Mytilus galloprovincialis releases immunologically functional haemocytes to the intervalvar space in response to tissue injury and infection.

Haemocytes of Mytilus galloprovincialis represent the main component of the internal self-defence system. Although haemocytes from haemolymph are usually studied to analyse these animals' immune response, the presence of haemocytes in the intervalvar liquid, which is essentially sea water, led us to characterize them. Several functional (ROS production, phagocytosis, gene expression, travel velocity and distance) and morphological (area, size and granularity) assays were performed by applying different stimuli to the mussels (waterborne infection, shell injury and their combination). Our results revealed that intervalvar liquid haemocytes share common characteristics with haemolymph haemocytes (for instance, the cell morphology and the cell population structure divided in three main groups) but also show significant differences in size (usually smaller in the intervalvar liquid), mobility (commonly faster in the intervalvar liquid), ROS production (higher in non-stimulated intervalvar liquid cells) and gene expression (IL17, Myd88 and CathL are over expressed in liquid intervalvar cells compared to haemolymph cells). Moreover, differences were observed when mussels were subjected to the mentioned treatments. These free intervalvar haemocytes could constitute the first line of defence as external sentinels extending the immunological alert system outside of the mussel body.

Effects of short-term hyposalinity stress on four commercially important bivalves: A proteomic perspective.

Increased heavy rainfall can reduce salinity to values close to 0 in estuaries. Lethal and sublethal physiological and behavioural effects of decreases in salinity below ten have already been found to occur in the commercially important clam species Venerupis corrugata, Ruditapes decussatus and R. philippinarum and the cockle Cerastoderma edule, which generate an income of ∼74 million euros annually in Galicia (NW Spain). However, studies of the molecular response to hyposaline stress in bivalves are scarce. This 'shotgun' proteomics study evaluates changes in mantle-edge proteins subjected to short-term hyposaline episodes in two different months (March and May) during the gametogenic cycle. We found evidence that the mantle-edge proteome was more responsive to sampling time than to hyposalinity, strongly suggesting that reproductive stages condition the stress response. However, hyposalinity modulated proteome profiles in V. corrugata and C. edule in both months and R. philippinarum in May, involving proteins implicated in protein folding, redox homeostasis, detoxification, cytoskeleton modulation and the regulation of apoptotic, autophagic and lipid degradation pathways. However, proteins that are essential for an optimal osmotic stress response but which are highly energy demanding, such as chaperones, osmoprotectants and DNA repair factors, were found in small relative abundances. In both months in R. decussatus and in March in R. philippinarum, almost no differences between treatments were detected. Concordant trends in the relative abundance of stress response candidate proteins were also obtained in V. corrugata and C. edule in the different months, but not in Ruditapes spp., strongly suggesting that the osmotic stress response in bivalves is complex and possibly influenced by a combination of controlled (sampling time) and uncontrolled variables. In this paper, we report potential molecular targets for studying the response to osmotic stress, especially in the most osmosensitive native species C. edule and V. corrugata, and suggest factors to consider when searching for biomarkers of hyposaline stress in bivalves.

Proteomic evidence of a paedomorphic evolutionary process within a marine snail species: a strategy for adapting to extreme ecological conditions?

The exposed and sheltered ecotypes of the marine snail Littorina saxatilis from European rocky shores are considered a key model system to study adaptation and ecological speciation. Previous studies showed that two ecotypes (RB and SU) of this species in NW Spain have adapted differently to different shore levels and microhabitats. In order to understand how this divergent adaptive process has been accomplished, we followed a quantitative proteomic approach to investigate the proteome variation in a number of different biological factors, that is, ecotype, ontogeny and their interactions. This approach allowed testing the hypothesis that one of the ecotypes has evolved by paedomorphosis, and also whether or not the molecular mechanisms related to ecotype differentiation are set up in early developmental stages. Additionally, the identification of some candidate proteins using mass spectrometry provides some functional insights into these evolutionary processes. Results from this study provided evidence of higher ontogenetic differentiation at proteome level in the RB (metamorphic) than in SU (paedomorphic) ecotype that point to the possibility of juvenile stage retention in this latter ecotype. The level of protein expression (proteome) differences between ecotypes maintained nearly constant from late embryonic stages to adulthood, although some proteins involved in these changes considerably differed in embryonic compared to other ontogenetic stages. Paedomorphosis may be the evolutionary response of the SU ecotype of solving the trade-off during sexually immaturity that is caused by the evolution of small size arising from adaptation to the wave-exposed habitat. Some potential candidate genes of adaptation related to energetic metabolism have been identified, providing a promising baseline for future functional analyses.