The fine structure of perinotochordal microfibrils in control and enzyme‐treated chick embryos

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Abstract
Microfibrils in the notochordal sheath of chick embryos of two to four days incubation age were analyzed electron microscopically. Collagenase, trypsin, hyaluronidase and alpha amylase were administered to both “living” and “fixed” embryos. Living embryos were either explanted on an agar‐albumen growth medium or were allowed to survive within the shell during experimental procedures. Fixed embryos were immersed in Karnovsky's aldehyde fixative prior to enzyme digestion. Both living and fixed specimens yielded similar results.Control embryos possessed microfibrils of ca. 200 Å, ca. 100 Å and less than 100 Å in diameter in the notochordal sheath. The smaller fibrils (100 Å and less) were present in all regions of the sheath, but were especially concentrated near the notochordal boundary (basement) membrane. The larger fibrils (200 Å) were farther removed from the notochord. Flaky amorphous material was attached to all fibrils and was abundant especially in the inner region of the sheath.Collagenase produced elimination of the 200 Å microfibrils, but the smaller ones remained intact. Trypsin caused digestion of all fibrils. Hyaluronidase digested fibrils chiefly 100 Å and less in diameter. Alpha amylase was similar to hyaluronidase in digesting the small fibrils. This study supports the hypothesis that microfibrils are primarily mucopolysaccharide‐protein precursors of larger collagen‐rich fibrils.