Cell-specific alterations in Pitx1 regulatory landscape activation caused by the loss of a single enhancer.

Developmental genes are frequently controlled by multiple enhancers sharing similar specificities. As a result, deletions of such regulatory elements have often failed to reveal their full function. Here, we use the Pitx1 testbed locus to characterize in detail the regulatory and cellular identity alterations following the deletion of one of its enhancers (Pen). By combining single cell transcriptomics and an in-embryo cell tracing approach, we observe an increased fraction of Pitx1 non/low-expressing cells and a decreased fraction of Pitx1 high-expressing cells. We find that the over-representation of Pitx1 non/low-expressing cells originates from a failure of the Pitx1 locus to coordinate enhancer activities and 3D chromatin changes. This locus mis-activation induces a localized heterochrony and a concurrent loss of irregular connective tissue, eventually leading to a clubfoot phenotype. This data suggests that, in some cases, redundant enhancers may be used to locally enforce a robust activation of their host regulatory landscapes.

Subsynovial connective tissue development in the rabbit carpal tunnel.

The carpal tunnel contains the digital flexor tendons and the median nerve, which are embedded in a unique network of fibrovascular interconnected subsynovial connective tissue (SSCT). Fibrous hypertrophy of the SSCT and subsequent adaptations in mechanical response are found in patients with carpal tunnel syndrome (CTS), but not much is known about the development of the SSCT. This observational study describes the morphological development of SSCT using histology and ultramicroscopy in an animal model at four time points between late-term fetuses through adulthood. A transition is seen between 3 days and 6 weeks post-partum from a dense solid SSCT matrix to a complex multilayered structure connected with collagenous fibrils. These preliminary data show a developmental pattern that matches an adaptive response of the SSCT to loading and motion. Understanding the anatomical development aids in recognizing the pathophysiology of CTS and supports research on new therapeutic approaches.

Erythropoietin Alleviates Burn-induced Muscle Wasting.

Background: Burn injury induces long-term skeletal muscle pathology. We hypothesized EPO could attenuate burn-induced muscle fiber atrophy. Methods: Rats were allocated into four groups: a sham burn group, an untreated burn group subjected to third degree hind paw burn, and two burn groups treated with weekly or daily EPO for four weeks. Gastrocnemius muscle was analyzed at four weeks post-burn. Results: EPO attenuated the reduction of mean myofiber cross-sectional area post-burn and the level of the protective effect was no significant difference between two EPO-treated groups (p=0.784). Furthermore, EPO decreased the expression of atrophy-related ubiquitin ligase, atrogin-1, which was up-regulated in response to burn. Compared to untreated burn rats, those receiving weekly or daily EPO groups had less cell apoptosis by TUNEL assay. EPO decreased the expression of cleaved caspase 3 (key factor in the caspase-dependent pathway) and apoptosis-inducing factor (implicated in the caspase-independent pathway) after burn. Furthermore, EPO alleviated connective tissue overproduction following burn via transforming growth factor beta 1-Smad2/3 pathway. Daily EPO group caused significant erythrocytosis compared with untreated burn group but not weekly EPO group. Conclusion: EPO therapy attenuated skeletal muscle apoptosis and fibrosis at four weeks post-burn. Weekly EPO may be a safe and effective option in muscle wasting post-burn.

GROWTH AND DEVELOPMENT SYMPOSIUM: STEM AND PROGENITOR CELLS IN ANIMAL GROWTH: The regulation of beef quality by resident progenitor cells1.

The intramuscular adipose tissue deposition in the skeletal muscle of beef cattle is a highly desired trait essential for high-quality beef. In contrast, the excessive accumulation of crosslinked collagen in intramuscular connective tissue contributes to beef toughness. Recent studies revealed that adipose tissue and connective tissue share an embryonic origin in mice and may be derived from a common immediate bipotent precursor in mice and humans. Having the same linkages in the development of adipose tissue and connective tissue in beef, the lineage commitment and differentiation of progenitor cells giving rise to these tissues may directly affect beef quality. It has been shown that these processes are regulated by some key transcription regulators and are subjective to epigenetic modifications such as DNA methylation, histone modifications, and microRNAs. Continued exploration of relevant regulatory pathways is very important for the identification of mechanisms influencing meat quality and the development of proper management strategies for beef quality improvement.

Mechanical force promotes the proliferation and extracellular matrix synthesis of human gingival fibroblasts cultured on 3D PLGA scaffolds via TGF­ß expression.

Human gingival fibroblasts (HGFs) are responsible for connective tissue repair and scarring, and are exposed to mechanical forces under physiological and pathological conditions. The exact mechanisms underlying gingival tissue reconstruction under mechanical forces remain unclear. The present study aimfed to investigate the effects of mechanical forces on the proliferation and extracellular matrix synthesis in HGFs by establishing a 3­dimensional (3D) HGF culture model using poly(lactide­co­glycolide) (PLGA) scaffolds. HGFs were cultured in 3D PLGA scaffolds and a mechanical force of 0, 5, 15, 25 or 35 g/cm2 was applied to HGFs for 24 h. A mechanical force of 25 g/cm2 induced the highest proliferation rate, and thus was selected for subsequent experiments. Cell viability was determined using the MTT assay at 0, 24, 48 and 72 h. The expression levels of type I collagen (COL­1) and matrix metallopeptidase (MMP)­1 were examined by reverse transcription­quantitative polymerase chain reaction and ELISA, and transforming growth factor (TGF)­ß expression was evaluated by ELISA. The application of mechanical force on HGFs cultured on the 3D PLGA scaffolds resulted in a significant increase in cell proliferation and COL­1 expression, as well as a decrease in MMP­1 expression. A TGF­ß1 inhibitor was also applied, which attenuated the effects of mechanical force on HGF proliferation, and COL­1 and MMP­1 expression, thus suggesting that TGF­ß signaling pathways may mediate the mechanical force­induced alterations observed in HGFs. In conclusion, these findings helped to clarify the mechanisms underlying mechanical force­induced HGF proliferation and ECM synthesis, which may promote the development of targeted therapeutics to treat various diseases, including gingival atrophy caused by orthodontic treatment.

Enhancement of wound healing by single-wall/multi-wall carbon nanotubes complexed with chitosan.

BACKGROUND: Impaired wound healing is commonly associated with many health problems, including diabetes, bedsores and extensive burns. In such cases, healing often takes a long time, which subjects patients to various complications. This study aims to investigate whether single-wall or multi-wall carbon nanotubes complexed with chitosan hydrogel can improve wound healing. MATERIALS AND METHODS: Initially, the effects of the complexes on the viability and functionality of fibroblasts were investigated in engineered connective tissues. Then, their activity on wound healing was investigated in a mouse model with induced full-thickness wounds, in which the wounds were treated daily with these complexes. Finally, the effect of the complexes on collagen deposition by fibroblasts was investigated in vitro. RESULTS: The engineered connective tissue studies showed that fibroblasts were viable in the presence of the complexes and were still able to effectively organize and contract the extracellular matrix. In vivo data showed that both types of complexes improved the re-epithelialization of the healing wounds; however, they also increased the percentage of wounds with higher fibrosis. In particular, the chitosan-multi-wall carbon nanotube complex significantly enhanced the extensiveness of this fibrosis, which is in line with in vitro data showing a concentration-dependent enhancement of collage deposition by these complexes. These observations were associated with an increase in inflammatory signs in the wound bed. CONCLUSION: Single-wall and multi-wall carbon nanotubes complexed with chitosan improved the re-epithelialization of wounds, but an increase in fibrosis was detected.

Maturation State and Matrix Microstructure Regulate Interstitial Cell Migration in Dense Connective Tissues.

Few regenerative approaches exist for the treatment of injuries to adult dense connective tissues. Compared to fetal tissues, adult connective tissues are hypocellular and show limited healing after injury. We hypothesized that robust repair can occur in fetal tissues with an immature extracellular matrix (ECM) that is conducive to cell migration, and that this process fails in adults due to the biophysical barriers imposed by the mature ECM. Using the knee meniscus as a platform, we evaluated the evolving micromechanics and microstructure of fetal and adult tissues, and interrogated the interstitial migratory capacity of adult meniscal cells through fetal and adult tissue microenvironments with or without partial enzymatic digestion. To integrate our findings, a computational model was implemented to determine how changing biophysical parameters impact cell migration through these dense networks. Our results show that the micromechanics and microstructure of the adult meniscus ECM sterically hinder cell mobility, and that modulation of these ECM attributes via an exogenous matrix-degrading enzyme permits migration through this otherwise impenetrable network. By addressing the inherent limitations to repair imposed by the mature ECM, these studies may define new clinical strategies to promote repair of damaged dense connective tissues in adults.

Changing While Staying the Same: Preservation of Structural Continuity During Limb Evolution by Developmental Integration.

More than 150 years since Charles Darwin published "On the Origin of Species", gradual evolution by natural selection is still not fully reconciled with the apparent sudden appearance of complex structures, such as the bat wing, with highly derived functions. This is in part because developmental genetics has not yet identified the number and types of mutations that accumulated to drive complex morphological evolution. Here, we consider the experimental manipulations in laboratory model systems that suggest tissue interdependence and mechanical responsiveness during limb development conceptually reduce the genetic complexity required to reshape the structure as a whole. It is an exciting time in the field of evolutionary developmental biology as emerging technical approaches in a variety of non-traditional laboratory species are on the verge of filling the gaps between theory and evidence to resolve this sesquicentennial debate.

[Histomorphometric evaluation of ridge preservation after molar tooth extraction].

OBJECTIVE: To evaluate bone formation in human extraction sockets with absorbed surrounding walls augmented with Bio-Oss and Bio-Gide after a 6-month healing period by histologic and histomorphometric analyses. METHODS: Six fresh molar tooth extraction sockets in 6 patients who required periodontally compromised moral tooth extraction were included in this study. The six fresh extraction sockets were grafted with Bio-Oss particle covered with Bio-Gide. The 2.8 mm×6.0 mm cylindric bone specimens were taken from the graft sites with aid of stent 6 months after the surgery. Histologic and histomorphometric analyses were performed. RESULTS: The histological results showed Bio-Oss particles were easily distinguished from the newly formed bone, small amounts of new bone were formed among the Bio-Oss particles, large amounts of connective tissue were found. Intimate contact between the newly formed bone and the small part of Bio-Oss particles was present. All the biopsy cylinders measurement demonstrated a high inter-individual variability in the percentage of the bone, connective tissues and Bio-Oss particles. The new bone occupied 11.54% (0-28.40%) of the total area; the connective tissues were 53.42% (34.08%-74.59%) and the Bio-Oss particles were 35.04% (13.92%-50.87%). The percentage of the particles, which were in contact with bone tissues, amounted to 20.13% (0-48.50%). CONCLUSION: Sites grafted with Bio-Oss particles covered with Bio-Gide were comprised of connective tissues and small amounts of newly formed bone surrounding the graft particles.

Sulfated glycosaminoglycan-derived oligosaccharides produced from chicken connective tissue promote iron uptake in a human intestinal Caco-2 cell line.

Food grade sulfated glycosaminoglycan (GAG) polysaccharides were successfully extracted from chicken cartilage and skin. Their respective oligosaccharides were obtained by bovine testicular hyaluronidase digestion. The antioxidant capacity was analyzed to determine the possible mechanism explaining how GAGs promote iron uptake by the Caco-2 cells. The sulfated GAG oligosaccharides derived from cartilage possessed the greatest DPPH scavenging and ferric reducing activities (p<0.05), but limited ferrous chelating activities. Both the cartilage and skin sulfated GAG polysaccharides showed greater ferritin formation compared to the negative control (p<0.05). Depolymerisation of GAG polysaccharides to oligosaccharides further improved ferritin formation by twofold. This research establishes that chicken sulfated GAG polysaccharides can enhance iron uptake by Caco-2 cells. The enhanced iron uptake through enzymatic GAG depolymerisation could be due to the combined effects of reduced molecular weight, increased amount of hydroxyl terminal groups and ferric reducing activities.

Silk based bioinks for soft tissue reconstruction using 3-dimensional (3D) printing with in vitro and in vivo assessments.

In the field of soft tissue reconstruction, custom implants could address the need for materials that can fill complex geometries. Our aim was to develop a material system with optimal rheology for material extrusion, that can be processed in physiological and non-toxic conditions and provide structural support for soft tissue reconstruction. To meet this need we developed silk based bioinks using gelatin as a bulking agent and glycerol as a non-toxic additive to induce physical crosslinking. We developed these inks optimizing printing efficacy and resolution for patient-specific geometries that can be used for soft tissue reconstruction. We demonstrated in vitro that the material was stable under physiological conditions and could be tuned to match soft tissue mechanical properties. We demonstrated in vivo that the material was biocompatible and could be tuned to maintain shape and volume up to three months while promoting cellular infiltration and tissue integration.

Fell-Muir Lecture: Regulatory mechanisms of skeletal and connective tissue development and homeostasis - lessons from studies of human disorders.

Studies of proliferative hemangiomas have led to the discovery that interactions of endothelial cells with extracellular matrix and/or Vascular Endothelial Growth Factor (VEGF)-A stimulate the expression of VEGFR1, the VEGF decoy receptor, and suppress VEGF-dependent VEGFR2 signalling by a mechanism that requires the matrix-binding receptor Anthrax Toxin Receptor (ANTXR)1, VEGFR2, ß1 integrin and the Nuclear Factor of Activated T cells (NFAT). In hemangioma endothelial cells, all these components are present, but are functionally compromised, so that the levels of VEGFR1 are extremely low and VEGFR2 signalling is constitutively active. Consequently, the levels of Hypoxia Inducible Factor (HIF)-1α and its transcriptional targets, VEGF-A and C-X-C motif chemokine 12 (CxCl12), are elevated and a positive VEGF-A feedback loop is established. Overexpression of ANTXR1, carrying a heterozygous Ala-to-Thr mutation, induces hemangioma-like signalling in control endothelial cells; VEGF signalling is normalized when wild-type ANTXR1 is overexpressed in hemangioma cells. These findings suggest that ANTXR1 functions as a negative regulator of VEGF-A signalling. Studies of a mouse model of the Growth Retardation, Alopecia, Pseudo-anodontia and Optic Atrophy (GAPO) syndrome, caused by the loss-of-function mutations in ANTXR1, as well as knock-in mice carrying the Ala-to-Thr ANTXR1 mutation, confirm that ANTXR1 functions as a suppressor of VEGF-A signalling. Cutaneous endothelial cells isolated from ANTXR1-deficient mice exhibit low levels of VEGFR1, elevated levels of VEGF-A, HIF-1α and CxCl12 and activated VEGFR2 signalling as in hemangioma. Increased numbers of myeloid cells in the skin of ANTXR1-deficient mice are associated with reduced vascularity and increased skin fibrosis, suggesting a mechanism for hemangioma involution and replacement by fibrotic scars. Through controlling VEGF-A signalling and extracellular matrix synthesis, ANTXR1 is emerging as a key regulator of skeletal and connective tissue development and homeostasis.

Impedance Changes and Fibrous Tissue Growth after Cochlear Implantation Are Correlated and Can Be Reduced Using a Dexamethasone Eluting Electrode.

BACKGROUND: The efficiency of cochlear implants (CIs) is affected by postoperative connective tissue growth around the electrode array. This tissue formation is thought to be the cause behind post-operative increases in impedance. Dexamethasone (DEX) eluting CIs may reduce fibrous tissue growth around the electrode array subsequently moderating elevations in impedance of the electrode contacts. METHODS: For this study, DEX was incorporated into the silicone of the CI electrode arrays at 1% and 10% (w/w) concentration. Electrodes prepared by the same process but without dexamethasone served as controls. All electrodes were implanted into guinea pig cochleae though the round window membrane approach. Potential additive or synergistic effects of electrical stimulation (60 minutes) were investigated by measuring impedances before and after stimulation (days 0, 7, 28, 56 and 91). Acoustically evoked auditory brainstem responses were recorded before and after CI insertion as well as on experimental days 7, 28, 56, and 91. Additionally, histology performed on epoxy embedded samples enabled measurement of the area of scala tympani occupied with fibrous tissue. RESULTS: In all experimental groups, the highest levels of fibrous tissue were detected in the basal region of the cochlea in vicinity to the round window niche. Both DEX concentrations, 10% and 1% (w/w), significantly reduced fibrosis around the electrode array of the CI. Following 3 months of implantation impedance levels in both DEX-eluting groups were significantly lower compared to the control group, the 10% group producing a greater effect. The same effects were observed before and after electrical stimulation. CONCLUSION: To our knowledge, this is the first study to demonstrate a correlation between the extent of new tissue growth around the electrode and impedance changes after cochlear implantation. We conclude that DEX-eluting CIs are a means to reduce this tissue reaction and improve the functional benefits of the implant by attenuating electrode impedance.

Early postnatal feed restriction reduces liver connective tissue levels and affects H3K9 acetylation state of regulated genes associated with protein metabolism in low birth weight pigs.

Intrauterine growth retardation is associated with metabolic consequences in adulthood. Since our previous data indicate birth weight-dependent effects of feed restriction (R) on protein degradation processes in the liver, it should be investigated whether effects on connective tissue turnover are obvious and could be explained by global changes of histone H3K9me3 and H3K9ac states in regulated genes. For this purpose, female littermate pigs with low (U) or normal (N) birth weight were subjected to 3-week R (60% of ad libitum fed controls) with subsequent refeeding (REF) for further 5 weeks. The 3-week R-period induced a significant reduction of connective tissue area by 43% in the liver of U animals at 98 d of age, which was not found in age-matched N animals. Of note, after REF at 131 d of age, in previously feed-restricted U animals (UR), the percentage of mean connective tissue was only 53% of ad libitum fed controls (UK), indicating a persistent effect. In U animals, R induced H3K9 acetylation of regulated genes (e.g. XBP1, ERLEC1, GALNT2, PTRH2), which were inter alia associated with protein metabolism. In contrast, REF was mostly accompanied by deacetylation in U and N animals. Thus, our epigenetic data may give a first explanation for the observed birth weight-dependent differences in this connective tissue phenotype.

Low-dose phase-based X-ray imaging techniques for in situ soft tissue engineering assessments.

In tissue engineering, non-invasive imaging of biomaterial scaffolds and tissues in living systems is essential to longitudinal animal studies for assessments without interrupting the repair process. Conventional X-ray imaging is inadequate for use in soft tissue engineering due to the limited absorption difference between the soft tissue and biomaterial scaffolds. X-ray phase-based imaging techniques that derive contrast from refraction or phase effects rather than absorption can provide the necessary contrast to see low-density biomaterial scaffolds and tissues in large living systems. This paper explores and compares three synchrotron phase-based X-ray imaging techniques-computed tomography (CT)-diffraction enhanced imaging (DEI), -analyzer based imaging (ABI), and -phase contrast imaging (PCI)-for visualization and characterization of low-density biomaterial scaffolds and tissues in situ for non-invasive soft tissue engineering assessments. Intact pig joints implanted with polycaprolactone scaffolds were used as the model to assess and compare the imaging techniques in terms of different qualitative and quantitative criteria. For long-term in vivo live animal imaging, different strategies for reducing the imaging radiation dose and scan time-reduced number of CT projections, region of interest, and low resolution imaging-were examined with the presented phase-based imaging techniques. The results demonstrated promising capabilities of the phase-based techniques for visualization of biomaterial scaffolds and soft tissues in situ. The low-dose imaging strategies were illustrated effective for reducing the radiation dose to levels appropriate for live animal imaging. The comparison among the imaging techniques suggested that CT-DEI has the highest efficiency in retaining image contrast at considerably low radiation doses.

Invited review: mesenchymal progenitor cells in intramuscular connective tissue development.

The abundance and cross-linking of intramuscular connective tissue contributes to the background toughness of meat, and is thus undesirable. Connective tissue is mainly synthesized by intramuscular fibroblasts. Myocytes, adipocytes and fibroblasts are derived from a common pool of progenitor cells during the early embryonic development. It appears that multipotent mesenchymal stem cells first diverge into either myogenic or non-myogenic lineages; non-myogenic mesenchymal progenitors then develop into the stromal-vascular fraction of skeletal muscle wherein adipocytes, fibroblasts and derived mesenchymal progenitors reside. Because non-myogenic mesenchymal progenitors mainly undergo adipogenic or fibrogenic differentiation during muscle development, strengthening progenitor proliferation enhances the potential for both intramuscular adipogenesis and fibrogenesis, leading to the elevation of both marbling and connective tissue content in the resulting meat product. Furthermore, given the bipotent developmental potential of progenitor cells, enhancing their conversion to adipogenesis reduces fibrogenesis, which likely results in the overall improvement of marbling (more intramuscular adipocytes) and tenderness (less connective tissue) of meat. Fibrogenesis is mainly regulated by the transforming growth factor (TGF) ß signaling pathway and its regulatory cascade. In addition, extracellular matrix, a part of the intramuscular connective tissue, provides a niche environment for regulating myogenic differentiation of satellite cells and muscle growth. Despite rapid progress, many questions remain in the role of extracellular matrix on muscle development, and factors determining the early differentiation of myogenic, adipogenic and fibrogenic cells, which warrant further studies.

Acceleration of hard and soft tissue healing in the oral cavity by a single transmucosal injection of fluvastatin-impregnated poly (lactic-co-glycolic acid) microspheres. An in vitro and rodent in vivo study.

Antihyperlipidemic drug statins reportedly promote both bone formation and soft tissue healing. We examined the effect of sustained-release, fluvastatin-impregnated poly(lactic-co-glycolic acid) (PLGA) microspheres on the promotion of bone and gingival healing at an extraction socket in vivo, and the effect of fluvastatin on epithelial cells and fibroblasts in vitro. The maxillary right first molar was extracted in rats, then one of the following was immediately injected, as a single dose, into the gingivobuccal fold: control (no administration), PLGA microspheres without a statin (active control), or PLGA microspheres containing 20 or 40 µg kg(-1) of fluvastatin. At days 1, 3, 7, 14, and 28 after injection, bone and soft tissue healing were histologically evaluated. Cell proliferation was measured under the effect of fluvastatin at dosages of 0, 0.01, 0.1, 1.0, 10, and 50 µM. Cell migration and morphology were observed at dosages of 0 and 0.1 µM. Following tooth extraction, the statin significantly enhanced bone volume and density, connective tissue volume, and epithelial wound healing. In the in vitro study, it promoted significant proliferation and migration of epithelial cells and fibroblasts. A single dose of topically administered fluvastatin-impregnated PLGA microspheres promoted bone and soft tissue healing at the extraction site.

Comparative study of muscle regeneration following cardiotoxin and glycerol injury.

In the present study, we examined muscle regeneration following two types of chemical injuries, cardiotoxin (CTX) and glycerol, in order to compare their effect on the morphological characteristics during muscle regeneration, in addition we studied the structural changes of the intramuscular connective tissue (IMCT) during the regeneration process, by scanning electron microscopy (SEM) after digestion of the cellular elements of the muscle with sodium hydroxide. Tibialis anterior (TA) muscles of adult male mice were injected either with CTX or glycerol. Muscle degeneration was greater in the CTX-injured model than in the glycerol-injured model at day 4 post injection. Muscle regeneration started at day 7 in both the CTX and glycerol models. However, the CTX-injured model showed a higher myotube density and larger myotube diameter than the glycerol-injured model at days 10 and 14 post injection. On other hand, adipocyte infiltration was detected in the glycerol-injured model. In contrast, no adipocytes could be detected in the CTX-injured model. Furthermore, ultrastructural analysis showed a significant difference in myofiber damage and regeneration between the two models. SEM of the IMCT showed a transient increase in endomysial collagen deposition at early stages of regeneration in the CTX-injured model. In contrast, glycerol-injured model showed slight endomysial collagen deposition. Our results suggest that changes in IMCT affect the efficiency of muscle regeneration. Studying the three dimensional structure of IMCT may help clinical therapies to reduce skeletal muscle fibrosis. To our knowledge this is the first time the changes in IMCT following CTX and glycerol injury using SEM-cell maceration technique have been compared.

Fetal programming in meat production.

Nutrient fluctuations during the fetal stage affects fetal development, which has long-term impacts on the production efficiency and quality of meat. During the early development, a pool of mesenchymal progenitor cells proliferate and then diverge into either myogenic or adipogenic/fibrogenic lineages. Myogenic progenitor cells further develop into muscle fibers and satellite cells, while adipogenic/fibrogenic lineage cells develop into adipocytes, fibroblasts and resident fibro-adipogenic progenitor cells. Enhancing the proliferation and myogenic commitment of progenitor cells during fetal development enhances muscle growth and lean production in offspring. On the other hand, promoting the adipogenic differentiation of adipogenic/fibrogenic progenitor cells inside the muscle increases intramuscular adipocytes and reduces connective tissue, which improves meat marbling and tenderness. Available studies in mammalian livestock, including cattle, sheep and pigs, clearly show the link between maternal nutrition and the quantity and quality of meat production. Similarly, chicken muscle fibers develop before hatching and, thus, egg and yolk sizes and hatching temperature affect long-term growth performance and meat production of chicken. On the contrary, because fishes are able to generate new muscle fibers lifelong, the impact of early nutrition on fish growth performance is expected to be minor, which requires further studies.

Analyzing the effects of mechanical and osmotic loading on glycosaminoglycan synthesis rate in cartilaginous tissues.

The glycosaminoglycan (GAG) plays an important role in cartilaginous tissues to support and transmit mechanical loads. Many extracellular biophysical stimuli could affect GAG synthesis by cells. It has been hypothesized that the change of cell volume is a primary mechanism for cells to perceive the stimuli. Experimental studies have shown that the maximum synthesis rate of GAG is achieved at an optimal cell volume, larger or smaller than this level the GAG synthesis rate decreases. Based on the hypothesis and experimental findings in the literature, we proposed a mathematical model to quantitatively describe the cell volume dependent GAG synthesis rate in the cartilaginous tissues. Using this model, we investigated the effects of osmotic loading and mechanical loading on GAG synthesis rate. It is found our proposed mathematical model is able to well describe the change of GAG synthesis rate in isolated cells or in cartilage with variations of the osmotic loading or mechanical loading. This model is important for evaluating the GAG synthesis activity within cartilaginous tissues as well as understanding the role of mechanical loading in tissue growth or degeneration. It is also important for designing a bioreactor system with proper extracellular environment or mechanical loading for growing tissue at the maximum synthesis rate of the extracellular matrix.