In the mammalian eye type VI collagen tetramers form three morphologicallydifferent aggregates

The organization of the aggregates occurring in the stroma: (1) of the muri ne and human cornea after incubation in an ATP acidic solution; (2) of surg ically excised epiretinal membranes (ERM); and (3) of the trabecular meshwo rk of monkey eyes was investigated morphologically and immunocytochemically on thin section electron microscopy. Morphology. The aggregates in the cor nea appeared as cross-banded fibrils. The bands were uniformly electron den se (single handed form); they were separated from each other by interbands consisting of a bundle of filaments emerging in cross section as small area s of randomly assembled dot-like structures. In the ERM, most of the aggreg ates stood out as heteromorphic cross-banded bodies showing dense bands wit h electron denser borders (double banded form) and interbands composed of l ongitudinally oriented, parallel sheets or laminae of amorphous material en closing thin, similarly oriented filaments. These extended, thinner and dou ble in number (since interlacing with similar components of the opposite sh eet), into the pale central zone of the dense band. The aggregates of the t rabecular meshwork were heteromorphic, had uniformly dense bands (single ba nded form as in the corneal, but their interbands displayed longitudinal sh eets las the ERM aggregates), Immunocytochemistry revealed type VI collagen in the three eye aggregates with gold particles preferentially localized a t the interbands. The specificity of the antibodies used was tested by West ern blot analysis of type VI collagen samples extracted from human placenta and on homogenates of human cornea. In conclusion, the results indicate th at the tetramers of type VI collagen may aggregate differently into structu res with distinct supramolecular arrangements. These are illustrated in sch ematic drawings. (C) 2001 Elsevier Science B.V./International Society of Ma trix Biology. All rights reserved.