A network system for vitellogenin synthesis in the mussel Mytilus galloprovincialis (L.)

Abstract

The aim of this study is to assess, by RT-PCR, in situ hybridization, electron microscopy, and immunohistochemistry, the site/s of vitellogenin (VTG) synthesis in the mussel Mytilus galloprovincialis. Our investigations demonstrate that, among the analyzed tissues, the synthesis of VTG occurs only in the female gonad, that is, within the oocyte and follicle and connective cells. Such a synthesis is just evident in early vitellogenic oocytes, whose cytoplasm is characterized by numerous RER cisternae and an extended Golgi complex surrounded by nascent yolk platelets. The synthesis of VTG goes on in vitellogenic oocytes assuming a pear form, and progressively reduces once the oocyte shows the pear or polygonal form, typical of those oocytes that have concluded the growth. The expression of VTG occurs also within follicle (auxiliary) and connective cells. In particular, it is noteworthy that follicle cells are characterized by numerous RER cisternae and an active Golgi complex surrounded by numerous vesicles and vacuoles containing electron dense material. The same material is also present along their plasma membrane, within the intercellular space between oocyte and follicle cells, and finally within invaginations of the oocyte surface, thus suggesting a VTG transfer to the oocyte via endocytosis. Differently, no VTG synthesis was observed within digestive gland. All together the findings here reported strongly suggest that in M. galloprovincialis, inside the gonad, the VTG synthesis occurs in the oocyte (autosynthesis) and in the follicle and adipogranular cells (heterosynthesis).

The expression of estrogen receptors during the Mytilus galloprovincialis ovarian cycle

“…Later (Stages II), labeling was within ADGs and in the ovarian follicles (Figure e,f). In particular, inside follicles, labeling for ER1 (Figure e), ER2 (Figure f ) mRNA was detectable within oogonia (Figure f, inset) and in vitellogenic oocytes and in follicle cells (Figure e, inset), both engaged in vitellogenesis (Agnese, Prisco, et al, ; Agnese, Verderame, et al, ). In Stage III, when ADGs are lacking, labeling was also detectable and localized in full growth oocytes (Figure g,h) that are ready for spawning.…”

“…Differently, the levels of ER2 mRNA are always very high reaching a maximum in correspondence with vitellogenesis. It is interesting to note that in M. galloprovincialis , during the Stage II, the oocyte synthesize and accumulate the highest level of vitellogenin, whose production occurs also in ADGs and follicles cells (Agnese, Prisco, et al, ; Agnese, Verderame, et al, ), that is in different districts of the ovary where the presence of ERs also occurs. Moreover, treatments in vitro with 17β‐estradiol induce an increase of E2 mRNA in M. galloprovincialis (Nagasawa et al, ), and that in bivalves estrogens have been reported to induce the synthesis of vitellogenin which is the major event during gonadal development (Li, Osada, Suzuki, & Mori, ; Osada et al, ).…”

“…Moreover, in M. edulis and Mytilus galloprovincialis , it has been identified a typical receptor of estrogen, reported also as ER2, as well as an estrogen‐related receptor not activated by estrogens, reported also as ER1 (Nagasawa et al, ). More recently, in M. galloprovincialis we highlighted a different expression of ER mRNA collected in different areas of Naples bay (Rosati, Agnese, et al, ), and the presence of key steroid sex hormone biosynthesis enzymes in the same cells (Rosati, Prisco, et al, ) engaged into the vitellogenesis (Agnese, Prisco, et al, ; Agnese, Verderame, et al, ).…”

“…The aim of this study is to identify, by real‐time polymerase chain reaction (RT‐PCR) and in situ hybridization, the ER expression in the ovary of M. galloprovincialis collected in the Naples Bay, during the different phases of the cycle, that is Stage 0 (stasis and previtellogenesis), Stage I (beginning of the oocyte growth), Stage II (vitellogenesis), and Stage III, the final stage of the oocyte growth, when the ovary is ripe and the full‐grown oocytes have to be stanned, as previously reported (Agnese, Prisco, et al, ; Agnese, Verderame, et al, ; Duinker, Haland, Hovgaard, & Mortensen, ; Rosati, Agnese, et al, ; Rosati, Prisco, et al, ).…”

Proteomic Analysis of the Reproductive Organs of the Hermaphroditic Gastropod Lymnaea stagnalis Exposed to Different Endocrine Disrupting Chemicals

“…This protein is the main yolk protein in oocytes in this species [63,80], whereas vitellogenin (Vtg), the precursor of egg yolk proteins in many species of vertebrates and invertebrates [81], has never been reported in freshwater gastropods. Alterations of Vtg production were reported in male fish affected by intersex in field and laboratory studies [42,82,83].…”