Glycosaminoglycans and glycosaminoglycan-degrading enzyme of Rana catesbeiana back skin during late stages of metamorphosis

Dermatan sulfate is the major metachromatic glycosaminoglycan in the integument of the anuran Bufo ictericus

Glycosaminoglycans from the ventral and dorsal integuments of the anuran Bufo ictericus were characterized based on biochemical and histochemical methods. Dermatan sulfate is the major metachromatic glycosaminoglycan found in these tissues, but small amount of heparan sulfate was also detected. The average molecular mass of the dermatan sulfate is approximately 20 kDa, similar to the glycosaminoglycan isolated from mammalian skin. In addition, the amphibian integument contains high amounts of hyaluronic acid, especially in the ventral area. We also observed that the glycosaminoglycans occur in the anuran integument as irregular deposits through the spongious dermis and in the mast cells, as revealed by histochemical analysis using Alcian blue, dimethylmethylene blue and toluidine blue stains. The concentration and composition of glycosaminoglycans found in the amphibian integument resemble those from mammalian skin except for the higher concentration of hyaluronic acid in the amphibian tissue. Possibly, this observation indicates that the function of the sulfated glycosaminoglycan in these tissues has been preserved during evolution, although the amphibian integument and the human skin have their own particular physiology.

Water content, body weight and acid mucopolysaccharides, hyaluronidase and beta-glucuronidase in response to aestivation in Australian desert frogs

This study investigates the effects of aestivation on body water content, body mass, acid mucopolysaccharide (AMPS) and some of its degrading enzymes in different tissues for some Australian desert frogs. The AMPS component of the liver, kidney, skin and cocoon alter during aestivation to help retain water, which is unchanged in most tissues of all frog species, and to protect the frogs from desiccation during extended periods of aestivation. Hepatic AMPS was unaltered in Cyclorana maini, C. platycephala and Neobatrachus sutor but increased significantly after 2 months of aestivation in C. australis. The level of AMPS in the kidney was elevated in all four frog species after 5 months of aestivation. Skin AMPS content in the skin of awake frogs decreases with aestivation period and increases in the cocoon. AMPS in the cocoon probably works as a cement between the cocoons' layers and its physical presence presumably contributes to preventing water flux. Changes in AMPS content in different tissues were accompanied by significant changes in both hyaluronidase and beta-glucuronidase activities, which play an important role in AMPS metabolism. Alcian blue staining of control and digested skin of C. australis and C. platycephala with testicular hyaluronidase indicated the presence of AMPS, concentrated in a thin layer (called ground substance, GS) located between stratum compactum and stratum spongiosum, and acid mucin concentrated in the mucous glands and in a 'tubular' structure which could be observed in the epidermal layer. Hyaluronidase digestion of the cocoon slightly changed the Alcian Blue colour, suggesting the presence of a large amount of acid mucin similar to that found in the skin mucous gland. The results of this study present data for the redistribution of AMPS, which may help in reducing water loss across the cocoon and reabsorption of water in the kidney during aestivation.

Structure and metabolism of proteoglycans and glycosaminoglycans

Proteoglycans and glycosaminoglycans have the common structural characteristics of linear polysaccharide chains consisting of a hexosamine alternating with another sugar. They play an important role in skin as part of the support matrix of connective tissue, and may be related to cell-cell, and cell-matrix interactions. In general the polysaccharide chains are covalently linked to protein and may contain varying amounts of sulfate resulting in a strong negative charge. Biosynthesis consists of the formation of the protein core followed by the sequential addition of sugars and sulfate to the nonreducing ends of growing chains. The synthetic process is highly organized with the final polysaccharide polymerization and sulfation taking place in the Golgi. Degradation of the proteoglycans is less well understood but probably involves endoglycosidases, exoglycosidases, and proteases which work in concert to degrade these substances.

Developmental changes in glycosaminoglycans, collagen and collagenase activity in embryonic chick skin

In order to study remodeling of connective tissue during development, changes in glycosaminoglycan, collagen and collagenase activity in embryonic chick skin at various stages have been studied. Collagen content in the skin increased rapidly during days 14 to 18, then leveled off until hatching. Prior to the increase of collagen deposition in the skin, a sharp decrease in chondroitin sulfate was observed between days 11 and 14, while dermatan sulfate increased almost 4 fold during days 12 to 14, then increased steadily until hatching. Hyaluronic acid decreased progressively during the stages investigated (days 11 to 20). At the same stage as the rate of collagen deposition in the tissue became maximal (day 16), the amount of dialyzable hydroxyproline showed a maximum, indicating that an increased rate of collagen deposition in the tissue was accompanied by accelerated collagenolysis. Culture of skin from various stages of embryonic development revealed that 16 day old tissue was potentially capable of secreting the highest levels of collagenase. This collagenase was mostly inactive against soluble collagen and collagen fibrils but could be activated by 3 M NaSCN treatment.

Prolactin-thyroxine antagonism and the metamorphosis of visual pigments in Rana catesbeiana tadpoles

The relationship between prolactin-thyroxin antagonism and the metamorphosis of visual pigments in larval amphibians has been investigated using bullfrog (Rana catesbeiana) tadpoles. Althought prolactin-thyroxine antagonism is demonstrable by morphological criteria, ovineprolactin does not appear to anatagonize thyroxine-induced rhodopsin synthesis. The hypothesisis offered that prolactin-thyroxine antagonism is the result of differential gene activities which are opposite in their physiological effects.

Hyaluronate inhibition of chondrogenesis: antagonism of thyroxine, growth hormone, and calcitonin

The formation of cartilage-like aggregates in high-density stationary cultures of trypsinized chick embryo precartilage cells is blocked by low concentrations of hyaluronate. Thyroxine (and triiodothyronine), growth hormone, calcitonin, and adenosine 3',5'-monophosphate prevented this inhibition by hyaluronate, whereas other hormones tested did not.