Effect of retinoic acid on chondrocyte glycosaminoglycan biosynthesis

Distinct patterns of gene expression in the superficial, middle and deep zones of bovine articular cartilage

Hyaline articular cartilage will not heal spontaneously, and lesions in hyaline articular cartilage often result in degenerative joint disease. Considerable progress has been made with respect to the responsive stem cells, inductive signals and extracellular scaffolding required for the optimal regeneration of cartilage. However, many challenges remain, such as topographic differences in the functional zones of articular cartilage. We hypothesized that a distinct set of differentially expressed genes define the surface, middle and deep zones of hyaline articular cartilage. Microarray analysis of bovine articular cartilage from the superficial and middle zones revealed 52 genes differentially expressed ≥ 10-fold and 114 additional genes differentially expressed ≥ five-fold. However, no genes were identified with a ≥ five-fold difference in expression when comparing articular cartilage from the middle and deep zones. There are distinct, differential gene expression patterns in the superficial and middle zones of hyaline articular cartilage that highlight the functional differences between these zones. This investigation has implications for the tissue engineering and regeneration of hyaline articular cartilage.

Choanal atresia: embryologic analysis and evolution of treatment, a 30-year experience

OBJECTIVES

Choanal atresia (CA) is a congenital obstruction of the posterior nasal apertures. Multiple surgical techniques have been proposed to repair the atresia. The purpose of this study is to review the basic science and embryology of CA with emphasis on the senior author's extensive experience, and refinement of the treatment of CA. In addition, we will review the outcomes after surgical correction of pediatric patients with CA.

PATIENTS AND METHOD

: Retrospective review of 73 pediatric patients. Demographic information was recorded, including type of CA, concomitant medical problems, surgical method, and date of last follow-up by the surgeon.

RESULTS

Our series show a 1.6:1 ratio of unilateral atresia to bilateral atresia. The incidence in males and females is statistically equal. High-arched palate and cross-bite deformities are particularly present if the patients undergo the transpalatal approach in the first year of life. The senior author has evolved to favoring the endoscopic approach, having a minimal long-term complication rate, and low stenosis rate (12%).

CONCLUSIONS

The first repair of choanal atresia is the one most likely to succeed. The nasal endoscopic technique is the favored technique. It has the advantages of a low restenosis rate, does not violate the palate, and does not cause the cross-bite and palate arch deformities seen in the transpalatal technique.

Milk growth factor (MGF) induces transformation into ATDC5 cells, prechondrocytes, and cooperates with retinoic acid to transform the cells into new forms

The effects of milk growth factor (MGF) showed the transformation of ATDC5 prechondrocytes and differed from that of retinoic acid (RA) as follows. MGF (200 ng/ml) did not suppress the proliferation of ATDC5 cells, though RA (1 x 10(-7) M) suppressed the cell proliferation. However, MGF showed the result as RA, which was verified to suppress the production of proteoglycan. The synthesis of vimentin in ATDC5 cells was slightly induced by RA, but its withdrawal induced the large-scale induction and the fibril formation of vimentin, which may indicate that the cells became fibroblastic cells, namely dedifferentiation. MGF, which hardly induced the vimentin synthesis in ATDC5 cells, induced its synthesis under control by the withdrawal. MGF suppressed the synthesis of alpha-smooth muscle actin (alpha-SM-actin), which was apt to reverse in its withdrawal. However, RA did not affect this synthesis of ATDC5 cells. The combination of MGF and RA enlarged the cells and enhanced the synthesis of vimentin due to RA under control, however, almost terminated alpha-SM-actin-synthesis in the cells. And its effect is almost irreversible. Furthermore, the combination of MGF and RA prevented the induction of fibroblasts due to RA in the cells. And the withdrawal of the mixture transformed prechondrocytes into hypertrophic cells. Then, MGF contributes to bone metabolism in prechondrocyte.

Discovery of sonic hedgehog expression in postnatal growth plate chondrocytes: differential regulation of sonic and Indian hedgehog by retinoic acid

Sonic hedgehog (Shh) is a key signal protein in early embryological patterning of limb bud development. Its analog, Indian hedgehog (Ihh), primarily expressed during early cartilage development in prehypertrophic chondrocytes, regulates proliferation and suppresses terminal differentiation of postnatal growth plate (GP) chondrocytes. We report here for the first time that both Shh and Ihh mRNA are expressed in the GP of rapidly growing 6-week-old broiler-strain chickens. They are also expressed in other tissues such as articular chondrocytes, kidney, and bone. In situ hybridization and RT-PCR analyses reveal Shh in all zones of the GP, with peak expression in late hypertrophy. Using primary cultures of GP chondrocytes in serum-containing medium, we followed the patterns of Shh and Ihh mRNA expression as the cultures matured and mineralized. We find a cyclical expression of both hedgehog genes during the early period of culture development between day 10 and 14; when one is elevated, the other tended to be suppressed, suggesting that the two hedgehogs may play complementary roles during GP development. Retinoic acid (RA), a powerful modulator of gene expression in cell differentiation, stimulates GP chondrocytes toward terminal differentiation, enhancing mineral formation. We find that RA strongly suppresses Ihh, but enhances expression of Shh in this system. While Ihh suppresses maturation of GP chondrocytes to hypertrophy, we hypothesize that Shh acts to push these cells toward hypertrophy.

In vitro retinoid-induced growth inhibition and morphologic differentiation of canine osteosarcoma cells

OBJECTIVE

To determine differentiation and growth inhibition effects of retinoids on canine osteosarcoma cells.

SAMPLE POPULATION

3 osteosarcoma cell lines established from osteosarcomas in dogs.

PROCEDURE

Osteosarcoma cells were incubated with various concentrations of all-trans-retinoic acid and 9-cis-retinoic acid or control medium, counted daily for 10 days, and evaluated for morphologic changes. Synthesis of DNA was measured by use of a cell proliferation ELISA. To analyze effect of retinoids on colony formation on plastic dishes, cells were cultured for 14 days, fixed, and stained; number of colonies was counted.

RESULTS

In a dose-dependent manner, both retinoids induced morphologic differentiation and growth inhibition in the 3 osteosarcoma cell lines and inhibited each cell's ability to form anchorage-dependent colonies.

CONCLUSION AND CLINICAL RELEVANCE

Retinoids induced differentiation of osteosarcoma cells of dogs, resulting in altered expression of their malignant phenotype. Induction of differentiation by retinoids may have potential as an adjunctive treatment for osteosarcoma in dogs.

Spatio-temporal distribution of chondromodulin-I mRNA in the chicken embryo: expression during cartilage development and formation of the heart and eye

To define genes specifically expressed in cartilage and during chondrogenesis, we compared by differential display-polymerase chain reaction (DD-PCR) the mRNA populations of differentiated sternal chondrocytes from chicken embryos with mRNA species modulated in vitro by retinoic acid (RA). Chondrocyte-specific gene expression is downregulated by RA, and PCR-amplified cDNAs from both untreated and RA-modulated cells were differentially displayed. Amplification products only from RNA of untreated chondrocytes were further analyzed, and a cDNA-fragment of the chondromodulin-I (ChM-I) mRNA was isolated. After obtaining full length cDNA clones, we have analyzed the mRNA expression patterns at different developmental stages by RNase protection assay and in situ hybridization. Analysis of different tissues and cartilage from 17-day-old chicken embryos showed ChM-I mRNA only in chondrocytes. During somitogenesis of the chicken embryo, ChM-I transcripts were detected in the notochord, the floor and the roof plate of the neural tube, and in cartilage precursor tissues such as the sclerotomes of the somites, the developing limbs, the pharyngeal arches, the otic vesicle, and the sclera. ChM-I continued to be expressed in differentiated cartilages derived from these tissues and also in noncartilaginous domains of the developing heart and retina. Thus, in the chicken, the expression of ChM-I is not restricted to mature cartilage but is already present during early development in precartilaginous tissues as well as in heart and eye.

Retinoids and their receptors in skeletal development

The embryonic vertebrate limb serves as an excellent experimental model system in which to study mechanisms that regulate morphogenesis of the skeleton. The appendicular skeleton arises through the process of endochondral ossification, whereby a cartilage template is initially formed and subsequently replaced by bone. One molecule that has a dramatic effect on these processes is the vitamin-A metabolite, retinoic acid (RA). RA functions through a class of nuclear hormone receptors, the retinoic acid receptors (RARs) and retinoid-X-receptors (RXRs), to regulate gene transcription. Experimental evidence from RA teratogenesis suggests that the presence of ligand-activated RARs and/or inappropriate expression of RARs inhibits chondrogenesis. Conversely, genetic analysis has shown that the absence of the receptors can lead to deficiencies in cartilage formation while also promoting chondrogenesis at ectopic sites. Taken together, these studies suggest that the RARs play a fundamental role in the early stages of skeletal development, specifically those involved in the formation of prechondrogenic condensations and their subsequent differentiation into chondroblasts.

Retinoic acid stimulates matrix calcification and initiates type I collagen synthesis in primary cultures of avian weight-bearing growth plate chondrocytes

The effect of retinoic acid (RA) on primary cultures of growth plate chondrocytes obtained from weight-bearing joints was examined, Chondrocytes were isolated from the tibial epiphysis of 6- to 8-week-old broiler-strain chickens and cultured in either serum-containing or serum-free media. RA was administered at low levels either transiently or continuously after the cells had become established in culture. Effects of RA on cellular protein levels, alkaline phosphatase (AP) activity, synthesis of proteoglycan (PG), matrix calcification, cellular morphology, synthesis of tissue-specific types of collagen, and level of matrix metalloproteinase (MMP) activity were explored. RA treatment generally increased AP activity and stimulated mineral deposition, especially if present continuously. RA also caused a shift in cell morphology from spherical/polygonal to spindle-like. This occurred in conjunction with a change in the type of collagen synthesized: type X and II collagens were decreased, while synthesis of type I collagen was increased. There was also a marked increase in the activity of MMP. Contrasting effects of continuous RA treatment on cellular protein levels were seen: they were enhanced in serum-containing media, but decreased in serum-free HL-1 media. Levels of RA as low as 10 nM significantly inhibited PG synthesis and caused depletion in the levels of PG in the medium and cell-matrix layer. Thus, in these appendicular chondrocytes, RA suppressed chondrocytic (PG, cartilage-specific collagens) and enhanced osteoblastic phenotype (cell morphology, type I collagen, alkaline phosphatase, and mineralization).

Chondrocyte differentiation

Data obtained while investigating growth plate chondrocyte differentiation during endochondral bone formation both in vivo and in vitro indicate that initial chondrogenesis depends on positional signaling mediated by selected homeobox-containing genes and soluble mediators. Continuation of the process strongly relies on interactions of the differentiating cells with the microenvironment, that is, other cells and extracellular matrix. Production of and response to different hormones and growth factors are observed at all times and autocrine and paracrine cell stimulations are key elements of the process. Particularly relevant is the role of the TGF-beta superfamily, and more specifically of the BMP subfamily. Other factors include retinoids, FGFs, GH, and IGFs, and perhaps transferrin. The influence of local microenvironment might also offer an acceptable settlement to the debate about whether hypertrophic chondrocytes convert to bone cells and live, or remain chondrocytes and die. We suggest that the ultimate fate of hypertrophic chondrocytes may be different at different microanatomical sites.

Differential and stage dependent effects of retinoic acid on chondrogenesis and synthesis of extracellular matrix macromolecules in chick craniofacial mesenchyme in vitro

Retinoic acid (RA) is well known to be a potent teratogen and induces a variety of facial defects in vivo, but at concentration levels lower than those that cause facial defects, RA seems to play an important role in normal facial development. In a previous study, we demonstrated the ability of RA to stimulate chondrogenesis in vitro in HH stage 23/24 chick mandibular (MND) but not frontonasal (FNP) mesenchyme cultured in a serum-free medium. The present study furthers these results by examining the effects of RA on chondrogenesis of chick facial mesenchyme at earlier embryonic stages and the effects on cell proliferation and synthesis of specific extracellular matrix macromolecules at stage 23/24. MND and FNP cells were cultured as micromasses for 4 days in defined media. As described previously, chondrogenesis in stage 23/24 MND cells was significantly enhanced by concentrations of RA of 0.1-1 ng/ml; however, at all earlier stages examined (18 to 22) RA at these concentrations had no significant effect. Higher concentrations of the retinoid inhibited chondrogenesis in MND cultures from all stages tested. Cells of the FNP from all stages displayed no significant change in chondrogenesis below 1 ng/ml RA and a dose dependent inhibition at higher concentrations. Thus RA's promotional effects in the face are not only tissue specific (MND), but also stage-dependent (HH 23/24). The specific effects of RA on matrix production and cell proliferation of stage 23/24 MND and FNP cells was examined by analysis of 35S sulfate, 3H thymidine and 3H proline incorporation. Analysis of 35S sulfate incorporation into sulfated proteoglycans confirmed that concentrations of RA of 0.1-1 ng/ml stimulated cartilage matrix production in MND but not FNP cultures. Above this level of RA, 35S sulfate incorporation was reduced in both. Likewise, 3H proline incorporation into collagenous protein, and to a lesser extent non-collagenous proteins, was stimulated by low levels of RA in MND, but not FNP cultures. Higher concentrations of the retinoid in either MND or FNP cultures did not lower collagen production, undoubtedly due to stimulation of non-chondrogenic cells within the population. This indicates that levels of RA as high as 100 ng/ml cause phenotypic change rather than cell death. This last point is corroborated by the analysis of 3H thymidine uptake in the cultures which was only transiently modified in most. The data indicate that cell proliferation occurred even in the presence of high RA levels.

Complete cDNA sequence of chicken vigilin, a novel protein with amplified and evolutionary conserved domains

The complete cDNA (4375 bp), coding for a new protein called vigilin, was isolated from chicken chondrocytes. The cDNA shows an open reading frame of 1270 amino acids which are organized in 14 tandemly repeated homologous domains. Each domain consists of two subdomains, one with a conserved sequence motif of 35 amino acids (subdomain A) and another one with a presumptive alpha-helical structure of 21-33 amino acids (subdomain B). 149 amino acids at the N-terminus and 71 amino acids at the C-terminus of vigilin do not show the characteristic domain structure. No sequence characteristic of a signal peptide has been found, which argues for an intracellular localisation of vigilin. Vigilin is highly expressed in freshly isolated chicken chondrocytes but little in chondrocytes after prolonged time in culture. Vigilin mRNA exists in two size species, 4.4 kb and 6.5 kb in length due to the usage of different polyadenylation sites. Comparison of the vigilin sequence with data bases showed a remarkable similarity to protein HX from Saccharomyces cerevisiae [Delahodde, A., Becam, A. M., Perea, J. & Jacq, C. (1986) Nucleic Acids Res. 14, 9213-9214]. The yeast protein consists of eight homologous domains with 11 conserved amino acid residues within a set of 35 amino acids. The N-terminal and C-terminal regions of vigilin and protein HX do not reveal any sequence similarity. These results, together with the demonstration of the characteristic vigilin sequence motif in a human cDNA clone, suggest that the repeats represent evolutionary conserved autonomous domains within a family of proteins found in yeast, chicken and man.

Hypertrophic chondrocytes undergo further differentiation in culture

Conditions have been defined for promoting growth and differentiation of hypertrophic chondrocytes obtained in culture starting from chick embryo tibiae. Hypertrophic chondrocytes, grown in suspension culture as described (Castagnola P., G. Moro, F. Descalzi Cancedda, and R. Cancedda. 1986. J. Cell Biol. 102:2310-2317), when they reached the stage of single cells, were transferred to substrate-dependent culture conditions in the presence of ascorbic acid. Cells showed a change in morphology, became more elongated and flattened, expressed alkaline phosphatase, and eventually mineralized. Type II and X collagen synthesis was halted and replaced by type I collagen synthesis. In addition the cells started to produce and to secrete in large amount a protein with an apparent molecular mass of 82 KD in reducing conditions and 63 KD in unreducing conditions. This protein is soluble in acidic solutions, does not contain collagenous domains, and is glycosylated. The Ch21 protein, a marker of hypertrophic chondrocytes and bone cells, was synthesized throughout the culture. We have defined this additional differentiation stage as an osteoblast-like stage. Calcium deposition in the extracellular matrix occurred regardless of the addition of beta glycerophosphate to the culture medium. Comparable results were obtained both when the cells were plated at low density and when they were already at confluence and maintained in culture without passaging up to 50 d. When retinoic acid was added to the hypertrophic chondrocyte culture between day 1 and day 5 the maturation of the cells to the osteoblast-like stage was highly accelerated. The switch in the collagen secretion was already observed after 2 d and the production of the 63-kD protein after 3 d. Mineralization was observed after 15-20 d.

Influence of retinol on human chondrocytes in agarose culture

Vitamin A and its congeners, collectively called retinoids, are known to have teratogenic potential and have induced craniofacial and limb malformations in numerous animal species. More importantly, retinoids are recognized as teratogenic to fetuses of pregnant women who have taken such preparations for dermatologic disorders. Information gathered from the study of animal models suggests that retinoids interfere with cartilage differentiation. If chondrogenesis in limb development is disturbed it may contribute to limb reductions and malformations. In vitro studies using various animal systems have shown that cartilage matrix macromolecules are altered to resemble those secreted by mesenchymal cells. The response of human chondrocytes to retinoids in vitro is not known. Culture of human chondrocytes in agarose maintains the cartilage phenotype and therefore serves as a model system to evaluate the influence of retinoids directly on human chondrogenesis. The studies presented in this paper were done to determine if the expression of specific matrix macromolecules of human chondrocytes in agarose culture is altered by retinol treatment. Immunocytochemistry demonstrated enhanced labeling of type I collagen while type II collagen labeling was reduced in cultures treated with retinol. In addition, morphometric analyses indicated a decrease in the size and number of chondrogenic clusters and that individual cells synthesized less alcian blue matrix when compared to parallel control cultures. The size of the proteoglycan monomers, glycosaminoglycan side chains as well as the disaccharide composition were not affected. However, there was a reduction in the quantity of proteoglycan monomers produced.

Retinoic acid treatment induces type X collagen gene expression in cultured chick chondrocytes

The vitamin A derivative retinoic acid (RA) is widely thought to be involved in cartilage development, but its precise roles and mechanisms of action in this complex process remain unclear. We have tested the hypothesis that RA is involved in chondrocyte maturation during endochondral ossification and, in particular, is an inducer of maturation-associated traits such as type X collagen and alkaline phosphatase. Immature chondrocytes isolated from the caudal region of Day 19 chick embryo sterna were seeded in secondary monolayer cultures and treated either with a high dose (100 nM) or with physiological doses (10-35 nM) of RA for up to 3 days. We found that after an initial lag of about 24 h, physiological doses of RA indeed induced type X collagen gene expression in the immature cells. This induction was not accompanied by obvious changes in expression of the type II collagen and large aggregating proteoglycan core protein genes. As revealed by immunocytochemistry, 30-35% of the cells in cultures treated with RA for 3 days were engaged in type X collagen production. Interestingly, these cells were relatively similar in size to chondrocytes in which no type X collagen was detected, suggesting that chondrocytes can initiate type X collagen production independent of cell hypertrophy. RA treatment also led to increased alkaline phosphatase activity occurring as early as 24 h after the start of treatment. The data in this study indicate that RA may have a role in endochondral ossification as an inducer/promoter of maturation-associated traits during chondrocyte maturation.

Differential effects of physiological concentrations of retinoic acid in vitro on chondrogenesis and myogenesis in chick craniofacial mesenchyme

Recent studies have shown that in the developing limb bud retinoic acid is a skeletal morphogen at physiological levels, but a potent teratogen at higher levels. Retinoic acid has also been shown to be teratogenic during facial development, but very low levels may have an as yet unspecified role in normal development. In the present study the effects of retinoic acid on chondrogenesis and myogenesis by craniofacial cells grown in micromass cell culture were investigated. Retinoic acid, at concentrations of 0.01-100 ng/ml, was supplied to cells derived from day-4 (H.H stage 23/24) chick embryo mandibular, maxillary and frontonasal processes, grown in micromass cultures for 4 days in both serum-containing and defined media. Based on Alcian-blue-staining, concentrations of retinoic acid of 0.1-1 ng/ml were found to enhance chondrogenesis by mandibular cells grown in defined medium, while greater concentrations up to 100 ng/ml inhibited chondrogenesis. By contrast, chondrogenesis was generally retarded by all concentrations of retinoic acid applied to frontonasal cells grown in defined medium and when applied to both mandibular and frontonasal cells when grown in serum-containing medium. Cells from stage-23/24 maxillae did not display any significant chondrogenic activity in either medium under these culture conditions. Unlike chondrogenesis, myogenesis in mandibular, frontonasal and maxillary cultures was greater in defined than serum-containing medium, based on the appearance of immunologically detectable muscle myosin, and was reduced considerably less in defined medium by all concentrations of retinoic acid tested. In the presence of serum however, myogenesis was retarded with increasing concentrations of retinoic acid beyond 1 ng/ml in micromass cultures from all three facial regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations between heparan sulfate metabolism and hepatoma growth

A rat hepatoma cell line (Gershenson et al., Science, 170:859-861, 1970) contains a dynamic steady-state pool of free heparan sulfate (HS) chains in the nucleus that increases in amount when growing cells reach confluence (Fedarko and Conrad, J. Cell Biol., 102:587-599, 1986). In logarithmically growing cells labeled with 35SO4(2-) steady-state levels of [35SO4]HS in the nucleus are altered by a variety of culture conditions. Rapidly dividing cells (doubling time = 18-22 h) growing under optimized conditions had steady-state levels of nuclear HS within the range of 40-50 pmol 35SO4 in nuclear HS/10(6) cells. The steady-state levels of nuclear HS were lowered by several changes in culture conditions, including 1) additions of 1 mM p-nitrophenyl-beta-D-xyloside, 0.25-0.5 mM (+)-catechin, 0.5 ng/ml transforming growth factor beta, 20 ng/ml phorbol-12-myristate-13-acetate, 1 mM dibutyryl cAMP, or 1 mM inositol-2-PO4; 2) decreased levels of D-glucose; or 3) deletions of serum, insulin, or inositol. In all cases lowering of the nuclear HS level was accompanied by an increase in the cell doubling times, suggesting a correlation in which nuclear HS levels must be optimized for maximal growth rates. When cells cultured under optimal growth conditions reached confluence, the level of nuclear HS increased threefold and the cells stopped dividing. The same culture conditions that lowered the steady-state levels of HS in the logarithmically growing cells prevented this rise in the nuclear HS as the cells reached confluence and resulted in loss of contact inhibition and overgrowth of the confluent cultures. These observations suggest a second correlation in which elevated nuclear HS levels are found when cell growth is inhibited at confluence; prevention of this rise results in continued growth. Consistent with this correlation between elevated nuclear HS and reduced growth rates, it was observed that addition of either 0.5 microgram/ml hydrocortisone or 0.05 microgram/ml retinoic acid to the culture medium of logarithmically growing cultures resulted in increases in steady-state levels of nuclear HS that were accompanied by increased cell doubling times. The two agents that increased the levels of nuclear HS in logarithmically growing cultures had little effect on levels of nuclear HS in confluent cells or on contact inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Commitment of adipocyte differentiation in 3T3 cells is inhibited by retinoic acid, and the expression of lipogenic enzymes is modulated through cytoskeleton stabilization

Retinoic acid (RA), at 1-10 microM, inhibited adipose conversion of 3T3-F442A cells as determined by the activities of lipogenic enzymes, glycerophosphate dehydrogenase (GPD) and malic enzyme. This inhibition was reversible by RA removal, but the increase in lipogenic enzyme activities was considerably delayed in a dose-dependent manner. The onset of the two lipogenic enzyme activities could be regulated somewhat independently, suggesting that expression of the two enzymes is subject to noncoordinated regulation. The RA-inhibited cells had a more flattened and elongated shape, suggesting cytoskeletal changes. Cytochalasin B (CB) did not prevent RA inhibition and did not promote adipose conversion in cultures supplemented with nonadipogenic medium. Reversion of inhibition was accelerated if cells were cultured for 3 days with adipogenic medium containing CB. The drug promoted an early increase in lipogenic enzyme activities. On the other hand, cells cultured on fibronectin-coated dishes, a condition that stabilizes actin cytoskeleton, do not undergo adipocyte differentiation. However, we show here that cells cultured on fibronectin and changed to nonadipogenic medium containing insulin underwent adipose conversion; in contrast, cells treated with RA and then supplemented with nonadipogenic medium containing insulin, but without the retinoid, did not undergo differentiation. We conclude that RA blocks adipose conversion probably before commitment to differentiation, and modulates lipogenic enzyme expression in a noncoordinated manner through changes in cytoskeletal elements, whereas fibronectin blocks phenotype expression in differentiating cells.

Teratogenic effects of retinoic acid and dimethylsulfoxide on embryonic chick wing and somite

In order to document the stage(s) at which the embryonic chick wing bud is sensitive to vitamin A teratogenesis and the kinds of defects produced by vitamin A insult to the embryonic chick wing, 1-microgram doses of retinoic acid (1 microliter RA in 90% DMSO at a concentration of 1 microgram/microliter) were locally applied to the right wing bud of chick embryos at stages 17-23 (Hamburger and Hamilton: J. Morphol., 88:49-92, '51), and the resulting limb skeleton anatomy was observed at 10 days of incubation. Local application of RA at stages 17-20 resulted in distal wing skeleton defects. There were significantly more wing skeleton defects among embryos treated at these stages with RA solution than among solvent (DMSO)-treated control embryos and than among untreated control embryos. Wings of embryos treated with RA at stages 21-23 were always normal. Scapular and vertebral defects were seen at 10 days of incubation among embryos which had been treated prior to stage 21 with both the RA solution and the solvent control. Statistical analysis and histological data suggest that scapular and vertebral defects were caused by DMSO-induced damage to somites.

Comparative effects of retinoic acid and jervine on chondrocyte differentiation

Jervine and retinoic acid are both teratogenic to structures which are initially modelled in cartilage. Differences in periods of maximal sensitivity, as well as in certain aspects of the morphological manifestations of exposure, indicate that these two teratogens act via different molecular mechanisms. Here we compare the effects of jervine and retinoic acid in three culture systems which represent sequential stages of the chondrocyte lineage. Proliferation of pluripotent C3H 10T 1/2 cells was decreased by exposure to jervine but was not affected by retinoic acid. Differentiation of high-density "spot" cultures of embryonic limb bud mesenchyme were sensitive to both compounds. Mature chondrocytes were resistant to jervine but "dedifferentiated" after 48-hour exposure to retinoic acid. We conclude that jervine compromises rapidly dividing chondrogenic precursors, whereas retinoic acid has little effect prior to the expression of cartilage-specific proteins.

The effect of retinoic acid on proteoglycan turnover in bovine articular cartilage cultures

This paper describes proteoglycan catabolism by adult bovine articular cartilage treated with retinoic acid as a means of stimulating the loss of this macromolecule from the extracellular matrix of cartilage. Addition of retinoic acid (10(-12)-10(-6) M) to adult bovine articular cartilage which had been labeled with [35S]sulfate for 6 h after 5 days in culture, resulted in a dose-dependent increase in the rate of loss of 35S-labeled proteoglycans from the matrix of the tissue. Concomitant with this loss was a decrease in the proteoglycan content of the tissue. Incubation of cultures treated with 1 microM retinoic acid, at 4 degrees C, or with 0.5 mM cycloheximide, resulted in a significant decrease in the rate of retinoic acid-induced loss of proteoglycans and demonstrated cellular involvement in this process. Analysis of the 35S-labeled proteoglycans remaining in the matrix showed that the percentage of radioactivity associated with the small proteoglycan species extracted from the matrix of articular cartilage explants labeled with [35S]sulfate after 5 days in culture was 15% and this increased to 22% in tissue maintained in medium alone. In tissue treated with 1 microM retinoic acid for 6 days, the percentage of radioactivity associated with the small proteoglycan was 58%. Approximately 93% of the 35S-labeled proteoglycans released into the medium of control and retinoic acid-treated cultures was recovered in high density fractions after CsCl gradient centrifugation and eluted on Sepharose CL-2B as a broad peak with a Kav of 0.30-0.37. Less than 17% of these proteoglycans was capable of aggregating with hyaluronate. These results indicate that in both control and retinoic acid-treated cultures the larger proteoglycan species is lost to the medium at a greater rate than the small proteoglycan species. The effect of retinoic acid on proteoglycan turnover was shown to be reversible. Cartilage cultures maintained with retinoic acid for 1 day then switched to medium with 20% (v/v) fetal calf serum for the remainder of the culture period exhibited decreased rates of loss of 35S-labeled proteoglycans from the matrix and increased tissue hexuronate contents to levels near those observed in tissue maintained in medium with 20% (v/v) fetal calf serum throughout. Furthermore, following switching to 20% (v/v) fetal calf serum, the relative proportions of the 35S-labeled proteoglycan species remaining in the matrix of these cultures were similar to those of control cultures.

Retinoic acid rapidly reduces cartilage matrix synthesis by altering gene transcription in chondrocytes

Retinoic acid can alter the differentiation of a variety of cell types, including chondrocytes. This action may explain the high incidence of craniofacial and limb defects resulting from exposure to retinoic acid during development, and may be the basis for the compound's inhibition of a chondrosarcoma tumor in vivo. In order to understand the mechanism of action of retinoic acid, we studied the expression of chondrocyte-specific proteins as well as other proteins that indicate a shift in the differentiated phenotype of the cell following exposure to retinoic acid. After 48 hr of exposure to retinoic acid chondrocytes stopped synthesizing the chondrocyte-specific pro alpha 1 (II) chain of collagen II and a 370-kDa precursor protein of a cartilage-specific proteoglycan. Instead, the cells synthesized increased amounts of fibronectin and the pro alpha 1 chain of collagen III. These changes could be detected as early as 12 hr after treatment. In addition, the steady-state levels of specific mRNA transcripts coding for these differentiation markers correlated with their protein synthesis levels. Also, nuclear runoff experiments indicated that retinoic acid down regulated transcription of the collagen II gene, while stimulating collagen III gene transcription. These observations suggest that retinoic acid may alter the expression of the chondrocyte phenotype by selectively changing the normal pattern of gene expression.

The effect of retinoic acid on proteoglycan biosynthesis in bovine articular cartilage cultures

The addition of retinoic acid to adult bovine articular cartilage cultures produces a concentration-dependent decrease in both proteoglycan synthesis and the proteoglycan content of the tissue. Total protein synthesis was not affected by the presence of retinoic acid, indicating that the inhibition of proteoglycan synthesis was not due to cytotoxicity. The proteoglycans synthesized in the presence of retinoic acid were similar in hydrodynamic size, ability to form aggregates with hyaluronate, and glycosaminoglycan composition to those of control cultures. However, the presence of larger glycosaminoglycan chains suggests that the core protein was substituted with fewer but longer glycosaminoglycan chains. In cultures maintained with retinoic acid, a decreased ratio of the large proteoglycan was synthesized relative to the small proteoglycan compared to that measured in control cultures. In cultures maintained with retinoic acid for 1 day and then switched to medium with 20% (v/v) fetal calf serum, the rate of proteoglycan synthesis and hexuronate contents increased within 5 days to levels near those of control cultures. Within 2 days of switching to medium with 20% (v/v) fetal calf serum, the relative proportions of the proteoglycan species were similar to those produced in cultures maintained in medium with 20% (v/v) fetal calf serum throughout. The rate of proteoglycan synthesis by bovine articular cartilage cultures exhibited an exponential decay following exposure to retinoic acid, with estimated half-lives of 11.5 and 5.3 h for tissue previously maintained in medium alone or containing 20% (v/v) fetal calf serum, respectively. The addition of 1 mM benzyl beta-D-xyloside only partially reversed the retinoic acid-mediated inhibition of proteoglycan synthesis. This indicates that the inhibition of proteoglycan synthesis by retinoic acid was due to both a decreased availability of xylosylated core protein and a decreased capacity of the chondrocytes to synthesize chondroitin sulfate chains.

Modulation of rabbit keratocyte production of collagen, sulfated glycosaminoglycans and fibronectin by retinol and retinoic acid

This study elucidates the biochemical response of rabbit corneal keratocytes (fibroblasts) to retinol and retinoic acid in their production of collagen, fibronectin, sulfated glycosaminoglycans, collagenase, and [3H]thymidine incorporation. The morphologic appearance of cultured keratocytes was not altered by retinoid treatment. Collagen production and [3H]thymidine incorporation demonstrated a parallel decline in response to retinoids. Collagen type was unaffected as was collagenase activity. Retinoids had minimal effect on cell layer-associated 35S-labeled glycosaminoglycans, however medium-soluble 35S-glycosaminoglycans were increased. The most dramatic effect was in fibronectin synthesis which was increased 2-3-fold. These data demonstrate that rabbit keratocytes alter their biosynthesis of extracellular matrices in response to retinoids. This may be significant in corneal pathology, since the delicate balance of these extracellular macromolecules is responsible for corneal integrity and stability.

Independence of cell shape and loss of cartilage matrix production during retinoic acid treatment of cultured chondrocytes

Retinoic acid has been shown to cause chondrocytes in culture to flatten and to inhibit the synthesis of cartilage specific components. Since the biochemical expression of chondrocytes is considered to be dependent on cell shape, it has been proposed that retinoic acid acts on these cells primarily by causing a change in cell morphology. This hypothesis was tested by culturing chick sternal chondrocytes suspended in methyl cellulose, which prevents cell flattening. Cultures were labeled with [35S]methionine and differentiation was assessed by polyacrylamide gel electrophoresis. The results showed that retinoic acid-treated chondrocytes in suspension remained rounded but synthesized proteins characteristic of flattened or dedifferentiated chondrocytes. Chondrocytes exposed to retinoic acid in suspension became fibroblastic when placed in monolayer culture in the absence of retinoic acid. This effect was irreversible after 2 weeks of culture. These results suggest that retinoic acid has a direct molecular or biochemical effect on the chondrocyte and that the cell shape change is secondary.

Influence of retinoic acid on the ultrastructure and hyaluronic acid synthesis of adult human epidermis in whole skin organ culture

Normal human skin was maintained in organ culture under chemically defined conditions. All-trans retinoic acid was added to the culture medium at the final concentration of 5 mumol/l. After 5 days in culture samples were either harvested for electron microscopy or labeled with 3H-glucosamine for 24 h. After labeling, epidermis was separated from dermis and both tissue compartments were analyzed for the content of 3H-labeled glycosaminoglycans (GAGs) using CPC-precipitation and thin layer chromatography after enzymatic degradation into specific disaccharides. Retinoic acid caused a marked change in the epidermal tissue architecture. The epidermal cells were flattened and contained fewer desmosomes and tonofilaments than control explants. Retinoic acid induced accumulation of fine granular material in the intercellular spaces in the upper, and less dense, flocculent material in the lower epidermis. The analysis of 3H-glycosaminoglycans showed that in the epidermis retinoic acid elevated the amount of labeled hyaluronate by 70%, whereas sulfated GAGs were not significantly increased. In dermis the incorporation of 3H-glucosamine into neither hyaluronate nor sulfated GAGs was stimulated by the retinoic acid. It is concluded that retinoic acid significantly modifies the differentiation of normal adult human epidermis by decreasing cytoskeleton components and by inducing the synthesis of new intercellular material, at least a part of which is hyaluronic acid. As a consequence, the cohesion between the epidermal cells was apparently weakened.

Retinoids inhibit the differentiation of embryonic-mouse mesenchymal cells in vitro

The influence of all-trans retinoic acid, 13-cis retinoid acid and two aromatic retinoids (Ro 10-1670, Ro 11-1430) on the chondrogenic differentiation of mesenchymal cells in vitro was studied electron-microscopically. Organ cultures of limb buds from mouse embryos (Day 11) and high-density cultures of embryonic-mouse mesenchymal cells (Day 12) were used as experimental models. After a 6-day culture in the control medium, the development of hyaline cartilage was observed in both systems. In cultures which were treated with retinoids from Day 1 through Day 3 and then incubated in the control medium for 3 more days, the mesenchymal cells still maintained the morphological features of the blastema stage; cartilage synthesis was reduced (low retinoid concentrations) or completely absent (high retinoid concentrations). These findings indicate that the treatment of embryonic-mouse mesenchymal cells with retinoids induces a persistent and dose-dependent inhibition of chondrogenic differentiation, which in quantitative terms, is variably expressed during treatment with different retinoids. These inhibitory effects of retinoids on chondrogenesis are probably implicated in the pathogenetic mechanisms of their teratogenic action in vivo.

Effect of retinoids on collagen production by chondrocytes in culture

The effect of vitamin A and of some of its derivatives on chondrocytes in culture has been studied. In the presence of retinoids the proliferation of the cells decreased and they lost their characteristic polygonal shape and assumed a fibroblast-like morphology. All retinoids also caused dedifferentiation of chondrocytes as indicated by the induction of types I and III collagen. 13-cis retinoic acid (= isotretinoin) was the most active derivative in this aspect. Since appropriate control of the synthesis of extracellular matrix proteins is a prerequisite for their normal physiological function, alterations such as those observed here may be involved in the pathogenesis of side effects which are observed during the treatment of dermatological disorders with retinoic acid derivatives.

Retinoic acid enhances the displacement of newly synthesized hyaluronate from cell layer to culture medium during early phases of chondrogenesis

Chondrogenic differentiation in mouse limb bud mesenchymal cells cultured at high density was suppressed by supplementation of the medium with retinoic acid (1 microgram/ml or 3.3 X 10(-6) M). Since in control medium overt chondrogenesis begins on day 3, retinoic acid was introduced on day 2 so that the relationship between initial biosynthetic changes and inhibition of chondrogenesis could be studied. During the first 24 h of exposure the treated cells remained viable but suffered 10% inhibition in growth and synthesized [3H]glucosamine-labeled glycosaminoglycan at a level 24% below untreated cells. The amount of labeled hyaluronic acid released into the culture medium by the treated cells was, however, 2-fold greater, on a per cell basis, than that in the untreated cultures. It is suggested that the displacement of hyaluronate may play a role in the disruption of mesenchymal cell differentiation and of limb morphogenesis as observed in other systems.

Prostaglandin stimulation of adenosine 3',5'-monophosphate accumulation in cultured chondrocytes in the presence or absence of parathyroid hormone

The effect of prostaglandin analogues on the cyclic AMP level in cultured chondrocytes were examined. Prostaglandin E1 at 0.4 to 30 microM, increased the intracellular concentration of cyclic AMP in chondrocytes. Its effect was rapid, being evident within 1 min and reaching a maximum in 10 to 20 min. The maximum level was sustained until 30 min after its addition and then decreased gradually. Prostaglandin D2 and E2 also increased the cyclic AMP level in chondrocytes, but they had less effect than prostaglandin E1. Prostaglandin A1 had no effect on the nucleotide level in chondrocytes, although they markedly increased the level in fibroblasts. The time course of stimulation of cyclic AMP accumulation in chondrocytes by prostaglandin E1, D2 or E2 was quite different from that by parathyroid hormone (PTH): the effect of prostaglandin was slower and more sustained than that of PTH. PTH potentiated the effect of prostaglandin E1, E2, or D2 on the cyclic AMP level in chondrocytes and that the combined effects of prostaglandin and PTH were more than additive. Addition of an inhibitor of cyclic nucleotide phosphodiesterase with prostaglandin, PTH or both produced a synergistic effect on the accumulation of cyclic AMP in the chondrocytes. These findings suggest that prostaglandin E1, E2, and D2 increase the synthesis of cyclic AMP and that the combined effect of the prostaglandins and PTH on the cyclic AMP level in chondrocytes is partly attributed to the synergistic synthesis of cyclic AMP in the cells.

Stimulation of cell proliferation by vitamin A derivatives on murine sarcoma virus-transformed mouse cells in serum-free culture

The effect of retinoids (Rds) on cell proliferation was studied in serum-free culture condition, using non-transformed and transformed derivatives of BALB 3T3. Cell proliferation of an SV40-transformed line was inhibited significantly by Rd treatment. However, proliferation of two cell lines that were transformed by a Kirsten and Moloney strain of murine sarcoma virus (MSV) and produced growth factor into culture medium, was remarkably stimulated by Rds. Addition of serum masked both the inhibitory and stimulatory effects of Rds.

Analysis of cartilage differentiation from skeletal muscle grown on bone matrix. III. Environmental regulation of glycosaminoglycan and proteoglycan synthesis

The ability of numerous nutritional and topographic factors to influence differentiation of embryonic mesenchyme has given rise to several theories which attempt to explain the development of muscle and cartilage from these similar-appearing cells. Some theories are challenged by the observation that a substratum of demineralized bone is capable of supporting the transformation of skeletal muscle into cartilage in vitro and that the potential to form cartilage still resides within cloned myoblasts and fibroblasts of skeletal muscle. In the present study, culture media CMRL-1066, minimal essential medium (MEM), and F-12 provide varied nutritional environments and are tested for their ability to support the morphological and biochemical transformation of skeletal muscle into cartilage. Morphologically, CMRL-1066 reproducibly supports hyaline cartilage formation, whereas MEM does so in only one out of three explants onto demineralized bone, and F-12 is incapable of supporting formation of a hyaline matrix. Biochemically, each medium is sufficient to elicit synthesis of cartilage-like patterns of sulfated glycosaminoglycans and proteoglycan monomer. Synthesis of hyaluronic acid (HA) initially increases in explants grown in CMRL-1066, but decreases prior to chondrogenesis. MEM elicits a similar increase in HA synthesis, but the subsequent decrease is not as rapid. In F-12, synthesis remains depressed throughout the experiment. The data show that increases in HA synthesis occur concurrent with the appearance of fibroblast-like cells, which normally precede chondroblasts. Decreases in HA synthesis correlate well with the onset of chondrogenesis. Explants grown in CMRL-1066 reproducibly from cartilage and synthesize the greatest amounts of proteoglycan aggregate. Those grown in MEM form cartilage infrequently, synthesize reduced amounts of proteoglycan aggregate-like material, and contain greater amounts of HA, of low molecular weight. The data demonstrate that chondrogenesis can be subtly regulated by environmental factors, and such factors regulate both the morphological and biochemical expression of the phenotype through HA synthesis.

Differentiation of 3T3-F442A cells into adipocytes is inhibited by retinoic acid

Retinoic acid at a concentration higher than 10(-6) M inhibited adipose conversion of 3T3-F442A cells in surface cultures. Since cells treated with 10(-5) M of the vitamin A analogue and the non-treated cells showed the same capacity to form colonies when seeded at low density, adipose conversion was not inhibited by a general toxic action of the retinoid. The inhibition produced was accompanied by changes in cell shape; adipose morphology was absent in retinoic acid treated cells, and they were more elongated and flattened without piling up. Adipose conversion of 3T3-F442A in Methocel suspended cultures was also inhibited by retinoic acid, suggesting the inhibition exerted by this compound was not related to the changes observed in cell shape. The inhibitory action of retinoic acid is manifested only when the cultures are treated before differentiation takes place; if the retinoid was added after some early events of adipose conversion, differentiation was not blocked. The inhibition was reversed when the drug was removed from the cultures and they were further incubated in adipogenic medium; incubation in medium without adipogenic factor did not permit reversion. On the other hand, vitamin A depleted serum showed a higher capacity to support adipose conversion than non-depleted serum. It is concluded that this vitamin A analogue blocks some early events before the cells undergo the commitment to differentiate into adipocytes.

Effects of all-trans-retinoic acid (retinoic acid) and 4-hydroxyphenylretinamide on synovial cells and articular cartilage

We studied the effects of two retinoids, naturally occurring all-trans-retinoic acid (retinoic acid) and the synthetic 4-hydroxyphenylretinamide (4-OH-PRT) on monolayer cultures of rabbit synovial fibroblasts and on explants of rabbit articular cartilage. Treatment of fibroblasts with phorbol myristate acetate (PMA; 10(-8) M) induced the synthesis and secretion of large amounts of collagenase: this was inhibited if the cells were treated with retinoic acid (10(-6) M) or dexamethasone (10(-7 M). Combined treatment with retinoic acid and the steroid prednisolone, at concentrations as low as 19(-10) M, gave an additive inhibition of collagenase production. Both retinoids inhibited collagenase production, but only 4-OH-PRT prevented the increase in prostaglandin E2 (PGE2) induced by PMA. Levels of plasminogen activator were also increased by treatment with PMA, and concomitant addition of either retinoid further enhanced this stimulation. Possible toxicity was assessed by measuring release of glycosaminoglycans (GAG) from explants of articular cartilage. Treatment with retinoic acid induced release of 80% of the total GAG, whereas treatment with 4-OH-PRT resulted in release of 40% of the total, a finding similar to that seen with untreated samples. 4-OH-PRT inhibited production of collagenase and PGE2 by rabbit synovial fibroblasts but was not toxic to articular cartilage.

Restoration by cyclic AMP of the differentiated phenotype of chondrocytes from de-differentiated cells pretreated with retinoids

Parathyroid hormone (PTH) increases the cyclic AMP level in rabbit costal chondrocytes in culture. PTH, dibutyryl cyclic AMP (DBcAMP), and 8-bromo cyclic AMP (8-Br cAMP)induce ornithine decarboxylase (ODC) and expression of the differentiated phenotype of chondrocytes in this cell system. On the other hand, retinoids inhibit expression of the differentiated phenotype of chondrocytes. In the present study, the effects of PTH, DBcAMP, and 8-Br cAMP on rabbit costal chondrocytes pretreated with retinoids were examined. PTH did not increase the cellular cyclic AMP level in de-differentiated cells that had been pretreated with retinyl acetate or retinoic acid for three days, but it did increase the cyclic AMP level four days after removal of retinoids. PTH did not stimulate ODC activity or expression of the differentiated phenotype of chondrocytes in the de-differentiated state. On the other hand, DBcAMP or 8-Br cAMP stimulated expression of the differentiated phenotype of chondrocytes even in de-differentiated cells, as judged by morphological and histological changes of the cells and increase in glycosaminoglycan synthesis. Cyclic AMP analogues also induced ODC in these cells.

Modulation of glycosaminoglycan biosynthesis by retinoids

In conclusion, retinoids modulate phenotypic changes such as morphology, adhesion, and growth rate. These changes also result in specific alterations of glycosaminoglycans. We have observed increases in the degree of sulfation in fibroblast matrix heparan sulfate and, a change in the ratio of sulfamido to ester sulfate in matrix heparan sulfate in 407 cell surface. Matrix glycosaminoglycans have been functionally implicated in cellular interactions, and have a specific role in adhesion and growth rates. Our results are consistent with the proposed role for heparan sulfate. It is possible that some of the modulation in cellular behavior resulting from retinoid treatment may be mediated by cell surface and cellular changes in heparan sulfate and other glycosaminoglycans.

Polyamine and differentiation: induction of ornithine decarboxylase by parathyroid hormone is a good marker of differentiated chondrocytes

The activity of ornithine decarboxylase (OD-Case:L-ornithine carboxy-lyase, EC 4.1.1.17) in rabbit costal chondrocytes in culture increased markedly after addition of parathyroid hormone (PTH), reaching a maximum 4 to 5 hr after PTH addition. The increase in ODCase activity was followed by increase in the intracellular concentrations of polyamines, especially putrescine, which increased in 6 hr to about 3-fold that of untreated cultures. The induction of ODCase by PTH was not observed in L, 3T3, HeLa, buffalo rat liver, or BHK cells. Retinyl acetate and retinoic acid both inhibited expression of the differentiated phenotype of chondrocytes by rabbit costal chondrocytes in culture within 3 days after their addition, as judged by morphological change and decrease in sulfate incorporation into glycosaminoglycans but did not inhibit cell proliferation. PTH could not induce an increase in ODCase in de-differentiated cells that had been pretreated with retinyl acetate or retinoic acid for 3 days. but 4 days after removal of the retinoids, these de-differentiated cells regained the ability to synthesize ODCase in response to PTH. These facts suggest that the induction of ODCase and the formation of putrescine by PTH are good markers of the differentiated phenotype of cultured chondrocytes.

Hypervitaminosis A and matrix alterations in maxillary explants from 16-day rat embryos

Hypervitaminosis A in treated pregnant rats has been shown to interfere with normal palatal closure and fusion, as demonstrated by the presence of cleft palates in offspring. The observation that palatal shelves of excess vitamin A exposed fetuses are stunted and delayed in rotation suggests that vitamin A may inhibit a biochemical event crucial to the successful contact of the palatal shelves. Maxillary explants from 16 day Wistar rat embryos cultured in the presence or absence of 30 IU/ml retinyl palmitate were analyzed for DNA, glycosaminoglycan, and collagen synthesis. Maxillary explants cultured in vitamin A-containing medium showed an inhibition in DNA, GAG, and collagen synthesis in comparison to control explants. Excess vitamin A in the culture medium of maxillary explants also resulted in a reduction of intermolecular cross-links in collagen. The possible significance of the results in terms of cleft palate and normal secondary palate formation is discussed.

Changes in chemical composition of chick embryos treated with a beta-xyloside and a lathyrogen

Nine-day chick embryos were treated with 4-methylumbelliferyl beta-D-xyloside or beta-aminopropionitrile fumarate, and their gross chemical composition was examined one week later. Total DNA was 10--20% less in embryos treated with either drug than it was in control embryos. Xyloside-treated embryos showed marked increases in percent wet weight and in sodium/DNA and chloride/DNA ratios, and small decreases in protein/DNA, hydroxyproline/DNA and sulfate/DNA. None of these parameters was affected in embryos treated with beta-aminopropionitrile. Approximately 85% of the uronic acid of control embryos was present as chondroitin sulfate, with a degree of sulfation of 80% and charge density of 1.8; all of this chondroitin sulfate was covalently linked to peptide and had a number-average molecular weight of 29,300. In embryos treated with beta-xyloside, 90% of the uronic acid was present as chondroitin sulfate, with a degree of sulfation of 40% and charge density ranging from 1 to 2; 27% of this chondroitin sulfate, with an average molecular weight of 25,400, was peptide linked, while 73% was linked to 4-methylumbelliferone and had an average molecular weight of 22,900. The chemical differences between embryos treated with the xyloside and embryos treated with the lathyrogen reinforce the conclusion on morphological grounds that these are distinct syndromes involving different aspects of the extracellular matrix.