Innate Immune Defense of the Sponge Suberites domuncula against Bacteria Involves a MyD88-dependent Signaling Pathway

Abstract

Sponges (phylum Porifera) are the phylogenetically oldest metazoa; as filter feeders, they are abundantly exposed to marine microorganisms. Here we present data indicating that the demosponge Suberites domuncula is provided with a recognition system for Gramnegative bacteria. The lipopolysaccharide (LPS)-interacting protein was identified as a receptor on the sponge cell surface, which recognizes the bacterial endotoxin LPS. The cDNA was isolated, and the protein (M r 49,937) was expressed. During binding to LPS, the protein dimerizes and interacts with MyD88, which was also identified and cloned. The sponge MyD88 (M r 28,441) is composed of two protein interaction domains, a Toll/interleukin-1 receptor domain (found in MyD88 and in Toll-like receptors) and a death domain (present in MyD88 and interleukin-1 receptor-associated kinase). Northern blot experiments and in situ hybridization studies showed that after LPS treatment, the level of the LPS-interacting protein remains unchanged, whereas MyD88 is strongly up-regulated. A perforin-like molecule (M r 74,171), the macrophage-expressed protein, was identified as an executing molecule of this pathway. This gene is highly expressed after LPS treatment, especially at the surfaces of the animals. The recombinant protein possesses biological activity and eliminates Gram-negative bacteria; it is inactive against Gram-positive bacteria. These data indicate that S. domuncula is provided with an innate immune system against Gramnegative bacteria; the ligand LPS (a pathogen-associated molecular pattern) is recognized by the pattern recognition receptor (LPS-interacting protein), which interacts with MyD88. A signal transduction is established, which results in an elevated expression of MyD88 as well as of the macrophage-expressed protein as an executing protein.

The Holo-Transcriptome of a Calcified Early Branching Metazoan

“…transcriptome (Table S5). MyD88 functions downstream of TLRs and has previously been identified in other sponges (Wiens et al, 2005;Srivastava et al, 2010;Riesgo et al, 2014; Figure 6). …”

“…The link between these pathways seems to require the participation of the adaptor protein ECSIT FIGURE 6 | Overview of innate immunity components in Porifera. Data derives from recent papers (Wiens et al, 2005(Wiens et al, , 2007Gauthier et al, 2010;Riesgo et al, 2014) and our own analysis. Different colors represent different sponge class; blue, Hexactinellid; purple, Demosponge; yellow, Calcarea; green, Homoscleromorpha; Colored square, component present; white square, component absent; gray square, unknown; *, includes unconventional Toll-like receptor with IG domains instead of LRR domains.…”

“…transcriptome. Wiens et al (2005) proposed an alternative pattern recognition system for antimicrobial defense, a cell surface protein named SLIP (sponge lipopolysaccharide (LPS)-interacting protein), which was suggested to be a substitute for the missing TLRs as it interacts in vivo with MyD88. The Vaceletia sp.…”

Toll-like receptor signal transduction

“…Recognition of PAMPs results in activation of macrophages, leading to a plethora of biological responses required for eliciting both the innate and adaptive arms of the immune response, and they are distributed all over the body (Table 1). TLRs are highly conserved through evolution and its presence is reported as low as the phylum from Porifera which includes sponges (Wiens et al, 2005). Toll was first discovered in…”

Stonefish toxin defines an ancient branch of the perforin-like superfamily

“…Together, this distribution suggests a deep evolutionary history for these genes, with considerable gene loss evident in multiple branches. The genomes of many ancient eukaryotes that contain SNTX-like genes also have readily identifiable MACPF-like proteins, such as Macrophage Perforin-like Encoded Gene-1 (28,29). Therefore, SNTX-like proteins represent an extensive and ancient third branch of the MACPF/CDC superfamily.…”