The perivitellinefluid is an extracellular fluid found in the eggs of most gastropods and constitutes the main source of nutrition and defense for their embryos. It replaces the egg yolk of other animals, which in snail eggs is reduced to non-nutritive proteinaceous granules with putative enzymatic function.[1]
The perivitelline fluid is synthesized by the albumen gland of female snails (also known as albumen gland-capsule gland complex or uterine gland), an accessory gland from the reproductive tract. Fertilized oocytes enter the albumen gland and, on their way out, are coated with the perivitelline fluid.[1][6][7] The amount of perivitelline fluid per egg vary considerably among species.[1] However, the amount of perivitelline fluid per egg is constant within a given species.[8] In this regard, it has been shown in Pomaceaapple snails that during the reproductive season, when the nutrient precursors decrease in the albumen gland due to successive ovipositions, females tend to reduce the number of eggs per clutch but not the amount allocated to each egg.[9]
Carbohydrate is invariably the most abundant component of the perivitelline fluid. Specifically, the eggs of most gastropod accumulate the polysaccharide galactogen,[8][10][11][12][13] which would provide the main energy source for the developing embryo. A small amount of soluble glucose was also detected in some species.[11][12]
Proteins, called perivitellins, are the second most abundant component of the perivitelline fluid. Perivitellins are also a source of nutrients for snail embryos [11][14] and play a role in protection against pathogens[12][14][15][16] and predators, and include non-digestible perivitellins, toxins and protease inhibitors.[12][17][18][19][20][21][22][23][24][25] These proteins were thoroughly studied in apple snails from the genus Pomacea, where they were originally grouped in two most abundant protein fractions perivitellin-1 or PV1, perivitellin-2 or PV2 (comprising approximately 70% of total protein), and a heterogeneous fraction dubbed perivitellin-3 or PV3 fraction.[26][27] Recent proteomic analyses, however, showed that the perivitelline fluid from Pomacea snails has between 34-38 different proteins with a wide variety of functions.[28][29][30]
Lipids are a minor component, mostly represented by membrane lipids, indicating that snails do not use lipids as a major energy reserve during reproduction.[11][12] Apart from structural lipids, some eggs also contain carotenoid pigments, notably astaxanthin.[12][17][27] These lipidic pigments have been associated with antioxidant and photoprotective functions,[27][31][32] and also provide Pomacea eggs with the typical bright color that would function as a warning signal (i.e. aposematism) to deter predators.[27][33][34][35]
Among the inorganic components, calcium ion is the most abundant in the perivitelline fluid. As these snails have direct development, calcium needs to be stored to allow the snail to develop the shell during organogenesis. Besides, calcium is the main component of the eggshell of those snails with aerial oviposition.[36]
References
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^Bluemink JG (1967). The subcellular structure of the blastula of Limnaea stagnalis L. (Mollusca) and the metabolization of the nutrient reserve (Ph.D. thesis). Utrecht.
^Favard P, Carasso N (1958). "Origine et ultrastructure des plaquettes vitelline de la planorbe". Arch. Anat. Mier. Morph. Exptl. 47: 211–229.
^Bottke W (1977). Ferritin-Dotter bei der Schnecke Planorbarius corneus L. Verh. Dtsch. Zool. Ges.. Stuttgart: Gustav Fischer Verlag. p. 301.
^Hayes KA, Cowie RH, Thiengo SC, Strong EE (2012). "Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda)". Zoological Journal of the Linnean Society. 166 (4): 723–753. doi:10.1111/j.1096-3642.2012.00867.x. ISSN1096-3642.
^Catalán M, Dreon MS, Heras H, Pollero RJ, Fernández SN, Winik B (June 2006). "Pallial oviduct of Pomacea canaliculata (Gastropoda): ultrastructural studies of the parenchymal cellular types involved in the metabolism of perivitellins". Cell and Tissue Research. 324 (3): 523–33. doi:10.1007/s00441-005-0132-x. PMID16453107. S2CID30906846.
^ abcHorstmann HG (1956). "Der galaktogengehalt der Eier von Lymnaea stagnalis während der embryonalentwicklung". Biochem. Z. 328: 342–347.
^Cadierno MP, Saveanu L, Dreon MS, Martín PR, Heras H (August 2018). "Biosynthesis in the Albumen Gland-Capsule Gland Complex Limits Reproductive Effort in the Invasive Apple Snail Pomacea canaliculata". The Biological Bulletin. 235 (1): 1–11. doi:10.1086/699200. hdl:11336/101954. PMID30160995. S2CID52135669.
^ abMorrill JB, Norris E, Smith SD (1964). "Electro- and immunoelectrophoretic patterns of egg albumen of the pond snail Limnea palustris". Acta Embryol. Morph. Exp. 7: 155–166.
^ abcdeHeras H, Garin CF, Pollero RJ (1998). "Biochemical composition and energy sources during embryo development and in early juveniles of the snail Pomacea canaliculata (Mollusca: Gastropoda)". Journal of Experimental Zoology. 280 (6): 375–383. doi:10.1002/(SICI)1097-010X(19980415)280:6<375::AID-JEZ1>3.0.CO;2-K.
^ abcdefgGiglio ML, Ituarte S, Pasquevich MY, Heras H (2016-09-12). "The eggs of the apple snail Pomacea maculata are defended by indigestible polysaccharides and toxic proteins". Canadian Journal of Zoology. 94 (11): 777–785. doi:10.1139/cjz-2016-0049. hdl:1807/74381.
^Raven CP (1972). "Chemical embriology of Mollusca". In Florkin M, Scheer BT (eds.). Chemical Zoology. New York: Academic Press. pp. 155–185.
^ abKamiya H, Sakai R, Jimbo M (2006). "Bioactive Molecules from Sea Hares". In Gavagnin G, Cimino M (eds.). Molluscs. Progress in Molecular and Subcellular Biology. Vol. 43. Berlin, Heidelberg: Springer. pp. 215–39. doi:10.1007/978-3-540-30880-5_10. ISBN978-3-540-30880-5. PMID17153345.
^ abDreon MS, Heras H, Pollero RJ (July 2004). "Characterization of the major egg glycolipoproteins from the perivitellin fluid of the apple snail Pomacea canaliculata". Molecular Reproduction and Development. 68 (3): 359–64. doi:10.1002/mrd.20078. PMID15112330. S2CID22032382.
^Heras H, Frassa MV, Fernández PE, Galosi CM, Gimeno EJ, Dreon MS (September 2008). "First egg protein with a neurotoxic effect on mice". Toxicon. 52 (3): 481–8. doi:10.1016/j.toxicon.2008.06.022. PMID18640143.
^Giglio ML, Ituarte S, Milesi V, Dreon MS, Brola TR, Caramelo J, et al. (August 2020). "Exaptation of two ancient immune proteins into a new dimeric pore-forming toxin in snails". Journal of Structural Biology. 211 (2): 107531. doi:10.1016/j.jsb.2020.107531. hdl:11336/143650. PMID32446810. S2CID218873723.
^ abcdPasquevich MY, Dreon MS, Heras H (March 2014). "The major egg reserve protein from the invasive apple snail Pomacea maculata is a complex carotenoprotein related to those of Pomacea canaliculata and Pomacea scalaris". Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology. 169: 63–71. doi:10.1016/j.cbpb.2013.11.008. hdl:11336/100510. PMID24291422.
^Sun J, Zhang H, Wang H, Heras H, Dreon MS, Ituarte S, et al. (August 2012). "First proteome of the egg perivitelline fluid of a freshwater gastropod with aerial oviposition". Journal of Proteome Research. 11 (8): 4240–8. doi:10.1021/pr3003613. hdl:11336/94414. PMID22738194.
^Mu H, Sun J, Cheung SG, Fang L, Zhou H, Luan T, et al. (February 2018). "Comparative proteomics and codon substitution analysis reveal mechanisms of differential resistance to hypoxia in congeneric snails". Journal of Proteomics. 172: 36–48. doi:10.1016/j.jprot.2017.11.002. hdl:10754/626132. PMID29122728.
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^Dreon MS, Ceolín M, Heras H (April 2007). "Astaxanthin binding and structural stability of the apple snail carotenoprotein ovorubin". Archives of Biochemistry and Biophysics. 460 (1): 107–12. doi:10.1016/j.abb.2006.12.033. PMID17324373.
^Ituarte S, Dreon MS, Ceolín M, Heras H (September 2008). "Isolation and characterization of a novel perivitellin from the eggs of Pomacea scalaris (Mollusca, Ampullariidae)". Molecular Reproduction and Development. 75 (9): 1441–8. doi:10.1002/mrd.20880. PMID18213678. S2CID24352602.
^Dreon MS, Schinella G, Heras H, Pollero RJ (February 2004). "Antioxidant defense system in the apple snail eggs, the role of ovorubin". Archives of Biochemistry and Biophysics. 422 (1): 1–8. doi:10.1016/j.abb.2003.11.018. PMID14725852.
^Tompa AS (1980). "Studies on the reproductive biology of gastropods: Part III. Calcium provision and the evolution of terrestrial eggs among gastropods". Journal of Conchology. 30: 145–154.