- Research article
- Open Access
Evolution of the osteoblast: skeletogenesis in gar and zebrafish
© Eames et al; licensee BioMed Central Ltd. 2012
- Received: 25 October 2011
- Accepted: 5 March 2012
- Published: 5 March 2012
Although the vertebrate skeleton arose in the sea 500 million years ago, our understanding of the molecular fingerprints of chondrocytes and osteoblasts may be biased because it is informed mainly by research on land animals. In fact, the molecular fingerprint of teleost osteoblasts differs in key ways from that of tetrapods, but we do not know the origin of these novel gene functions. They either arose as neofunctionalization events after the teleost genome duplication (TGD), or they represent preserved ancestral functions that pre-date the TGD. Here, we provide evolutionary perspective to the molecular fingerprints of skeletal cells and assess the role of genome duplication in generating novel gene functions. We compared the molecular fingerprints of skeletogenic cells in two ray-finned fish: zebrafish (Danio rerio)--a teleost--and the spotted gar (Lepisosteus oculatus)--a "living fossil" representative of a lineage that diverged from the teleost lineage prior to the TGD (i.e., the teleost sister group). We analyzed developing embryos for expression of the structural collagen genes col1a2, col2a1, col10a1, and col11a2 in well-formed cartilage and bone, and studied expression of skeletal regulators, including the transcription factor genes sox9 and runx2, during mesenchymal condensation.
Results provided no evidence for the evolution of novel functions among gene duplicates in zebrafish compared to the gar outgroup, but our findings shed light on the evolution of the osteoblast. Zebrafish and gar chondrocytes both expressed col10a1 as they matured, but both species' osteoblasts also expressed col10a1, which tetrapod osteoblasts do not express. This novel finding, along with sox9 and col2a1 expression in developing osteoblasts of both zebrafish and gar, demonstrates that osteoblasts of both a teleost and a basally diverging ray-fin fish express components of the supposed chondrocyte molecular fingerprint.
Our surprising finding that the "chondrogenic" transcription factor sox9 is expressed in developing osteoblasts of both zebrafish and gar can help explain the expression of chondrocyte genes in osteoblasts of ray-finned fish. More broadly, our data suggest that the molecular fingerprint of the osteoblast, which largely is constrained among land animals, was not fixed during early vertebrate evolution.
- Runx2 Expression
- Molecular Fingerprint
- Col2a1 Expression
- Mesenchymal Condensation
- Transcription Factor Sox9
Skeletal tissues provide invaluable traits to document vertebrate evolution and to reveal the mechanistic basis for evolutionary change. Two main processes underlie skeletal development: histogenesis--histological differentiation of skeletal tissues--and morphogenesis--acquisition of skeletal element location, shape, and size. Skeletal histogenesis involves overt differentiation of cells that secrete the extracellular matrix of cartilage and bone (chondrocytes and osteoblasts, respectively), and follows the mesenchymal condensation of skeletogenic cells. Skeletal morphogenesis directs such differentiation events in space and time. While many studies propose a molecular genetic basis for evolutionary changes to skeletal morphogenesis [1–5], the evolution of skeletal histogenesis among vertebrates is fertile ground for additional molecular analyses [6, 7].
Comparisons among human, mouse, and chick skeletal tissues suggest that the molecular fingerprints of chondrocytes or osteoblasts do not vary greatly among tetrapods (Figure 1A). Tetrapods exhibit one type of bone tissue, but they have three types of cartilage: elastic cartilage, hyaline cartilage, and fibrocartilage [6, 23, 24]. Here, we focus on the predominant type of cartilage in vertebrates, hyaline cartilage, which serves as the template for bone during endochondral ossification. Collagens are the most abundant proteinaceous skeletal matrix components, and tetrapod chondrocytes and osteoblasts typically express different fibrillar collagens. In tetrapods, Collagen type 1 alpha 2 (Col1a2) is expressed abundantly in bone and is absent from cartilage, while Collagen type 2 alpha 1 (Col2a1) typifies cartilage and is not expressed in tetrapod bone [23, 24]. Hyaline cartilage chondrocytes undergo a maturation process during development, when they express Collagen type 10 alpha 1 (Col10a1), but tetrapod bone does not express Col10a1 [15, 25]. Despite these fundamental differences in collagen expression of tetrapod osteoblasts and chondrocytes, their molecular fingerprints also overlap; for example, both cell types express Collagen type 11 alpha 2 (Col11a2; ).
Skeletogenic transcription factors control molecular fingerprints of chondrocytes and osteoblasts; Sox9 is required for chondrocyte differentiation, while Runx2 is necessary for osteoblast differentiation . Sox9 and Runx2 dictate skeletal cell differentiation by binding to and promoting the transcription of genes that impart identity to skeletal tissues. For instance, Sox9 directly regulates Col2a1 expression, while Runx2 activates Col1a2 transcription [27, 28]. Much of the overlap in molecular fingerprints of tetrapod chondrocytes and osteoblasts can be attributed to Runx2 activity, which is required for chondrocyte maturation in addition to its role in osteoblast differentiation [29, 30]. Perhaps such overlap is not surprising, considering that tetrapod chondrocytes and osteoblasts differentiate from a bipotential progenitor cell, the osteochondroprogenitor, during both embryonic and adult stem cell development [31, 32]. Indicative of the delicate balance required for these transcription factors to direct discrete cell lineages, Sox9 can repress Runx2 activity [31, 32].
Although hyaline cartilage chondrocytes show conserved molecular fingerprints among vertebrate clades, a few studies in fish suggest that the molecular fingerprint of osteoblasts varies among vertebrates (Figure 1A). In contrast to tetrapod osteoblasts, zebrafish osteoblasts express col10a1, and various teleosts show evidence of Col2 in their bone matrix [11, 12, 33, 34]. A lineage-specific genome duplication event, the teleost genome duplication (TGD, or R3), occurred at the base of the teleost radiation, and genome duplications have been thought to facilitate the origin of new gene capabilities [35–40]. For example, Sox9 does not have a direct effect on osteoblast differentiation in tetrapods, but a Sox9 duplicate in teleosts (sox9b) has been reported to affect bone development . Therefore, one of at least three evolutionary scenarios might explain differences in the molecular fingerprint of tetrapod and teleost osteoblasts (Figure 1B). Hypothesis 1 proposes that a new function for these collagens in osteoblasts evolved in the teleost lineage, perhaps facilitated by the TGD (i.e., neofunctionalization). Hypothesis 2, like Hypothesis 1, proposes that collagen gene neofunctionalization occurred, but that this event happened in the ancestral actinopterygian osteoblast, and hence ruling out the hypothesis that the TGD facilitated this novel gene function. Hypothesis 3 proposes that the last common ancestor to both tetrapods and teleosts had osteoblast expression patterns found in today's teleosts, but that these patterns were lost secondarily in the tetrapod lineage (Figure 1B). To distinguish among these possibilities, we compared molecular fingerprints of skeletogenic cells in the teleost Danio rerio with the spotted gar Lepisosteus oculatus, a member of a teleost sister group that diverged before the TGD. Currently, the molecular fingerprints of chondrocytes and osteoblasts are completely unknown for any non-teleost actinopterygian.
Results demonstrated that gar and zebrafish share molecular fingerprints of both chondrocytes and osteoblasts. As an indication of skeletal cell molecular fingerprints, we used in situ hybridization on developing gar and zebrafish embryos. Specifically, we analyzed expression of the structural collagen genes col1a2, col2a1, col10a1, and col11a2 in well-developed cartilage and bone, and also revealed expression of the transcription factor genes sox9 and runx2 during mesenchymal condensation. We found that, like osteoblasts in the teleost Danio rerio, gar osteoblasts expressed col2a1 and col10a1. Therefore, these data refute by parsimony the role of the TGD in the origin of lineage-specific skeletal molecular fingerprints (Hypothesis 1) and furthermore argue that the expression of "chondrocyte" genes in osteoblasts is a shared feature of actinopterygians. More experiments will be required to distinguish between Hypotheses 2 and 3. In efforts to explain the actinopterygian expression patterns reported here, we found, surprisingly, that the "chondrogenic" transcription factor sox9 was expressed in developing gar and zebrafish osteoblasts. We discuss these findings in a phylogenetic context and suggest that the molecular fingerprint of the primitive vertebrate osteoblast was less fixed than previously expected from studies of tetrapods.
All fish and embryos were maintained with IACUC approval, according to established protocols [42, 43]. Wild-type zebrafish were of the AB strain; gar originated from animals collected in Lafourche Parish, Louisiana (courtesy of Drs. A. Ferrara and Q. Fontenot).
Histology and confocal microscopy
Embryos and larvae were processed for Alcian blue/Alizarin red staining and sectioned for histology as described previously . For zebrafish, we used transgenic lines to help visualize the location and organization of specific populations of cells. Tg(foxp2.A:EGFP)zc42 fish produce chondrocyte fluorescence , Tg(sp7:EGFP)b1212 fish make fluorescent osteoblasts , and Tg(fli1a:EGFP)y1 fish have fluorescence broadly among neural crest cells of the head . Animals were imaged live under a confocal microscope while stained with the vital dye Alizarin red, as described previously .
Molecular cloning and section in situ hybridization
Early and late stages of ceratohyal and dentary development
Chondrocyte molecular fingerprint
We next sought to explore the molecular fingerprints of well-developed chondrocytes in gar and zebrafish. In both gar and zebrafish, col1a2 expression was absent or very low in chondrocytes of the well-formed ceratohyal, although it was expressed clearly in cells of the perichondrium of both species (Figure 3F, H). Ceratohyals in both gar and zebrafish had high levels of col2a1 transcripts (Figure 3G, I), although more mature, mid-diaphyseal chondrocytes appeared to have down-regulated transcript levels (data not shown), which is consistent with similar findings in tetrapods . In addition, col2a1 expression was detected in the perichondrium of the ceratohyal in both gar and zebrafish. Expression of col10a1 was high in mature chondrocytes and in perichondral cells of both gar and zebrafish ceratohyals, whereas surrounding, less mature chondrocytes did not express col10a1 (Figure 3J, L). Transcripts for col11a2 were evident in both chondrocytes and perichondral cells of gar and zebrafish ceratohyals, although the levels of expression in mature chondrocytes appeared to be reduced relative to adjacent chondrocytes (Figure 3K, M, and data not shown), which again is consistent with published reports in tetrapods .
Phylogenetic comparison of chondrocyte molecular fingerprint
collagen type 1a2
collagen type 2a1
collagen type 10a1
collagen type 11a2
Osteoblast molecular fingerprint
Phylogenetic comparison of osteoblast molecular fingerprint
collagen type 1a2
collagen type 2a1
collagen type 10a1
collagen type 11a2
Due to their preservation in the fossil record, cartilage and bone serve as invaluable traits in understanding vertebrate evolution. Evolutionary inferences, however, often assume that the histogenesis of skeletal tissues themselves remains constant among vertebrate lineages. To be fair, cells that produce cartilage and bone (i.e., chondrocytes and osteoblasts, respectively) may have been free to evolve since their appearance roughly 500 million years ago [55, 56]. Here, we ask explicitly: To what extent do vertebrate clades share expression of the sets of genes that characterize skeletogenic cell types (i.e., molecular fingerprints; [6, 8, 9])?
A molecular fingerprint that is shared among vertebrate clades would suggest evolutionary constraints on that skeletal cell type (i.e., skeletal cell types are not free to vary). For instance, cells in cranial and appendicular skeletal tissues have different embryologic origins, and so developmental constraints may limit the molecular fingerprint of a skeletal cell that appears in both regions. While future experiments can test this hypothesis more extensively, skeletogenic cells in different embryonic regions (i.e., cranial vs. appendicular) of a given individual have been shown to exhibit a conserved molecular fingerprint . Another interesting potential embryonic constraint is the fact that osteoblasts have two evolutionary and developmental origins within vertebrates. During vertebrate phylogeny, bone originated in the dermis (i.e., exoskeleton), and then later appeared in the perichondrium surrounding cartilage templates (i.e., endoskeleton) . While not a focus of this study, we did not find differences between molecular fingerprints of osteoblasts from the exoskeleton (e.g., those in the dentary) and endoskeleton (e.g., those surrounding the ceratohyal). Therefore, our results do not support the notion that the exoskeleton and endoskeleton have separate embryonic constraints on the molecular fingerprints of osteoblasts, but testing this hypothesis could be a fruitful avenue of future research.
A molecular fingerprint that varies among clades suggests relaxed constraints on the evolution of that cell type. One might expect variation in molecular fingerprints of skeletogenic cells among various vertebrate lineages, especially given the different selective pressures to which each vertebrate clade has been exposed. For example, the skeletons of land animals withstand a stronger effective gravitational force than do the skeletons of water-borne animals . Some aquatic lineages, including sharks and other "cartilaginous" fish, and some Antarctic fish, have even lost the majority of their bony skeleton at some point during phylogeny [13, 58]. Are signatures of the embryonic response to these varied selective pressures seen in the molecular fingerprints of skeletogenic cells across vertebrates?
Spurred by the reported and unexpected expression of col10a1 and Col2, two markers of tetrapod chondrocytes, in osteoblasts of teleosts (Figure 1, Tables 1, 2; [11, 12]), we pursued the hypothesis that molecular fingerprints of skeletogenic cells vary among vertebrate clades. Experiments revealed collagen and transcription factor gene expression in skeletal cells of hyaline cartilage and bone in the zebrafish--a teleost--and gar, which diverged in the actinopterygian lineage prior to the teleost-specific genome duplication (TGD; Figure 1; ). Specifically, our data distinguish among competing hypotheses to explain why osteoblasts of teleosts express col10a1 and Col2, which are not expressed in osteoblasts of tetrapods. Osteoblast expression of these collagens either represents a neofunctionalization event that was specific either to the teleost lineage subsequent to the TGD (Hypothesis 1) or to the actinopterygian lineage (Hypothesis 2), or they were expressed in osteoblasts of the common ancestor of tetrapods and teleosts and subsequently lost in tetrapods (Hypothesis 3, Figure 1). Admittedly, evaluation of molecular fingerprints based upon expression of a few genes is a limited approach, but our findings on gene expression in chondrocytes and osteoblasts of the gar and zebrafish suggest evolutionary trends that could be embellished by massively parallel transcriptomics (e.g., RNA-seq; ).
We demonstrate that gar and zebrafish share molecular fingerprints of both chondrocytes and osteoblasts (Tables 1, 2). Despite evidence that genome duplication can facilitate the origin of new gene functions [35, 36, 39, 40], our data reject the proposed teleost neofunctionalization hypothesis for osteoblast evolution (Hypothesis 1, Figure 1). Because both gar and zebrafish express col2a1 and col10a1 in their osteoblasts, the most parsimonious explanation is that these markers were present in the molecular fingerprint of the ancestral actinopterygian osteoblast. Therefore, parsimony favors Hypothesis 2, although our results do not reject Hypothesis 3, and more experiments are required to distinguish between these two possibilities. The notion that osteoblasts achieved collagen neofunctionalization somewhere in the actinopterygian lineage (Hypothesis 2, Figure 1) could be tested further by revealing the molecular fingerprint of osteoblasts in bichir, an actinopterygian diverging more basally than the gar lineage . Similar studies of the lungfish or coelocanth, basally-diverging sarcopterygians, would test the possibility that col2a1 and col10a1 expression was present in osteoblasts of the ancestral bony fish and subsequently was lost somewhere in the sarcopterygian lineage leading to tetrapods (Hypothesis 3, Figure 1).
Our studies of skeletogenic transcription factors suggest a functional framework to explain why col2a1 and col10a1 are expressed in osteoblasts of actinopterygians, but not in osteoblasts of sarcopterygians (Table 2). In addition to runx2 expression, gar and zebrafish osteoblasts express sox9 during mesenchymal condensation of dermal bones. Developing osteoblasts of tetrapods typically express Runx2 but not Sox9 during mesenchymal condensation of dermal bones [19, 31, 61]. We propose that the expression of sox9 in gar and zebrafish osteoblasts may explain the presence of col2a1 and col10a1 transcripts, given two assumptions. First, actinopterygian osteoblasts would have to translate the sox9 transcript we observed into Sox9 protein. Second, Sox9-responsive cis-acting regulatory elements that drive Col2a1 expression in tetrapods  would have to operate similarly in actinopterygian lineages. In support of this latter notion, col2a1 gene expression is extinguished in sox9 mutant zebrafish . Currently, Sox9 has not been shown to bind to the Col10a1 promoter, but mis-expression of Sox9 in developing avian osteoblasts causes ectopic Col10a1 expression, and loss of Sox9 can abrogate Col10a1 expression in mouse [31, 62], showing that Col10a1 is downstream of Sox9 control. Deciphering the molecular mechanism by which sox9 expression in developing osteoblasts can vary among vertebrate clades will shed light on the evolution of cell type-specific molecular fingerprints.
If the primitive condition for osteoblasts in the common ancestor of actinopterygians and sarcopterygians included expression of sox9, col2a1, and col10a1, then tetrapod osteoblasts would have lost expression of these genes secondarily, as outlined in Hypothesis 3. This possibility would give an entirely fresh phylogenetic context to reports of a transient chondrogenic phase during tetrapod dermal bone development [61, 63]. Interestingly, sub-populations of chondrocytes in the zebrafish may lose sox9 and col2a1 expression as they transition to osteocytes in response to Hh signaling , so a developmental precedence may exist for the transitions in molecular fingerprints that Hypothesis 3 proposes during evolution. More broadly, we reveal fundamental differences between the molecular fingerprints of osteoblasts in actinopterygian and sarcopterygian clades, a finding consistent with the hypothesis that the primitive osteoblast-like cell was under reduced constraint (i.e., free to vary) during early vertebrate phylogeny.
Comparison of our data with published data for tetrapods further argues that, while the osteoblast has evolved differently between actinopterygian and sarcopterygian lineages, the molecular fingerprint of the chondrocyte appears to be conserved among vertebrates (Tables 1, 2). Although sampling of vertebrate lineages in this manner is as yet too restricted to be confident of making generalizations, limited studies on chondrocytes of hyaline cartilage in amphibians and reptiles do support this conclusion [65–67].
What mechanisms allow the osteoblast to vary among extant vertebrates, then, but constrain the chondrocyte? We argue that cell types that appear earlier in phylogeny and ontogeny are less free to vary during subsequent evolution. Cartilage appeared in the fossil record in the primitive chordate Haikouella 530 million years ago, and hyaline cartilage is a shared trait among chordates, hemichordates, and even some disparate protostome taxa [6, 56, 68]. Apart from two clades of diverged agnathans (i.e., hagfish and lamprey), all vertebrate lineages develop bone, which appeared in fossilized conodonts from 515 million years ago [55, 69]. Therefore, cartilage appeared before bone during phylogeny. In addition, cartilage appears before bone during ontogeny. Taken together, we suggest that because the chondrocyte appears before the osteoblast during both phylogeny and ontogeny, the molecular fingerprint of the chondrocyte is more constrained than that of the osteoblast. As such, our interpretation is consistent with the notion of phyletic constraint  and may provide a novel system by which to analyze molecular details of a developmental constraint.
While the molecular genetic basis for evolutionary changes to skeletal morphology has received much attention, similar studies on the evolution of skeletal cell types is limited. The set of genes, or molecular fingerprint, expressed by a cartilage- or bone-forming cell (chondrocyte or osteoblast, respectively) has been determined largely from human, mouse, and chick, thus providing an extremely limited sampling among vertebrate clades. A couple of studies demonstrated that teleost osteoblasts express collagens that normally are expressed only in chondrocytes of tetrapods, allowing us to generate specific hypotheses on the evolution of the osteoblast among vertebrates (Figure 1). Here, we test the hypothesis that the molecular fingerprint of the osteoblast underwent neofunctionalization in the teleost lineage specifically, perhaps as a result of the teleost-specific genome duplication (TGD). We compare expression of collagen and transcription factor genes during embryonic development of cartilage and bone in the teleost zebrafish Danio rerio and the spotted gar Lepisosteus oculatus, which diverged in the actinopterygian lineage prior to TGD. We find equivalent expression patterns of these genes in chondrocytes and osteoblasts of zebrafish and gar, thus refuting by parsimony the hypothesis. In addition, we show expression of the "chondrocyte" transcription factor sox9 in developing osteoblasts of zebrafish and gar, providing a molecular explanation for the expression of "chondrocyte" genes in fish osteoblasts. Finally, we argue from comparing our results to those of tetrapods that the molecular fingerprint of the osteoblast was not fixed during early vertebrate evolution, which supports previous work on bone and dentine tissues in the fossil record [57, 71], whereas the molecular fingerprint of the hyaline chondrocyte is constrained among vertebrate clades.
We wish to thank Allyse Ferrara and Quentin Fontenot of Nicholls State University for gar embryos, Poh Kheng Loi, Adam Burch, Charles Kimmel, and Ruth BreMiller for help with frozen sectioning, in situ hybridization, and section histology. We also recognize John Dowd, Amanda Rapp, and the Fish Facility at the University of Oregon for tremendous fish housing and husbandry. This work was supported in part by grant numbers F32 DE016778-03 (B.F.E.) and P01 HD22486 and R01 RR020833 (J.H.P.) from the National Institutes of Health.
- Cresko WA, Amores A, Wilson C, Murphy J, Currey M, Phillips P, Bell MA, Kimmel CB, Postlethwait JH: Parallel genetic basis for repeated evolution of armor loss in Alaskan threespine stickleback populations. Proc Natl Acad Sci USA. 2004, 101 (16): 6050-6055. 10.1073/pnas.0308479101.PubMedPubMed CentralView ArticleGoogle Scholar
- Depew MJ, Lufkin T, Rubenstein JL: Specification of jaw subdivisions by Dlx genes. Science. 2002, 298 (5592): 381-385. 10.1126/science.1075703.PubMedView ArticleGoogle Scholar
- Harris MP, Rohner N, Schwarz H, Perathoner S, Konstantinidis P, Nusslein-Volhard C: Zebrafish eda and edar mutants reveal conserved and ancestral roles of ectodysplasin signaling in vertebrates. PLoS Genet. 2008, 4 (10): e1000206-10.1371/journal.pgen.1000206.PubMedPubMed CentralView ArticleGoogle Scholar
- Kimmel CB, Walker MB, Miller CT: Morphing the hyomandibular skeleton in development and evolution. J Exp Zool B Mol Dev Evol. 2007, 308 (5): 609-624.PubMedView ArticleGoogle Scholar
- Colosimo PF, Hosemann KE, Balabhadra S, Villarreal G, Dickson M, Grimwood J, Schmutz J, Myers RM, Schluter D, Kingsley DM: Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles. Science. 2005, 307 (5717): 1928-1933. 10.1126/science.1107239.PubMedView ArticleGoogle Scholar
- Cole AG: A review of diversity in the evolution and development of cartilage: the search for the origin of the chondrocyte. Eur Cell Mater. 2011, 21: 122-129.PubMedGoogle Scholar
- Hecht J, Stricker S, Wiecha U, Stiege A, Panopoulou G, Podsiadlowski L, Poustka AJ, Dieterich C, Ehrich S, Suvorova J, et al: Evolution of a core gene network for skeletogenesis in chordates. PLoS Genet. 2008, 4 (3): e1000025-10.1371/journal.pgen.1000025.PubMedPubMed CentralView ArticleGoogle Scholar
- Arendt D: Genes and homology in nervous system evolution: comparing gene functions, expression patterns, and cell type molecular fingerprints. Theory Biosci. 2005, 124 (2): 185-197.PubMedView ArticleGoogle Scholar
- Arendt D: The evolution of cell types in animals: emerging principles from molecular studies. Nat Rev Genet. 2008, 9 (11): 868-882. 10.1038/nrg2416.PubMedView ArticleGoogle Scholar
- Volkmann D, Baluska F: Gravity: one of the driving forces for evolution. Protoplasma. 2006, 229 (2-4): 143-148. 10.1007/s00709-006-0200-4.PubMedView ArticleGoogle Scholar
- Eames BF, Singer A, Smith GA, Wood ZA, Yan YL, He X, Polizzi SJ, Catchen JM, Rodriguez-Mari A, Linbo T, et al: UDP xylose synthase 1 is required for morphogenesis and histogenesis of the craniofacial skeleton. Dev Biol. 2010, 341 (2): 400-415. 10.1016/j.ydbio.2010.02.035.PubMedView ArticleGoogle Scholar
- Benjamin M, Ralphs JR: Extracellular matrix of connective tissues in the heads of teleosts. J Anat. 1991, 179: 137-148.PubMedPubMed CentralGoogle Scholar
- Albertson RC, Yan YL, Titus TA, Pisano E, Vacchi M, Yelick PC, Detrich HW, Postlethwait JH: Molecular pedomorphism underlies craniofacial skeletal evolution in Antarctic notothenioid fishes. BMC Evol Biol. 2010, 10: 4-10.1186/1471-2148-10-4.PubMedPubMed CentralView ArticleGoogle Scholar
- Kluver N, Kondo M, Herpin A, Mitani H, Schartl M: Divergent expression patterns of Sox9 duplicates in teleosts indicate a lineage specific subfunctionalization. Dev Genes Evol. 2005, 215 (6): 297-305. 10.1007/s00427-005-0477-x.PubMedView ArticleGoogle Scholar
- Eames BF, de la Fuente L, Helms JA: Molecular Ontogeny of the Skeleton. Birth Defects Research (Part C). 2003, 69: 93-101. 10.1002/bdrc.10016.View ArticleGoogle Scholar
- Marks SC, Lundmark C, Christersson C, Wurtz T, Odgren PR, Seifert MF, Mackay CA, Mason-Savas A, Popoff SN: Endochondral bone formation in toothless (osteopetrotic) rats: failures of chondrocyte patterning and type X collagen expression. Int J Dev Biol. 2000, 44 (3): 309-316.PubMedGoogle Scholar
- Bronckers AL, Sasaguri K, Engelse MA: Transcription and immunolocalization of Runx2/Cbfa1/Pebp2alphaA in developing rodent and human craniofacial tissues: further evidence suggesting osteoclasts phagocytose osteocytes. Microsc Res Tech. 2003, 61 (6): 540-548. 10.1002/jemt.10377.PubMedView ArticleGoogle Scholar
- de Crombrugghe B, Lefebvre V, Behringer RR, Bi W, Murakami S, Huang W: Transcriptional mechanisms of chondrocyte differentiation. Matrix Biol. 2000, 19 (5): 389-394. 10.1016/S0945-053X(00)00094-9.PubMedView ArticleGoogle Scholar
- Eames BF, Helms JA: Conserved molecular program regulating cranial and appendicular skeletogenesis. Dev Dyn. 2004, 231 (1): 4-13. 10.1002/dvdy.20134.PubMedView ArticleGoogle Scholar
- Eames BF, Schneider RA: The genesis of cartilage size and shape during development and evolution. Development. 2008, 135 (23): 3947-3958. 10.1242/dev.023309.PubMedPubMed CentralView ArticleGoogle Scholar
- Merrill AE, Eames BF, Weston SJ, Heath T, Schneider RA: Mesenchyme-dependent BMP signaling directs the timing of mandibular osteogenesis. Development. 2008, 135 (7): 1223-1234. 10.1242/dev.015933.PubMedPubMed CentralView ArticleGoogle Scholar
- Walchli C, Koch M, Chiquet M, Odermatt BF, Trueb B: Tissue-specific expression of the fibril-associated collagens XII and XIV. J Cell Sci. 1994, 107 (Pt 2): 669-681.PubMedGoogle Scholar
- Gray H, Williams PL: Gray's anatomy. 1989, Edinburgh: C. LivingstoneGoogle Scholar
- Ham AW, Cormack DH: Ham's histology. 1987, Philadelphia: Lippincott, 9Google Scholar
- Linsenmayer TF, Eavey RD, Schmid TM: Type X collagen: a hypertrophic cartilage-specific molecule. Pathol Immunopathol Res. 1988, 7 (1-2): 14-19. 10.1159/000157085.PubMedView ArticleGoogle Scholar
- Li SW, Arita M, Kopen GC, Phinney DG, Prockop DJ: A 1,064 bp fragment from the promoter region of the Col11a2 gene drives lacZ expression not only in cartilage but also in osteoblasts adjacent to regions undergoing both endochondral and intramembranous ossification in mouse embryos. Matrix Biol. 1998, 17 (3): 213-221. 10.1016/S0945-053X(98)90060-9.PubMedView ArticleGoogle Scholar
- Lefebvre V, Huang W, Harley VR, Goodfellow PN, de Crombrugghe B: SOX9 is a potent activator of the chondrocyte-specific enhancer of the pro alpha1(II) collagen gene. Mol Cell Biol. 1997, 17 (4): 2336-2346.PubMedPubMed CentralView ArticleGoogle Scholar
- Kern B, Shen J, Starbuck M, Karsenty G: Cbfa1 contributes to the osteoblast-specific expression of type I collagen genes. J Biol Chem. 2001, 276 (10): 7101-7107. 10.1074/jbc.M006215200.PubMedView ArticleGoogle Scholar
- Hoshi K, Komori T, Ozawa H: Morphological characterization of skeletal cells in Cbfa1-deficient mice. Bone. 1999, 25 (6): 639-651. 10.1016/S8756-3282(99)00223-9.PubMedView ArticleGoogle Scholar
- Kim IS, Otto F, Zabel B, Mundlos S: Regulation of chondrocyte differentiation by Cbfa1. Mech Dev. 1999, 80 (2): 159-170. 10.1016/S0925-4773(98)00210-X.PubMedView ArticleGoogle Scholar
- Eames BF, Sharpe PT, Helms JA: Hierarchy revealed in the specification of three skeletal fates by Sox9 and Runx2. Dev Biol. 2004, 274 (1): 188-200. 10.1016/j.ydbio.2004.07.006.PubMedView ArticleGoogle Scholar
- Zhou G, Zheng Q, Engin F, Munivez E, Chen Y, Sebald E, Krakow D, Lee B: Dominance of SOX9 function over RUNX2 during skeletogenesis. Proc Natl Acad Sci USA. 2006, 103 (50): 19004-19009. 10.1073/pnas.0605170103.PubMedPubMed CentralView ArticleGoogle Scholar
- Avaron F, Hoffman L, Guay D, Akimenko MA: Characterization of two new zebrafish members of the hedgehog family: atypical expression of a zebrafish indian hedgehog gene in skeletal elements of both endochondral and dermal origins. Dev Dyn. 2006, 235 (2): 478-489. 10.1002/dvdy.20619.PubMedView ArticleGoogle Scholar
- Li N, Felber K, Elks P, Croucher P, Roehl HH: Tracking gene expression during zebrafish osteoblast differentiation. Dev Dyn. 2009, 238 (2): 459-466. 10.1002/dvdy.21838.PubMedView ArticleGoogle Scholar
- Brodie ED: How an ancient genome duplication electrified modern fish. Proc Natl Acad Sci USA. 2010, 107 (51): 21953-21954. 10.1073/pnas.1016298108.PubMedPubMed CentralView ArticleGoogle Scholar
- Wagner A: Gene duplications, robustness and evolutionary innovations. Bioessays. 2008, 30 (4): 367-373. 10.1002/bies.20728.PubMedView ArticleGoogle Scholar
- Amores A, Force A, Yan YL, Joly L, Amemiya C, Fritz A, Ho RK, Langeland J, Prince V, Wang YL, et al: Zebrafish hox clusters and vertebrate genome evolution. Science. 1998, 282 (5394): 1711-1714.PubMedView ArticleGoogle Scholar
- Postlethwait J, Amores A, Cresko W, Singer A, Yan YL: Subfunction partitioning, the teleost radiation and the annotation of the human genome. Trends Genet. 2004, 20 (10): 481-490. 10.1016/j.tig.2004.08.001.PubMedView ArticleGoogle Scholar
- Ohno S: Gene duplication and the uniqueness of vertebrate genomes circa 1970-1999. Semin Cell Dev Biol. 1999, 10 (5): 517-522. 10.1006/scdb.1999.0332.PubMedView ArticleGoogle Scholar
- Taylor JS, Raes J: Duplication and divergence: the evolution of new genes and old ideas. Annu Rev Genet. 2004, 38: 615-643. 10.1146/annurev.genet.38.072902.092831.PubMedView ArticleGoogle Scholar
- Yan YL, Willoughby J, Liu D, Crump JG, Wilson C, Miller CT, Singer A, Kimmel C, Westerfield M, Postlethwait JH: A pair of Sox: distinct and overlapping functions of zebrafish sox9 co-orthologs in craniofacial and pectoral fin development. Development. 2005, 132 (5): 1069-1083. 10.1242/dev.01674.PubMedView ArticleGoogle Scholar
- Westerfield M: The zebrafish book. A guide for the laboratory use of zebrafish (Danio rerio). 2007, Eugene: Univ. of Oregon PressGoogle Scholar
- Amores A, Catchen J, Ferrara A, Fontenot Q, Postlethwait JH: Genome evolution and meiotic maps by massively parallel DNA sequencing: spotted gar, an outgroup for the teleost genome duplication. Genetics. 2011, 188 (4): 799-808. 10.1534/genetics.111.127324.PubMedPubMed CentralView ArticleGoogle Scholar
- Eames B, Yan Y, Swartz M, Levic D, Knapik E, Postlethwait J, Kimmel C: Mutations in fam20b and xylosyltransferase1 reveal that cartilage matrix controls timing of endochondral ossification through inhibition of chondrocyte maturation. PLoS Genet. 2011, 7 (8): e1002246-10.1371/journal.pgen.1002246.PubMedPubMed CentralView ArticleGoogle Scholar
- Bonkowsky JL, Wang X, Fujimoto E, Lee JE, Chien CB, Dorsky RI: Domain-specific regulation of foxP2 CNS expression by lef1. BMC Dev Biol. 2008, 8: 103-10.1186/1471-213X-8-103.PubMedPubMed CentralView ArticleGoogle Scholar
- DeLaurier A, Eames BF, Blanco-Sanchez B, Peng G, He X, Swartz ME, Ullmann B, Westerfield M, Kimmel CB: Zebrafish sp7:EGFP: a transgenic for studying otic vesicle formation, skeletogenesis, and bone regeneration. Genesis. 2010, 48 (8): 505-511. 10.1002/dvg.20639.PubMedPubMed CentralView ArticleGoogle Scholar
- Crump JG, Swartz ME, Eberhart JK, Kimmel CB: Moz-dependent Hox expression controls segment-specific fate maps of skeletal precursors in the face. Development. 2006, 133 (14): 2661-2669. 10.1242/dev.02435.PubMedView ArticleGoogle Scholar
- Rodriguez-Mari A, Yan YL, Bremiller RA, Wilson C, Canestro C, Postlethwait JH: Characterization and expression pattern of zebrafish Anti-Mullerian hormone (Amh) relative to sox9a, sox9b, and cyp19a1a, during gonad development. Gene Expr Patterns. 2005, 5 (5): 655-667. 10.1016/j.modgep.2005.02.008.PubMedView ArticleGoogle Scholar
- Yokoi H, Yan YL, Miller MR, BreMiller RA, Catchen JM, Johnson EA, Postlethwait JH: Expression profiling of zebrafish sox9 mutants reveals that Sox9 is required for retinal differentiation. Dev Biol. 2009, 329 (1): 1-15. 10.1016/j.ydbio.2009.01.002.PubMedPubMed CentralView ArticleGoogle Scholar
- Zhao Q, Eberspaecher H, Lefebvre V, De Crombrugghe B: Parallel expression of Sox9 and Col2a1 in cells undergoing chondrogenesis. Dev Dyn. 1997, 209 (4): 377-386. 10.1002/(SICI)1097-0177(199708)209:4<377::AID-AJA5>3.0.CO;2-F.PubMedView ArticleGoogle Scholar
- Wai AW, Ng LJ, Watanabe H, Yamada Y, Tam PP, Cheah KS: Disrupted expression of matrix genes in the growth plate of the mouse cartilage matrix deficiency (cmd) mutant. Dev Genet. 1998, 22 (4): 349-358. 10.1002/(SICI)1520-6408(1998)22:4<349::AID-DVG5>3.0.CO;2-6.PubMedView ArticleGoogle Scholar
- Ducy P, Zhang R, Geoffroy V, Ridall AL, Karsenty G: Osf2/Cbfa1: a transcriptional activator of osteoblast differentiation. Cell. 1997, 89 (5): 747-754. 10.1016/S0092-8674(00)80257-3.PubMedView ArticleGoogle Scholar
- Ng LJ, Wheatley S, Muscat GE, Conway-Campbell J, Bowles J, Wright E, Bell DM, Tam PP, Cheah KS, Koopman P: SOX9 binds DNA, activates transcription, and coexpresses with type II collagen during chondrogenesis in the mouse. Dev Biol. 1997, 183 (1): 108-121. 10.1006/dbio.1996.8487.PubMedView ArticleGoogle Scholar
- Flores MV, Tsang VW, Hu W, Kalev-Zylinska M, Postlethwait J, Crosier P, Crosier K, Fisher S: Duplicate zebrafish runx2 orthologues are expressed in developing skeletal elements. Gene Expr Patterns. 2004, 4 (5): 573-581. 10.1016/j.modgep.2004.01.016.PubMedView ArticleGoogle Scholar
- Sansom IJ, Smith MP, Armstrong HA, Smith MM: Presence of the earliest vertebrate hard tissue in conodonts. Science. 1992, 256 (5061): 1308-1311. 10.1126/science.1598573.PubMedView ArticleGoogle Scholar
- Chen J-Y, Huang D-Y, Li C-W: An early Cambrian craniate-like chordate. Nature. 1999, 402 (6761): 518-522. 10.1038/990080.View ArticleGoogle Scholar
- Smith MM, Hall BK: Development and evolutionary origins of vertebrate skeletogenic and odontogenic tissues. Biol Rev Camb Philos Soc. 1990, 65 (3): 277-373. 10.1111/j.1469-185X.1990.tb01427.x.PubMedView ArticleGoogle Scholar
- Eames BF, Allen N, Young J, Kaplan A, Helms JA, Schneider RA: Skeletogenesis in the swell shark Cephaloscyllium ventriosum. J Anat. 2007, 210 (5): 542-554. 10.1111/j.1469-7580.2007.00723.x.PubMedPubMed CentralView ArticleGoogle Scholar
- Tariq MA, Kim HJ, Jejelowo O, Pourmand N: Whole-transcriptome RNAseq analysis from minute amount of total RNA. Nucleic Acids Res. 2011, 39 (18): e120-10.1093/nar/gkr547.PubMedPubMed CentralView ArticleGoogle Scholar
- Inoue JG, Miya M, Tsukamoto K, Nishida M: Basal actinopterygian relationships: a mitogenomic perspective on the phylogeny of the "ancient fish". Mol Phylogenet Evol. 2003, 26 (1): 110-120. 10.1016/S1055-7903(02)00331-7.PubMedView ArticleGoogle Scholar
- Aberg T, Rice R, Rice D, Thesleff I, Waltimo-Siren J: Chondrogenic potential of mouse calvarial mesenchyme. J Histochem Cytochem. 2005, 53 (5): 653-663. 10.1369/jhc.4A6518.2005.PubMedView ArticleGoogle Scholar
- Ikegami D, Akiyama H, Suzuki A, Nakamura T, Nakano T, Yoshikawa H, Tsumaki N: Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways. Development. 2011, 138 (8): 1507-1519. 10.1242/dev.057802.PubMedView ArticleGoogle Scholar
- Abzhanov A, Rodda SJ, McMahon AP, Tabin CJ: Regulation of skeletogenic differentiation in cranial dermal bone. Development. 2007, 134 (17): 3133-3144. 10.1242/dev.002709.PubMedView ArticleGoogle Scholar
- Hammond CL, Schulte-Merker S: Two populations of endochondral osteoblasts with differential sensitivity to Hedgehog signalling. Development. 2009, 136 (23): 3991-4000. 10.1242/dev.042150.PubMedView ArticleGoogle Scholar
- Moriishi T, Shibata Y, Tsukazaki T, Yamaguchi A: Expression profile of Xenopus banded hedgehog, a homolog of mouse Indian hedgehog, is related to the late development of endochondral ossification in Xenopus laevis. Biochem Biophys Res Commun. 2005, 328 (4): 867-873. 10.1016/j.bbrc.2005.01.032.PubMedView ArticleGoogle Scholar
- Kerney R, Hanken J: Gene expression reveals unique skeletal patterning in the limb of the direct-developing frog, Eleutherodactylus coqui. Evol Dev. 2008, 10 (4): 439-448. 10.1111/j.1525-142X.2008.00255.x.PubMedView ArticleGoogle Scholar
- Lopez D, Duran AC, de Andres AV, Guerrero A, Blasco M, Sans-Coma V: Formation of cartilage in the heart of the Spanish terrapin, Mauremys leprosa (Reptilia, Chelonia). J Morphol. 2003, 258 (1): 97-105. 10.1002/jmor.10134.PubMedView ArticleGoogle Scholar
- Rychel AL, Smith SE, Shimamoto HT, Swalla BJ: Evolution and development of the chordates: collagen and pharyngeal cartilage. Mol Biol Evol. 2006, 23 (3): 541-549.PubMedView ArticleGoogle Scholar
- Janvier P: Early vertebrates. 1996, Oxford: Oxford University PressGoogle Scholar
- Gilbert SF: Developmental Biology. 1988, Sunderland: Sinauer Associates, Inc, 2Google Scholar
- Donoghue PC, Sansom IJ, Downs JP: Early evolution of vertebrate skeletal tissues and cellular interactions, and the canalization of skeletal development. J Exp Zool B Mol Dev Evol. 2006, 306 (3): 278-294.PubMedView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.