ISSN 1062-3604, Russian Journal of Developmental Biology, 2008, Vol. 39, No. 4, pp. 232–235. © Pleiades Publishing, Inc., 2008.
Original Russian Text © I.V. Medvedev, 2008, published in Ontogenez, 2008, Vol. 39, No. 4, pp. 289–293.
The ability to restore body integrity after tissue
damage or loss is a fundamental property of living
organisms (Bronsted, 1969). It is observed in all
branches of the phylogenetic tree from protozoans
(Korotkova, 1997) to higher mammals (Karlson, 1986)
and throughout the ontogeny (Tokin, 1959). In the wide
sense, regeneration is the replacement of various struc-
tures (from cell parts to large body parts) after natural
degeneration or natural loss (Korotkova, 1997).
Freshwater planarians are a classical subject of
regeneration studies due to their extremely high rege-
nerative capacity (Korotkova, 1997).
Mercury toxicity and metabolism are actively stud-
ied using different techniques involving several con-
centrations and long exposure periods. Mercury is an
active metal with high afﬁnity to various macromole-
cules; it can bind DNA both in vitro and in vivo, which
results in the modiﬁcation of these molecules (Grover
et al., 2001).
The anthropogenic emission of mercury to the
atmosphere is comparable with its quantities in the nat-
ural global cycle (Fitzgerald, 1995). One of key proper-
ties distinguishing mercury from other heavy metals is
its methylation in water bodies yielding methylmercury
compounds that are accumulated in the tissues and
organs of aquatic animals. The methylmercury level
increases in the aquatic food chain from beginning to
end (Bloom et al., 1991).
Water ecosystems contain no other compounds with
such strong neurotoxic effect, and the mechanism of
mercury effect on poikilotherms remains underex-
plored. Most publications explore the effect of inor-
ganic mercury compounds, which are less toxic com-
pared to organic ones (Rodier, 1995). Little is known
about the effect of methylmercury compounds on life
(in particular, regeneration) of predatory ﬂatworms, a
permanent biocenotic component of most water bodies
(Medvedev and Komov, 2005).
The goal of this work was to quantitatively evaluate
regeneration in two freshwater planarians,
, under different conditions
of natural methylmercury accumulation using the mor-
MATERIALS AND METHODS
occur in water bodies of West-
ern Europe and European Russia including the Yaro-
slavl Region (Porﬁr’eva and Dyganova, 1987). Repre-
sentatives of this species are 10 to 12 mm long. The
worms were collected in water bodies of the Yaroslavl
Region and transferred to aquaria, where they laid
cocoons. One month after the emergence from cocoons,
planarians that reached 10 to 12 mm in length were
fed on substrates with low (0.02–0.07 mg/kg) or
high (0.30–0.50 mg/kg wet weight) concentration of
methylmercury compounds for 6 months.
are widespread in Western
and Central Europe; in Eastern Europe they do not
occur beyond the Volga River (Porﬁr’eva and Dyga-
nova, 1987). Worms of this species reach 20 mm in
length. Similar to
young animals one month
after the emergence from cocoons were used in experi-
Regeneration in Two Freshwater Planarian
Species Exposed to Methylmercury Compounds
I. V. Medvedev
Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl oblast, 152742 Russia
Received February 8, 2007; in ﬁnal form, May 30, 2007.
—The regeneration rate was studied by the morphometric method in planarians
after different periods of exposure on food substrates with high (0.30–0.50 mg/kg wet weight)
and low (0.02–0.07 mg/kg) concentration of methylmercury compounds. The planarian growth and the ratio
of regenerating tissue area to the total fragment area after transverse cutting were evaluated. The rate of size
increment was lower in animals with high level than with low level of methylmercury than with low level
of methylmercury. The highest relative and absolute body area increment after amputation was observed in
, respectively. Thus, natural methylmercury compounds were shown to inhibit tissue
regeneration in planarians in a dose-dependent manner.
planarians, regeneration, methylmercury compounds.