Identification of β integrin‐like‐ and fibronectin‐like proteins in the bivalve mollusk Mytilus trossulus

Abstract

Integrins play a key role in the intermediation and coordination between cells and extracellular matrix components. In this study, we first determined the presence of the b integrin-like protein and its presumptive ligand, fibronectin-like protein, during development and in some adult tissues of the bivalve mollusc Mytilus trossulus. We found that b integrin-like protein expression correlated with the development and differentiation of the digestive system in larvae. Besides the presence of b integrin-like protein in the digestive epithelial larval cells, this protein was detected in the hemocytes and some adult tissues of M. trossulus. The fibronectin-like protein was detected firstly at the blastula stage and later, the FN-LP-immunoreactive cells were scattered in the trochophore larvae. The fibronectin-like protein was not expressed in the b integrin-positive cells of either the veliger stage larvae or the adult mussel tissues and the primary hemocyte cell culture. Despite the b integrin-and fibronectin-like proteins being expressed in different cell types of mussel larvae, we do not exclude the possibility of direct interaction between these two proteins during M. trossulus development or in adult tissues.

Extracellular Matrix Components in Bivalvia: Shell and ECM Components in Developmental and Adult Tissues

“…In contrast to these data, recent genomic and transcriptomic data of bivalves indicate that FN-like and FN III-containing domains exist in genome of bivalves [25,27]. Moreover, the immuno detection of a β integrin-like protein (β integrin-LP) and FN-LP was determined in the bivalve mollusc M. trossulus [32]. Double (integrin/fibronectin) immunofluorescence labelling of adult tissues showed β integrin-LP in the hepatopancreas/stomach, adductor muscle, and male gonad.…”

“…Possibly, in addition to the immunopositive basal membranes, the antibodies against integrin recognized different subpopulations of M. trossulus hemocytes in tissues. These results indicate that antibodies against β1 integrin specifically recognize the mussel target proteins and can be used for their detection in adult mussel tissues and could be useful for cell biological studies [32]. Despite that FN antibodies recognize the basal membranes and hemocytes in adult bivalves, the confirmatory foradditional proof of cross-reaction properties of FN are needed in future.…”

“…Integrin-like-positive cells (probably hemocytes) were found in the adult mussel mantle ( Figure 1). Fibronectin immunoreactivity was not detected in the male gonad [32], but was spatially distributed in other adult mussel tissues from the intracellular (cytoplasmic) localization of the hepatopancreas/ stomach and adductor muscle to an extracellular location, with the formation of FN-like positive fibers in the gill and mantle (Figure 1) [32]. Possibly, in addition to the immunopositive basal membranes, the antibodies against integrin recognized different subpopulations of M. trossulus hemocytes in tissues.…”

“…Immunodetection was not performed for the aforementioned bivalve ECM components because specific antibodies were lacking for them, and the bivalve larvae were small and difficult to cultivate. Nevertheless, a few studies detected certain components of the ECM in bivalve development and in vitro [32,35,36].…”

“…In our previous study, we evaluated the localization of a β-integrinlike protein (β-integrin-LP) during the early development of the bivalve M. trossulus [32]. The first β1-like integrin-positive signal appeared at the early trochophore stage (19 hpf) in 5% of the Mytilus larvae.…”