RESUMEN
The colony formation in Mediterranean coral Corallium rubrum is initiated by a larva that metamorphoses into the first polyp of the emerging colony approximately two weeks after settlement. The primary polyp then sets up a slow process that eventually, at least after a few years, gives rise to a tree-like rigid colony structure on which other polyps flourish. For a mature colony, this axial skeleton provides support for new polyps. However, the first emergence of the characteristic axial skeleton can take two years or more from the larva stage. The early colony morphology, instead, is shaped exclusively by the polyps' abundant deposition of sclerites, a magnesian calcite biomineral that has a different granularity from the distinctive red-coloured skeleton. With the appearance of the first polyp, a growing sclerite heap in a mesoglea layer provides a base for the emerging colony. In this paper, to elucidate the mechanical processes of early skeleton development in C. rubrum colonies, we present a computational model whereby the mesoglea layer provides a diffusion medium for the sclerites that the polyps deposit. We show that our stochastic model with three parameters captures the dynamic variability observed in measurements on living colonies. Our simulation results provide evidence for a diffusion process whereby the interplay between polyp budding and sclerite deposition are the main determinants of structure in early colony formation. Our model demonstrates that the frequency of budding events in an early colony can be described as a function of the available mesoglea surface whereas the number of polyps on the colony plays a secondary role in determining this frequency. We show that these model predictions are confirmed by direct observations on the colonies in our sample. Moreover, our results indicate that diffusion is a prevalent mechanism of colony development also at later stages of a colony's life span.
Asunto(s)
Antozoos , Animales , Carbonato de CalcioRESUMEN
We have identified a novel shell protein, accripin11, as a major soluble component of the calcitic prisms of the fan mussel Pinna nobilis. Initially retrieved from a cDNA library, its full sequence is confirmed here by transcriptomic and proteomic approaches. The sequence of the mature protein is 103 residues with a theoretical molecular weight of 11 kDa and is moderately acidic (pI 6.74) except for its C-terminus which is highly enriched in aspartic acid. The protein exhibits a peculiar cysteine pattern in its central domain. The full sequence shares similarity with six other uncharacterized molluscan shell proteins from the orders Ostreida, Pteriida and Mytilida, all of which are pteriomorphids and produce a phylogenetically restricted pattern of nacro-prismatic shell microstructures. This suggests that accripin11 is a member of a family of clade-specific shell proteins. A 3D model of accripin11 was predicted with AlphaFold2, indicating that it possesses three short alpha helices and a disordered C-terminus. Recombinant accripin11 was tested in vitro for its ability to influence the crystallization of CaCO3 , while a polyclonal antibody was able to locate accripin11 to prismatic extracts, particularly in the acetic acid-soluble matrix. The putative functions of accripin11 are further discussed in relation to shell biomineralization.
Asunto(s)
Bivalvos , Proteómica , Animales , Bivalvos/genética , Bivalvos/química , Bivalvos/metabolismo , Proteínas/química , Carbonato de Calcio/metabolismo , Ácido AspárticoRESUMEN
Spatial localizing of skeletal proteins in biogenic minerals remains a challenge in biomineralization research. To address this goal, we developed a novel in situ mapping technique based on molecular recognition measurements via atomic force microscopy (AFM), which requires three steps: (1) the development and purification of a polyclonal antibody elicited against the target protein, (2) its covalent coupling to a silicon nitride AFM tip ('functionalization'), and (3) scanning of an appropriately prepared biomineral surface. We applied this approach to a soluble shell protein - accripin11 - recently identified as a major component of the calcitic prisms of the fan mussel Pinna nobilis [1]. Multiple tests reveal that accripin11 is evenly distributed at the surface of the prisms and also present in the organic sheaths surrounding the calcitic prisms, indicating that this protein is both intra- and inter-crystalline. We observed that the adhesion force in transverse sections is about twice higher than in longitudinal sections, suggesting that accripin11 may exhibit preferred orientation in the biomineral. To our knowledge, this is the first time that a protein is localized by molecular recognition atomic force microscopy with antibody-functionalized tips in a biogenic mineral. The 'pros' and 'cons' of this methodology are discussed in comparison with more 'classical' approaches like immunogold. This technique, which leaves the surface to analyze clean, might prove useful for clinical tests on non-pathological (bone, teeth) or pathological (kidney stone) biomineralizations. Studies using implants with protein-doped calcium phosphate coating can also benefit from this technology. STATEMENT OF SIGNIFICANCE: Our paper deals with an unconventional technical approach for localizing proteins that are occluded in biominerals. This technique relies on the use of molecular recognition atomic force microscopy with antibody-functionalized tips. Although such approach has been employed in other system, this is the very first time that it is developed for biominerals. In comparison to more classical approaches (such as immunogold), AFM microscopy with antibody-functionalized tips allows higher magnification and keeps the scanned surface clean for other biophysical characterizations. Our method has a general scope as it can be applied in human health, for non-pathological (bone, teeth) and pathological (kidney stone) biomineralizations as well as for bone implants coated with protein-doped calcium phosphate.