Mechanism for the regulation of post-translational modifications of procollagens synthesized by matrix-free cells from chick embryos

Three possible mechanisms are considered to account for the variations of post-translational modifications in different collagen types. 1) The cells have different amounts of post-translational modifying enzymes, 2) the rate of prolylhydroxylation of different procollagen types is varied, and 3) the rate of chain association of pro-alpha chains of different collagen types is modulated. In an attempt to examine the three possibilities, we have determined the activities of prolyl hydroxylase and lysyl hydroxylase, and we have examined the kinetics of the secretion of procollagens and the kinetics of pro-gamma chain formation of different procollagen types in matrix-free cells isolated from tissues of 17-day-old chick embryos. Type II collagen synthesized by cartilage cells contains more hydroxylysine than type I collagen synthesized by tendon and cornea cells. It was found, however, that cartilage cells contain significantly less lysyl hydroxylase than tendon and cornea cells. In contrast, we found only a small difference in the amount of prolyl hydroxylase in tendon, cornea, and cartilage cells. The secretion of type I procollagen by tendon and cornea cells can be described by two first order processes. In contrast, the secretion of type II procollagen by cartilage cells, type IV procollagen by lens cells, and type V procollagen by cornea cells can be described by single first order processes. Examination of the formation of pro-gamma components of procollagen types I and II revealed that it occurs via intermediate dimers of two pro-alpha chains. The formation or pro-gamma(I) chains in tendon and cornea cells is about three times faster than the formation of pro-gamma(II) chains in cartilage cells. These results are consistent with the hypothesis that the rate of association of pro-alpha chains regulates the synthesis of procollagens with different degrees of post-translational modifications.

Biosynthesis of procollagens and collagens by tissue explants and matrix-free cells from embryonic chick cornea

Tendon and cornea of 17-day-old chick embryos primarily synthesize type I collagen as the major collagenous component nd type V collagen as a minor collagenous component. Matrix-free cells isolated from cornea and tendon synthesize and secrete mainly type I procollagen. A short lag period for the secretion of collagenous polypeptides into the medium of cell suspensions is observed. There is no significant difference in the synthesis and secretion of type I procollagen between matrix-free cells from tendon or cornea, except that cornea cells contain more free pro alpha 2(I) chains. The pro alpha 2(I) chain does not contain interchain disulfide linkages and can be separated from type I procollagen by ion exchange chromatography. However, no free pro alpha 2(I) chain can be detected in the medium of cell suspensions, suggesting that free pro alpha 2(I) is probably not secreted normally and may be rapidly degraded intracellularly. These results suggest that proper chain composition of type I procollagen is not regulated at the transcriptional or translational levels. Rather it is determined by the primary structure of the pro alpha chains and/or a posttranslational factor.

Plastic sectioning for light microscopy of Pyrenomycetes

In preparation for light microscopy, ascocarps of Sordaria fimicola Ces. & DeNot. were embedded in Spurr's medium and sectioned at 1-1.5 mum on an ultramicrotome. Sections were floated on Giemsa staining solution at 60 C for 10-30 min, washed in distilled water, affixed to slides by drying, and mounted in immersion oil. Best preservation of the delicate sterile tissues of the centrum was obtained by fixation in 1% KMnO4 for 2.5-3 hr, followed by the Giemsa stain. This method is suggested for future studies on the morphology of perithecial ascomycetes.