In Search of the Aplysia Immunome: an in silico Study

The immune repertoires of mollusks beyond commercially important organisms such as the pacific oyster Crassostrea gigas or vectors for human pathogens like the bloodfluke planorb Biomphalaria glabrata are understudied. Despite being an important model for neural aging and the role of inflammation in neuropathic pain, the immune repertoire of Aplysia californica is poorly understood. Recent discovery of a neurotropic nidovirus in Aplysia has highlighted the need for a better understanding of the Aplysia immunome. To address this gap in the literature, the Aplysia reference genome was mined using InterProScan and OrthoFinder for putative immune genes. The Aplysia genome encodes orthologs of all critical components of the classical Toll-like receptor (TLR) signaling pathway. The presence of many more TLRs and TLR associated adapters than known from vertebrates suggest yet uncharacterized, novel TLR associated signaling pathways. Aplysia also retains many nucleotide receptors and antiviral effectors known to play a key role in viral defense in vertebrates. However, the absence of key antiviral signaling adapters MAVS and STING in the Aplysia genome suggests divergence from vertebrates and bivalves in these pathways. The resulting immune gene set of this in silico study provides a basis for interpretation of future immune studies in this important model organism.