Transcriptomic analysis of mouse limb tendon cells during development (original) (raw)
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Development (Cambridge, England), 2016
The molecular program underlying tendon development is not fully identified. Interactions with components of the musculoskeletal system are important for limb tendon formation. Limb tendons initiate their development independently of muscles, however muscles are required for further tendon differentiation. We show that both FGF/ERK MAPK and TGFβ/SMAD2/3 signalling pathways are required and sufficient for SCX expression in chick undifferentiated limb cells, while the FGF/ERKMAPK pathway inhibits Scx expression in mouse undifferentiated limb mesodermal cells. During differentiation, muscle contraction is required to maintain SCX, TNMD and THBS2 expression in chick limbs. The activities of FGF/ERKMAPK and TGFβ/SMAD2/3 signalling pathways are decreased in tendons under immobilisation conditions. Application of FGF4 or TGFβ2 ligands prevents SCX downregulation in limbs in immobilisation conditions. TGFβ2 but not FGF4 prevent TNMD and THBS2 downregulation in immobilisation conditions. We ...
Development, 2009
Tendons and ligaments mediate the attachment of muscle to bone and of bone to bone to provide connectivity and structural integrity in the musculoskeletal system. We show that TGFβ signaling plays a major role in the formation of these tissues. TGFβ signaling is a potent inducer of the tendon progenitor (TNP) marker scleraxis both in organ culture and in cultured cells, and disruption of TGFβ signaling in Tgfb2 -/-;Tgfb3 -/double mutant embryos or through inactivation of the type II TGFβ receptor (TGFBR2; also known as TβRII) results in the loss of most tendons and ligaments in the limbs, trunk, tail and head. The induction of scleraxis-expressing TNPs is not affected in mutant embryos and the tendon phenotype is first manifested at E12.5, a developmental stage in which TNPs are positioned between the differentiating muscles and cartilage, and in which Tgfb2 or Tgfb3 is expressed both in TNPs and in the differentiating muscles and cartilage. TGFβ signaling is thus essential for maintenance of TNPs, and we propose that it also mediates the recruitment of new tendon cells by differentiating muscles and cartilage to establish the connections between tendon primordia and their respective musculoskeletal counterparts, leading to the formation of an interconnected and functionally integrated musculoskeletal system.
TGF-β signaling is critical for maintenance of the tendon cell fate
Studies of cell fate focus on specification, but little is known about maintenance of the differentiated state. We find that TGFβ signaling plays an essential role in maintenance of the tendon cell fate. To examine the role TGFβ signaling in tenocytes TGFb type II receptor was targeted in the Scleraxis cell lineage. Tendon development was not disrupted in mutant embryos, but shortly after birth tenocytes lost differentiation markers and reverted to a more stem/progenitor state. Targeting of Tgfbr2 using other Cre drivers did not cause tenocyte dedifferentiation suggesting a critical significance for the spatio-temporal activity of ScxCre. Viral reintroduction of Tgfbr2 to mutants was sufficient to prevent and even rescue mutant tenocytes suggesting a continuous and cell-autonomous role for TGFβ signaling in cell fate maintenance. These results uncover the critical importance of molecular pathways that maintain the differentiated cell fate and a key role for TGFβ signaling in these p...
Lineage Tracing of Resident Tendon Progenitor Cells during Growth and Natural Healing
PLoS ONE, 2014
Unlike during embryogenesis, the identity of tissue resident progenitor cells that contribute to postnatal tendon growth and natural healing is poorly characterized. Therefore, we utilized 1) an inducible Cre driven by alpha smooth muscle actin (SMACreERT2), that identifies mesenchymal progenitors, 2) a constitutively active Cre driven by growth and differentiation factor 5 (GDF5Cre), a critical regulator of joint condensation, in combination with 3) an Ai9 Cre reporter to permanently label SMA9 and GDF5-9 populations and their progeny. In growing mice, SMA9+ cells were found in peritendinous structures and scleraxis-positive (ScxGFP+) cells within the tendon midsubstance and myotendinous junction. The progenitors within the tendon midsubstance were transiently labeled as they displayed a 4-fold expansion from day 2 to day 21 but reduced to baseline levels by day 70. SMA9+ cells were not found within tendon entheses or ligaments in the knee, suggesting a different origin. In contrast to the SMA9 population, GDF5-9+ cells extended from the bone through the enthesis and into a portion of the tendon midsubstance. GDF5-9+ cells were also found throughout the length of the ligaments, indicating a significant variation in the progenitors that contribute to tendons and ligaments. Following tendon injury, SMA9+ paratenon cells were the main contributors to the healing response. SMA9+ cells extended over the defect space at 1 week and differentiated into ScxGFP+ cells at 2 weeks, which coincided with increased collagen signal in the paratenon bridge. Thus, SMA9-labeled cells represent a unique progenitor source that contributes to the tendon midsubstance, paratenon, and myotendinous junction during growth and natural healing, while GDF5 progenitors contribute to tendon enthesis and ligament development. Understanding the mechanisms that regulate the expansion and differentiation of these progenitors may prove crucial to improving future repair strategies.
Transcriptional profiling of mESC-derived tendon and fibrocartilage cell fate switch
Nature Communications, 2021
The transcriptional regulators underlying induction and differentiation of dense connective tissues such as tendon and related fibrocartilaginous tissues (meniscus and annulus fibrosus) remain largely unknown. Using an iterative approach informed by developmental cues and single cell RNA sequencing (scRNA-seq), we establish directed differentiation models to generate tendon and fibrocartilage cells from mouse embryonic stem cells (mESCs) by activation of TGFβ and hedgehog pathways, achieving 90% induction efficiency. Transcriptional signatures of the mESC-derived cells recapitulate embryonic tendon and fibrocartilage signatures from the mouse tail. scRNA-seq further identify retinoic acid signaling as a critical regulator of cell fate switch between TGFβ-induced tendon and fibrocartilage lineages. Trajectory analysis by RNA sequencing define transcriptional modules underlying tendon and fibrocartilage fate induction and identify molecules associated with lineage-specific differentia...
Journal of Biological Chemistry, 2009
Transforming growth factor  (TGF) signaling has an increasing interest in regenerative medicine as a potential tool to repair cartilages, however the chondrogenic effect of this pathway in developing systems is controversial. Here we have analyzed the function of TGF signaling in the differentiation of the developing limb mesoderm in vivo and in high density micromass cultures. In these systems highest signaling activity corresponded with cells at stages preceding overt chondrocyte differentiation. Interestingly treatments with TGFs shifted the differentiation outcome of the cultures from chondrogenesis to fibrogenesis. This phenotypic reprogramming involved downregulation of Sox9 and Aggrecan and up-regulation of Scleraxis, and Tenomodulin through the Smad pathway. We further show that TGF signaling up-regulates Sox9 in the in vivo experimental model system in which TGF treatments induce ectopic chondrogenesis. Looking for clues explaining the dual role of TGF signaling, we found that TGFs appear to be direct inducers of the chondrogenic gene Sox9, but the existence of transcriptional repressors of TGF signaling modulates this role. We identified TGF-interacting factor Tgif1 and SKI-like oncogene SnoN as potential candidates for this inhibitory function. Tgif1 gene regulation by TGF signaling correlated with the differential chondrogenic and fibrogenic effects of this pathway, and its expression pattern in the limb marks the developing tendons. In functional experiments we found that Tgif1 reproduces the profibrogenic effect of TGF treatments.
International Journal of Molecular Sciences, 2021
We generated and characterized a transgenic mouse line with the tendon-specific expression of a double fluorescent reporter system, which will fulfill an unmet need for animal models to support real-time monitoring cell behaviors during tendon development, growth, and repair in vitro and in vivo. The mScarlet red fluorescent protein is driven by the Scleraxis (Scx) promoter to report the cell lineage alteration. The blue fluorescent protein reporter is expressed under the control of the 3.6kb Collagen Type I Alpha 1 Chain (Col1a1) proximal promoter. In this promoter, the existence of two promoter regions named tendon-specific cis-acting elements (TSE1, TSE2) ensure the specific expression of blue fluorescent protein (BFP) in tendon tissue. Collagen I is a crucial marker for tendon regeneration that is a major component of healthy tendons. Thus, the alteration of function during tendon repair can be estimated by BFP expression. After mechanical stimulation, the expression of mScarlet...
2021
Tendon injuries occur commonly in equine athletes. Adult tendons undergo poor natural regeneration, resulting in scar-tissue which is prone to re-injury. Fetal tendons however are capable of completely scar-less regeneration, a property which is intrinsic to the fetal cells themselves. Novel cell therapies should therefore try to recapitulate this scar-less fetal tendon regeneration. This thesis builds on previous research into the use of horse embryonic stem cells (ESCs) to aid tendon regeneration. The aim of this thesis was to determine if tendon cells derived from ESCs were more similar to fetal or adult tendon cells, as well as try to understand if scleraxis (SCX), an essential gene in tendon formation, has different roles at different stages of tendon development. Equine adult, fetal and ESC-derived tenocytes were cultured in a three-dimensional environment, with histological, morphological and transcriptomic differences compared. Additionally, the effects on gene expression of...
TGFβ signaling is required for tenocyte recruitment and functional neonatal tendon regeneration
ABSTRACTTendon injuries are common with poor healing potential. The paucity of therapies for tendon is due to our limited understanding of the cells and molecules that drive tendon regeneration. Using a model of neonatal mouse tendon regeneration, we determined the molecular basis for regeneration and identify TGFβ signaling as a major pathway. Through targeted gene deletion, small molecule inhibition, and lineage tracing, we elucidated TGFβ-dependent and –independent mechanisms underyling tendon regeneration. Importantly, functional recovery depended on TGFβ signaling and loss of function is due to impaired tenogenic cell recruitment from bothScxlinand non-Scxlinsources. We show that TGFβ signaling is required directly in neonatal tenocytes for recruitment and that TGFβ is positively regulated in tendons. Collectively, these results are the first to show a functional role for TGFβ signaling in tendon regeneration and offer new insights toward the divergent cellular activities that ...
Developmental Dynamics, 2008
Tendon is one of the least understood tissues of the musculoskeletal system in terms of development and morphogenesis. Collagen fibrillogenesis has been the most studied aspect of tendon development, focusing largely on the role of matrix molecules such as collagen type III and decorin. While involvement of matrix molecules in collagen fibrillogenesis during chick tendon development is well understood, the role of growth factors has yet to be elucidated. This work examines the expression patterns of TGF-ß1, -ß2, and -ß3, and their receptors with respect to expression patterns of collagen type III, decorin, and fibronectin. We focus on the intermediate stages of tendon development in the chick embryo, a period during which the tendon micro-and macro-architecture are being established. Our findings demonstrate for the first time that TGF-ß1, -ß2, and -ß3 have distinct spatiotemporal developmental protein localization patterns in the developing tendon and strongly suggest that these isoforms have independent roles in tendon development.