INTRODUCTION
As potent neurotoxin, Tetrodotoxin (TTX) and Saxitoxin (STX) can
specifically bind to sodium channels of animals by sharing one binding
site with high affinities4,5,6, which could lead to
poisoning and death of animals. However, some animals can accumulate TTX
or STX in their body to defense the external environment since they
possibly could be resistant to toxins by target site insensitivity, such
as in fish, frog and mullusca1,2,3,32. Understanding
how TTX is accumulated in animals and how animals resist to TTX in
genetic level would be particularly critical for adaptive evolution
research and toxin poisoning cure in medicine.
Some proteins which were possibly related with TTX binding and
transportation were found in puffer fish2,17. Takashi
et al (2000)34 firstly purified some TTX-binding
proteins in puffer fish. Yotsu-Yamashita et al (2010 and
2013)2,17 reported the distribution and localization
of TTX-binding protein and their homologous proteins in puffer fish,
which possibly be related with TTX transportation. Feroudj et al
(2014)19 employed DNA microarray analysis revealed
some gene candidates related with TTX accumulation in puffer
fish19. But the detailed accumulation mechanism of TTX
is needed to be well understood in a wide range of animals. Except
pufferfish, STX and TTX resistance also appears in various kinds of
animals, such as snails7, xanthid
crab8, blue-ringed octopus 9, and
and frogs3,10-12. It has been reported that the
mutation in sodium channel genes13 can block the
binding of toxin and thus result in the toxin
resistance1,2,3,14-16. Understanding how organisms
resist TTX on genetic level would contribute to investigate adaptive
evolution in ecological communities.
Nassarius , a species-rich genus of Nassariinae, is important in
maintaining the balance of marine ecological system. For a long time,Nassarius is consumed as popular food in Asian countries as
economic species21. However, eating nassariids ofNassarius have caused hundreds of food poisoning and death
incidents in the last several years, especially in China. Our previous
studies detected that the food poisoning incident was due to TTX
accumulated in Nassarius sp’s body and the toxicity of differentNassarius species and different populations within oneNassarius species was different22, which means
that some Nassarius species and populations can accumulate TTX in
their body but some others do not accumulate. This is possibly related
with the sea environments they live which could lead to adaptive
evolution for different communities.
Currently the genetic basis involving TTX accumulation and resistance inNassarius is unclear. Here we performed transcriptional analysis
for both toxic and non-toxic specimens in two Nassarius species
(Nassarius succinctus and Nassarius variciferus ), aiming
to reveal their genetic patterns for TTX accumulation and resistance in
genetic expression and mutation level for better understanding the
adaptive evolution for toxin.