Skeletal matrix proteins Comparative analysis of ofinvertebrate their animals : amino acid sequences

The genetic bases of skeletogenesis are expected to shed light on the origins of metazoan biomineralization. Here we review aspeets of genetic machineries of inyertebrate sk letogenesis, including regulutory genes involyed in hiomi"eralization as well, and with an enumerative reference to the genes encoding skeletal mahix proteins. The complete primary structure has been determilled for a total of 77 skeletal matrix proteins in invertebrates r presenting fiye animal phyla. Presence of repeated seque"ces and prevalence of acidic proteins stand as common features ilmong those proteins. Similarities are interpreted as conyergence because these proteins are not similar at the primary structure leyel. C-type lectin-like domains are shared by the calcium carbonate skeletal matrix proteins of moll"scs and deuterostomes. However, the important sites for carbohydrate binding are not conserved between these two groups. Seyeral arthropod skeletal matrix proteins have the Rebers-Riddiford consensus seqllence which is characteristic of nonca]cified cuticular proteins of arthropods, indicating that these skeletal matrix proteins were recruited from the non-cakified cuticular proteins after arthropods diyerged from other metazoan groups. Dermatopontin, a molluscan shell matrix protein, is also inferred to represent a cooption for biominerulization after molluscs diyerged from other metazofin groups based on the molecniar phylogemetic analysis. Those findings support the premise that the genetic machineries of biomineralization eyolyed independently many times after the diyergence of metazoan phyla, and that some common genes that served for other functions haye been coopted for biomineralization in various lineages.