The Main Protein of the Aggregation Factor Responsible for Species-specific Cell Adhesion in the Marine Sponge Microciona prolifera Is Highly Polymorphic

Abstract

Species-specific cell recognition in sponges, the oldest living metazoans, is based on a proteoglycan-like aggregation factor. We have screened individual sponge cDNA libraries, identifying multiple related forms for the aggregation factor core protein (MAFp3). Northern blots show the presence in several human tissues of transcripts strongly binding a MAFp3-specific probe. The open reading frame for MAFp3 is not interrupted in the 5 direction, revealing variable protein sequences that contain numerous introns equally spaced. We have studied tissue histocompatibility within a sponge population, finding 100% correlation between rejection behavior and the individual-specific restriction fragment length polymorphism pattern using aggregation factorrelated probes. PCR amplifications with specific primers showed that at least some of the MAFp3 forms are allelic and distribute in the population used. A pronounced polymorphism is also observed when analyzing purified aggregation factor in polyacrylamide gels. Protease digestion of the polymorphic glycosaminoglycancontaining bands indicates that glycans are also responsible for the variability. The data presented reveal a high polymorphism of aggregation factor components, which matches the elevated sponge alloincompatibility, suggesting an involvement of the cell adhesion system in sponge allogeneic reactions.

Supramolecular Structure of a New Family of Circular Proteoglycans Mediating Cell Adhesion in Sponges

“…If each of the 20 globular structures observed in the MAF ring represents a MAFp3 molecule, we would expect one or two g-200 units on each MAFp3. Accordingly, the cDNA-deduced sequence of MAFp3 contains two to three putative N-glycosylation sites, depending on the particular MAFp3 form (Fernà ndez-Busquets et al, 1996, 1998Fernà ndez-Busquets and Burger, 1997). In our AFM images, one or two short linear structures protrude from each of the 20 globular structures forming the ring of MAF (Fig.…”

“…In general, 12 units of Streptomyces hyalurolyticus hyaluronidase (Merck) was used to digest samples containing ϳ30 g of carbohydrate in 10 mM citrate, pH 5, with overnight incubation at 37°C. PNGase F digestions were done as specified (Fernà ndez-Busquets and Burger, 1997).…”

Cyclosporin A Suspends Transplantation Reactions in the Marine SpongeMicrociona prolifera

“…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).…”

“…The frequency of graft rejection in sponges is very high (19), requiring an extensive genetic polymorphism at the locus or loci controlling graft acceptance and rejection. Sponge cell adhesion is based on extracellular matrix (ECM) 3 proteoglycans termed aggregation factors (AFs) (20).…”

Very Large G Protein-coupled Receptor-1, the Largest Known Cell Surface Protein, Is Highly Expressed in the Developing Central Nervous System

“…Although the 7-TM domain of VLGR1 was related to those of Flamingo and latrophilin, its putative ectodomain was unique, consisting mostly of seven imperfect calcium exchanger ␤ (Calx-␤) repeats (8) resembling the calcium-binding regulatory domains of sodium-calcium exchangers. Calx-␤ repeats are also found in the core protein of the proteoglycan aggregation factor that mediates species-specific aggregation in marine sponges, suggesting that they can play a role in cell-cell adhesion (9).…”