Cell cultures derived from foetal bovine ligamentum nuchae accumulate extracellular fibrils morphologically identical with elastic-tissue microfibrils. Two glycoproteins synthesized by the ligament cells are closely related to the matrix microfibrils as assessed by immunological and chemical extraction techniques.

The foetal ligamentum nuchae showed two distinct stages of development, each characterised by its cell population and fibre products. Fibroblasts of the early phase have extensive ergastoplasm apparently associated with collagen production; those of the late phase have an "attenuated" cytoplasm and coincide with an increase of elastic tissue content. The elastic fibre comprised a core of fine elastin fibrils (100--130 nm diameter) and a surrounding mantle of microfibrillar protein. As development proceeded, the elastin fibrils appeared to coalesce with each other and also with elastin fibrils from adjacent fibres to form composite mature elastic fibre--a process which was accompanied by a loss of microfibrils. A characteristic of elastic fibres from adult ligament, not apparent in the foetal tissue, was that of bifurcation.

The formation of collagen fibrils under physiological conditions of ionic strength, pH and temperature was markedly affected by the presence of small amounts of bovine tendon glycoprotein. The absorbance of the gels at 400nm was decreased, and they took longer to form. Over the range of concentration tested, the negative specific absorbance, -AA,p., and the specific retardation, Rs,., both increased with the glycoprotein to collagen ratio.When added during the nucleation phase, glycoprotein was still able to exert its effect almost fully, and so must act to inhibit the later stages of fibril formation. Several pieces of evidence showed that glycoprotein acts via a weak binding to the collagen molecule. Electron microscopy established that fibrils formed in the presence of glycoprotein had a normal cross-striation pattern, but were significantly thinner than fibrils formed in control gels. The results suggest that glycoprotein could act in tissues to help regulate the diameter of collagen fibrils.

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