The transcription factors L-Sox5 and Sox6 are essential for cartilage formation

Redundancy in regulation of chondrogenesis in MIA/CD-RAP-deficient mice

Recent in vitro analysis of MIA/CD-RAP-deficient (MIA(-/-)) mesenchymal stem cells revealed altered chondrogenic differentiation, characterised by enhanced proliferation and delayed differentiation. However, adult MIA(-/-) mice develop normally and show only ultrastructural defects of the cartilage but no major abnormalities. We therefore focused, in this study, on chondrogenesis in vivo in MIA(-/-) mouse embryos to reveal potential molecular changes during embryogenesis and possible redundant mechanisms, which explain the almost normal phenotype despite MIA/CD-RAP loss. In situ hybridisation analysis revealed larger expression areas of Col2a1 and Sox9 positive, proliferating chondrocytes at day 15.5 and 16.5 of embryogenesis in MIA(-/-) mice. The initially diminished zone of Col10a1-expressing hypertrophic chondrocytes at day 15.5 was compensated at day 16.5 in MIA(-/-) embryos. Supported by in vitro studies using mesenchymal stem cells, we discovered that chondrogenesis in MIA(-/-) mice is modified by enhanced Sox9, Sox6 and AP-2α expression. Finally, we identified reduced AP1 and CRE activity, analysed by reporter gene- and electrophoretic mobility shift assays, important for redundancy mechanism which rescued delayed hypertrophic differentiation and allows normal development of MIA(-/-) mice. In summary, as observed in other knockout models of molecules important for cartilage development and differentiation, viability and functional integrity is reached by remarkable molecular redundancy in MIA/CD-RAP knockout mice.

Ribosome biogenesis in skeletal development and the pathogenesis of skeletal disorders

The skeleton affords a framework and structural support for vertebrates, while also facilitating movement, protecting vital organs, and providing a reservoir of minerals and cells for immune system and vascular homeostasis. The mechanical and biological functions of the skeleton are inextricably linked to the size and shape of individual bones, the diversity of which is dependent in part upon differential growth and proliferation. Perturbation of bone development, growth and proliferation, can result in congenital skeletal anomalies, which affect approximately 1 in 3000 live births [1]. Ribosome biogenesis is integral to all cell growth and proliferation through its roles in translating mRNAs and building proteins. Disruption of any steps in the process of ribosome biogenesis can lead to congenital disorders termed ribosomopathies. In this review, we discuss the role of ribosome biogenesis in skeletal development and in the pathogenesis of congenital skeletal anomalies. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.

Roles of microRNAs in prenatal chondrogenesis, postnatal chondrogenesis and cartilage-related diseases

Cartilage has limited repair and regeneration capacity, thus damage of cartilage often results in its dysfunction and even chronic diseases like osteoarthritis (OA). Chondrogenesis induced by tissue-engineering methods is essential to treating cartilage-related diseases. MicroRNAs (miRNAs) are a class of small non-coding single-stranded RNAs which exert their biological effects by binding to the target messenger RNAs (mRNAs), resulting in decay or translation suppression of target mRNAs. There are emerging evidence indicating that miRNAs may play important roles in regulating both prenatal and postnatal chondrogenesis. During embryonic skeletal development, prenatal chondrogenesis is thought to be a precondition for formation of cartilage in developing limbs. Plenty of studies on different types of stem cells have undoubtedly proven their capacity of differentiating into chondrocytes. MiRNAs are found to comprehensively modulate these processes by establishing an interaction network with target genes, transcription factors and cytokines et al. In addition, translational application of miRNA technology has also been explored. In this review, we focus on the up-dated progress on regulatory mechanisms of miRNAs in prenatal and postnatal chondrogenesis. In addition, several miRNA target genes and roles of miRNAs in cartilage-related diseases are also discussed. This will contribute to studies of chondrogenesis mechanisms and development of new treating methods.

Molecular study of a Hoxa2 gain-of-function in chondrogenesis: a model of idiopathic proportionate short stature

In a previous study using transgenic mice ectopically expressing Hoxa2 during chondrogenesis, we associated the animal phenotype to human idiopathic proportionate short stature. Our analysis showed that this overall size reduction was correlated with a negative influence of Hoxa2 at the first step of endochondral ossification. However, the molecular pathways leading to such phenotype are still unknown. Using protein immunodetection and histological techniques comparing transgenic mice to controls, we show here that the persistent expression of Hoxa2 in chondrogenic territories provokes a general down-regulation of the main factors controlling the differentiation cascade, such as Bapx1, Bmp7, Bmpr1a, Ihh, Msx1, Pax9, Sox6, Sox9 and Wnt5a. These data confirm the impairment of chondrogenic differentiation by Hoxa2 overexpression. They also show a selective effect of Hoxa2 on endochondral ossification processes since Gdf5 and Gdf10, and Bmp4 or PthrP were up-regulated and unmodified, respectively. Since Hoxa2 deregulation in mice induces a proportionate short stature phenotype mimicking human idiopathic conditions, our results give an insight into understanding proportionate short stature pathogenesis by highlighting molecular factors whose combined deregulation may be involved in such a disease.

Gene expression profiles in human and mouse primary cells provide new insights into the differential actions of vitamin D3 metabolites

1α,25-Dihydroxyvitamin D₃ (1α,25(OH)₂D₃) had earlier been regarded as the only active hormone. The newly identified actions of 25-hydroxyvitamin D₃ (25(OH)D₃) and 24R,25-dihydroxyvitamin D₃ (24R,25(OH)₂D₃) broadened the vitamin D₃ endocrine system, however, the current data are fragmented and a systematic understanding is lacking. Here we performed the first systematic study of global gene expression to clarify their similarities and differences. Three metabolites at physiologically comparable levels were utilized to treat human and mouse fibroblasts prior to DNA microarray analyses. Human primary prostate stromal P29SN cells (hP29SN), which convert 25(OH)D₃ into 1α,25(OH)₂D₃ by 1α-hydroxylase (encoded by the gene CYP27B1), displayed regulation of 164, 171, and 175 genes by treatment with 1α,25(OH)₂D₃, 25(OH)D₃, and 24R,25(OH)₂D₃, respectively. Mouse primary Cyp27b1 knockout fibroblasts (mCyp27b1^−/−), which lack 1α-hydroxylation, displayed regulation of 619, 469, and 66 genes using the same respective treatments. The number of shared genes regulated by two metabolites is much lower in hP29SN than in mCyp27b1^−/−. By using DAVID Functional Annotation Bioinformatics Microarray Analysis tools and Ingenuity Pathways Analysis, we identified the agonistic regulation of calcium homeostasis and bone remodeling between 1α,25(OH)₂D₃ and 25(OH)D₃ and unique non-classical actions of each metabolite in physiological and pathological processes, including cell cycle, keratinocyte differentiation, amyotrophic lateral sclerosis signaling, gene transcription, immunomodulation, epigenetics, cell differentiation, and membrane protein expression. In conclusion, there are three distinct vitamin D₃ hormones with clearly different biological activities. This study presents a new conceptual insight into the vitamin D₃ endocrine system, which may guide the strategic use of vitamin D₃ in disease prevention and treatment.

Sox6 up-regulation by macrophage migration inhibitory factor promotes survival and maintenance of mouse neural stem/progenitor cells

Macrophage migration inhibitory factor (MIF) has important roles in supporting the proliferation and/or survival of murine neural stem/progenitor cells (NSPCs), but downstream effectors remain unknown. We show here that MIF robustly increases the expression of Sox6 in NSPCs in vitro. During neural development, Sox6 is expressed in the ventricular zone of the ganglionic eminence (GE) of mouse brains at embryonic day 14.5 (E14.5), cultured NSPCs from E14.5 GE, and NSPCs in the subventricular zone (SVZ) around the lateral ventricle (LV) of the adult mouse forebrain. Retroviral overexpression of Sox6 in NSPCs increases the number of primary and secondary neurospheres and inhibits cell differentiation. This effect is accompanied with increased expression of Hes1 and Bcl-2 and Akt phosphorylation, thus suggesting a role for Sox6 in promoting cell survival and/or self-renewal ability. Constitutive activation of the transcription factor Stat3 results in up-regulation of Sox6 expression and chromatin immunoprecipitation analysis showed that MIF increases Stat3 binding to the Sox6 promoter in NSPCs, indicating that Stat3 stimulates Sox6 expression downstream of MIF. Finally, the ability of MIF to increase the number of primary and secondary neurospheres is inhibited by Sox6 gene silencing. Collectively, our data identify Sox6 as an important downstream effector of MIF signaling in stemness maintenance of NSPCs.

MiR-499 regulates cell proliferation and apoptosis during late-stage cardiac differentiation via Sox6 and cyclin D1

Background

MiR-499 is a cardiac-abundant miRNA. However, the biological functions of miR-499 in differentiated cardiomyocytes or in the cardiomyocyte differentiation process is not very clear. Sox6 is believed to be one of its targets, and is also believed to play a role in cardiac differentiation. Therefore, our aim was to investigate the association between Sox6 and miR-499 during cardiac differentiation.

Methodology/Principal Findings

Using a well-established invitro cardiomyocyte differentiation system, mouse P19CL6 cells, we found that miR-499 was highly expressed in the late stage of cardiac differentiation. In cells stably transfected with miR-499 (P-499 cells), it was found that miR-499 could promote the differentiation into cardiomyocytes at the early stage of cardiac differentiation. Notably, cell viability assay, EdU incorporation assay, and cell cycle profile analysis all showed that the P-499 cells displayed the distinctive feature of hyperplastic growth. Further investigation confirmed that miR-499 could promote neonatal rat cardiomyocyte proliferation. MiR-499 knock-down enhanced apoptosis in the late differentiation stage in P19CL6 cells, but overexpression of miR-499 resulted in a decrease in the apoptosis rate. Sox6 was identified as a direct target of miR-499 and its expression was detected from day 8 or day 10 of cardiac differentiation of P19CL6 cells. Sox6 played a role in cell viability, inhibited cell proliferation and promoted cell apoptosis in P19CL6 cells and cardiomyocytes. The overexpression of Sox6 could reverse the proliferation and anti-apoptosis effects of miR-499. It was also found that miR-499 might exert its function by regulating cyclin D1 via its influence on Sox6.

Conclusions/Significance

miR-499 probably regulates the proliferation and apoptosis of P19CL6 cells in the late stage of cardiac differentiation via its effects on Sox6 and cyclin D1.

New insights into osteogenic and chondrogenic differentiation of human bone marrow mesenchymal stem cells and their potential clinical applications for bone regeneration in pediatric orthopaedics

Human mesenchymal stem cells (hMSCs) are pluripotent adult stem cells capable of being differentiated into osteoblasts, adipocytes, and chondrocytes. The osteogenic differentiation of hMSCs is regulated either by systemic hormones or by local growth factors able to induce specific intracellular signal pathways that modify the expression and activity of several transcription factors. Runt-related transcription factor 2 (Runx2) and Wnt signaling-related molecules are the major factors critically involved in the osteogenic differentiation process by hMSCs, and SRY-related high-mobility-group (HMG) box transcription factor 9 (SOX9) is involved in the chondrogenic one. hMSCs have generated a great interest in the field of regenerative medicine, particularly in bone regeneration. In this paper, we focused our attention on the molecular mechanisms involved in osteogenic and chondrogenic differentiation of hMSC, and the potential clinical use of hMSCs in osteoarticular pediatric disease characterized by fracture nonunion and pseudarthrosis.

Silencing of the Drosophila ortholog of SOX5 in heart leads to cardiac dysfunction as detected by optical coherence tomography

The SRY-related HMG-box 5 (SOX5) gene encodes a member of the SOX family of transcription factors. Recently, genome-wide association studies have implicated SOX5 as a candidate gene for susceptibility to four cardiac-related endophenotypes: higher resting heart rate (HR), the electrocardiographic PR interval, atrial fibrillation and left ventricular mass. We have determined that human SOX5 has a highly conserved Drosophila ortholog, Sox102F, and have employed transgenic Drosophila models to quantitatively measure cardiac function in adult flies. For this purpose, we have developed a high-speed and ultrahigh-resolution optical coherence tomography imaging system, which enables rapid cross-sectional imaging of the heart tube over various cardiac cycles for the measurement of cardiac structural and dynamical parameters such as HR, dimensions and areas of heart chambers, cardiac wall thickness and wall velocities. We have found that the silencing of Sox102F resulted in a significant decrease in HR, heart chamber size and cardiac wall velocities, and a significant increase in cardiac wall thickness that was accompanied by disrupted myofibril structure in adult flies. In addition, the silencing of Sox102F in the wing led to increased L2, L3 and wing marginal veins and increased and disorganized expression of wingless, the central component of the Wnt signaling pathway. Collectively, the silencing of Sox102F resulted in severe cardiac dysfunction and structural defects with disrupted Wnt signaling transduction in flies. This implicates an important functional role for SOX5 in heart and suggests that the alterations in SOX5 levels may contribute to the pathogenesis of multiple cardiac diseases or traits.

Usefulness of polyglycolic acid-polypropylene composite scaffolds for three-dimensional cartilage regeneration in a large-animal autograft model

BACKGROUND

Approaches to auricular reconstruction have shown improved outcome when a basic fibroblast growth factor (bFGF) slow-release system and fibrin spraying are combined with biodegradable polymers. More complex, three-dimensional structures, such as those that replicate the human auricle, are often lost because of biodegradation of the synthetic scaffold.

METHODS

To improve the mechanical strength of regenerated cartilage, the authors grafted canine autologous chondrocytes after seeding onto scaffolds made of a complex of polyglycolic acid and polypropylene, incorporating a slow-release bFGF system with a fibrin spray coating.

RESULTS

Five weeks after grafting, thicker cartilage with increased bending stress was obtained with the slow-release bFGF. In a three-polyglycolic acid-layer construct sandwiched around polypropylene, simulating a three-dimensional auricular structure, greater cartilage regeneration and angiogenesis were found around the implant. Sox5-positive cells were identified, indicative of maturation of neocartilage with chondroblast proliferation.

CONCLUSION

These results support the usefulness of combining absorbable and nonabsorbable materials (polyglycolic acid and polypropylene) in composite scaffolds for autologous cartilage regeneration in a large-animal autograft model.

Progenitors of the protochordate ocellus as an evolutionary origin of the neural crest

The neural crest represents a highly multipotent population of embryonic stem cells found only in vertebrate embryos. Acquisition of the neural crest during the evolution of vertebrates was a great advantage, providing Chordata animals with the first cellular cartilage, bone, dentition, advanced nervous system and other innovations. Today not much is known about the evolutionary origin of neural crest cells. Here we propose a novel scenario in which the neural crest originates from neuroectodermal progenitors of the pigmented ocelli in Amphioxus-like animals. We suggest that because of changes in photoreception needs, these multipotent progenitors of photoreceptors gained the ability to migrate outside of the central nervous system and subsequently started to give rise to neural, glial and pigmented progeny at the periphery.

Induction of mesenchymal stem cell chondrogenesis by polyacrylate substrates

Mesenchymal stem cells (MSCs) can generate chondrocytes in vitro, but typically need to be cultured as aggregates in the presence of transforming growth factor beta (TGF-β), which makes scale-up difficult. Here we investigated if polyacrylate substrates modelled on the functional group composition and distribution of the Arg-Gly-Asp (RGD) integrin-binding site could induce MSCs to undergo chondrogenesis in the absence of exogenous TGF-β. Within a few days of culture on the biomimetic polyacrylates, both mouse and human MSCs, and a mesenchymal-like mouse-kidney-derived stem cell line, began to form multi-layered aggregates and started to express the chondrocyte-specific markers, Sox9, collagen II and aggrecan. Moreover, collagen II tended to be expressed in the centre of the aggregates, similarly to developing limb buds in vivo. Surface analysis of the substrates indicated that those with the highest surface amine content were most effective at promoting MSC chondrogenesis. These results highlight the importance of surface group functionality and the distribution of those groups in the design of substrates to induce MSC chondrogenesis.

Cartilage-specific over-expression of CCN family member 2/connective tissue growth factor (CCN2/CTGF) stimulates insulin-like growth factor expression and bone growth

Previously we showed that CCN family member 2/connective tissue growth factor (CCN2) promotes the proliferation, differentiation, and maturation of growth cartilage cells in vitro. To elucidate the specific role and molecular mechanism of CCN2 in cartilage development in vivo, in the present study we generated transgenic mice overexpressing CCN2 and analyzed them with respect to cartilage and bone development. Transgenic mice were generated expressing a ccn2/lacZ fusion gene in cartilage under the control of the 6 kb-Col2a1-enhancer/promoter. Changes in cartilage and bone development were analyzed histologically and immunohistologically and also by micro CT. Primary chondrocytes as well as limb bud mesenchymal cells were cultured and analyzed for changes in expression of cartilage-related genes, and non-transgenic chondrocytes were treated in culture with recombinant CCN2. Newborn transgenic mice showed extended length of their long bones, increased content of proteoglycans and collagen II accumulation. Micro-CT analysis of transgenic bones indicated increases in bone thickness and mineral density. Chondrocyte proliferation was enhanced in the transgenic cartilage. In in vitro short-term cultures of transgenic chondrocytes, the expression of col2a1, aggrecan and ccn2 genes was substantially enhanced; and in long-term cultures the expression levels of these genes were further enhanced. Also, in vitro chondrogenesis was strongly enhanced. IGF-I and IGF-II mRNA levels were elevated in transgenic chondrocytes, and treatment of non-transgenic chondrocytes with recombinant CCN2 stimulated the expression of these mRNA. The addition of CCN2 to non-transgenic chondrocytes induced the phosphorylation of IGFR, and ccn2-overexpressing chondrocytes showed enhanced phosphorylation of IGFR. Our data indicates that the observed effects of CCN2 may be mediated in part by CCN2-induced overexpression of IGF-I and IGF-II. These findings indicate that CCN2-overexpression in transgenic mice accelerated the endochondral ossification processes, resulting in increased length of their long bones. Our results also indicate the possible involvement of locally enhanced IGF-I or IGF-II in this extended bone growth.

Interleukin-27 suppresses osteoclastogenesis via induction of interferon-γ

Interleukin (IL)-27 is a heterodimeric cytokine that is known to have both stimulatory and inhibitory functions during immune responses. We investigated the effects of IL-27 on arthritis and bone erosion in the murine collagen-induced arthritis (CIA) model. We demonstrate that the inhibitory effect of IL-27 on osteoclastogenesis is associated with interferon-γ (IFN-γ) production by using an IFN-γ knockout mouse model. The IL-27-Fc was injected into both CIA and IFN-γ-deficient mice. The effects of IL-27-Fc on osteoclast differentiation were evaluated both in vitro and in vivo. The IL-27-Fc-injected mice showed significantly lower arthritis indices and fewer tartrate-resistant acid-phosphatase-positive osteoclasts in their joint tissues than untreated mice. Interleukin-27 inhibited osteoclastogenesis from bone marrow-derived mononuclear cells in vitro, which was counteracted by the addition of anti-IFN-γ antibody. The IL-27-Fc did not affect arthritis in IFN-γ knockout mice. Interleukin-27 also suppressed osteoclast differentiation in human and intriguingly, it could promote the expression of IFN-γ on priming osteoclasts. These results imply that IL-27 suppressed the generation of CIA and osteoclastogenesis, which were mediated by the induction of IFN-γ.

Genome-wide map of quantified epigenetic changes during in vitro chondrogenic differentiation of primary human mesenchymal stem cells

Background

For safe clinical application of engineered cartilage made from mesenchymal stem cells (MSCs), molecular mechanisms for chondrogenic differentiation must be known in detail. Changes in gene expression and extracellular matrix synthesis have been extensively studied, but the epigenomic modifications underlying these changes have not been described. To this end we performed whole-genome chromatin immunoprecipitation and deep sequencing to quantify six histone modifications, reduced representation bisulphite sequencing to quantify DNA methylation and mRNA microarrays to quantify gene expression before and after 7 days of chondrogenic differentiation of MSCs in an alginate scaffold. To add to the clinical relevance of our observations, the study is based on primary bone marrow-derived MSCs from four donors, allowing us to investigate inter-individual variations.

Results

We see two levels of relationship between epigenetic marking and gene expression. First, a large number of genes ontogenetically linked to MSC properties and the musculoskeletal system are epigenetically prepatterned by moderate changes in H3K4me3 and H3K9ac near transcription start sites. Most of these genes remain transcriptionally unaltered. Second, transcriptionally upregulated genes, more closely associated with chondrogenesis, are marked by H3K36me3 in gene bodies, highly increased H3K4me3 and H3K9ac on promoters and 5' end of genes, and increased H3K27ac and H3K4me1 marking in at least one enhancer region per upregulated gene. Within the 7-day time frame, changes in promoter DNA methylation do not correlate significantly with changes in gene expression. Inter-donor variability analysis shows high level of similarity between the donors for this data set.

Conclusions

Histone modifications, rather than DNA methylation, provide the primary epigenetic control of early differentiation of MSCs towards the chondrogenic lineage.

Differential gene expression by Osterix knockdown in mouse chondrogenic ATDC5 cells

Osterix (Osx) is a transcription factor required for osteoblast differentiation during intramembranous and endochondral ossification. Recently, several reports have described novel functions of Osx in chondrocyte differentiation. In an in vitro study, in which the effects of Osx gene silencing were examined in mouse chondrogenic ATDC5 cells, chondrocyte marker genes were found to be expressionally downregulated and chondrocyte differentiation reduced. On the other hand, in vivo studies based on chondrocyte-specific Osx knockouts demonstrated impaired endochondral bone formation with delayed chondrocyte differentiation and reduced cartilage matrix ossification. However, little is known about the mechanism or targets of Osx involved in the control of chondrocyte differentiation. Here, we attempted to high-density of Affymetrix GeneChip microarray to investigate global gene expression profile changes caused by Osx knockdown in ATDC5 chondrocytes. The mRNA expressions of 112 genes were significantly modified by Osx knockdown: 68 genes were upregulated and 44 genes downregulated. Functional categories of gene expression classified by gene ontology demonstrated that genes related to cell adhesion, development, and signal transduction were highly affected by Osx knockdown. The expressions of differential genes, such as Sfrp2, Sema3a, Nox4, Rgs4, Zfp521, Has2, Sox6, Scn2a1, Sirpa, and Thbs2, were validated by quantitative real-time PCR. This study shows that expression profiling can be used to identify genes that are transcriptionally modified following Osx knockdown and to reveal the molecular mechanism of chondrocyte differentiation regulated by Osx.

Development of the endochondral skeleton

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.

Grape-seed proanthocyanidin extract as suppressors of bone destruction in inflammatory autoimmune arthritis

Chronic autoimmune inflammation, which is commonly observed in rheumatoid arthritis (RA), disrupts the delicate balance between bone resorption and formation causing thedestruction of the bone and joints. We undertook this study to verify the effects of natural grape-seed proanthocyanidin extract (GSPE), an antioxidant, on chronic inflammation and bone destruction. GSPE administration ameliorated the arthritic symptoms of collagen-induced arthritis (CIA), which are representative of cartilage and bone destruction. GSPE treatment reduced the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and osteoclast activity and increased differentiation of mature osteoblasts. Receptor activator of NFκB ligand expression in fibroblasts from RA patients was abrogated with GSPE treatment. GSPE blocked human peripheral blood mononuclear cell-derived osteoclastogenesis and acted as an antioxidant. GSPE improved the arthritic manifestations of CIA mice by simultaneously suppressing osteoclast differentiation and promoting osteoblast differentiation. Our results suggest that GSPE may be beneficial for the treatment of inflammation-associated bone destruction.

Haploinsufficiency of SOX5, a member of the SOX (SRY-related HMG-box) family of transcription factors is a cause of intellectual disability

Intellectual disability (ID) is a clinically and genetically heterogeneous condition; the cause is unknown in most non-specific and sporadic cases. To establish an etiological basis in those patients represents a difficult challenge. Over the last years it has become apparent that chromosomal rearrangements below the detection level of conventional karyotyping contribute significantly to the cause of ID. We present three patients with non-specific intellectual disability who all have overlapping microdeletions in the chromosomal region 12p12.1. De novo occurrence of the deletion could be proven in the two cases from which parental samples were available. All three identified deletions have different breakpoints and range in size from 120 kb to 4.9 Mb. The smallest deletion helps to narrow down the critical region to a genomic segment (chr12:23,924,800-24,041,698, build 37/hg19) encompassing only one gene, SOX5. SOX5 is a member of the SOX (SRY-related HMG-box) family of transcription factors shown to play roles in chondroblast function, oligodendrocyte differentiation and migration, as well as ensuring proper development of specific neuronal cell types. Because of these biological functions, mutations in SOX5 are predicted to cause complex disease syndromes, as it is the case for other SOX genes, but such mutations have not yet been identified. Our findings indicate that haploinsufficiency of SOX5 is a cause of intellectual disability without any striking physical anomalies.

The genetic pleiotropy of musculoskeletal aging

Musculoskeletal aging is detrimental to multiple bodily functions and starts early, probably in the fourth decade of an individual's life. Sarcopenia is a health problem that is expected to only increase as a greater portion of the population lives longer; prevalence of the related musculoskeletal diseases is similarly expected to increase. Unraveling the biological and biomechanical associations and molecular mechanisms underlying these diseases represents a formidable challenge. There are two major problems making disentangling the biological complexity of musculoskeletal aging difficult: (a) it is a systemic, rather than "compartmental," problem, which should be approached accordingly, and (b) the aging per se is neither well defined nor reliably measurable. A unique challenge of studying any age-related condition is a need of distinguishing between the "norm" and "pathology," which are interwoven throughout the aging organism. We argue that detecting genes with pleiotropic functions in musculoskeletal aging is needed to provide insights into the potential biological mechanisms underlying inter-individual differences insusceptibility to the musculoskeletal diseases. However, exploring pleiotropic relationships among the system's components is challenging both methodologically and conceptually. We aimed to focus on genetic aspects of the cross-talk between muscle and its "neighboring" tissues and organs (tendon, bone, and cartilage), and to explore the role of genetics to find the new molecular links between skeletal muscle and other parts of the "musculoskeleton." Identification of significant genetic variants underlying the musculoskeletal system's aging is now possible more than ever due to the currently available advanced genomic technologies. In summary, a "holistic" genetic approach is needed to study the systems's normal functioning and the disease predisposition in order to improve musculoskeletal health.

Mapping genetic variants associated with beta-adrenergic responses in inbred mice

β-blockers and β-agonists are primarily used to treat cardiovascular diseases. Inter-individual variability in response to both drug classes is well recognized, yet the identity and relative contribution of the genetic players involved are poorly understood. This work is the first genome-wide association study (GWAS) addressing the values and susceptibility of cardiovascular-related traits to a selective β₁-blocker, Atenolol (ate), and a β-agonist, Isoproterenol (iso). The phenotypic dataset consisted of 27 highly heritable traits, each measured across 22 inbred mouse strains and four pharmacological conditions. The genotypic panel comprised 79922 informative SNPs of the mouse HapMap resource. Associations were mapped by Efficient Mixed Model Association (EMMA), a method that corrects for the population structure and genetic relatedness of the various strains. A total of 205 separate genome-wide scans were analyzed. The most significant hits include three candidate loci related to cardiac and body weight, three loci for electrocardiographic (ECG) values, two loci for the susceptibility of atrial weight index to iso, four loci for the susceptibility of systolic blood pressure (SBP) to perturbations of the β-adrenergic system, and one locus for the responsiveness of QTc (p<10⁻⁸). An additional 60 loci were suggestive for one or the other of the 27 traits, while 46 others were suggestive for one or the other drug effects (p<10⁻⁶). Most hits tagged unexpected regions, yet at least two loci for the susceptibility of SBP to β-adrenergic drugs pointed at members of the hypothalamic-pituitary-thyroid axis. Loci for cardiac-related traits were preferentially enriched in genes expressed in the heart, while 23% of the testable loci were replicated with datasets of the Mouse Phenome Database (MPD). Altogether these data and validation tests indicate that the mapped loci are relevant to the traits and responses studied.

Haploinsufficiency of SOX5 at 12p12.1 is associated with developmental delays with prominent language delay, behavior problems, and mild dysmorphic features

SOX5 encodes a transcription factor involved in the regulation of chondrogenesis and the development of the nervous system. Despite its important developmental roles, SOX5 disruption has yet to be associated with human disease. We report one individual with a reciprocal translocation breakpoint within SOX5, eight individuals with intragenic SOX5 deletions (four are apparently de novo and one inherited from an affected parent), and seven individuals with larger 12p12 deletions encompassing SOX5. Common features in these subjects include prominent speech delay, intellectual disability, behavior abnormalities, and dysmorphic features. The phenotypic impact of the deletions may depend on the location of the deletion and, consequently, which of the three major SOX5 protein isoforms are affected. One intragenic deletion, involving only untranslated exons, was present in a more mildly affected subject, was inherited from a healthy parent and grandparent, and is similar to a deletion found in a control cohort. Therefore, some intragenic SOX5 deletions may have minimal phenotypic effect. Based on the location of the deletions in the subjects compared to the controls, the de novo nature of most of these deletions, and the phenotypic similarities among cases, SOX5 appears to be a dosage-sensitive, developmentally important gene.

The protein kinase MLTK regulates chondrogenesis by inducing the transcription factor Sox6

Sox9 acts together with Sox5 or Sox6 as a master regulator for chondrogenesis; however, the inter-relationship among these transcription factors remains unclear. Here, we show that the protein kinase MLTK plays an essential role in the onset of chondrogenesis through triggering the induction of Sox6 expression by Sox9. We find that knockdown of MLTK in Xenopus embryos results in drastic loss of craniofacial cartilages without defects in neural crest development. We also find that Sox6 is specifically induced during the onset of chondrogenesis, and that the Sox6 induction is inhibited by MLTK knockdown. Remarkably, Sox6 knockdown phenocopies MLTK knockdown. Moreover, we find that ectopic expression of MLTK induces Sox6 expression in a Sox9-dependent manner. Our data suggest that p38 and JNK pathways function downstream of MLTK during chondrogenesis. These results identify MLTK as a novel key regulator of chondrogenesis, and reveal its action mechanism in chondrocyte differentiation during embryonic development.

L-Sox5 and Sox6 proteins enhance chondrogenic miR-140 microRNA expression by strengthening dimeric Sox9 activity

Sox9 plays a critical role in early chondrocyte initiation and promotion as well as repression of later maturation. Fellow Sox family members L-Sox5 and Sox6 also function as regulators of cartilage development by boosting Sox9 activation of chondrocyte-specific genes such as Col2a1 and Agc1; however, the regulatory mechanism and other target genes are largely unknown. MicroRNAs are a class of short, non-coding RNAs that act as negative regulators of gene expression by promoting target mRNA degradation and/or repressing translation. Analysis of genetically modified mice identified miR-140 as a cartilage-specific microRNA that could be a critical regulator of cartilage development and homeostasis. Recent findings suggest Sox9 promotes miR-140 expression, although the detailed mechanisms are not fully understood. In this study we demonstrate that the proximal upstream region of pri-miR-140 has chondrogenic promoter activity in vivo. We found an L-Sox5/Sox6/Sox9 (Sox trio) response element and detailed binding site in the promoter region. Furthermore, detailed analysis suggests the DNA binding and/or transactivation ability of Sox9 as a homodimer is boosted by L-Sox5 and Sox6. These findings provide new insight into cartilage-specific gene regulation by the Sox trio.

Intrathymic programming of effector fates in three molecularly distinct γδ T cell subtypes

Innate γδ T cells function in the early phase of immune responses. Although innate γδ T cells have often been studied as one homogenous population, they can be functionally classified into effector subsets on the basis of the production of signature cytokines, analogous to adaptive helper T cell subsets. However, unlike the function of adaptive T cells, γδ effector T cell function correlates with genomically encoded T cell antigen receptor (TCR) chains, which suggests that clonal TCR selection is not the main determinant of the differentiation of γδ effector cells. A high-resolution transcriptome analysis of all emergent γδ thymocyte subsets segregated on the basis of use of the TCR γ-chain or δ-chain indicated the existence of three separate subtypes of γδ effector cells in the thymus. The immature γδ subsets were distinguished by unique transcription-factor modules that program effector function.

Fine mapping of a QTL for ear size on porcine chromosome 5 and identification of high mobility group AT-hook 2 (HMGA2) as a positional candidate gene

Background

Ear size and shape are distinct conformation characteristics of pig breeds. Previously, we identified a significant quantitative trait locus (QTL) influencing ear surface on pig chromosome 5 in a White Duroc × Erhualian F₂ resource population. This QTL explained more than 17% of the phenotypic variance.

Methods

Four new markers on pig chromosome 5 were genotyped across this F₂ population. RT-PCR was performed to obtain expression profiles of different candidate genes in ear tissue. Standard association test, marker-assisted association test and F-drop test were applied to determine the effects of single nucleotide polymorphisms (SNP) on ear size. Three synthetic commercial lines were also used for the association test.

Results

We refined the QTL to an 8.7-cM interval and identified three positional candidate genes i.e. HMGA2, SOX5 and PTHLH that are expressed in ear tissue. Seven SNP within these three candidate genes were selected and genotyped in the F₂ population. Of the seven SNP, HMGA2 SNP (JF748727: g.2836 A > G) showed the strongest association with ear size in the standard association test and marker-assisted association test. With the F-drop test, F value decreased by more than 97% only when the genotypes of HMGA2 g.2836 A > G were included as a fixed effect. Furthermore, the significant association between g.2836 A > G and ear size was also demonstrated in the synthetic commercial Sutai pig line. The haplotype-based association test showed that the phenotypic variance explained by HMGA2 was similar to that explained by the QTL and at a much higher level than by SOX5. More interestingly, HMGA2 is also located within the dog orthologous chromosome region, which has been shown to be associated with ear type and size.

Conclusions

HMGA2 was the closest gene with a potential functional effect to the QTL or marker for ear size on chromosome 5. This study will contribute to identify the causative gene and mutation underlying this QTL.

Vinculin functions as regulator of chondrogenesis

To identify the genes involved in chondrocytic differentiation, we applied gene trap mutagenesis to a murine mesenchymal chondrogenic cell line ATDC5 and isolated a clone in which the gene encoding vinculin was trapped. The trapped allele was assumed to express a fusion protein containing a truncated vinculin lacking the tail domain and the geo product derived from the trap vector. The truncated vinculin was suggested to exert a dominant negative effect. Impaired functioning of vinculin caused by gene trapping in ATDC5 cells or knockdown in primary chondrocytes resulted in the reduced expression of chondrocyte-specific genes, including Col2a1, aggrecan, and Col10a1. The expression of Runx2 also was suppressed by the dysfunctional vinculin. On the other hand, the expression of Sox9, encoding a key transcription factor for chondrogenesis, was retained. Knockdown of vinculin in metatarsal organ cultures impaired the growth of the explants and reduced the expression of Col2a1 and aggrecan. Gene trapping or knockdown of vinculin decreased the phosphorylation of ERK1/2 but increased that of Src homology 2 domain-containing tyrosine phosphatase 2 (SHP2) and Akt during chondrocytic differentiation, suggesting a disturbance of signaling by insulin-like growth factor I (IGF-I). Knockdown of vinculin in the metatarsal organ culture abrogated the IGF-I-induced growth and inhibited the up-regulation of Col2a1 and aggrecan expression by IGF-I. Loss of vinculin function in differentiating chondrocytes impaired the activation of the p38 MAPK pathway also, suggesting its involvement in the regulation of chondrogenesis by vinculin. Our results indicate a tissue-specific function of vinculin in cartilage whereby it controls chondrocytic differentiation.

MiR-194 regulates chondrogenic differentiation of human adipose-derived stem cells by targeting Sox5

Osteoarthritis, also known as degenerative arthritis or degenerative joint disease, causes pain and disability worldwide. Cartilage regeneration is key to finding a cure for this disease. Adipose-derived stem cells (ASCs) are capable of differentiating into cartilage lineages in vitro and they have shown promise in the field of regenerative medicine. However, the underlying mechanisms remain unclear. In this study, we demonstrated that miR-194 levels gradually decreased during the chondrogenic differentiation of human ASCs (hASCs). After predicting the target of miR-194 using Pictar and Targetscan, we hypothesized that Sox5 is potentially the key link between miR-194 and the chondrogenesis of ASCs. Initially, we demonstrated that Sox5 is a target of miR194 according to luciferase assay analysis. We further demonstrated that the differentiation of ASCs can be controlled by miR-194 through gain or loss of function experiments, and we observed that the down-regulation of miR-194 increases its direct target gene, Sox5, and results in enhanced chondrogenic differentiation of hASCs, whereas up-regulation decreases Sox5 and inhibits chondrogenesis. We also found that miR-194 correlates with Sox5 in osteoarthritis. These findings, taken together, are the first to illustrate the critical role of miR-194 in hASC chondrogenesis, and may provide novel insight beneficial to cell manipulation methods during cartilage regeneration.

Genetic loci on chromosomes 4q25, 7p31, and 12p12 are associated with onset of lone atrial fibrillation before the age of 40 years

BACKGROUND

Three distinct genetic loci on chromosomes 1q21, 4q25, and 16q22 have been associated with atrial fibrillation (AF) in genome-wide association studies (GWAS). Five additional loci have been associated primarily with the PR interval and subsequently with AF. We aimed to investigate if 8 single nucleotide polymorphisms (SNPs), representing the 8 genomic loci previously linked with AF in genome-wide association studies, were associated with early-onset lone AF.

METHODS

We included 209 patients with early-onset lone AF, and a control group consisting of 534 individuals free of AF. The 8 SNPs were genotyped using TaqMan assays (Applied Biosystems, Foster City, CA).

RESULTS

Three SNPs were found to be significantly associated with early-onset lone AF: rs2200733 closest to PITX2 (odds ratio [OR], 1.62; 95% confidence interval [CI], 1.16-2.27; P = 0.004), rs3807989 near to CAV1 (OR 1.35; 95% CI, 1.06-1.72; P = 0.015), and rs11047543 near to SOX5 (OR 1.70; 95% CI, 1.18-2.44; P = 0.004). When correcting for multiple testing, rs2200733 and rs11047543 were still significantly associated with AF.

CONCLUSIONS

Three SNPs, rs2200733 (4q25), rs3807989 (7p31), and rs11047543 (12p12), were associated with early-onset lone AF. All 3 SNPs are positioned close to genes that in previous studies have been demonstrated to be important for cardiac morphology/development, thereby suggesting a link between these SNPs and structural heart disease. Our results however, indicate that variants in these 3 loci are associated with AF through mechanisms that do not involve major structural abnormalities in the heart.

Genetic variants in the SOX6 gene are associated with bone mineral density in both Caucasian and Chinese populations

SUMMARY

Given the biological function of SOX6 and recent genome-wide association finding, we performed a fine-mapping association analyses to investigate the relationship between SOX6 and BMD both in Caucasian and Chinese populations. We identified many single-nucleotide polymorphisms (SNPs) within or near the SOX6 gene to be significantly associated with hip bone mineral density (BMD).

INTRODUCTION

SOX6 gene is an essential transcription factor in chondrogenesis and cartilage formation. Recent genome-wide association studies (GWAS) detected a SNP (rs7117858) located at the downstream of SOX6 significantly associated with hip BMD.

METHODS

Given the biological function of SOX6 and the GWAS finding, we considered SOX6 as a new candidate for BMD and osteoporosis. Therefore, in this study, we performed a fine-mapping association analyses to investigate the relationship between SNPs within and near the SOX6 gene and BMD at both hip and spine. A total of 301 SNPs were tested in two independent US Caucasian populations (2,286 and 1,000 unrelated subjects, respectively) and a Chinese population (1,627 unrelated Han subjects).

RESULTS

We confirmed that the previously reported rs7117858-A was associated with reduced hip BMD, with combined P value of 2.45 × 10(-4). Besides this SNP, we identified another 19 SNPs within or near the SOX6 gene to be significantly associated with hip BMD after false discovery rate adjustment. The most significant SNP was rs1347677 located at the intron 3 (P = 3.15 × 10(-7)). Seven additional SNPs in high linkage disequilibrium with rs1347677 were also significantly associated with hip BMD. SNPs in SOX6 showed significant skeletal site specificity since no SNP was detected to be associated with spine BMD.

CONCLUSION

Our study identified many SNPs in the SOX6 gene associated with hip BMD even across different ethnicities, which further highlighted the importance of the SOX6 gene influencing BMD variation and provided more information to the understanding of the genetic architecture of osteoporosis.

How selective sweeps in domestic animals provide new insight into biological mechanisms

Genetic studies of domestic animals are of general interest because there is more phenotypic diversity to explore in these species than in any experimental organism. Some mutations with favourable phenotypic effects have been highly enriched and gone through selective sweeps during the process of domestication and selective breeding. Three such selective sweeps are described in this review. All three mutations are intronic and constitute cis-acting regulatory mutations. Two of the mutations constitute structural changes (one duplication and one copy number expansion). These examples illustrate a general trend that noncoding mutations and structural changes have both contributed significantly to the evolution of phenotypic diversity in domestic animals. How the molecular characterization of trait loci in domestic animals can provide new basic knowledge of relevance for human medicine is discussed.

SOX trio-co-transduced adipose stem cells in fibrin gel to enhance cartilage repair and delay the progression of osteoarthritis in the rat

The aim of this study was to test the hypotheses that retroviral gene transfer of SOX trio enhances the in vitro chondrogenic differentiation of ASCs, and that SOX trio-co-transduced ASCs in fibrin gel promote the healing of osteochondral defects, and arrest the progression of surgically-induced osteoarthritis in a rat model. ASCs isolated from inguinal fat in rats were transduced with SOX trio genes using retrovirus, and further cultured in vitro in pellets for 21 days, then analyzed for gene and protein expression of SOX trio and chondrogenic markers. SOX trio-co-transduced ASCs in fibrin gel were implanted on the osteochondral defect created in the patellar groove of the distal femur, and also injected into the knee joints of rats with surgically-induced osteoarthritis. Rats were sacrificed after 8 weeks, and analyzed grossly and microscopically. After 21 days, ASCs transduced with SOX-5, -6, or -9 had hundreds-fold greater gene expression of each gene compared with the control with the SOX protein expression matching gene expression. SOX trio-co-transduction significantly increased GAG contents as well as type II collagen gene and protein expression. ASCs co-transduced with SOX trio significantly promoted the in vivo cartilage healing in osteochondral defect model, and prevented the progression of degenerative changes in surgically-induced osteoarthritis.

Myostatin (GDF-8) inhibits chondrogenesis and chondrocyte proliferation in vitro by suppressing Sox-9 expression

Here, we investigate a possible direct role for myostatin in chondrogenesis. First, we examined the effects of myostatin on the proliferation of bone marrow stromal cells (BMSCs) and epiphyseal growth plate (EGP) chondrocytes (EGPCs) isolated from myostatin-deficient mice. Results show that myostatin deficiency is associated with a significant (P < 0.001) increase in proliferation of both BMSCs (+25%) and EGPCs (+35%) compared with wild-type cells. Next, we examined the effects of myostatin treatment on chondrogenic differentiation of BMSCs. These experiments show that myostatin treatment starting at either 0 or 48 h induces a significant decrease in collagen type II protein synthesis by 31% (P < 0.001) and 25% (P < 0.05), respectively. Real-time PCR reveals significant (P < 0.01) down regulation of Sox9 mRNA expression with 10 and 100 ng/ml treatments. Together, these findings suggest that myostatin has direct effects on chondrogenesis, and may, therefore, represent a potential therapeutic target for improving bone repair.

Pannexin 3 is a novel target for Runx2, expressed by osteoblasts and mature growth plate chondrocytes

Pannexins are a class of chordate channel proteins identified by their homology to insect gap junction proteins. The pannexin family consists of three members, Panx1, Panx2, and Panx3, and the role each of these proteins plays in cellular processes is still under investigation. Previous reports of Panx3 expression indicate enrichment in skeletal tissues, so we have further investigated this distribution by surveying the developing mouse embryo with immunofluorescence. High levels of Panx3 were detected in intramembranous craniofacial flat bones, as well as long bones of the appendicular and axial skeleton. This distribution is the result of expression in both osteoblasts and hypertrophic chondrocytes. Furthermore, the Panx3 promoter contains putative binding sites for transcription factors involved in bone formation, and we show that the sequence between bases -275 and -283 is responsive to Runx2 activation. Taken together, our data suggests that Panx3 may serve an important role in bone development, and is a novel target for Runx2-dependent signaling.

Electroporation-mediated transfer of SOX trio genes (SOX-5, SOX-6, and SOX-9) to enhance the chondrogenesis of mesenchymal stem cells

The purpose of this study was to test the hypothesis that the SOX trio genes (SOX-5, SOX-6, and SOX-9) have a lower level of expression during the chondrogenic differentiation of mesenchymal stem cells (MSCs) compared with chondrocytes and that the electroporation-mediated gene transfer of SOX trio promotes chondrogenesis from human MSCs. An in vitro pellet culture was carried out using MSCs or chondrocytes at passage 3 and analyzed after 7 and 21 days. Then, MSCs were transfected with SOX trio genes and analyzed for the expression of chondrogenic markers after 21 days of in vitro culture. Without transforming growth factor-β1, the untransfected MSCs had a lower level of SOX trio gene and protein expression than chondrocytes. However, the level of SOX-9 gene expression increased in MSCs when treated with transforming growth factor-β1. GAG level significantly increased 7-fold in MSCs co-transfected with SOX trio, which was corroborated by Safranin-O staining. SOX trio co-transfection significantly increased COL2A1 gene and protein and decreased COL10A1 protein in MSCs. It is concluded that the SOX trio have a significantly lower expression in human MSCs than in chondrocytes and that the electroporation-mediated co-transfection of SOX trio enhances chondrogenesis and suppresses hypertrophy of human MSCs.

The regulation of valvular and vascular sclerosis by osteogenic morphogens

Vascular calcification increasingly afflicts our aging, dysmetabolic population. Once considered only a passive process of dead and dying cells, vascular calcification has now emerged as a highly regulated form of biomineralization organized by collagenous and elastin extracellular matrices. During skeletal bone formation, paracrine epithelial-mesenchymal and endothelial-mesenchymal interactions control osteochondrocytic differentiation of multipotent mesenchymal progenitor cells. These paracrine osteogenic signals, mediated by potent morphogens of the bone morphogenetic protein and wingless-type MMTV integration site family member (Wnt) superfamilies, are also active in the programming of arterial osteoprogenitor cells during vascular and valve calcification. Inflammatory cytokines, reactive oxygen species, and oxylipids-increased in the clinical settings of atherosclerosis, diabetes, and uremia that promote arteriosclerotic calcification-elicit the ectopic vascular activation of osteogenic morphogens. Specific extracellular and intracellular inhibitors of bone morphogenetic protein-Wnt signaling have been identified as contributing to the regulation of osteogenic mineralization during development and disease. These inhibitory pathways and their regulators afford the development of novel therapeutic strategies to prevent and treat valve and vascular sclerosis.

Genome-wide mapping of Sox6 binding sites in skeletal muscle reveals both direct and indirect regulation of muscle terminal differentiation by Sox6

Background

Sox6 is a multi-faceted transcription factor involved in the terminal differentiation of many different cell types in vertebrates. It has been suggested that in mice as well as in zebrafish Sox6 plays a role in the terminal differentiation of skeletal muscle by suppressing transcription of slow fiber specific genes. In order to understand how Sox6 coordinately regulates the transcription of multiple fiber type specific genes during muscle development, we have performed ChIP-seq analyses to identify Sox6 target genes in mouse fetal myotubes and generated muscle-specific Sox6 knockout (KO) mice to determine the Sox6 null muscle phenotype in adult mice.

Results

We have identified 1,066 Sox6 binding sites using mouse fetal myotubes. The Sox6 binding sites were found to be associated with slow fiber-specific, cardiac, and embryonic isoform genes that are expressed in the sarcomere as well as transcription factor genes known to play roles in muscle development. The concurrently performed RNA polymerase II (Pol II) ChIP-seq analysis revealed that 84% of the Sox6 peak-associated genes exhibited little to no binding of Pol II, suggesting that the majority of the Sox6 target genes are transcriptionally inactive. These results indicate that Sox6 directly regulates terminal differentiation of muscle by affecting the expression of sarcomere protein genes as well as indirectly through influencing the expression of transcription factors relevant to muscle development. Gene expression profiling of Sox6 KO skeletal and cardiac muscle revealed a significant increase in the expression of the genes associated with Sox6 binding. In the absence of the Sox6 gene, there was dramatic upregulation of slow fiber-specific, cardiac, and embryonic isoform gene expression in Sox6 KO skeletal muscle and fetal isoform gene expression in Sox6 KO cardiac muscle, thus confirming the role Sox6 plays as a transcriptional suppressor in muscle development.

Conclusions

Our present data indicate that during development, Sox6 functions as a transcriptional suppressor of fiber type-specific and developmental isoform genes to promote functional specification of muscle which is critical for optimum muscle performance and health.

Insights into the genetics of osteoporosis from recent genome-wide association studies

Osteoporosis, which is characterised by reduced bone mineral density (BMD) and an increased risk of fragility fractures, is the result of a complex interaction between environmental factors and genetic variants that confer susceptibility. Heritability studies have shown that BMD and other osteoporosis-related traits such as ultrasound properties of bone, skeletal geometry and bone turnover have significant inheritable components. Although previous linkage and candidate gene studies have provided few replicated loci for osteoporosis, genome-wide association approaches have produced clear and reproducible findings. To date, 20 genome-wide association studies (GWASs) for osteoporosis and related traits have been conducted, identifying dozens of genes. Further meta-analyses of GWAS data and deep resequencing of rare variants will uncover more novel susceptibility loci and ultimately provide possible therapeutic targets for fracture prevention.

Genetics and function of neocortical GABAergic interneurons in neurodevelopmental disorders

A dysfunction of cortical and limbic GABAergic circuits has been postulated to contribute to multiple neurodevelopmental disorders in humans, including schizophrenia, autism, and epilepsy. In the current paper, I summarize the characteristics that underlie the great diversity of cortical GABAergic interneurons and explore how the multiple roles of these cells in developing and mature circuits might contribute to the aforementioned disorders. Furthermore, I review the tightly controlled genetic cascades that determine the fate of cortical interneurons and summarize how the dysfunction of genes important for the generation, specification, maturation, and function of cortical interneurons might contribute to these disorders.

Wwp2 is essential for palatogenesis mediated by the interaction between Sox9 and mediator subunit 25

Sox9 is a direct transcriptional activator of cartilage-specific extracellular matrix genes and has essential roles in chondrogenesis. Mutations in or around the SOX9 gene cause campomelic dysplasia or Pierre Robin Sequence. However, Sox9-dependent transcriptional control in chondrogenesis remains largely unknown. Here we identify Wwp2 as a direct target of Sox9. Wwp2 interacts physically with Sox9 and is associated with Sox9 transcriptional activity via its nuclear translocation. A yeast two-hybrid screen using a cDNA library reveals that Wwp2 interacts with Med25, a component of the Mediator complex. The positive regulation of Sox9 transcriptional activity by Wwp2 is mediated by the binding between Sox9 and Med25. In zebrafish, morpholino-mediated knockdown of either wwp2 or med25 induces palatal malformation, which is comparable to that in sox9 mutants. These results provide evidence that the regulatory interaction between Sox9, Wwp2 and Med25 defines the Sox9 transcriptional mechanisms of chondrogenesis in the forming palate.

Nfat1 regulates adult articular chondrocyte function through its age-dependent expression mediated by epigenetic histone methylation

The development of disease-modifying pharmacologic therapy for osteoarthritis (OA) currently faces major obstacles largely because the regulatory mechanisms for the function of adult articular chondrocytes remain unclear. We previously demonstrated that lack of Nfat1, one of the nuclear factor of activated T cells (NFAT) transcription factors, causes OA-like changes in adult mice. This study aimed to identify whether Nfat1 specifically regulates adult articular chondrocyte function and its age-dependent regulatory mechanism using both Nfat1-deficient and wild-type mice. Deletion of Nfat1 did not induce OA-like articular chondrocyte dysfunction (e.g., overexpression of proinflammatory cytokines and matrix-degrading proteinases) until the adult stage. RNAi-mediated Nfat1 knockdown caused dysfunction of wild-type adult articular chondrocytes. Nfat1 expression in wild-type articular chondrocytes was low in the embryonic but high in the adult stage. Chromatin immunoprecipitation assays demonstrated that an increase in Nfat1 expression in articular chondrocytes was associated with increased H3K4me2 (a histone modification linked to transcriptional activation), whereas a decrease in Nfat1 expression in articular chondrocytes was correlated with increased H3K9me2 (a histone modification linked to transcriptional repression). Knockdown of lysine-specific demethylase-1 (Lsd1) in embryonic articular chondrocytes upregulated Nfat1 expression concomitant with increased H3K4me2 at the Nfat1 promoter. Knockdown of Jmjc-containing histone demethylase-2a (Jhdm2a) in 6-month articular chondrocytes downregulated Nfat1 expression concomitant with increased H3K9me2 at the Nfat1 promoter. These results suggest that Nfat1 is an essential transcriptional regulator of chondrocyte homeostasis in adult articular cartilage. Age-dependent Nfat1 expression in articular chondrocytes is regulated by dynamic histone methylation, one of the epigenetic mechanisms that regulate gene transcription.

The expressions of the SOX trio, PTHrP (parathyroid hormone-related peptide)/IHH (Indian hedgehog protein) in surgically induced osteoarthritis of the rat

This study was performed to investigate the expressions of the SOX trio, PTHrP (parathyroid hormone-related peptide) and IHH (Indian hedgehog protein) in OA (osteoarthritis) using surgically induced rat OA model. After 12 weeks, the articular cartilage from the distal femur was harvested. The expressions of the SOX trio, PTHrP and IHH were explored at gene, protein and epigenetic levels by real-time PCR (n = 5), immunohistochemistry (n = 5) and MSP (methylation-specific PCR). The findings from OA cartilage of the right knees were compared with those from the left knees as the control. The gene expressions of SOX-5, -6, -9 decreased by 58, 20 and 40%, respectively, in the OA cartilage, while their respective protein expressions increased. The PTHrP and IHH gene expressions decreased by 75 and 81%, respectively, although their protein expressions increased. Findings from MSP demonstrated increased methylation in the promoter regions of SOX-5 and -9 genes. This study demonstrated that increased methylation in the promoters of these genes may explain the low gene expression in the surgically induced OA model, whereas elevated protein expression is speculated to be from lag effect in the gene-protein expression.