Phylogenetic Position of the Hexactinellida Within the Phylum Porifera Based on the Amino Acid Sequence of the Protein Kinase C from Rhabdocalyptus dawsoni

Abstract

Recent analyses of genes encoding proteins typical for multicellularity, especially adhesion molecules and receptors, favor the conclusion that all metazoan phyla, including the phylum Porifera (sponges), are of monophyletic origin. However, none of these data includes cDNA encoding a protein from the sponge class Hexactinellida. We have now isolated and characterized the cDNA encoding a protein kinase C, belonging to the C subfamily (cPKC), from the hexactinellid sponge Rhabdocalyptus dawsoni. The two conserved regions, the regulatory part with the pseudosubstrate site, the two zinc fingers, and the C2 domain, as well as the catalytic domain were used for phylogenetic analyses. Sequence alignment and construction of a phylogenetic tree from the catalytic domains revealed that the yeast Saccharomyces cerevisiae and the protozoan Trypanosoma brucei are at the base of the tree, while the hexactinellid R. dawsoni branches off first among the metazoan sequences; the other two classes of the Porifera, the Calcarea (the sequence from Sycon raphanus was used) and the Demospongiae (sequences from Geodia cydonium and Suberites domuncula were used), branch off later. The statistically robust tree also shows that the two cPKC sequences from the higher invertebrates Drosophila melanogaster and Lytechinus pictus are most closely related to the calcareous sponge. This finding was also confirmed by comparing the regulatory part of the kinase gene. We suggest, that (i) within the phylum Porifera, the class Hexactinellida diverged first from a common ancestor to the Calcarea and the Demospongiae, which both appeared later, and (ii) the higher invertebrates are more closely related to the calcareous sponges.

Reconstructing early sponge relationships by using the Burgess Shale fossil Eiffelia globosa , Walcott

“…Unfortunately, molecular phylogenies have failed to resolve the relationships and polarity of the sponge classes, although two scenarios have received most of the support: (i) (Hexactinellida plus Demospongea) (Calcarea plus Eumetazoa) (5,6,(33)(34)(35)(36)(37) in which Silicspongea is monophyletic, and (ii) Hexactinellida (Demospongea (Calcarea plus Eumetazoa)) (8,(38)(39)(40)(41), which gives a paraphyletic Silicispongea. The balance of recent molecular phylogenies, based on a range of genes, is approximately equal (42), but with an increasing shift toward silicisponge monophyly [albeit with Homoscleromorpha excluded from both Demospongiae (43) and Silicispongea (44)], particularly in light of corroborative biochemical (7), paleontological (45), and of course mineralogical data.…”

Molecular biology of demosponge axial filaments and their roles in biosilicification

“…Although the detailed interrelationships of the poriferan classes still remain unresolved (Adams et al, 1999;Cavalier-Smith et al, 1996;Kruse et al, 1998), *The terminal branches of the desmas (antler-like spicules) and their remarkable interlocking connections (Fig. 11) are reported to extend beyond the limits of the occluded axial filaments (Simpson, 1984) and thus raise perplexing questions about the possible mechanisms controlling their mutually conforming higher-order structural organization.…”

Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellidMonorhaphis chuni

“…Porifera are grouped into three classes, the Hexactinellida and the Demospongiae being both composed of a siliceous skeleton, as well as the class of Calcarea whose skeleton is made of calcium carbonate (Bergquist, 1978). Fossil records (Brasier et al, 1997;Steiner et al, 1993) and 'molecular clock' analyses (Schäcke et al, 1994;Kruse et al, 1998) indicate that the Hexactinellida evolved before to the Demospongiae, between 665 and 650·million years ago. Both sponge classes, which share a common ancestor, appeared prior to one major 'snowball earth event', the Varanger-Marinoan ice age [605 to 585·million years ago (Hoffman et al, 1998)] when the earth was covered by an almost continuous ice layer.…”