Extravascular fluid dynamics of the embryonic chick wing bud

Principles of tissue engineered regeneration of skeletal tissues

The regeneration of adult skeletal tissues can be controlled by tissue engineered implants. The logic and general approach are outlined as an introduction to the manuscripts in this volume.

Macromolecular permeability of chick wing microvessels: an intravital confocal study

The development of the vertebrate limb requires the formation of a normal vasculature to nurture the soft and hard tissue phenotypes. The pattern of embryonic limb bud vessels has been extensively studied, but little is known about the permeability characteristics of the developing circulation. In the present study, the microvascular endothelial cell phenotype was examined by in vivo confocal microscopy following the systemic injection of a graded series of fluorescent dextrans (40,000, 70,000, 150,000 molecular weight) into chick embryos at stages 21-23 in order to determine how selective is the endothelial lining of microvessels as a partition between the blood vessels and the interstitium. Videodensitometry, over a gray scale range of 0-255, was used to quantitate the amount of tracer found within the interstitial compartment of the limb. The tracers of larger molecular weight (70,000, 150,000) were confined exclusively to the vascular lumina, whereas that of smaller molecular weight (40,000) was found to cause perivascular brightening due to extravasation into the surrounding interstitium. The reported differences in permeability were not dependent upon the stage of the embryo used in this study, but were due to the size of the tracer. These data indicate that embryonic wing microvessels demonstrate permselectivity to macromolecular efflux across the endothelium. The present results provide a basis for additional studies concerned with the dynamic characteristics of the limb microvasculature and challenge our concepts about the role of diffusible morphogens in vertebrate limb development.

Role of transforming growth factor-beta in chondrogenic pattern formation in the embryonic limb: stimulation of mesenchymal condensation and fibronectin gene expression by exogenenous TGF-beta and evidence for endogenous TGF-beta-like activity

The possible role of TGF-beta-like molecules in skeletal pattern formation in the embryonic vertebrate limb was studied by analyzing the mechanism of enhancement of chondrogenesis in chick wing bud mesenchyme in vitro and testing for the presence and distribution of endogenous TGF-beta-like activity in this tissue. Transient exposure (3-6 hr) to TGF-beta 1 (1-2 ng/ml) on the day after plating resulted in a 1.5- to 2-fold enhancement of accumulation of Alcian blue (pH 1.0)-stainable extracellular matrix 5 days later. The enhancement of differentiation was preceded by an acceleration and an increase in the extent of precartilage condensation formation, visualized by Hoffman Modulation Contrast microscopy a day after TGF-beta treatment. In contrast, neither condensation nor subsequent chondrogenesis was stimulated by transient treatment with TGF-beta 1 on the day of plating. The effectiveness of a TGF-beta treatment regimen in enhancing chondrogenesis was correlated with its effectiveness in stimulating condensation formation. Exposures to the factor for 3-6 hr on the day after plating, which most consistently stimulated both condensation formation and chondrogenesis, also corresponded to a peak in the enhancement of the steady-state level of fibronectin mRNA (fourfold to eightfold over control levels) measured at the end of the treatment period. The elevation in fibronectin mRNA levels brought about by this treatment persisted throughout the period of condensation. Endogenous TGF-beta-like activity was detected in limb mesenchyme: extracts of freshly isolated and cultured limb tissues contained 6-25 pg TGF-beta-like activity per 1 x 10(6) cells by the Mv1Lu cell proliferation inhibition assay, and indirect immunofluorescence using a polyclonal antibody directed against a TGF-beta-related peptide indicated a patchy distribution of endogenous TGF-beta-like reactivity within a day after culture. These findings are discussed in relation to the "fibronectin prepattern" hypothesis for limb pattern formation.

Endothelial heterogeneity in the chick wing bud: a morphometric study

The microvascular endothelium of the chick wing bud at stages 22, 27, and 32 was evaluated by ultrastructural morphometry. The rationale for this study is based on the hypothesis that endothelial cells exhibit variation in structure and function during cytodifferentiation. The microvessels had a luminal diameter range such that they were classified as capillaries. The thin continuous endothelium was devoid of a basal lamina. The endothelium had a very small number of plasmalemmal vesicles; vacuoles were however present for all stages and in some cases were abundant. The temporal findings were that endothelial cell thickness increases, plasmalemmal vesicle densities decrease, and the densities of cytoplasmic vacuoles increase. The spatial results were that endothelial cells in proximal regions of the limb have a greater thickness, contain fewer vesicles and have more vacuoles than those in distal regions. In general, these results indicate that endothelial ultrastructural heterogeneity occurs within a 3 1/2 day time-span of wing bud development. The discussion considers the results with regard to recent reports on endothelial cell heterogeneity.

Distribution of retinoids in the chick limb bud: analysis with monoclonal antibody

Retinoic acid induces anteroposterior duplicate formation in developing chick limb bud, and it may be a natural morphogen involved in limb pattern formation. Retinoic acid is produced from retinol locally in the limb bud via retinal, and thus, to elucidate the distribution of these retinoids in the limb bud seems to be important for the understanding of the morphogen formation. We produced a monoclonal antibody against the retinoids with BSA-RA (bovine serum albumin-retinoic acid) conjugate for antigen, and investigated the distribution of retinoids in the chick limb bud. The antibody predominantly bound to retinoic acid, but weakly to retinol and retinal. Retinoids appeared in the limb bud at stage 18 and were distributed through stages 20-24, when the pattern formation in distal mesoderm was in progress. Initially they were found evenly in the whole mesoderm, but disappeared gradually from core mesoderm and remained only in the region of peripheral mesoderm at stage 24. At stage 26, retinoids were detected only in ectoderm. These results support the idea that the retinoids actually play roles in limb pattern formation and suggest that the retinoids in the peripheral mesoderm are important for pattern formation. Further, the role of retinoids in epidermis development at later limb bud stages is also suggested.