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.

[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.

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.

Connective tissue fibroblast properties are position-dependent during mouse digit tip regeneration

A key factor that contributes to the regenerative ability of regeneration-competent animals such as the salamander is their use of innate positional cues that guide the regeneration process. The limbs of mammals has severe regenerative limitations, however the distal most portion of the terminal phalange is regeneration competent. This regenerative ability of the adult mouse digit is level dependent: amputation through the distal half of the terminal phalanx (P3) leads to successful regeneration, whereas amputation through a more proximal location, e.g. the subterminal phalangeal element (P2), fails to regenerate. Do the connective tissue cells of the mammalian digit play a role similar to that of the salamander limb in controlling the regenerative response? To begin to address this question, we isolated and cultured cells of the connective tissue surrounding the phalangeal bones of regeneration competent (P3) and incompetent (P2) levels. Despite their close proximity and localization, these cells show very distinctive profiles when characterized in vitro and in vivo. In vitro studies comparing their proliferation and position-specific interactions reveal that cells isolated from the P3 and P2 are both capable of organizing and differentiating epithelial progenitors, but with different outcomes. The difference in interactions are further characterized with three-dimension cultures, in which P3 regenerative cells are shown to lack a contractile response that is seen in other fibroblast cultures, including the P2 cultures. In in vivo engraftment studies, the difference between these two cell lines is made more apparent. While both P2 and P3 cells participated in the regeneration of the terminal phalanx, their survival and proliferative indices were distinct, thus suggesting a key difference in their ability to interact within a regeneration permissive environment. These studies are the first to demonstrate distinct positional characteristics of connective tissue cells that are associated with their regenerative capabilities.

[Functional morphology of conjunctive tissue stroma of spleen in the age aspect]

The article presents the data on the structural and functional changes of conjunctive tissue of the spleen in postnatal ontogenesis of a person. The study was performed on 125 cadaveric spleens of the people of both sexes, who died from traumas and diseases not causing pathologic changes in the spleen. Definition of ontogenetic phases and chronological confines of age periods was identified according to Bunak V. V. (1965). The measurement of linear dimensions and mass of organ, histological, histochemical study and morphometry were performed. According to factual evidence, at the age from birth to 4 years the content of lymphatic follicles increases against a background of decrease of conjunctive tissue component and red pulp in the area of spleen section. By 8 or 10 years the part of lymphoid tissue decreases, but the part of conjunctive tissue and red pulp increases. Ageing symptoms are revealed at the age of 18, the increase of volume of conjunctive tissue component and destruction of external elastic membrane of trabecular artery of spleen take place. The destruction of elastic and reticulin fibers of soft skeleton, reduction of cellular elements (cells, fibroblasts and fibrocytes) and conjunctive tissue stroma collagenization are observed at a mature and old age.

[Experimental study on pulp revitalization of Beagle dog's immature permanent teeth after pulpectomy]

OBJECTIVE

To observe the process of pulp revitalization of immature permanent teeth after pulpectomy.

METHODS

Thirty-two single-rooted teeth with open apices from 4 Beagle dogs aged 4 months were included in the study. The pulpal tissues of 8 front teeth with single root of each dog were removed, and a blood clot was produced to the level of the cementoenamel junction followed by a double seal of mineral trioxide aggregate and composite resin. At day 7, 14, 21 and 28, respectively after operation, the dog was sacrificed, and then longitudinal paraffin sections were made for histologic investigation.

RESULTS

After 7 days, about one thirth of the pulp chamber had an ingrowth of new tissue. After 14, 21, 28 days, there were more and more new tissue in the chamber. This new tissue consisted of well-organized and well-vascularized connective tissue. Hard tissue was too observed in the root canal. In some cases, the newly generated hard tissue even deposited against the canal dentinal walls.

CONCLUSIONS

The pulp of immature permanent teeth can revitalize after removal of the original pulp tissue under suitable conditions.

[The effects of microenvironment on tissue-engineered osteochondral composite]

It is currently reported that extracellular matrix, biological scaffolds, conditions of stress, nutrients and metabolic waste play very important roles in tissue-engineered osteochondral composite. In this paper, we have made a review of their effects on such composite.

[Juxtaoral organ of Chievitz]

This review presents the analysis of the systematized data on human juxtaoral organ (JOO) development, structure and function based on the results of classical and recent morphological studies. JOO morphogenesis is traced, including the appearance of its anlage at the bottom of the primitive mouth, epithelial invagination into the mesenchyme, JOO detachment from the oral epithelium, its innervation, connective tissue capsule formation, and final maturation. The analysis of the results of macroscopical, histological, electron microscopical, histochemical and immunohistochemical studies is presented, suggesting high metabolic and synthetic activity of its epithelium, which expresses several neural markers, and emphasizing a rich innervation of both its epithelial and stromal components. The findings supporting the concepts of JOO secretory and mechanosensory functions, are examined. The data on the differential diagnosis between JOO and tumoral processes are discussed, as well as the pathological changes of JOO itself and their significance for the diagnosis of the diseases.

Urotensin II is an autocrine/paracrine growth factor for aortic adventitia of rat

Urotensin II (UII) is a potent vasoconstrictive peptide; however, its significance in vascular adventitia has not been clearly elucidated. In this study, rat aortic adventitia showed mRNA expression and immunoreactivity of UII and its receptor (UT). Moreover, radioligand-binding assay showed that maximum binding capacity (Bmax) of [(125)I]-UII was higher in adventitia than in media (28.60+/-1.94 vs. 20.21+/-1.11 fmol/mg, P<0.01), with no difference in binding affinity (dissociation constant [Kd] 4.27+/-0.49 vs. 4.60+/-0.40 nM, P>0.05). Furthermore, in cultured adventitial fibroblasts, UII stimulated DNA synthesis, collagen synthesis and secretion in a concentration-dependent manner. These effects were inhibited by the UII receptor antagonist urantide (10(-6) mol/l), Ca(2+) channel blocker nicardipine (10(-5) mol/l), protein kinase C inhibitor H7 (10(-6) mol/l), and mitogen-activated protein kinase inhibitor PD98059 (10(-6) mol/l) but not the phosphatidyl inositol-3 kinase inhibitor wortmannin (10(-7) mol/l). UII may act as an autocrine/paracrine factor through its receptor and the Ca(2+) channel, protein kinase C, and mitogen-activated protein kinase signal transduction pathways, in the pathogenesis of vascular remodeling by activating vascular adventitia.

The zinc transporter SLC39A13/ZIP13 is required for connective tissue development; its involvement in BMP/TGF-beta signaling pathways

BACKGROUND

Zinc (Zn) is an essential trace element and it is abundant in connective tissues, however biological roles of Zn and its transporters in those tissues and cells remain unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report that mice deficient in Zn transporter Slc39a13/Zip13 show changes in bone, teeth and connective tissue reminiscent of the clinical spectrum of human Ehlers-Danlos syndrome (EDS). The Slc39a13 knockout (Slc39a13-KO) mice show defects in the maturation of osteoblasts, chondrocytes, odontoblasts, and fibroblasts. In the corresponding tissues and cells, impairment in bone morphogenic protein (BMP) and TGF-beta signaling were observed. Homozygosity for a SLC39A13 loss of function mutation was detected in sibs affected by a unique variant of EDS that recapitulates the phenotype observed in Slc39a13-KO mice.

CONCLUSIONS/SIGNIFICANCE

Hence, our results reveal a crucial role of SLC39A13/ZIP13 in connective tissue development at least in part due to its involvement in the BMP/TGF-beta signaling pathways. The Slc39a13-KO mouse represents a novel animal model linking zinc metabolism, BMP/TGF-beta signaling and connective tissue dysfunction.

Periostin regulates collagen fibrillogenesis and the biomechanical properties of connective tissues

Periostin is predominantly expressed in collagen-rich fibrous connective tissues that are subjected to constant mechanical stresses including: heart valves, tendons, perichondrium, cornea, and the periodontal ligament (PDL). Based on these data we hypothesize that periostin can regulate collagen I fibrillogenesis and thereby affect the biomechanical properties of connective tissues. Immunoprecipitation and immunogold transmission electron microscopy experiments demonstrate that periostin is capable of directly interacting with collagen I. To analyze the potential role of periostin in collagen I fibrillogenesis, gene targeted mice were generated. Transmission electron microscopy and morphometric analyses demonstrated reduced collagen fibril diameters in skin dermis of periostin knockout mice, an indication of aberrant collagen I fibrillogenesis. In addition, differential scanning calorimetry (DSC) demonstrated a lower collagen denaturing temperature in periostin knockout mice, reflecting a reduced level of collagen cross-linking. Functional biomechanical properties of periostin null skin specimens and atrioventricular (AV) valve explant experiments provided direct evidence of the role that periostin plays in regulating the viscoelastic properties of connective tissues. Collectively, these data demonstrate for the first time that periostin can regulate collagen I fibrillogenesis and thereby serves as an important mediator of the biomechanical properties of fibrous connective tissues.

Porous tantalum in reconstructive surgery of the knee: a review

Porous tantalum represents an alternative metal for primary and revision total knee arthroplasty (TKA) with several unique properties. Tantalum is a transition metal, which in its bulk form has shown excellent biocompatibility and is safe to use in vivo as evidenced by its current application in pacemaker electrodes, cranioplasty plates, and as radiopaque markers. Current designs for orthopedic implants maintain a high volumetric porosity (70%-80%), low modulus of elasticity (3 MPa), and high frictional characteristics, making this metal conducive to biologic fixation. The low modulus of elasticity of such components allows for more physiologic load transfer and relative preservation of bone stock. Its more bioactive nature and ingrowth properties have led to its use in primary as well as revision knee components with good early clinical results reported. In revision arthroplasty, it has been used as a structural bone graft substitute. Formation of a bone-like apatite coating in vivo affords strong fibrous ingrowth properties and allows for substantial soft-tissue attachment with the potential for use in cases such as mega-prostheses and patella salvage. Although porous tantalum is in its early stages of evolution, the initial clinical data and basic science studies support its use as an alternative to traditional orthopedic implant materials.

Differential Effects of EGF and TGF-β1 on Fibroblast Activity in Fibrin-Based Tissue Equivalents

Transforming growth factor-beta1 (TGF-beta1) is commonly used to promote matrix production for engineered tissues in vitro, yet it also enhances fibroblast contractility. For applications where contraction is undesirable, we hypothesized that epidermal growth factor (EGF) would yield equivalent mechanical properties without enhancing contractility. In this study, the response of human dermal fibroblasts to EGF (5 ng/mL) and TGF-beta1 (5 ng/mL) was determined within hemispheric fibrin-based gels by assessing matrix compaction and strength, cell number, collagen production, and contractility. After 3 weeks, both cytokines enhanced compaction relative to controls, and EGF roughly doubled matrix strength over controls and TGF-beta1-treated samples. TGF-beta1 induced alpha-smooth muscle actin (alphaSMA) expression whereas EGF did not. TGF-beta1 also increased retraction following substrate release while EGF reduced retraction. Treatment with cytochalasin D revealed that, regardless of growth factor, approximately 10% of the total retraction was due to residual matrix stress accumulated during cell-mediated remodeling. EGF increased the cell number by 17%, whereas TGF-beta1 decreased the cell number by 63% relative to controls. EGF and TGF-beta1 stimulated greater collagen content than controls by 49% and 33%, respectively. These data suggest that EGF may be an attractive alternative to TGF-beta1 for engineering fibrin-based connective tissue substitutes with adequate strength and minimal tissue contractility.

Computational modeling of morphogenesis regulated by mechanical feedback

Mechanical forces cause changes in form during embryogenesis and likely play a role in regulating these changes. This paper explores the idea that changes in homeostatic tissue stress (target stress), possibly modulated by genes, drive some morphogenetic processes. Computational models are presented to illustrate how regional variations in target stress can cause a range of complex behaviors involving the bending of epithelia. These models include growth and cytoskeletal contraction regulated by stress-based mechanical feedback. All simulations were carried out using the commercial finite element code ABAQUS, with growth and contraction included by modifying the zero-stress state in the material constitutive relations. Results presented for bending of bilayered beams and invagination of cylindrical and spherical shells provide insight into some of the mechanical aspects that must be considered in studying morphogenetic mechanisms.

Morphogenesis of the peri-implant mucosa: an experimental study in dogs

PURPOSE

The objective of the present experiment was to study the morphogenesis of the mucosal attachment to implants made of c.p. titanium.

MATERIAL AND METHODS

All mandibular premolars were extracted in 20 Labrador dogs. After a healing period of 3 months, four implants (ITI Dental Implant System) were placed in the right and left sides of the mandible. A non-submerged implant installation technique was used and the mucosal tissues were secured to the conical marginal portion of the implants with interrupted sutures. The sutures were removed after 2 weeks and a plaque control program including daily cleaning of the remaining teeth and the implants was initiated. The animals were sacrificed and biopsies were obtained at various intervals to provide healing periods extending from Day 0 (2 h) to 12 weeks. The mandibles were removed and placed in the fixative. The implant sites were dissected using a diamond saw and processed for histological analysis.

RESULTS

Large numbers of neutrophils infiltrated and degraded the coagulum that occupied the compartment between the mucosa and the implant during the initial phase of healing. At 2 weeks after surgery, fibroblasts were the dominating cell population in the connective tissue interface but at 4 weeks the density of fibroblasts had decreased. Furthermore, the first signs of epithelial proliferation were observed in specimens representing 1-2 weeks of healing and a mature barrier epithelium occurred after 6-8 weeks of healing. The collagen fibers of the mucosa were organized after 4-6 weeks of healing.

CONCLUSION

It is suggested that the soft-tissue attachment to implants placed using a non-submerged installation procedure is properly established after several weeks following surgery.

Regulation of adult intestinal epithelial stem cell development by thyroid hormone duringXenopus laevis metamorphosis

During amphibian metamorphosis, most or all of the larval intestinal epithelial cells undergo apoptosis. In contrast, stem cells of yet-unknown origin actively proliferate and, under the influence of the connective tissue, differentiate into the adult epithelium analogous to the mammalian counterpart. Thus, amphibian intestinal remodeling is useful for studying the stem cell niche, the clarification of which is urgently needed for regenerative therapies. This review highlights the molecular aspects of the niche using the Xenopus laevis intestine as a model. Because amphibian metamorphosis is completely controlled by thyroid hormone (TH), the analysis of TH response genes serves as a powerful means for clarifying its molecular mechanisms. Although functional analysis of the genes is still on the way, recent progresses in organ culture and transgenic studies have gradually uncovered important roles of cell-cell and cell-extracellular matrix interactions through stromelysin-3 and sonic hedgehog/bone morphogenetic protein-4 signaling pathway in the epithelial stem cell development.

Shh/BMP-4 signaling pathway is essential for intestinal epithelial development duringXenopuslarval-to-adult remodeling

During amphibian larval-to-adult intestinal remodeling, progenitor cells of the adult epithelium actively proliferate and differentiate under the control of thyroid hormone (TH) to form the intestinal absorptive epithelium, which is analogous to the mammalian counterpart. We previously found that TH-up-regulated expression of bone morphogenetic protein-4 (BMP-4) spatiotemporally correlates with adult epithelial development in the Xenopus laevis intestine. Here, we aimed to clarify the role of BMP-4 in intestinal remodeling. Our reverse transcriptase-polymerase chain reaction and in situ hybridization analyses indicated that mRNA of BMPR-IA, a type I receptor of BMP-4, is expressed in both the developing connective tissue and progenitor cells of the adult epithelium. More importantly, using organ culture and immunohistochemical procedures, we have shown that BMP-4 not only represses cell proliferation of the connective tissue but promotes differentiation of the intestinal absorptive epithelium. In addition, we found that the connective tissue-specific expression of BMP-4 mRNA is up-regulated by sonic hedgehog (Shh), whose epithelium-specific expression is directly induced by TH. These results strongly suggest that the Shh/BMP-4 signaling pathway plays key roles in the amphibian intestinal remodeling through epithelial-connective tissue interactions.

Post-embryonic remodelling of neurocranial elements: a comparative study of normal versus abnormal eye migration in a flatfish, the Atlantic halibut

The process of eye migration in bilaterally symmetrical flatfish larvae starts with asymmetrical growth of the dorsomedial parts of the ethmoid plate together with the frontal bones, structures initially found in a symmetrical position between the eyes. The movement of these structures in the future ocular direction exerts a stretch on the fibroblasts in the connective tissue found between the moving structures and the eye that is to migrate. Secondarily, a dense cell population of fibroblasts ventral to the eye starts to proliferate, possibly cued by the pulling forces exerted by the eye. The increased growth ventral to the eye pushes the eye dorsally. Osteoblasts are deposited in the dense cell layer, forming the dermal part of the lateral ethmoid, and at full eye migration this will cover the area vacated by the migrated eye. When the migrating eye catches up with the previous migrated dermal bones, the frontals, these bones will be remodelled to accommodate the eye. Our findings suggest that a combination of extremely localized signals and more distant factors may impinge upon the outcome of the tissue remodelling. Early normal asymmetry of signalling factors may cascade on a series of events.

Procollagen C proteinase enhancer 1 genes are important determinants of the mechanical properties and geometry of bone and the ultrastructure of connective tissues

Procollagen C proteinases (pCPs) cleave type I to III procollagen C propeptides as a necessary step in assembling the major fibrous components of vertebrate extracellular matrix. The protein PCOLCE1 (procollagen C proteinase enhancer 1) is not a proteinase but can enhance the activity of pCPs approximately 10-fold in vitro and has reported roles in inhibiting other proteinases and in growth control. Here we have generated mice with null alleles of the PCOLCE1 gene, Pcolce, to ascertain in vivo roles. Although Pcolce-/- mice are viable and fertile, Pcolce-/- male, but not female, long bones are more massive and have altered geometries that increase resistance to loading, compared to wild type. Mechanical testing indicated inferior material properties of Pcolce-/- male long bone, apparently compensated for by the adaptive changes in bone geometry. Male and female Pcolce-/- vertebrae both appeared to compensate for inferior material properties with thickened and more numerous trabeculae and had a uniquely altered morphology in deposited mineral. Ultrastructurally, Pcolce-/- mice had profoundly abnormal collagen fibrils in both mineralized and nonmineralized tissues. In Pcolce-/- tendon, 100% of collagen fibrils had deranged morphologies, indicating marked functional effects in this tissue. Thus, PCOLCE1 is an important determinant of bone mechanical properties and geometry and of collagen fibril morphology in mammals, and the human PCOLCE1 gene is identified as a candidate for phenotypes with defects in such attributes in humans.

Tissue integration and tolerance to meshes used in gynecologic surgery: An experimental study

OBJECTIVE

To evaluate the tissue integration of and tolerance to five different mesh types used in genital prolapse surgery to provide mechanical support.

STUDY DESIGN

We placed five different meshes (Vicryl, Vypro, Prolene, Prolene soft, and Mersuture) on the peritoneums of 12 pigs. After 10 weeks, we used light microscopy to analyze the tissue integration of and tolerance to these meshes. We looked for inflammation, vascularization, fibroblasts, collagen fibers and the organization of connective tissue.

RESULTS

The absorbable prostheses made of polyglactin 910 (Vicryl) and the non-absorbable prostheses made of polypropylene (Prolene and Prolene soft) induced the least severe inflammatory reactions. Tissue integration was best with the polypropylene meshes, which allowed the development of a well-organized, fibrous, mature, connective tissue.

CONCLUSION

The tissue response to prosthetic meshes depends on the material used and its structure. This work highlights the feasibility of carrying out experimental studies to test the tolerance to and integration of biomaterials used in gynecology. Such studies need to be carried out whenever new prostheses become available to validate their use in common practice.

Dermal connective tissue development in mice: an essential role for tenascin-X

Deficiency of the extracellular matrix protein tenascin-X (TNX) causes a recessive form of Ehlers-Danlos syndrome (EDS) characterized by hyperextensible skin and hypermobile joints. It is not known whether the observed alterations of dermal collagen fibrils and elastic fibers in these patients are caused by disturbed assembly and deposition or by altered stability and turnover. We used biophysical measurements and immunofluorescence to study connective tissue properties in TNX knockout and wild-type mice. We found that TNX knockout mice, even at a young age, have greatly disturbed biomechanical properties of the skin. No joint abnormalities were noted at any age. The spatio-temporal expression of TNX during normal mouse skin development, during embryonic days 13-19 (E13-E19), was distinct from tropoelastin and the dermal fibrillar collagens type I, III, and V. Our data show that TNX is not involved in the earliest phase (E10-E14) of the deposition of collagen fibrils and elastic fibers during fetal development. From E15 to E19, TNX starts partially to colocalize with the dermal collagens and elastin, and in adult mice, TNX is present in the entire dermis. In adult TNX knockout mice, we observed an apparent increase of elastin. We conclude that TNX knockout mice only partially recapitulate the phenotype of TNX-deficient EDS patients, and that TNX could potentially be involved in maturation and/or maintenance of the dermal collagen and elastin network.

In vivo comparison of suburethral sling materials

In vivo tissue responses were compared for three commercially available polypropylene suburethral slings that differ markedly in fabric structure and in size of resulting interstices and pores. All three elicited the same basic inflammatory response; however, individual fabric structures produced distinct differences in tissue formation within each mesh. The presence of numerous, closely spaced, small diameter filaments prevented formation of extensive fibrous connective tissue within two slings (ObTape and IVS Tunneller mesh). The much larger diameter monofilament and open knit structure of the Monarc sling permitted the most extensive fibrous tissue integration. These differences may be of interest to physicians considering clinical use.

A technique for augmenting the palatal connective tissue donor site: clinical case report and histologic evaluation

This case report describes a simple method for augmenting tissue at prospective palatal connective tissue donor sites. The patient was referred for treatment of facial marginal tissue recession on the maxillary left canine. Clinical examination indicated that the palatal mucosa was thin and did not provide an adequate volume of soft tissue for donor harvesting, precluding the use of a palatal connective tissue graft for treatment of the recession defect. Sterile lyophilized bovine collagen sponge was therefore surgically inserted between a full-thickness palatal flap and bone at the prospective donor site. Eight weeks postoperative, the augmented palatal donor area showed a significant clinical increase in thickness and volume and served as a connective tissue donor source in the treatment of the facial marginal tissue recession. Histologic analysis of the donor tissue demonstrated normal structure, fibrous connective tissue, and abundant collagen. Clinical examination 6 months following surgery showed complete root coverage, with tissue texture, volume, and color similar to those of the adjacent soft tissue. Healing of the donor site was uneventful. This case report demonstrates that sterile lyophilized collagen sponge material may be used to augment palatal donor connective tissue and can subsequently be used as a donor source for soft tissue grafting.

De novo engineering of reticular connective tissue in vivo by silk fibroin nonwoven materials

Biologically tolerated biomaterials are the focus of intense research. In this work, we examined the biocompatibility of three-dimensional (3D) nonwovens of sericin-deprived, Bombyx mori silk fibroin (SF) in beta-sheet form implanted into the subcutaneous tissue of C57BL6 mice, using sham-operated mice as controls. Both groups of mice similarly healed with no residual problem. Macroarray analysis showed that an early (day 3) transient expression of macrophage migration inhibitory factor (MIF) mRNA, but not of the mRNAs encoding for 22 additional proinflammatory cytokines, occurred solely at SF-grafted places, where no remarkable infiltration of macrophages or lymphocytes subsequently happened. Even an enduring moderate increase in total cytokeratins without epidermal hyperkeratosis and a transient (days 10-15) upsurge of vimentin occurred exclusively at SF-grafted sites, whose content of collagen type-I, after a delayed (day 15) rise, ultimately fell considerably under that proper of sham-operated places. By day 180, the interstices amid and surfaces of the SF chords, which had not been appreciably biodegraded, were crammed with a newly produced tissue histologically akin to a vascularized reticular connective tissue, while some macrophages but no lymphocytic infiltrates or fibrous capsules occurred in the adjoining tissues. Therefore, SF nonwovens may be excellent candidates for clinical applications since they both enjoy a long-lasting biocompatibility, inducing a quite mild foreign body response, but no fibrosis, and efficiently guide reticular connective tissue engineering.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by lysophosphatidic acid

Lysophosphatidic acid (LPA) is a bioactive phospholipid having growth factor-like activity on fibroblasts and is involved in cardiovascular diseases such as hypertension and heart failure by inducing vascular remodeling, characterized by fibroblast proliferation and migration in adventitia. Among various bioactive factors that LPA works with, adrenomedullin (ADM) is a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We studied rat aortic adventitia to explore the possible paracrine/autocrine interaction between endogenous ADM and LPA. LPA stimulation of the adventitia to secrete ADM and express its mRNA was concentration dependent. ADM inhibited LPA-induced proliferation in adventitial cells and attenuated the activity of mitogen-activated protein kinase (MAPK) stimulated by LPA. In contrast, treatment with specific antagonists of the ADM receptor potentiated the LPA-induced proliferation in adventitial cells. We concluded that LPA stimulates the adventitia to produce and secrete ADM, which in turn regulates the vascular biological effects of LPA.

Modelling of anisotropic growth in biological tissues. A new approach and computational aspects

In this contribution, we develop a theoretical and computational framework for anisotropic growth phenomena. As a key idea of the proposed phenomenological approach, a fibre or rather structural tensor is introduced, which allows the description of transversely isotropic material behaviour. Based on this additional argument, anisotropic growth is modelled via appropriate evolution equations for the fibre while volumetric remodelling is realised by an evolution of the referential density. Both the strength of the fibre as well as the density follow Wolff-type laws. We however elaborate on two different approaches for the evolution of the fibre direction, namely an alignment with respect to strain or with respect to stress. One of the main benefits of the developed framework is therefore the opportunity to address the evolutions of the fibre strength and the fibre direction separately. It is then straightforward to set up appropriate integration algorithms such that the developed framework fits nicely into common, finite element schemes. Finally, several numerical examples underline the applicability of the proposed formulation.

Blubber development in bottlenose dolphins (Tursiops truncatus)

Blubber, the lipid-rich hypodermis of cetaceans, functions in thermoregulation, buoyancy control, streamlining, metabolic energy storage, and locomotion. This study investigated the development of this specialized hypodermis in bottlenose dolphins (Tursiops truncatus) across an ontogenetic series, including fetuses, neonates, juveniles, subadults, and adults. Blubber samples were collected at the level of the mid-thorax, from robust specimens (n = 25) that stranded along the coasts of North Carolina and Virginia. Blubber was dissected from the carcass and its mass, and the depth and lipid content at the sample site, were measured. Samples were prepared using standard histological methods, viewed by light microscopy, and digital images of blubber captured. Images were analyzed through the depth of the blubber for morphological and structural features including adipocyte size, shape, and numbers, and extracellular, structural fiber densities. From fetus to adult, blubber mass and depth increased proportionally with body mass and length. Blubber lipid content increased dramatically with increasing fetal length. Adult and juvenile blubber had significantly higher blubber lipid content than fetuses, and this increase was reflected in mean adipocyte size, which increased significantly across all robust life history categories. In juvenile, subadult, and adult dolphins, this increase in cell size was not uniform across the depth of the blubber, with the largest increases observed in the middle and deep blubber regions. Through-depth counts of adipocytes were similar in all life history categories. These results suggest that blubber depth is increased during postnatal growth by increasing cell size rather than cell number. In emaciated adults (n = 2), lipid mobilization, as evidenced by a decrease in adipocyte size, was localized to the middle and deep blubber region. Thus, in terms of both lipid accumulation and depletion, the middle and deep blubber appear to be the most metabolically dynamic. The superficial blubber likely serves a structural role important in streamlining the animal. This study demonstrates that blubber is not a homogeneous tissue through its depth, and that it displays life history-dependent changes in its morphology and lipid content.

Connective tissues: signalling by tenascins

Different connective tissue cells secrete different types of tenascins. These glycoproteins contribute to extracellular matrix (ECM) structure and influence the physiology of the cells in contact with the tenascin containing environment. Tenascin-C expression is regulated by mechanical stress. It shows highest expression in connective tissue surrounding tumors, in wounds and in inflamed tissues where it may regulate cell morphology, growth, and migration by activating diverse intracellular signalling pathways. Thus, integrin and syndecan signalling is influenced by tenascin-C and the levels and/or activies of several proteins involved in intracellular signalling pathways are regulated by its presence. Tenascin-X is important for the proper deposition of collagen fibers in dermis and patients with a tenascin-X deficiency suffer from Ehlers Danlos syndrome. Tenascin-R (and -C) is prominent in the nervous system and has an impact on neurite outgrowth and synaptic functions, and tenascin-W is found in the extracellular matrix of bone, muscle, and kidney. Cell facts:bone: osteoblasts produce tenascin-C, -W cartilage: perichondrial cells produce tenascin-C tendon: fibroblasts produce tenascin-C smooth muscle cells produce tenascin-W, -C skeletal muscle: endo-, peri-, and epimysial fibroblasts produce tenascin-X dermal fibroblasts produce tenascin-X tumors: stromal fibroblasts produce tenascin-C wounds: fibroblasts produce tenascin-C nervous system: glial cells produce tenascin-R, -C, -X.

Dural closure, cord approximation, and clot removal: enhancement of tissue sparing in a novel laceration spinal cord injury model

OBJECT

Laceration-induced spinal cord injury (SCI) results in the invasion of a connective tissue scar, progressive damage to the spinal cord due to complex secondary injury mechanisms, and axonal dieback of descending motor pathways. The authors propose that preparation of the spinal cord for repair strategies should include hematoma removal and dural closure, resulting in apposition of the severed ends of the spinal cord. Such procedures may reduce the size of the postinjury spinal cord cyst as well as limit scar formation.

METHODS

Using a novel device, the Vibraknife, the authors created a dorsal hemisection of the spinal cord at C-6 in the adult rat. In Group 1 (eight rats), the dura mater was repaired with apposition of the two stumps of the spinal cord to reduce the lesion gap. In Group 2 (10 rats), the dura was not closed and the two cord stumps were not approximated. All rats were killed at 4 weeks postinjury, and the spinal cords from each group were removed and examined using histological, stereological, and immunohistochemical methods. In Group 1 rats a significant reduction of the total lesion volume and connective tissue scar was observed compared with those in Group 2 (Student t-test, p < 0.05). Approximation of the stumps did not promote the regeneration of corticospinal tract fibers or sensory axons through the lesion site.

CONCLUSIONS

Apposition of the severed ends of the spinal cord by dural closure reduces the lesion gap, cystic cavitation, and connective tissue scar formation. These outcomes may collectively reduce secondary tissue damage at the injury site and shorten the length of the lesion gap, which will facilitate transplantation-mediated axonal regeneration after laceration-induced SCI.

Age-dependent morphometrical changes in the thymus of male propranolol-treated rats

In order to elucidate a putative role of neurally derived noradrenaline in the thymus development, and in maintenance of adult thymus structure, sexually immature male rats (21-day-old at the beginning of treatment) and young adult animals (75-day-old on the beginning of treatment) were treated with the non-selective beta-adrenoceptor antagonist propranolol (0.40 mg/100 g BW/day, s.c.) for 15 consecutive days, and their thymuses were analyzed stereologically. The effects of beta-adrenoceptor blockade were much more pronounced in sexually immature than in adult rats. In immature propranolol-treated rats the thymus size and volumes of both the main compartments (cortex and medulla) were significantly decreased reflecting, at least partly, a reduction in the overall number of thymocytes. Furthermore, in both the cortical subcompartments (outer and deep cortex) the mean diameter of thymocytes was increased. However, in adult rats exposed to propranolol treatment, only the volume of interlobular connective tissue was enlarged, whereas in the outer part of the cortex the mean thymocyte diameter was increased. These results indicate that the lack of sympathetic input (via beta-adrenoceptors) during the prepubertal period of development diminishes the normal thymus growth and/or accelerates the thymic involution that starts at puberty, immediately after its maximum size is reached, while it is less significant for the maintenance of the thymus size and structure in adults. Additionally, they suggest that distinct cell types, as well as thymocyte subsets, are sensitive to lack of beta-adrenoceptor-mediated influences in sexually immature and adult rats.

Age-dependent remodeling of connective tissue: role of fibronectin and laminin

Connective tissues differ from other tissues in their more abundant extracellular matrix (ECM). This matrix is composed of a relatively large number of macromolecules interacting with each other as well as with the cells they are surrounding. Such cells, fibroblasts, chondrocytes and others, secrete the macromolecules of ECM according to a genetically and environmentally regulated "program". It appeared recently that one type of macromolecular interactions is characterized by the selective cleavage of some of the ECM components. Some of these proteolytic cleavage products were shown to possess remarkable biological activities absent from the parent molecules. Such mechanisms were shown to play an important role in aging processes. Also called matricryptins such peptides and their activities are produced from several matrix components. Of special interest are these matricryptins which are derived from fibronectin, laminin and elastin. Their production by proteolytic attack of the original ECM components, followed by their novel biological activities, form in some instances autoamplifying vicious circles. Such "epigenetic", post-translational mechanisms are not coded in the genome, they are neither "accidental", nor "chaotic" but remarkably predictable, the result of the presence in several ECM components of "matricryptic" sites and coregulated synthesis of matrix components carrying such sites and of proteolytic enzymes producing the matricryptins. Some examples will be discussed, derived from the experiments carried out in our laboratory and others over the years, involved in aging and in some of the age-dependent pathologies.

Remodelling of continuously distributed collagen fibres in soft connective tissues

Extracellular matrix remodelling plays an essential role in tissue engineering of load-bearing structures. The goal of this study is to model changes in collagen fibre content and orientation in soft connective tissues due to mechanical stimuli. A theory is presented describing the mechanical condition within the tissue and accounting for the effects of collagen fibre alignment and changes in fibre content. A fibre orientation tensor is defined to represent the continuous distribution of collagen fibre directions. A constitutive model is introduced to relate the fibre configuration to the macroscopic stress within the material. The constitutive model is extended with a structural parameter, the fibre volume fraction, to account for the amount of fibres present within the material. It is hypothesised that collagen fibre reorientation is induced by macroscopic deformations and the amount of collagen fibres is assumed to increase with the mean fibre stretch. The capabilities of the model are demonstrated by considering remodelling within a biaxially stretched cube. The model is then applied to analyse remodelling within a closed stented aortic heart valve. The computed preferred fibre orientation runs from commissure to commissure and resembles the fibre directions in the native aortic valve.

Microenvironment and phenotypic stability specify tissue formation by human articular cartilage-derived cells in vivo

During in vitro expansion, adult human articular cartilage-derived cells (HACDC) lose their phenotypic stability and capacity to form cartilage in vivo after 4-6 population doublings (PD). Nevertheless, HACDC can be efficiently expanded for up to 20 PD. Here we show that HACDC can generate cartilage, fibrous tissue, skeletal muscle, bone, and adipocytes depending on the balance between phenotypic stability and environmental cues. When 5 x 10(6) cells were injected intramuscularly into nude mice, early-passage (EP)-HACDC formed cartilage; late-passage (LP)-HACDC formed mostly fibrous tissue, but a limited number of cells contributed to muscle formation. When 0.5 x 10(6) cells were injected into regenerating mouse muscle, both EP- and LP-HACDC integrated with host myofibers and expressed muscle genes, but a number of EP-HACDC maintained collagen type II expression. HACDC seeded into Collagraft and implanted subcutaneously into nude mice formed scattered bone islands displaying immunoreactivity for human osteocalcin, and expressing human bone-specific genes. Importantly, neither collagen type II transcript nor cartilage tissue was detected at 8 weeks after implantation. Myogenic, osteogenic, and adipogenic differentiation was induced in vitro using specific culture conditions. These findings provide evidence that in vivo tissue formation by HACDC is specified by a balance between environmental cues and the inherent phenotypic stability.

Magnetic resonance image attributes of the bovine corpus luteum during development and regression

To determine whether magnetic resonance (MR) image attributes of the corpus luteum (CL) reflect its physiologic status at different phases of the bovine ovarian cycle, we analyzed the numerical pixel values (NPVs), relaxation rates, proton densities (PDs), and apparent diffusion coefficients (ADCs) from T(1)-, T(2)-, and diffusion-weighted in vitro images and maps of the CL acquired at defined phases of luteal function. Ovaries were removed and serum samples taken on days 3, 6, and 10, or >/=17 (day 0 = ovulation), representing metestrus (n = 10), early diestrus (n = 7), mid-diestrus (n = 9), and proestrus (n = 7), respectively. Regions of interest (ROIs) in each quadrant of the CL (which occupied at least 20% of the quadrant) were selected for analysis. Three MR image slices were analyzed: the slice with the greatest cross-sectional area of the CL, and the slices acquired immediately before and after that slice. The mean NPVs of the CL in T(1)-weighted images increased at each phase from metestrus (1,104 +/- 40 msec) to early diestrus (1,119 +/- 77 msec), to late diestrus (1,206 +/- 43 msec) and proestrus (1446 +/- 80 msec; P < 0.001). The mean NPVs in T(1)-weighted images were higher in regressing CL (proestrous) than in any other phase (P < 0.002). Grayscale heterogeneity of CL in T(1)-weighted images tended to increase during regression (P < 0.07). Regressing CL (proestrus) exhibited higher T(1)-weighted mean NPVs (P < 0.01) and tended to have greater heterogeneity (P < 0.06) than growing (metestrus) and mature (diestrus) CL, even though similar progesterone concentrations were observed. The increased brightness and heterogeneity of regressing CL in T(1)-weighted images appeared to be correlated with increased connective tissue and triglyceride content and decreased vascularity. It is anticipated that diagnostic markers for luteal viability and atresia in the in vitro bovine model will be applied to in vivo studies in women.

Suture growth modulated by the oscillatory component of micromechanical strain

Sutures are fibrous connective tissue articulations between intramembranous craniofacial bones. Sutures are composed of fibroblastic cells with their matrices in the center and osteogenic cells in the periphery producing a matrix that is mineralized during skeletal growth. Whether oscillatory forces stimulate sutural growth is unknown. In the present work, we applied static and cyclic forces with the same peak magnitude of 5N to the maxilla in growing rabbits and quantified (1) acute in vivo sutural bone strain responses and (2) chronic growth responses in the premaxillomaxillary suture (PMS) and nasofrontal suture (NFS). Bone strain recordings showed that the waveforms of static force and 1-Hz cyclic force were expressed as corresponding static and cyclic sutural strain patterns in both the PMS and NFS, with the mean peak PMS strain (-1451 +/- 137 microepsilon for the cyclic and -1572 +/- 138 microepsilon for the static) approximately 10-fold higher than the mean peak NFS strain (124 +/- 9 microepsilon for the cyclic and 134 +/- 9 microepsilon for the static). Strain polarity was the opposite: compressive for the PMS but tensile for the NFS. However, on application of repetitive 5N cyclic and static forces in vivo for 10 minutes/day over 12 days, cyclic loading induced significantly greater sutural widths for the compressed PMS (95.1 +/- 8.3 microm) than sham control (69.8 +/- 8.2 microm) and static loading (58.9 +/- 2.8 microm; p < 0.01). Interestingly, the same trend was true for the NFS under tensile strain: significantly greater sutural width for cyclic loading (267.4 +/- 64.2 microm) than sham control (196.0 +/- 10.1 microm) and static loading (169.9 +/- 11.4 microm). Cell counting in 110 x 110 microm grids laid over sutures disclosed significantly more sutural cells on repetitive cyclic loading than sham control and static loading (p < 0.05) for both the PMS and NFS. Fluorescent labeling of newly formed sutural bone demonstrated more osteogenesis on cyclic loading in comparison with sham control and static loading. Thus, the oscillatory component of cyclic force or more precisely the resulting cyclic strain experienced in sutures is a potent stimulus for sutural growth. The increased sutural growth by cyclic mechanical strain in the tensed NFS and compressed PMS suggests that both microscale tension and compression induce anabolic sutural growth response.

Decorin expression during development of bovine skeletal muscle and its role in morphogenesis of the intramuscular connective tissue

Decorin is a small leucine-rich proteoglycan suspected of playing an important role in tissue morphogenesis. However, its role in the development of skeletal muscle is less clear. In the present study, the expression and spatial distribution of decorin in developing skeletal muscle of bovine fetuses were investigated, in order to provide a background for understanding the function of decorin in morphogenesis of the intramuscular connective tissue that supports muscle fibres. Western blot analysis showed that decorin already existed in skeletal muscle by 2.5 months of fetal development, and that decorin had a longer glycosaminoglycan chain in the early fetal stages than in later development, but its core protein was of the same size. Decorin mRNA was expressed at 1 month of fetal development, although its level was relatively low. Indirect immunofluorescence microscopy demonstrated that decorin was located in the perimysium which consisted of collagen fibres, but not in the endomysium which was composed of collagen fibril networks in fetal skeletal muscle. The relatively integrated structure of the perimysium had already formed by 2.5 months of fetal development, when muscle fibres were not tightly assembled and the surrounding endomysium was not well organized. These results suggest that decorin contributes to the formation and stabilization of collagen fibres in the perimysium that support muscle fibres assembled with myogenesis.

Development of different mast cell types in the opossum Didelphis albiventris

Previous studies have disclosed three types of mast cell in opossums: connective tissue (CTMC), mucosal (MMC), and lymphatic sinus (LSMC). In contrast to most opossum lymph nodes, the mesenteric lymph node is virtually devoid of LSMC, displaying medullary cord CTMC. The present study aimed to describe the development of these mast cell populations. Toluidine blue staining and a histochemical method for demonstrating heparin allowed the identification of immature and mature mast cells. Immature CTMC devoid of detectable heparin were rare until postnatal day 10. Mature CTMC filled with heparin-containing granules became numerous by day 30 to day 40. In the ileum, despite the presence of mature CTMC in the submucosa and mucosa (villus base), immature mast cells first appeared in the villus core by day 65 and adult features were apparent by day 100. In LSMC-containing lymph nodes, immature mast cells were found in lymphatic sinuses by day 10. Clear signs of LSMC differentiation were observed from day 20. Compared with the 10-day value, the mean diameter of cytoplasmic granules at day 40 had doubled and that at day 110 had tripled. In the mesenteric lymph nodes, immature mast cells differentiated into lymphatic sinus CTMC-like cells. After day 80, most of them were located in medullary cords. Weaning and complete maturation of mucosa preceded the differentiation of MMC. In lymph nodes, LSMC differentiation occurred in parallel with the development of the medullary region and deep cortex units.

Altered expression of connective tissue genes in postnatal chondroinduced human dermal fibroblasts

In a novel model for postnatal chondroinduction, normal human dermal fibroblasts (hDFs) cultured with demineralized bone powder (DBP) express chondrocyte features after 7 days. Representational difference analysis (RDA) prior to overt chondroblastogenesis (3 days) revealed altered expression of connective tissue genes (collagens, collagen receptors, and post-translational enzymes). Northern or RT-PCR analysis at 3, 7, 14, or 21 d showed different expression patterns for those genes. COL3A1 was transiently upregulated, whereas upregulation of COL11A1, integrin alpha-11, lysyl oxidase, and lysyl hydroxylase 2 mRNAs persisted for 7 days. Downregulation of decorin was sustained for 21 d. The expression of the post-translational enzymes induced by DBP was unique when compared with human skin and human articular chondrocytes. Thus, the data suggest an "induced chondroblast" stage with a unique connective tissue gene expression profile that may result in a matrix supportive of chondrogenesis by postnatal cells.

Bone mineral and soft tissue measurements by dual-energy X-ray absorptiometry during growth

There have been several previous compilations of reference ranges of total body bone mineral measured by dual-energy X-ray absorptiometry (DXA) in children and young adults during growth, but little attempt to compare the results or to consider differences arising from the use of instruments from different manufacturers. We measured bone mineral and soft tissue in 216 girls, aged 11-17 years, using a Hologic scanner. Our results were compared with those from four other studies, all performed on white subjects, but in different countries, and including measurements performed with Hologic, Lunar, and Norland scanners. The general pattern of bone growth with age was very similar in all the studies. Quantitative differences could largely be accounted for by known differences of calibration of DXA scanners from the different manufacturers. When bone mass was plotted against lean or total mass instead of age there were also close similarities. An apparent difference between boys and girls in one study was shown to be due to differences in soft tissue composition, rather than different patterns of bone growth. Conclusions from this apparent difference concerning the effect of estrogen at puberty were shown to be unwarranted.

Morphogenesis of the branchial vascular sector

The branchial and dorsal cephalic vascular sectors correspond to the blood vessels contained within evolutionarily recent and ancestral parts of the head, respectively. Recent work demonstrates that neural crest cells (NCCs) provide the pericytes, and connective and smooth muscle cells to the entire branchial sector in an ordered fashion. Initial NCC position is transposed to the vascular distal-to-proximal axis, explaining why circumscribed cephalic vascular anomalies are often associated with reproducible malformations in head tissues derived from the neural crest. Unlike the rest of the central nervous system, the forebrain requires mesenchyme-containing vascular-competent NCCs to survive during embryogenesis and beyond.

Isolation of connective-tissue-specific genes involved in Xenopus intestinal remodeling: thyroid hormone up-regulates Tolloid/BMP-1 expression

To clarify connective-tissue-specific genes involved in adult epithelial development during amphibian intestinal remodeling, we have isolated 16 cDNA clones derived from the anterior part of Xenopus laevis intestine cultured in vitro by using subtractive suppression hybridization. Among four genes identified, the expression of Xtld, a Xenopus homolog of Drosophila Tolloid closely related to bone morphogenic protein-1 (BMP-1), was most remarkably up-regulated during metamorphosis. To further explore the roles of Xtld in intestinal remodeling, we examined its developmental expression in the X. laevis intestine by in situ hybridization and northern blot analysis. Xtld mRNA first became detectable in the connective tissue just before the appearance of adult epithelial primordia. Subsequently, the level of Xtld mRNA reached a high in the connective tissue, concomitantly with adult epithelial development along the anteroposterior axis of the intestine. Thereafter, towards the completion of metamorphosis, the expression of Xtld mRNA was down-regulated. Thus, the expression profile of Xtld mRNA spatiotemporally correlates well with adult epithelial development in vivo. Furthermore, the present culture study has shown that thyroid hormone (TH) up-regulates the expression of Xtld mRNA organ-autonomously in the anterior part of the intestine, but not in its posterior part, and that TH up-regulation of Xtld expression is not mediated by the epithelium. These results suggest that TH directly up-regulates Xtld expression in the connective tissue along the anteroposterior axis, which in turn plays important roles in adult epithelial development during amphibian intestinal remodeling.

Development of components of the extracellular matrix, basal lamina and sarcomere in chick quadriceps and pectoralis muscles

1. The purpose of this study was to investigate differences in the development of components of the cell/matrix linkage in two functionally different muscle types: the pectoralis muscle, a major locomotory muscle in birds but not particularly functional in chickens, and the quadriceps muscle, a smaller and more functionally active muscle in the chicken. 2. The development of the extracellular matrix, basal lamina and sarcomere in the pectoralis and quadriceps muscles in chick embryos was examined biochemically to determine differences in the rate of development between these two muscles. Samples of these muscle types were dissected out from chick embryos from embryonic day 10 until 8 weeks post hatch. 3. Using SDS-PAGE electrophoresis and western blotting with antibodies against sarcomeric actin, laminin and collagens I, III and IV, it was apparent that muscle development begins earlier in the quadriceps muscle than in the pectoralis, and that late in the developmental process (d 18) both muscle types were well differentiated. The final concentration of collagens in the mature muscle remained higher in the quadriceps than in the pectoralis muscle. 4. The onset of development of the extracellular matrix, basal lamina and sarcomere was earlier in the quadriceps than the pectoralis, which could have functional implications for these muscles as a whole.

Fibrous tissue armoring increases the mechanical strength of an impacted bone graft

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.

Thyroid-hormone-dependent and fibroblast-specific expression of BMP-4 correlates with adult epithelial development during amphibian intestinal remodeling

We have identified one of the genes that are up-regulated by thyroid hormone (TH) in Xenopus laevis small intestine as the Xenopus homolog of bone morphogenetic protein-4 (BMP-4). To clarify possible roles of BMP-4 in intestinal remodeling during metamorphosis, we have examined its expression in X. laevis intestine by using in situ hybridization and organ culture techniques. At the beginning of metamorphic climax, BMP-4 mRNA first becomes detectable in the connective tissue, concurrently with the appearance of adult epithelial primordia. Subsequently, when the adult epithelial primordia are actively proliferating, BMP-4 mRNA becomes more abundant only in the connective tissue with a gradient toward the epithelium. Thereafter, as the adult primordia differentiate, the level of BMP-4 mRNA gradually decreases. Thus, BMP-4 expression correlates well with cell proliferation and/or initial differentiation of the adult epithelium, but not with apoptosis of the larval epithelium. Furthermore, the present culture study indicates that (1) TH-induced expression of BMP-4 mRNA is higher in the anterior part of the intestine than in the posterior part, which agrees with the better development of the adult epithelium in the more anterior part, and that (2) the expression of BMP-4 mRNA is up-regulated by TH in the presence of epithelium, but not in its absence. Therefore, BMP-4, which is indirectly induced by TH through some epithelial factor(s), probably plays important roles in adult epithelial development during amphibian intestinal remodeling.

How is a tissue built?

Tissues change in many ways in the period that they are part of a living organism. They are created in fairly repeatable structural patterns, and we know that the patterns are due to both the genes and the (mechanical) environment, but we do not know exactly what part or percentage of a particular pattern to consider the genes, or the environment, responsible for. We do not know much about the beginning of tissue construction (morphogenesis) and we do not know the methods of tissue construction. When the tissue structure is altered to accommodate a new loading, we do not know how the decision is made for the structural reconstruction. We do know that tissues grow or reconstruct themselves without ceasing to continue with their structural function, but we do not understand the processes that permit them to accomplish this. Tissues change their structures to altered mechanical environments, but we are not sure how. Tissues heal themselves and we understand little of the structural mechanics of the process. With the objective of describing the interesting unsolved mechanics problems associated with these biological processes, some aspects of the formation, growth, and adaptation of living tissues are reviewed. The emphasis is on ideas and models. Beyond the objective is the hope that the work will stimulate new ideas and new observations in the mechanical and chemical aspects of developmental biology.

Age-related decrease of the perineuronal satellite cell number in the rabbit spinal ganglia

This study was undertaken to establish whether a change in the perineuronal satellite cell number contributes to the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies, observed to occur in rabbit spinal ganglia. The volumes of the nerve cell bodies and the numbers of the related satellite cell nuclei were estimated on serial semithin sections from young adult and old rabbits. As satellite cells are mononucleate, the number of the nuclei corresponds to that of these cells. The satellite cell sheaths in both age groups were also examined under the electron microscope. The mean number of satellite cells was significantly smaller in the aged animals than in the young adults although the mean volume of the nerve cell bodies was significantly larger in the former. Cytoplasmic vacuoles, invaginations of the connective tissue and autophagic vacuoles were more frequent in the old rabbits. Satellite cells with pyknotic nuclei and remnants of degenerated satellite cells were only found in aged animals, although rather rarely. The decrease in the satellite cell number is one of the mechanisms by which the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies takes place. The decrease in the satellite cell number seems to occur, at least in part, through cell degeneration. However, other mechanisms (e.g., detachment of satellite cells from the perineuronal sheaths) cannot be excluded. Since satellite cells play a role in neuronal support, the significant decrease in their number probably has negative consequences for neuronal activity.