Immunofluorescent localization of collagen types I, III, IV, fibronectin and laminin during morphogenesis of scales and scaleless skin in the chick embryo

A Potential Role for MMPs during the Formation of Non-Neurogenic Placodes

The formation of non-neurogenic placodes is critical prior to the development of several epithelial derivatives (e.g., feathers, teeth, etc.) and their development frequently involves morphogenetic proteins (or morphogens). Matrix metalloproteinases (MMPs) are important enzymes involved in extracellular matrix remodeling, and recent research has shown that the extracellular matrix (ECM) can modulate morphogen diffusion and cell behaviors. This review summarizes the known roles of MMPs during the development of non-neurogenic structures that involve a placodal stage. Specifically, we discuss feather, hair, tooth, mammary gland and lens development. This review highlights the potential critical role MMPs may play during placode formation in these systems.

Multiple mechanisms contribute to the avoidance of avian epidermis by sensory axons

In birds, sensory innervation of skin is restricted to dermis, with few axons penetrating into the epidermis. This pattern of innervation is maintained in vitro, where sensory neurites avoid explants of epidermis but grow readily on dermis. We have used this coculture paradigm to investigate the mechanisms that impede innervation of avian epidermis. The lack of epidermal innervation in birds has been attributed to diffusible chondroitin sulfate proteoglycans (CSPGs) secreted by the epidermis, although direct experimental evidence is weak. We found that elimination of CSPG function with either chondroitinase or neutralizing antibodies did not promote growth of DRG neurites onto epidermis in vitro, indicating that CSPGs alone are not responsible for preventing epidermal innervation. Moreover, the failure of sensory neurites to invade epidermis is not due exclusively to soluble chemorepulsive factors, since sensory neurites also avoid dead epidermis. This inhibition can be overridden, however, by coating epidermis with the growth-promoting molecule laminin, but only if the tissue is killed first. Epidermal innervation of laminin-coated epidermis is even more robust when CSPGs are also eliminated. Thus, the absence of growth-promoting or permissive molecules, such as laminin, may contribute to the failure of sensory neurites to invade avian epidermis. Together these results show that the inhibitory character of avian epidermis is complex. Cell- or matrix-associated CSPGs clearly contribute to the inhibition, but are not solely responsible.

Dorsal dermis of the scaleless (sc/sc) embryo directs normal feather pattern formation until day 8 of development

We have examined the ability of the scaleless (sc/sc) backskin dermis (6 to 16 days of incubation) to regulate pattern formation using the presumptive scutate scale epidermis from 11-day normal embryos as the responding tissue. Prior to 8 days of incubation the sc/sc backskin dermis is able to induce hexagonally patterned and uniformly oriented feather germs in normal epidermis. This ability is lost during day 8 and follows a central to lateral gradient. Such gradients are characteristic of normal feather development in the spinal tract. We discuss the change in the inductive ability of the sc/sc dermis in relation to the stabilization of the feather pattern, which occurs all at once throughout the dorsal dermis at 7.5-8 days of development. After day 8 until day 10, the sc/sc backskin dermis only supports the formation of sporadic, unpatterned feather germs; thereafter it will not support feather formation.

Tissue-nonspecific alkaline phosphatase participates in the establishment and growth of feather germs in embryonic chick skin cultures

Alkaline phosphatase activity is present in the mesoderm of embryonic chick skin and becomes spatially restricted to the dermal condensation of the developing feather germs. Inhibitors to tissue-nonspecific (liver/bone/kidney), but not intestinal alkaline phosphatase inhibit the establishment and growth of feather germs in cultured skins. A window of maximum sensitivity to the inhibitor was observed to be the first day of culture when early development and establishment of pattern takes place. The cDNA for the avian tissue-nonspecific alkaline phosphatase was cloned and sequenced, and Southern analysis revealed a single copy of this gene in the avian genome. Northern analysis revealed that a 2.8 kb transcript for this form of alkaline phosphatase is present in developing skin.

Pattern formation in chick feather development: distribution of beta 1-integrin in normal and scaleless embryos

We have examined the immunolocalization of beta 1-integrin during feather development in the spino-lumbar tract of the backskin from normal and scaleless chick embryos. beta 1-integrin appears during early feather development in three distinct phases which correspond to important developmental events. The first phase (5-5 1/2 days of incubation; Hamburger and Hamilton [H.H.] stage 27) represents the period prior to the formation of dermis. During this phase, beta 1-integrin antiserum labels mesenchymal cells located in the central region of the spino-lumbar tract where the initiation site for feather development is located. The second phase (5 1/2-7 1/2 days of incubation; H.H. stages 28-32) corresponds to the period during which dermis is formed. The cells that make up the dermis are readily distinguished by their lack of beta 1-integrin immunostaining. The third phase (7 1/2-10 days of incubation; H.H. stages 33-36) begins with the sudden appearance of beta 1-integrin in the central and lateral regions of the dermis. The pattern of beta 1-integrin immunostaining in scaleless backskin becomes different from that of normal backskin during this phase. In normal backskin the dermal condensations of feather germs are not labeled with the beta 1-integrin antiserum. This produces a heterogeneous immunostaining pattern very similar to the pattern seen for Type I collagen (Mauger et al. [1982] Dev. Biol. 94:93-105). In contrast, homogeneous immunostaining is observed in the dermis of scaleless backskin. The initial time of appearance, manner of appearance, and pattern of integrin expression in the third phase suggest that beta 1-integrin may be involved in the stabilization of the feather pattern. We also observed the appearance of beta 1-integrin on the epidermal basal cells during the time of feather follicle formation. The beta 1-integrin antiserum reacts strongly with the baso-lateral surfaces of normal basal cells, yet the basal surfaces of the scaleless basal cells are unstained. This lack of immunostaining along the basal surfaces of the scaleless basal cells may relate to the abnormal adhesion between the epidermis and dermis in scaleless backskin.

Microinjection of antifibronectin antibodies in the chicken blastoderm: inhibition of mesoblast cell migration but not of cell ingression at the primitive streak

The involvement of fibronectin in adhesion and migration of individual mesoblast cells during chicken gastrulation was examined after microinjection of functional and nonfunctional antifibronectin antibodies in the blastoderm during the period of rapid migration of mesoblast cells. The injection of affinity-purified polyclonal antihuman fibronectin antibody (total IgG or Fab fragment) or of monoclonal antichicken cellular fibronectin caused a thickening of the primitive streak, which was composed of loosely connected cells. This effect was most evident at the level of Hensen's node, and very few mesoblast cells were observed migrating in the space between upper layer and deep layer. The obvious explanation of this effect was that the de-epithelialization of upper layer cells persisted in the presence of antibodies, but ingressed cells failed to emigrate from the primitive streak. Immunostaining of microinjected antibodies showed binding to the basement membrane, to the cell surface of mesoblast cells that had migrated before microinjection occurred, and to the cell surface of deep layer cells. Cells that ingressed and detached in the course of reincubation of the embryo possessed little immunolabelling along their cell surface. The results suggest that the failure of ingressed cells to emigrate from the primitive streak and to form mesoblast was due (1) to alterations in adhesion between newly ingressed primitive streak cells, which had the ability to detach but possessed relatively little fibronectin along their cell surfaces and a small number of cell protrusions, and (2) probably to a lack of adhesion of detached cells to the basement membrane, which was blocked by the presence of antifibronectin antibodies. We conclude that the presence of fibronectin in the basement membrane is required for emigration of ingressed cells and migration of mesoblast cells to occur. Once migration has commenced, fibronectin is also deposited along the cell surface of migrating cells, a factor that may increase their mutual adhesion.

Avian scale development. XVII: The epidermis of the scaleless (sc/sc) anterior metatarsal skin is determined, but the dermis lacks permissive cues for the patterned expression of the determined state

Embryos homozygous for the gene scaleless (sc/sc) completely lack scutate scales and the beta strata which characterize terminal differentiation of the scale ridges located on the anterior metatarsal region of the foot. Although the sc/sc epidermis cannot undergo scale morphogenesis, it can respond to the inductive dermal ridges of normal scutate scales by generating beta strata. Recently, we discovered that the anterior metatarsal epidermis of normal embryos becomes committed to the formation of beta strata prior to morphogenesis of definitive scale ridges. Here, we examined the possibility that the sc/sc anterior metatarsal epidermis also becomes determined, i.e., committed to scutate scale-specific terminal differentiation. Experimental tissue recombinants were used to assess the ability of the sc/sc epidermis to generate beta strata. The results show that the germinative cells of the 15-day sc/sc epidermis are committed to generating beta strata, even though they have not undergone scutate scale morphogenesis. Thus, the mechanisms involved in establishing epidermal determination must differ form those regulating scale morphogenesis. In addition, we examined the formation of patterned, permissive cues in the anterior metatarsal and footpad dermises of sc/sc embryos. Analysis of recombinants showed that both the 15- and 20-day dermises from the sc/sc anterior metatarsal region fail to provide cues for beta stratum formation, when associated with the determined 15-day scutate scale epidermis. Likewise, the 15-day sc/sc footpad dermis cannot support beta stratum formation. However, 20-day sc/sc footpad dermis is able to support the generation of a few abnormally patterned beta strata, demonstrating that sc/sc dermis which has experienced even limited morphogenesis is able to provide permissive cues for the terminal differentiation of the scutate scale epidermis.

The initial expression and patterned appearance of tenascin in scutate scales is absent from the dermis of the scaleless (sc/sc) chicken

Morphogenesis of the anterior metatarsal skin (scutate scale region), from 9.5 to 12 days of development, results in the formation of orderly patterned scale ridges. It is after the initial formation of the Definitive Scale Ridge that the characteristic outer and inner epidermal surfaces differentiate. The hard, plate-like beta stratum, with its unique beta keratins, characterizes the epidermis of the outer surface, while the epidermis of the inner surface elaborates an alpha stratum. The anterior metatarsal region of the scaleless mutant does not undergo scale morphogenesis. Therefore, scale ridges do not form nor do the outer and inner epidermal surfaces with their characteristic beta and alpha strata. We have found that the extracellular matrix molecule, tenascin, first appears in the scutate scale dermis at 12 days of development when the scale ridge is established. Tenascin is found in the dermis only under the scale ridge and is not associated with the dermal-epidermal junction. Tenascin is not found in scaleless anterior metatarsal dermis at this time. As outgrowth of the Definitive Scale Ridge takes place, tenascin distribution correlates closely with the formation of the outer epidermal surface of each scale ridge. By 16 days of development tenascin is also found in close association with the dermal-epidermal junction. Tenascin does not appear in scaleless anterior metatarsal dermis until 16 days of development and then it is randomly and sparsely distributed at the dermal-epidermal junction. Tenascin's initial appearance and pattern of distribution in the scutate scale dermis and its abnormal expression in the scaleless dermis suggest that morphogenesis plays a significant role in regulation of its expression.

Avian scale development. XIII. Epidermal germinative cells are committed to appendage-specific differentiation and respond to patterned cues in the dermis

The ability of the germinative cell population of scutate scale epidermis to continue to generate cells that undergo their appendage-specific differentiation (beta stratum formation), when associated with foreign dermis, was examined. Tissue recombination experiments were carried out which placed anterior metatarsal epidermis (scutate scale forming region) from normal 15-day chick embryos with either the anterior metatarsal dermis from 15-day scaleless (sc/sc) embryos or the dermis from the metatarsal footpad (reticulate scale forming region) of 15-day normal embryos. Neither of these dermal tissues are able to induce beta stratum formation in the simple ectodermal epithelium of the chorion, however, the footpad dermis develops an appendage-specific pattern during morphogenesis of the reticulate scales, while the sc/sc dermis does not. Morphological and immunohistological criteria were used to assess appendage-specific epidermal differentiation in these recombinants. The results show that the germinative cell population of the 15-day scutate scale epidermis is committed to generating suprabasal cells that follow their appendage-specific pathways of histogenesis and terminal differentiation. Of significance is the observation that the expression of this determined state occurred only when the epidermis differentiated in association with the footpad dermis, not when it was associated with the sc/sc dermis. The consistent positioning of the newly generated beta strata to the apical regions of individual reticulate-like appendages demonstrates that the dermal cues necessary for terminal epidermal differentiation are present in a reticulate scale pattern. The observation that beta stratum formation is completely missing in the determined scutate scale epidermis when associated with the sc/sc dermis adds to our understanding of the sc/sc defect. The present data support the conclusion of earlier studies that the anterior metatarsal dermis from 15-day sc/sc embryos lacks the ability to induce beta stratum formation in a foreign epithelium. In addition, these observations evoke the hypothesis that the sc/sc dermis either lacks the cues (generated during scutate and reticulate scale morphogenesis) necessary for terminal differentiation of the determined scutate scale epidermis or inhibits the generation of a beta stratum.

Spatial disorder of collagens in the great vessels, associated with congenital heart defects

Surgical ablation of the cardiac neural crest from the chicken embryo results in persistent truncus arteriosus (PTA) and a change in the elastic laminae of the great vessels, wherein elastin and the elastin microfibril show significant spatial disorder. The purpose of this study was to test the hypothesis that the interstitial collagens would also be disordered in the elastic laminae of chicken embryos with PTA. The birefringence characteristics of interstitial collagen were examined to evaluate spatial ordering. The results showed that collagen in the elastic laminae assumed an orderly configuration of well-defined fiber bundles in the great vessel walls of control embryos, whereas vessels from embryos with PTA lacked any distinct spatial order. Collagens type I and III were localized in the vessel walls. Type III collagen was the principal collagen of the elastic laminae, but was absent from the intima of all vessels. In the elastic laminae of vessels from control embryos, collagen type III showed well-defined fiber bundles whereas embryos with PTA had diffuse collagen type III in poorly defined laminae that were not separated by discrete layers of smooth muscle cells. Collagen type I was a minor component of the elastic laminae but formed robust pericellular fiber bundles throughout the media and intima. Collagen type I fibers appeared to be coarsened and less uniform in the vessels from embryos with PTA.

Identification and characterization of a proteoglycan in embryonic chicken skin that can interact with hyaluronic acid

Sulfated proteoglycans of the dorsal skin of 8.5-day-old chick embryos have been characterized in terms of their extractability from the tissue, solubility, and sedimentation and chromatographic behavior. The proteoglycans described in this communication are those that remain soluble after dialysis against 0.5 m NaCl. Two chondroitin sulfate proteoglycans (PGCS-A and PGCS-C) and a heparan sulfate proteoglycan (PGHS) have been identified. PGCS-A is the only proteoglycan found in the medium in which the skins were cultured. Under associative conditions (0.4 M guanidine-HCl) PGCS-A and PGHS are extracted. The dissociative solvents (4 M guanidine-HCl) extract more PGCS-A and PGCS-C. PGCS-C has been shown to interact with hyaluronic acid to form aggregates. These proteoglycans have densities ranging from 1.49 to at least 1.59 g/ml. In contrast cartilage proteoglycans that can aggregate with hyaluronic acid have a density of at least 1.59 g/ml. It was not possible to determine if the PGCS-C aggregates exist in vivo.

Altered proteoglycan synthesis disrupts feather pattern formation in chick embryonic skin

We have tested the role of proteoglycans in the development of feather pattern by culturing 7-day-old embryonic chick skins on medium containing para-nitrophenyl-beta-D-xyloside (2 mM). Xylosides compete with core proteins of proteoglycans by acting as exogenous acceptors for the synthesis of glycosaminoglycans leading to the synthesis of under- or unglycosylated core proteins and free glycosaminoglycans. We have demonstrated that xyloside treatment alters the structure of the proteoglycans synthesized by embryonic skin and disrupts the feather pattern. The altered pattern is seen as the fusion of individual feather rudiments. Fusion can occur diagonally, and in an anteroposterior and mediolateral direction. The effect induced by the disruption of proteoglycan structure takes place during the first 24 hr of culture during which time all the rows of feather rudiments are being established. The effect is reversible if the skins are returned to control medium after 24 hr but not after 48 hr of treatment with xyloside. Once established during the first 24 hr the feather pattern can only be slightly distorted by the xyloside treatment. The results are interpreted to mean that proteoglycans play a developmental role in the establishment of the feather pattern but not in its maintenance, suggesting that the two processes are under different developmental control. The altered feather pattern obtained by disrupting proteoglycan structure is highly similar to that obtained when skins are cultured in the presence of antibodies to L-CAM (W.J. Gallin, C.-M., Chuong, L.H. Finkel, and G.M. Edelman (1986), Proc. Natl. Acad. Sci. USA 83, 8235-8239). This observation suggests that there may be a functional relationship between the extracellular matrix and cell adhesion molecules in the establishment of feather pattern.

Immunocytochemical localization of extracellular-matrix proteins in relation to rat intestinal morphogenesis

Various extracellular-matrix proteins were detected by indirect immunofluorescence in rat intestine at various stages of development ranging from 14 days of gestation to the adult stage. At the earliest stage studied, laminin, nidogen and type-IV collagen were present at the epithelial/mesenchymal interface, whereas fibronectin and type-III procollagen were found throughout the whole mesenchyme. We were able to relate some changes in the staining patterns of extracellular-matrix proteins to morphogenetic processes. As early as 15 days of gestation, i.e. before villus formation, modifications in the distribution or in the staining intensity of all of the antigens within the mesenchyme paralleled the orientation and segregation of mesenchymal cells in the region surrounding the basal membrane and in the presumptive peripheral muscular layers. During villus outgrowth, the transient disappearance of fibronectin and particularly type-III procollagen from the top of the protruding villus core was evident. During the perinatal period, i.e. when crypts develop, the linear staining for the basal-membrane proteins became restricted to the base of the villi, their labelling along the remaining portion of the villi being more irregular. In mature rat intestine, no major modifications in matrix proteins along the crypt-villus axis in relation to epithelial differentiation were found, except that the labelling for fibronectin and type-III procollagen, which are at this stage more closely related to the basement membrane, was less pronounced in the upper part of villi.

Appearance and persistence of fibronectin in cartilage. Specific interaction of fibronectin with collagen type II

Binding of fibronectins (FN) to collagen types I-IV were studied using polyclonal antibodies against human and chicken FNs, proteoglycan monomers, collagen type II and monoclonal antibodies reacting with both soluble and insoluble forms of human FN. Plasma fibronectin and type II collagen were shown to interact specifically in a homologous system. Type II collagen, however, proved to be less effective in inhibition assays compared to other types of collagen. In high density cultures of chicken limb bud cells, fibronectin was first localized within the fibroblast-like cells of 4 hr cultures and an extensive extracellular filamentous network developed by the end of day 1. Fibronectin was present in the newly formed cartilage nodules although it seemed to disappear by day 6, when the proteoglycan accumulation became more intensive. Enzyme treatments (testicular hyaluronidase, chondroitinase ABC) helped to localize FN at this stage of development of chicken cartilage, in microdroplet high density cultures of human fetal chondrocytes and in articular cartilage. Fibronectin was localized only in the pericellular ring of intact human articular cartilage using monoclonal antibodies with the biotin-avidin system.

Altered keratin biosynthesis follows inhibition of scale morphogenesis by hydrocortisone

Hydrocortisone, administered onto the chorioallantoic membrane (CAM) of 7- to 10-day-old chick embryos, inhibits scale development, in a dose- and stage-dependent manner. The response is also region specific in that hydrocortisone treatment, at a specific dose and time, will completely block scutellate and interstitial scale development while leaving other scale types unaffected. Using histological, biochemical, and immunofluorescence techniques, we have shown that inhibition of scutellate scale morphogenesis prevents the subsequent formation of a beta stratum and alters expression of the alpha keratins. These data support the hypotheses that each avian scale type has its own distinctive temporal, morphological, and biochemical pattern of development; and in the case of scutellate scale development, hydrocortisone treatment alters keratin biosynthesis by interfering with earlier steps in morphogenesis.

Immunofluorescent localization of extracellular matrix components during muscle morphogenesis. II. In chick embryos with hereditary muscular dysgenesis (cn/cn)

The immunofluorescent distribution of types I and III collagen, fibronectin, and laminin during muscle morphogenesis of the crooked neck dwarf mutant chick embryo differs from that of the normal chick. The drastic difference is related to the inability of the mutant embryo to maintain a harmonious muscle pattern. The first sign of the defect is the disaggregation of type I collagen fibers of the tendons and the disorganization of the intermuscular spaces. The organization of the connective tissue never proceeds beyond the appearance of an epimysial envelope, rich in types I and III collagen, which becomes disorganized shortly after. No perimysial envelopes displaying types I and III collagen fibers and fibronectin, nor endomysial sheaths develop. Only large spaces filled with types I and III collagen fibers subdivide groups of muscle cells irregularly. On the whole, type III collagen is less abundant than type I collagen. Fibronectin disappears from the periphery of the muscle cell. Laminin is more thickly deposited in the basal lamina around irregularly sized muscle cells than around the normal muscle cell. The results are discussed in terms of morphogenetic interactions between connective tissue cells and muscle cells, and in terms of fibrosis, which characterizes some muscle diseases.

Avian scale development. XI. Initial appearance of the dermal defect in scaleless skin

The chicken mutant, scaleless, is characterized by the total absence of scutate scales. Previous experiments have shown that the scaleless defect is expressed by the epidermal cells while the dermal cells are able to participate in normal scale morphogenesis. However, in association with 14- to 16-day scaleless dermis, normal epidermis or the simple ectoderm of the chorion failed to develop scutate scale epidermis with its characteristic beta stratum. Thus the question arises: since the scaleless dermis starts out functioning normally, when does it become defective? Heterogenetic, heterotopic associations have been performed between 7.5-day to 11.5-day scaleless dermis and a neutral responding tissue, the midventral apteric epidermis, from 10.5-day normal embryos. The results show that up until 9.5 day of incubation the scaleless dermis is able to give instructions for normal scutate scale formation, if combined with normal epidermis. However, after 9.5 days, the scaleless dermis is not able to induce scale formation in normal apteric epidermis. Thus, the functional defect of the scaleless dermis occurs during the time (9 to 10 days of incubation) when epidermal placodes appear in normal embryos. From the present data, at least two explanations are possible. Either the scaleless epidermis is unable to respond to the placode inducing properties being provided by the scaleless dermis and because an epidermal placode does not form the scaleless dermis becomes defective, or the scaleless epidermis does not provide some earlier cue necessary for the scaleless dermis to acquire its placode inducing capabilities.

Influence of collagen and fibronectin substrates on the behaviour of cultured embryonic dermal cells

The effect of extracellular matrix components on cell patterning was studied in cultures of 7-day chick embryo dorsal dermal cells. A scale of ten stages based on cell density, distribution, and patterning has been defined. Starting from a seeding density of 3.5 X 10(5) cells per dish (diameter 35 mm) in 1.7-1.8 ml of medium supplemented with 5% fetal calf serum, cultures reached stage 8 in 7 days. When cells were cultured on a substrate of native bovine type I collagen, their patterning was retarded by 3 to 4 stages. A substrate of human fibronectin had no effect on the rate of cell patterning, when compared with a plastic substrate. However, when fibronectin was adsorbed on collagen-coated dishes, the retarding effect of collagen was suppressed, and a 'normal' rate of cell patterning was restored. When fibronectin was locally adsorbed on plastic or collagen substrates, so as to offer a heterogeneous substrate to the cells, the border between fibronectin and plastic or between fibronectin and collagen was perceived by the cells as a borderline along which they tended to align.