Accumulation in Marine Sponge Grafts of the mRNA Encoding the Main Proteins of the Cell Adhesion System

Abstract

Specific cell adhesion in the marine sponge Microciona prolifera is mediated by an extracellular aggregation factor complex, whose main protein component, termed MAFp3, is highly polymorphic. We have now identified MAFp4, an ϳ400-kDa protein, from the aggregation factor that is translated from the same mRNA as MAFp3. The existence of multiple potential sites for Nglycosylation and calcium binding suggests a direct involvement of MAFp4 in the species-specific aggregation of sponge cells. The deduced partial polypeptide consists of a 16-fold reiterated motif that shows significant similarity to a repeat in an endoglucanase from the symbiontic bacterium Azorhizobium caulinodans and to the intracellular loop of mammalian Na ؉ -Ca 2؉ exchangers. Restriction fragment length polymorphism analysis indicated that the genomic variability of MAFp4 is high and comparable to that of MAFp3. Their combined polymorphism correlates with allogeneic responses studied in a population of 23 sponge individuals. Peptide mass fingerprinting of tryptic digests of the polymorphic MAFp3 bands observed on polyacrylamide gels after chemical deglycosylation of the Microciona aggregation factor revealed that the variability detected on Southern blots at least partially reflects the individual variability of aggregation factor protein components. Polyclonal antibodies raised against MAFp3 strongly crossreacted with a 68-kDa protein localized in sponge cell membranes. Immunohistochemical use of the antiMAFp3 antibodies strongly stained a cell layer along the line of contact in allogeneic grafts. We show that the transcription level of the MAFp3/MAFp4 mRNA in sponge allo-and isografts is clearly increased in comparison with non-grafted tissue. These data are discussed with respect to a possible evolutionary relationship between cell adhesion and histocompatibility systems.Species-specific cell recognition in sponges is mediated by proteoglycan-like extracellular complexes termed aggregation factors (AFs), 1 unidentified so far in other phyla, although Northern blots suggested the existence, in several human tissues, of proteins related to those found in the AF of the marine sponge Microciona prolifera (1). Cell adhesion in this species is mediated by calcium-dependent carbohydrate interactions of homologous Microciona AF (MAF) molecules via N-linked glycans. A proposed model suggested that species specificity could be at least partially provided by the different spacing of glycosaminoglycan chains on the protein core (2), thus postulating the existence of a different AF core protein in each species. Unexpectedly, an extraordinarily high intraspecific variability was found for the MAF core protein (1), suggesting that AFs might also be involved in individual specificity.The immune and cell adhesion systems are clearly related, as deduced from phylogenetic relationships between molecules of both groups (3) and as expected from the fact that the cells of the immune system depend on regulated interactions with other cells to be activated (4). An evo...

Cyclosporin A Suspends Transplantation Reactions in the Marine SpongeMicrociona prolifera

“…The adhesion force exerted by AFs between sponge cells has been calculated to be very strong, comparable per surface area to that found in focal contacts (39). AF proteins have arginineglycine-aspartic acid (RGD) sequences (22) that could act synergically with integrin, resulting in high binding forces upon the overexpression of both molecules. An inverse correlation between integrin up-regulation and cell motility has been described in systems other than the sponge (40).…”

“…The extracellular nature of AFs makes them or closely related molecules good candidates to act as diffusible signals for isogeneic/allogeneic recognition. In addition, AF proteins have abundant calcium-binding motifs (22), potential transmembrane regions (49), and an elevated sequence homology with the intracellular loop of Na ϩ -Ca 2ϩ exchangers (50). It is conceivable then that some AF isoforms may be involved in intracellular Ca 2ϩ signaling, a pathway network where cell motility and (in higher animals at least) immune responses converge, both through calcineurin-dependent and calcineurin-independent mechanisms (51).…”

“…AFs are necessary and sufficient to aggregate sponge cells species-specifically, but the observation that sponges possess a wide variety of eumetazoan cell adhesion molecules hints that an AF-only model might be incomplete (21). In contrast, the elevated polymorphism of AF proteins (19,22) suggests that some of them represent diverging forms adapted to a different function. It is therefore possible that the cell adhesion machinery can be shared in sponges, at least to a certain degree, with an incipient histocompatibility system (6).…”

“…It is therefore possible that the cell adhesion machinery can be shared in sponges, at least to a certain degree, with an incipient histocompatibility system (6). In parabiotic grafting experiments it has been shown that the intraspecific variability of AFs rivals that of the vertebrate MHC; any two individuals rejecting each other have different genomic sequences for AF proteins as indicated by restriction fragment length polymorphism analysis (19,22). Other molecules involved in cell-ECM interactions such as ␣ and ␤ integrins and the hyaluronan receptor CD44 have been found to be differentially expressed in sponge isografts and allografts (7,23).…”

Self-nonself recognition: genomic and transcriptomic insights from the sponge aggregation factors

“…allorecognition molecules in sponges (Bonner and Slifkin 1949;Moscona 1968;Humphreys 1970;Henkart et al 1973;Müller and Zahn 1973;Fernàndez-Busquets et al 1998;Fernàndez-Busquets and Burger 1999), are also encoded by a set of clustered genes in the A. queenslandica genome. Here, five AF genes sit within an 80 kb cluster of the genome, with a sixth putative AF sitting alone elsewhere in the genome (Gauthier 2009).…”