title: Altered proteoglycan synthesis by micromelial limbs induced by 6-aminonicotinamide. Appearance of abnormal forms of cartilage-characteristic proteoglycan (PG-H).
abstract: Since administration of 6-aminonicotinamide (10 micrograms) to day-4 chick embryos in ovo was shown to induce micromelial limbs, biosynthesis of cartilage-characteristic proteoglycan-H (PG-H) as an important index of limb chondrogenesis was examined in day-7 normal and micromelial hind limbs by biochemical and immunological methods. (1) Metabolic labelling of the micromelial limbs with [6-3H]glucosamine and either [35S]sulphate or [35S]methionine, followed by analyses of labelled PG-H by glycerol density-gradient centrifugation under dissociative conditions, showed a marked reduction in the PG-H synthesis. (2) PG-H synthesized by the micromelial limbs was much lower than that synthesized by the normal limbs in the biosynthetic ratio of chondroitin sulphate to keratan sulphate and glycoprotein-type oligosaccharide, although no significant difference was observed in the immunological properties of these proteoglycans. (3) The degree of sulphation of chondroitin sulphates of PG-H was lowered in the micromelial limbs as judged by the increase of unsulphated disaccharide (delta Di-OS) released by chrondroitinase ABC digestion, although there were no significant differences between the normal and the micromelial limbs in the average molecular size (Mr = 38,000) of labelled chondroitin sulphates of PG-H. (4) Addition of beta-D-xyloside, an artificial initiator for chondroitin sulphate synthesis, to the micromelial limbs in culture recovered the incorporation of labelled glucosamine into chondroitin sulphate to that comparable with the normal control with beta-D-xyloside, although the incorporation of [35S]sulphate was lower in the micromelia than in the control with beta-D-xyloside. These results suggest that the reduction in the biosynthesis of the PG-H as well as the production of altered forms of PG-H induced by 6-aminonicotinamide during a critical period of limb morphogenesis may be an important factor for the micromelia.
mesh_terms: D015120:6-Aminonicotinamide / Q000494:pharmacology*; D000014:Abnormalities, Drug-Induced / Q000196:embryology / Q000378:metabolism*; D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D002499:Centrifugation, Density Gradient; D002642:Chick Embryo; D002850:Chromatography, Gel; D005121:Extremities / Q000187:drug effects / Q000196:embryology; D005944:Glucosamine / Q000378:metabolism; D006027:Glycosides / Q000494:pharmacology; D017880:Limb Deformities, Congenital; D009536:Niacinamide / Q000031:analogs & derivatives*; D011509:Proteoglycans / Q000096:biosynthesis*; D013431:Sulfates / Q000378:metabolism
chemical_list: D002241:Carbohydrates; D006027:Glycosides; D011509:Proteoglycans; D013431:Sulfates; C010807:xylosides; D009536:Niacinamide; D015120:6-Aminonicotinamide; D005944:Glucosamine