Development of the Endochondral Skeleton
TL;DR: This review aims to integrate the known functions of extracellular signals and transcription factors that regulate development of the endochondral skeleton.
Abstract: Much of the mammalian skeleton is composed of bones that originate from cartilage templates through endochondral ossification. Elucidating the mechanisms that control endochondral bone development is critical for understanding human skeletal diseases, injury response, and aging. Mouse genetic studies in the past 15 years have provided unprecedented insights about molecules regulating chondrocyte formation, chondrocyte maturation, and osteoblast differentiation, all key processes of endochondral bone development. These include the roles of the secreted proteins IHH, PTHrP, BMPs, WNTs, and FGFs, their receptors, and transcription factors such as SOX9, RUNX2, and OSX, in regulating chondrocyte and osteoblast biology. This review aims to integrate the known functions of extracellular signals and transcription factors that regulate development of the endochondral skeleton.
Citations
More filters
TL;DR: This review summarizes the recent advances in the understanding of TGF-β/BMP signaling in osteoblast differentiation, chondrocyte differentiation, skeletal development, cartilage formation, bone formation,Bone homeostasis, and related human bone diseases caused by the disruption of T GF-β / BMP signaling.
Abstract: Transforming growth factor-beta (TGF-β) and bone morphogenic protein (BMP) signaling has fundamental roles in both embryonic skeletal development and postnatal bone homeostasis. TGF-βs and BMPs, acting on a tetrameric receptor complex, transduce signals to both the canonical Smad-dependent signaling pathway (that is, TGF-β/BMP ligands, receptors, and Smads) and the non-canonical-Smad-independent signaling pathway (that is, p38 mitogen-activated protein kinase/p38 MAPK) to regulate mesenchymal stem cell differentiation during skeletal development, bone formation and bone homeostasis. Both the Smad and p38 MAPK signaling pathways converge at transcription factors, for example, Runx2 to promote osteoblast differentiation and chondrocyte differentiation from mesenchymal precursor cells. TGF-β and BMP signaling is controlled by multiple factors, including the ubiquitin-proteasome system, epigenetic factors, and microRNA. Dysregulated TGF-β and BMP signaling result in a number of bone disorders in humans. Knockout or mutation of TGF-β and BMP signaling-related genes in mice leads to bone abnormalities of varying severity, which enable a better understanding of TGF-β/BMP signaling in bone and the signaling networks underlying osteoblast differentiation and bone formation. There is also crosstalk between TGF-β/BMP signaling and several critical cytokines' signaling pathways (for example, Wnt, Hedgehog, Notch, PTHrP, and FGF) to coordinate osteogenesis, skeletal development, and bone homeostasis. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in osteoblast differentiation, chondrocyte differentiation, skeletal development, cartilage formation, bone formation, bone homeostasis, and related human bone diseases caused by the disruption of TGF-β/BMP signaling.
981 citations
TL;DR: The genetic evidence implicating BMP superfamily signalling in vertebrate bone and joint development is examined, a selection of human skeletal disorders associated with altered BMP signalling is discussed, and the status of modulating the BMP pathway as a therapeutic target for skeletal trauma and disease is summarized.
Abstract: Since the identification in 1988 of bone morphogenetic protein 2 (BMP2) as a potent inducer of bone and cartilage formation, BMP superfamily signalling has become one of the most heavily investigated topics in vertebrate skeletal biology. Whereas a large part of this research has focused on the roles of BMP2, BMP4 and BMP7 in the formation and repair of endochondral bone, a large number of BMP superfamily molecules have now been implicated in almost all aspects of bone, cartilage and joint biology. As modulating BMP signalling is currently a major therapeutic target, our rapidly expanding knowledge of how BMP superfamily signalling affects most tissue types of the skeletal system creates enormous potential to translate basic research findings into successful clinical therapies that improve bone mass or quality, ameliorate diseases of skeletal overgrowth, and repair damage to bone and joints. This Review examines the genetic evidence implicating BMP superfamily signalling in vertebrate bone and joint development, discusses a selection of human skeletal disorders associated with altered BMP signalling and summarizes the status of modulating the BMP pathway as a therapeutic target for skeletal trauma and disease.
566 citations
TL;DR: The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states and highlight the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression.
Abstract: Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.
337 citations
TL;DR: It is concluded that HH signaling is a key factor in the regulation of adult tissue homeostasis and repair, acting via multiple different routes to regulate distinct cellular outcomes, including maintenance of plasticity, in a context-dependent manner.
Abstract: The hedgehog (HH) pathway is well known for its mitogenic and morphogenic functions during development, and HH signaling continues in discrete populations of cells within many adult mammalian tissues. Growing evidence indicates that HH regulates diverse quiescent stem cell populations, but the exact roles that HH signaling plays in adult organ homeostasis and regeneration remain poorly understood. Here, we review recently identified functions of HH in modulating the behavior of tissue-specific adult stem and progenitor cells during homeostasis, regeneration and disease. We conclude that HH signaling is a key factor in the regulation of adult tissue homeostasis and repair, acting via multiple different routes to regulate distinct cellular outcomes, including maintenance of plasticity, in a context-dependent manner.
333 citations
TL;DR: The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair.
Abstract: Bone development occurs through a series of synchronous events that result in the formation of the body scaffold. The repair potential of bone and its surrounding microenvironment — including inflammatory, endothelial and Schwann cells — persists throughout adulthood, enabling restoration of tissue to its homeostatic functional state. The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair. Increased understanding of bone development, as well as normal and aberrant bone repair, has important therapeutic implications for the treatment of bone disease and ageing-related degeneration. This Review discusses the cell types, critical genes and transcription factors involved in bone development and repair. The dysfunctional cellular and molecular signalling that results in clinical bone disease is also outlined, thus informing the current state of science and clinical practice.
312 citations
References
More filters
TL;DR: Notch signaling defines an evolutionarily ancient cell interaction mechanism, which plays a fundamental role in metazoan development, providing a general developmental tool to influence organ formation and morphogenesis.
Abstract: Notch signaling defines an evolutionarily ancient cell interaction mechanism, which plays a fundamental role in metazoan development. Signals exchanged between neighboring cells through the Notch receptor can amplify and consolidate molecular differences, which eventually dictate cell fates. Thus, Notch signals control how cells respond to intrinsic or extrinsic developmental cues that are necessary to unfold specific developmental programs. Notch activity affects the implementation of differentiation, proliferation, and apoptotic programs, providing a general developmental tool to influence organ formation and morphogenesis.
5,834 citations
"Development of the Endochondral Ske..." refers background in this paper
...NOTCH signaling mediates communication between neighboring cells to control cell fate decisions in all metazoans (Artavanis-Tsakonas et al. 1999; Chiba 2006)....
[...]
TL;DR: The data suggest that both intramembranous and endochondral ossification were completely blocked, owing to the maturational arrest of osteoblasts in the mutant mice, and demonstrate that Cbfa1 plays an essential role in osteogenesis.
4,196 citations
"Development of the Endochondral Ske..." refers background in this paper
...Homozygous deletion of RUNX2 or its nuclear targeting signal in mice resulted in a complete lack of osteoblasts (Komori et al. 1997; Otto et al. 1997), whereas haploinsufficiency of RUNX2 in either mice or humans causes cleidocranial dysplasia (Lee et al. 1997; Mundlos et al. 1997; Choi et al.…...
[...]
...Homozygous deletion of RUNX2 or its nuclear targeting signal in mice resulted in a complete lack of osteoblasts (Komori et al. 1997; Otto et al. 1997), whereas haploinsufficiency of RUNX2 in either mice or humans causes cleidocranial dysplasia (Lee et al....
[...]
...Interestingly, in the absence of RUNX2, the perichondrium (normally containing osteogenic progenitors) becomes hypoplastic (Komori et al. 1997; Otto et al. 1997), indicating that RUNX2 may be necessary for the production and/or maintenance of the progenitors....
[...]
TL;DR: It is proposed that Runx2/Cbfa1-expressing preosteoblasts are still bipotential cells, because Osx null preostEoblasts express typical chondrocyte marker genes, and Osx acts downstream of Runx 2/C bfa1.
3,283 citations
"Development of the Endochondral Ske..." refers background in this paper
...Deletion of OSX results in a complete absence of osteoblasts in the mouse embryo, even though expression of RUNX2 is relatively normal (Nakashima et al. 2002)....
[...]
...These results, together with the observation that Osx expression is abolished in Runx2 – / – mice (Nakashima et al. 2002), indicate that OSX functions downstream from RUNX2 as another indispensable regulator of osteoblast differentiation....
[...]
...…leads to a hypoplastic perichondrium, loss of OSX causes ectopic cartilage formation beneath a thickened perichondrium at the midshaft of long bones (where a bone collar normally forms), possibly because of a fate switch of progenitors from osteoblasts to chondrocytes (Nakashima et al. 2002)....
[...]
...Whereas RUNX2 deletion leads to a hypoplastic perichondrium, loss of OSX causes ectopic cartilage formation beneath a thickened perichondrium at the midshaft of long bones (where a bone collar normally forms), possibly because of a fate switch of progenitors from osteoblasts to chondrocytes (Nakashima et al. 2002)....
[...]
TL;DR: This Review highlights recent studies in Notch signaling that reveal new molecular details about the regulation of ligand-mediated receptor activation, receptor proteolysis, and target selection.
3,120 citations
TL;DR: In their screen for mutations that disrupt the Drosophila larval body plan, these authors identified several that cause the duplication of denticles and an accompanying loss of naked cuticle, characteristic of the posterior half of each segment.
Abstract: Since their isolation in the early 1990s, members of the Hedgehog family of intercellular signaling proteins have come to be recognized as key mediators of many fundamental processes in embryonic development. Their activities are central to the growth, patterning, and morphogenesis of many different regions within the body plans of vertebrates and insects, and most likely other invertebrates. In some contexts, Hedgehog signals act as morphogens in the dose-dependent induction of distinct cell fates within a target field, in others as mitogens regulating cell proliferation or as inducing factors controlling the form of a developing organ. These diverse functions of Hedgehog proteins raise many intriguing questions about their mode of operation. How do these proteins move between or across fields of cells? How are their activities modulated and transduced? What are their intracellular targets? In this article we review some well-established paradigms of Hedgehog function inDrosophila and vertebrate development and survey the current understanding of the synthesis, modification, and transduction of Hedgehog proteins. Embryological studies over much of the last century that relied primarily on the physical manipulation of cells within the developing embryo or fragments of the embryo in culture, provided many compelling examples for the primacy of cell–cell interactions in regulating invertebrate and vertebrate development. The subsequent identification of many of the signaling factors that mediate cellular communication has led to two general conclusions. First, although there are many important signals, most of these fall into a few large families of secreted peptide factors: theWnt (Wodarz and Nusse 1998), fibroblast growth factor (Szebenyi and Fallon 1999), TGFsuperfamily (Massague and Chen 2000), plateletderived growth factor (Betsholtz et al. 2001), ephrin (Bruckner and Klein 1998), and Hedgehog families. Second, parallel studies in invertebrate and vertebrate systems have shown that although the final outcome might look quite different (e.g., a fly vs. a mouse), there is a striking conservation in the deployment of members of the same signaling families to regulate development of these seemingly quite different organisms. This review focuses on one of the most intriguing examples of this phenomenon, that of the Hedgehog family. As with many of the advances in our understanding of the genetic regulation of animal development, hedgehog (hh) genes owe their discovery to the pioneering work of Nusslein-Volhard and Wieschaus (1980). In their screen for mutations that disrupt the Drosophila larval body plan, these authors identified several that cause the duplication of denticles (spiky cuticular processes that decorate the anterior half of each body segment) and an accompanying loss of naked cuticle, characteristic of the posterior half of each segment (see Fig. 1). The ensuing appearance of a continuous lawn of denticles projecting from the larval cuticle evidently suggested the spines of a hedgehog to the discoverers, hence the origin of the name of one of these genes. Other loci identified by mutants with this phenotype included armadillo, gooseberry, and wingless (wg). In contrast, animals mutant for the aptly named naked gene showed the converse phenotype, with denticle belts replaced by naked cuticle in every segment. On the basis of these mutant phenotypes, Nusslein-Volhard and Wieschaus (1980) proposed that these so-called segment-polarity genes regulate pattern within each of the segments of the larval body, individual genes acting within distinct subregions of the emerging segmental pattern. The first important breakthrough in unraveling how segment-polarity genes act came in the mid-1980s with the cloning of two members of the class, wingless and engrailed (en). Wg was shown to be the ortholog of the vertebrate proto-oncogene int1 (subsequently renamed Wnt1 and the founder member of the Wnt family of secreted peptide factors; Rijsewijk et al. 1987), whereas the sequence of en revealed that it encodes a homeodomaincontaining transcription factor (Fjose et al. 1985; Poole et al. 1985). Intriguingly, the two genes were found to be expressed in adjacent narrow stripes of cells in each segment (Martinez Arias et al. 1988). A close spatial relationship between Wnt1 and En expression domains was also reported in the primordial midbrain and hindbrain of the vertebrate embryo (McMahon et al. 1992). AnalyWe dedicate this review to the memory of our dear friend and colleague Rosa Beddington, whose encouragement led to our initial collaboration. 3Corresponding authors. E-MAIL p.w.ingham@sheffield.ac.uk; FAX 0114-222-288. E-MAIL amcmahon@biosun.harvard.edu; FAX (617) 496-3763. Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/ gad.938601.
2,919 citations