Collaborators from other institutions
Hong Kong University, Hong Kong. Republica Popular de China
INIFTA -Research Institute of Theoretical and Applied Physical Chemistry (CONICET - CCT- La Plata) UNLP. La Plata. Province of Buenos Aires. Argentina
Cathedra of Pathology, Faculty of Veterinary Science. UNLP. La Plata. Province of Buenos Aires. Argentina
National University of Tucumán. Province of Tucumán. Argentina
Animal model: An Invasive Snail: pest and host of parasites
Our main model is the Apple snail Pomacea canaliculata (also called ampularia in Spanish and Apfelschnecke in German), which is very frequent in Argentinean rivers, springs and ponds. The natural range of the species spreads from Southern Buenos Aires province up to Mesopotamia, center and NOA provinces.
In the last three decades this snail has spread through Southeast Asia, North America, Spain and some Pacific islands, being listed within the 100 top invasive species.It became a serious pest of rice and taro fields as well as an intermediate host of Angiostrongylus cantonensis, the causative agent of eosinophilic encephalitis, and a potencially lethal desease.
The spread of the species is probably related to its high fecundity rate (a female lays about 10,000 pink eggs outside the water) and also to the unusual characteristics of the egg-proteins, which we study.
Despite being rich in proteins and carbohydrates, the eggs of this species are devoid of predators within the native range of the species (South America) and have only one or two occasional predators in Asia.
To study structure-function relationships in these proteins we combine classical biochemistry techniques with molecular biology, biophysics, histopathology and also bioassays with laboratory animals.
Structural aspects of the perivitelins
The major glyco-lipoproteins present in the eggs are high molecular weight oligomers: ovorubin and PV2 in P. canaliculata and scalarin in P. scalaris. Ovorubin and scalarin are composed of three highly glycosylated subunits, and carry carotenoid pigments, i.e. they are carotenoproteins. PV2 is an octamer, composed of four disulfide linked heterodimers.
We have shown that these perivitellins are thermally stable; ovorubin is stable up to 95°C, PV2 up to 60°C and scalarin up to 80°C.
Particularly, ovorubin and scalarin are also stable in a wide pH range; ovorubin between pH 4.0 and 12.0 and scalarin between pH 2.0 and 10.0.
Finally, the three perivitellins are resistant to proteolitic digestion by pepsin (the major gastric protease in mammals) and trypsin (a highly conserved protease in both vertebrates and invertebrates).
Functional aspects related to embryo defenses against predation
Given that ovorubin is a trypsin inhibitor, which is stable in a wide pH range and also resists proteolitic attack, a mammalian model was used to test ovorubin’s effects in vivo. It was found that the protein diminishes the growth rate in rats when administered orally.
These results indicate that ovorubin is part of the egg defenses by inhibiting the predator proteases, thus limiting the digestion of the egg proteins (antidigestive defense). This kind of defense system had not been reported in animals before, but is typical of plant defense against herbivores. Moreover, ovorubin binds a carotenoid molecule (astaxanthin) which provides the eggs a bright reddish coloration, probably working as a warning signal (aposematic coloration).
Functional studies with in vivo experiments showed that PV2 is a neurotoxin with lethal effect on mice, the first toxin to be reported in an egg, and in a freshwater mollusk. Moreover, PV2 reaches the intestine in a biologically active form (antinutritive defense).
The major perivitellin of P. scalaris eggs, may also be involved in egg antinutritive defense, since it resists proteolitic digestion. Similar to ovorubin, this protein binds a carotenoid pigment and gives the eggs a bright coloration which may function as a warning signal.
This antinutritive/antidigestive system would be the only animal defense reported so far, with no trade-off between aposematism and toxicity, since both components are encoded in the same macromolecule.
We have shown that these multifunctional perivitellins provide the embryo not only with reserve components, but also with antidigestive, antinutritive and, possibly, aposematic defenses. These defenses would account for the rapid expansion of the species in non-native environments, and also for the virtual absence of egg predators. It is notable in this sense that, when predating the adult female snails, the snail kite (Rostrhamus sociabilis) and other birds reject the gland that synthesizes the egg components.
It seems that before being consumed by the embryo, perivitellins endow the eggs with one of the most effective defense systems. This opens new perspectives for ecological and evolutionary studies of reproductive strategies.
Book - Book Chapters
Lavarías, S; Heras, H; Pedrini, N; Turnier, H; Ansaldo, M.
2011. Comp. Biochem. Physiol. 153 C: 415-421. doi:10.1016/j.cbpc.2011.02.002
Pasquevich, M. Y; Dreon, M. S; Lavarías, S; Heras, H.
2011. Comp. Biochem. Physiol. 160 B: 201-207. doi:10.1016/j.cbpb.2011.08.006
Frassa, V; Ceolin, M; Dreon, M. S; Heras, H.
2010. Biochimica and biophysica acta. Elsevier. vol. 1804, p. 1492-1499
Dreón, M. S; Ituarte, S; Heras, H.
2010. Plos one. Public Library Science. vol. 5, n 12, p. 15059-15068
Ituarte, S; Dreón, M. S; Pasquevich, M. Y; Fernández, P. E; Heras, H.
2010. Comparative biochemistry and physiology. part b, biochemistry & molecular biology. Elsevier Science Inc. vol. 157, p. 66-72
Ituarte, S; Dreon, M. S; Ceolin, M; Heras, H.
2008. Molecular reproduction and development.Wiley-Liss, vol. 75, p. 1441-1448
Heras, H; Frassa, V; Fernández, P. E; Galosi, C. M; Gimeno, E; Dreon, M. S.
2008. Toxicon. Elsevier, vol. 52, p. 481-488
Dreón, M. S; Ituarte, S; Ceolín, M; Heras, H.
2008. Febs journal. Blackwell Pub. on behalf of the Federation of European Biochemical Societies, vol. 275, n° 18, p. 4522-4530. ISSN 1742-464X
Dreon, M. S; Ceolin, M; Heras, H.
2007. Archives of biochemistry and biophysics. vol. 30, p. 359-365
Heras, H; Dreon, M. S; Ituarte, S; Pollero, R. J.
2007. Comparative biochemistry and physiology. toxicology & pharmacology. vol. 146, p. 158-167
Fernández, P. E; Frassa, V; Gimeno, E. J; Dreon, M; Heras, H.
2011. Edited by Riet-Correa, F., Pfister J., Schild A.L. and Panter K. CAB International, Oxfordshire, UK 482-498. ISBN 13 978 1 84593 833 8. Chapter 83
Book - Book Chapters