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.