Fig 1.
Confocal microscopy of Haliotis sp. nacre samples treated with WGA bound to fluorescein isothiocyanate (FITC).
A. Experimental sample, with strong fluorescence at the contacts between plates (intertabular membranes). B. Control sample, in which no signal is observed.
Fig 2.
A. General aspect of the nacre. The spiral and fingerprint-like pattern of nacre growth fronts are particularly well developed. B, C. Untreated specimen in which the last formed ILM extends horizontal between the growing plates (seen by transparency). The fibrous aspect of the ILM is particularly evident in the close up view (C). D. Specimen in which the last-formed ILM has stuck onto the previous lamella around the edges of the plates (arrows). E, F. Frayed portions of ILMs subtending from platelets, showing the formation of type 1 fibers. Some of these fibers continue into type 2 fibers in F. G, H. Same situation as in E and F, in which, in addition, type 2 fibers slightly stand out from the ILMs. I, J. Type 2 fibers sprouting from nacre platelets (arrows). K, L. Nacre particles obtained by scraping and containing type 2 fibers.
Fig 3.
Secondary electron (SE, left) and backscattered electron (BSE, right) paired images of membranes labelled for protein (small lucent dots in the BSE, right images,) and chitin (big dots).
A-F. The tracings of several fibers of type 2 are evident (some of them have been outlined in red in the BSE images). Most of the big particles fall onto any of such fibers. Some labeling appears in the upper right tablet, despite the fact that the ILM is absent on it. G-H. Frayed membrane. The junctions between type 1 fibers are frequently the sites of deposition of big particles.
Fig 4.
A, B. Control C1. Secondary electron (SE, left) and backscattered electron (BSE, right) views of a labeled sample not treated with proteinase K. No labelling is evident in the BSE image. C, D. Control C2. Samples treated with chitinase. The nacre platelets appear superficially corroded and dislodged. E, F. Control C3a. SE (left) and BSE (right) views of a sample treated without anti-lectin antibody. The BSE image shows the absence of labelling. G, H. Control C3b. SE (left) and BSE (right) views of a sample treated without both anti-lectin antibody and proteinase K. No labelling appears in the BSE image.
Fig 5.
Sketch depicting the ultrastructure of the ILMs of nacre.
A. General structure of the nacre of bivalves. Platelets arrange into terraces and the ILMs extend on top of the last formed lamella, beyond the growth of the lamella. B. General structure of an ILM. It has a fibrous aspect, with the long fibres seemingly disoriented and extending within the plane of the membrane. C. Detail of the ultrastructure of the ILM. It is composed by protein fibers which surround a chitin core fiber, thus forming a chitin-protein complex. The network is embedded in an additional protein matrix.