Adaptive evolution of scn4aa in Takifugu and Tetraodon

Tetrodotoxin(TTX)is a potent neurotoxin firstly discovered in the ovary of pufferfish.The genetic basis of voltage-gated sodium channel resistance to TTX has been widely studied,but it remains unclear in the evolution history of voltage-gated sodium channel resistance to TTX in pufferfish with different TTX concentrations.In this study,six scn4aa coding sequences of pufferfish were firstly cloned and sequenced,then used to investigate the adaptive evolution of scn4aa associated with TTX concentration and reconstruct ancestral sequences with seven scn4aa of other fishes.The result of CODEML(codon substitution model)program from the PAML(phylogenetic analysis by maximum likelihood)package shows only in the genus of Takifugu,which contains TTX highly in the liver,under positive selection.The result also indicates that three of four positively selected sites are located in the intracellular regions,which may compensate for normal function.The ancestral sequence reconstruction may suggest that the replacements providing weak toxin resistance might have appeared first in scn4aa,then the genus Takifugu evolved stronger resistance to TTX later.These results contribute to the explanation of the evolutional history of voltage-gated sodium channel resistance to TTX in pufferfish.

Gonadal development and silvering of the Japanese Eel(Anguilla japonica)in the Yangtze River during downstream migration

The Yangtze River and its branches are important habitats for the Japanese Eel(Anguilla japonica),however,there are few data on gonadal development and silvering indices of eels during the downstream spawning migration.This study investigates gonadal development in 121 Japanese eels caught downstream from the Jingjiang Reach of the Yangtze River in October 2012.We found that in females the ovaries of most of the out-migrating population developed earlier than the testes in males,that is,the ovaries reached stage 3(F3)or early stage 4(eF4),while the testes were at stage 2(M2)or stage 3(M3).Gonadal development in eels collected in 2012 was earlier than that of samples caught from the same region in 2007e2008 and from the Pearl River Estuary in 1972e1973.The average age,body size and gonadal-somatic index of females were significantly greater than those in males.For both females and males,there were no significant differences between the two stages of gonadal development in any of the morphological indices,which indicates that gonadal development of the Japanese Eel is independent of body size.These results help us to understand the spawning population of Japanese Eels in the Yangtze River.

The double mutations of acvr2aa and acvr2ba leads to muscle hypertrophy in zebrafish

Activin A receptor,type II(Acvr2)is a member of the transforming growth factor beta receptor family and can function as a negative regulator of skeletal muscle mass.Acvr2 plays an important role in regulating muscle development that can inhibit skeletal muscle growth in mice.However,there is very little research reported on the function of acvr2 in muscle development of teleost.In this study,we analyzed the effect of acvr2aa and acvr2ba on muscle development in zebrafish.Growth rates of WT and acvr2a^(-/-b-/-)􀀀were measured from juvenile stage to adult stage.In addition,effects of acvr2 on skeletal muscle were tested in histological,protein and molecular levels.As a result,acvr2a^(-/-b-/-)􀀀exhibited a wider body trunk than WT and showed a significant increase in body weight and width from two months old.Histological analysis of skeletal muscle indicated that the size of muscle fiber in acvr2a^(-/-b-/-)􀀀(female:1809±123μm^(2);male:2261±130μm^(2))was larger than that in WT(709.8±49μm^(2);815±53μm^(2)).In addition,western blot of fast MyLc protein showed the protein synthesis of acvr2a^(-/-b-/-)􀀀are increased.Besides,Histological analysis of heart showed the ventricle area is aslo increased in acvr2a^(-/-b-/-)􀀀.Our results demonstrated acvr2 attends the development of muscle fiber and will cause muscle hypertrophy when they were knocked out in zebrafish.In conclusion,acvr2 in zebrafish can control the development of muscle fibers during posthatch growth.

Eye location, cranial asymmetry, and swimming behavior of different variants of Solea senegalensis

Many flatfish species,such as Scophthalmus maximus,Paralichthys olivaceus,Solea senegalensis,are extensively cultured worldwide.In flatfishes,eye migration varies among different species and even within the same species.The genetic mechanism underlying eye migration is still unclear,and it is the key to improve metamorphosis in flatfish aquaculture and understand flatfish evolution.In this study,the high frequency of eye location variants in an artificial S.senegalensis population allowed us to investigate the eye preference during migration;completeness of the eye migration;and other related left-right asymmetric characteristics,such as asymmetrical skull remodeling and lying down on one side.The different frequencies of eye preference during migration,completeness of the eye migration,and settling side suggest that they are determined by different genotypes and imply independent evolutionary events during flatfish evolution.We found that the swimming time may be related to the completeness of eye migration,and further the migration of the eye,the more time the fish spent at the sea bottom.The left-right asymmetric degrees of not only the frontal bones and lateral ethmoids but also the jaw bone,including the premaxillary,maxillary,and dentary bones,depend on the completeness of eye migration.Finally,we proposed a hypothesis for the asymmetric origin of flatfish that provides reasonable explanations for the selective advantages of primitive flatfish species.