Histamine and histidine decarboxylase in the olfactory system and brain of the common cuttlefish Sepia officinalis (Linnaeus, 1758)

Identification of a New Set of Polypeptidic Sex Pheromones from Cuttlefish (Sepia officinalis)

The common English Channel cuttlefish (Sepia officinalis) reproduces every year on very localized coastal spawning areas after a west-east horizontal migration of several tens of kilometers (80-200 km). The massive arrival of spawners on the coasts of west Cotentin and the Bay of Seine is suspected to be driven by the action of sex pheromones expressed and secreted by the genitals of sexually mature females. The present study aims to verify the existence of polypeptide pheromones, of a higher molecular weight than those described above. Their size could confer them a wider range of action than that of the previously identified peptide pheromones. The implementation of an experimental strategy combining transcriptomics and proteomics with functional tests and an in silico study led to the identification of a cocktail of pheromones with molecular weights ranging between 22 and 26 kDa. Proteomic analyses combined to functional tests revealed partial pheromone release in the environment, and their accumulation in the outer capsule of the egg, suggesting the eggs as pheromone diffusers, also able to induce stimulation by contact when the eggs are handled by females.

Exploration of chemosensory ionotropic receptors in cephalopods: the IR25 gene is expressed in the olfactory organs, suckers, and fins of Sepia officinalis

While they are mostly renowned for their visual capacities, cephalopods are also good at olfaction for prey, predator, and conspecific detection. The olfactory organs and olfactory cells are well described but olfactory receptors-genes and proteins-are still undescribed in cephalopods. We conducted a broad phylogenetic analysis of the ionotropic glutamate receptor family in mollusks (iGluR), especially to identify IR members (Ionotropic Receptors), a variant subfamily whose involvement in chemosensory functions has been shown in most studied protostomes. A total of 312 iGluRs sequences (including 111 IRs) from gastropods, bivalves, and cephalopods were identified and annotated. One orthologue of the gene coding for the chemosensory IR25 co-receptor has been found in Sepia officinalis (Soff-IR25). We searched for Soff-IR25 expression at the cellular level by in situ hybridization in whole embryos at late stages before hatching. Expression was observed in the olfactory organs, which strongly validates the chemosensory function of this receptor in cephalopods. Soff-IR25 was also detected in the developing suckers, which suggests that the unique « taste by touch » behavior that cephalopods execute with their arms and suckers share features with olfaction. Finally, Soff-IR25 positive cells were unexpectedly found in fins, the two posterior appendages of cephalopods, mostly involved in locomotory functions. This result opens new avenues of investigation to confirm fins as additional chemosensory organs in cephalopods.