derived mesenchymal stem cells induces bone formation in vivo: implication for postnatal bone repair. Am J Pathol, 2010, 177(6): 3100-3111.

[103] Horikiri Y, Shimo T, Kurio N. Sonic hedgehog regulates osteoblast function by focal adhesion kinase signaling in the process of fracture healing. PLoS One, 2013, 8(10): e76785.

[104] Fuchs S, Dohle E, Kirkpatrick CJ. Sonic Hedgehog-mediated synergistic effects guiding angiogenesis and osteogenesis. Vitam Horm, 2012, 88: 491-506.

[105] Petrova R, Joyner AL. Roles for Hedgehog signaling in adult organ homeostasis and repair. Development, 2014, 141(18): 3445-3457.

[106] Mesenchymal stem cells overexpressing Ihh promote bone repair. J Orthop Surg Res 2014; 9(1): 102.

[107] Kramann R, Schneider RK, DiRocco DP. Perivascular Gli1⁺ progenitors are key contributors to injury-induced organ fibrosis. Cell Stem Cell, 2015, 16(1): 51-66.

[108] Zhao H, Feng J, Seidel K. Secretion of shh by a neurovascular bundle niche supports mesenchymal stem cell homeostasis in the adult mouse incisor. Cell Stem Cell, 2014, 14(2): 160-173.

[109] Gao B, Guo J, She C. Mutations in IHH, encoding Indian hedgehog, cause brachydactyly type A-1. Nat Genet, 2001, 28(4): 386-388.

[110] Gao B, He L. Answering a century old riddle: brachydactyly type A1. Cell Res, 2004, 14(3): 179-187.

[111] Gao B, Hu J, Stricker S. A mutation in Ihh that causes digit abnormalities alters its signalling capacity and range. Nature, 2009, 458(7242): 1196-1200.

[112] Vortkamp A, Gessler M, Grzeschik KH. GLI3 zinc-finger gene interrupted by translocations in Greig syndrome families. Nature, 1991, 352(6335): 539-540.

[113] Kang S, Graham JM Jr, Olney AH. GLI3 frameshift mutations cause autosomal dominant Pallister-Hall syndrome. Nat Genet, 1997, 15(3): 266-268.

[114] Radhakrishna U, Wild A, Grzeschik KH. Mutation in GLI3 in postaxial polydactyly type A. Nat Genet, 1997, 17(3): 269-271.

[115] Rittler M, Paz JE, Castilla EE. VACTERL association, epidemiologic definition and delineation. Am J Med Genet, 1996, 63(4): 529-536.

[116] Shefer S, Salen G, Batta AK. Markedly inhibited 7-dehydrocholesterol-delta 7-reductase activity in liver microsomes from Smith-Lemli-Opitz homozygotes. J Clin Invest, 1995, 96(4): 1779-1785.

[117] Bale SJ, Amos CI, Parry DM. Relationship between head circumference and height in normal adults and in the nevoid basal cell carcinoma syndrome and neurofibromatosis type I. Am J Med Genet, 1991, 40(2): 206-210.

[118] Gorlin RJ. Nevoid basal cell carcinoma syndrome. Dermatol Clin, 1995, 13(1): 113-125.

[119] Kimonis VE, Goldstein AM, Pastakia B. Clinical manifestations in 105 persons with nevoid basal cell carcinoma syndrome. Am J Med Genet, 1997, 69(3): 299-308.

[120] Lettre G, Jackson AU, Gieger C. Identification of ten loci associated with height highlights new biological pathways in human growth. Nat Genet, 2008, 40(5): 584-591.

[121] Sun Y, Liu R, Zhao G. Genome-wide linkage analysis and association study identifies loci for polydactyly in chickens. G3: Bethesda, 2014, 4(6): 1167-1172.

[122] Eddy MC, Jan De Beur SM, Yandow SM. Deficiency of the alpha-subunit of the stimulatory G protein and severe extraskeletal ossification. J Bone Miner Res, 2000, 15(11): 2074-2083.

[123] Kaplan FS, Hahn GV, Zasloff MA. Heterotopic ossification: two rare forms and what they can teach us. J Am Acad Orthop Surg, 1994, 2(5): 288-296.

[124] Shore EM, Ahn J, Jan de Beur S. Paternally inherited inactivating mutations of the GNAS1 gene in progressive osseous heteroplasia. N Engl J Med, 2002, 346(2): 99-106.

[125] Plagge A, Kelsey G, Germain-Lee EL. Physiological functions of the imprinted Gnas locus and its protein variants Galpha(s) and XLalpha(s) in human and mouse. J Endocrinol, 2008, 196(2): 193-214.

[126] He X, Zhang L, Chen Y. The G protein α subunit Gαs is a tumor suppressor in Sonic hedgehog-driven medulloblastoma. Nat Med, 2014, 20(9): 1035-1042.

[127] Tiet TD, Alman BA. Developmental pathways in musculoskeletal neoplasia: involvement of the Indian Hedgehog-parathyroid hormone-related protein pathway. Pediatr Res, 2003, 53(4): 539-543.

[128] Wang W, Lian N, Ma Y. Chondrocytic Atf4 regulates osteoblast differentiation and function via Ihh. Development, 2012, 139(3): 601-611.

[129] Felber K, Croucher P, Roehl HH. Hedgehog signalling is required for perichondral osteoblast differentiation in zebrafish. Mech Dev, 2011, 128(1/2): 141-152.

[130] Shimoyama A, Wada M, Ikeda F. Ihh/Gli2 signaling promotes osteoblast differentiation by regulating Runx2 expression and function. Mol Biol Cell, 2007, 18(7): 2411-2418.

[131] Oliveira FS, Bellesini LS, Defino HL. Hedgehog signaling and osteoblast gene expression are regulated by purmorphamine in human mesenchymal stem cells. J Cell Biochem, 2012, 113(1): 204-208.

[132] Liu TM, Lee EH. Transcriptional regulatory cascades in Runx2-dependent bone development. Tissue Eng Part B Rev, 2013, 19(3): 254-263.

[133] Cai J, Deng L. Regulations of Hedgehog signaling pathway on mesenchymal stem cells. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi, 2010, 24(8): 993-996.

[134] Maeda Y, Nakamura E, Nguyen MT. Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone. Proc Natl Acad Sci U S A, 2007, 104(15): 6382-6387.