Sex determination mechanisms in fish

In fish, sex determination (SD) system shows high variation. The SD mechanisms include environmental and genetic regulation. The research on SD system and related genes in intensively studied fish species was reviewed. Although some genes have been described as sex-related, only DMRTlbY can be considered as a master sex determination gene and none of them has been util-ized in aquaculture. The variation of fish SD system, the importance of sex-related genes in evolution research and the relations be-tween environmental factors and sex-related genes were also discussed. The fish sex determination mechanism remains largely un-known. Further research needs to be done considering the significance of fish SD studies in basic and applied aspects.     

鱼类MHC基因的研究概况

主要组织相容性复合体(MHC)是在脊椎动物中发现的编码免疫球蛋白样受体的高度多态的基因群,因其在免疫系统中的重要作用而备受关注.近年来,随着发现鱼类中也存在MHC基因,自1990年代开始对鱼类的MHC进行了广泛的研究,获得了许多重要信息.本文对近年鱼类MHC的结构、基因数目、多态、表达、功能以及在鱼类研究中的应用等方面的研究作了简要介绍.     

Analysis of new microsatellite markers developed from reported sequences of Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

The expressed sequence tags (ESTs) of Japanese flounder, Paralichthys olivaceus, were selected from GenBank to identify simple sequence repeats (SSRs) or microsatellites. A bioinformatic analysis of 11111 ESTs identified 751 SSR-containing ESTs, including 440 dinucleotide, 254 trinucleotide, 53 tetranucleotide, 95 pentanucleotide and 40 hexanucleotide microsatellites respectively. The CA/TG and GA/TC repeats were the most abundant microsatellites. AT-rich types were predominant among trinucleotide and tetranucleotide microsatellites. PCR primers were designed to amplify 10 identified microsatellites loci. The PCR results from eight pairs of primers showed polymorphisms in wild populations. In 30 wild individuals, the mean observed and expected heterozygosities of these 8 polymorphic SSRs were 0.71 and 0.83 respectively and the average PIC value was 0.8. These microsatellite markers should prove to be a useful addition to the microsatellite markers that are now available for this species.     

Cytogenetic characterization of olive flounder Paralichthys olivaceus: DNA content, karyotype, AgNORs and location of major ribosomal genes

A cytogenetic analysis of Paralichthys olivaceus was carried out using the flow cytometry method for DNA content, silver staining for the nucleolus organizer region (AgNORs) identification and one-color fluorescence in situ hybridization (FISH) for chromosomal mapping of major ribosomal genes. Nuclear DNA content was estimated by flow cytometry method using Gallus domesticus erythrocytes as the internal reference standard. The C-value of this species was (0.737±0.024) pg, and the DNA contents of each chromo...     

Screening of eye-position related genes with DD-RT-PCR and RDA in the hybrids between Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> and stone flounder <Emphasis Type="Italic">Kareius bicoloratus</Emphasis>

Flatfish or flounder moves one eye to change body proportion into vertebral asymmetry during metamorphosis, during which some become sinistral while others dextral. However, the mechanism behinds the eye-position has not been well understood. In this research, hybrids between Japanese flounder(♀) and stone flounder (♂) show mixed eye-location in both dextral type and sinistral type, and thus become good samples for studying the eye-migration. mRNAs from pro-metamorphosis sinistral and dextral hybrids larvae were screened with classical differential display RT-PCR (DD-RT-PCR) and representational difference analysis of cDNA (cDNA-RDA); 30 and 47 putative fragments were isolated, respectively. The cDNA fragments of creatine kinase and trypsinogen 2 precursor genes isolated by cDNA-RDA exhibited eye-position expression patterns during metamorphosis. However, none of the fragments was proved to be related to flatfishes’ eye-position specifically. Therefore, further studies and more sensitive gene isolated methods are needed to solve the problems. Supported by National Natural Science Foundation of China (No. 30600455) and the National Basic Research Program of China (973 Program, No.2004CB117402)     

Sequence polymorphism of two major histocompatibility (MH) class II B genes and their association with Vibrio anguillarum infection in half-smooth tongue sole (Cynoglossus semilaevis)

Major histocompatibility complex (MHC) class Ⅱ B molecules play an important role in the adaptive immune response in fish. Previous study has reported that two highly polymorphic class ⅡB genes, Cyse-DAB and Cyse-DBB exist in half-smooth tongue sole (Cynoglossus semilaevis). In this study, the polymorphism within exon 2 of the class Ⅱ B genes following bacterial challenge was evaluated. Two hundred C. semilaevis individuals were injected intraperitoneally with Vibrio anguillarum. Muscle tissue from the first 20 dead and 20 of the survivors was collected for genotyping. Sixty alleles from the 40 individuals were isolated, of which 32 belonged to Cyse-DAB and 28 belonged to Cyse-DBB. The rate of dN (non-synonymous substitution) was higher than that of dS (synonymous substitution) in the PBRs (peptide binding residues) of both class Ⅱ B genes. Conversely, the rate of dS was higher than dN in the non-PBRs and the complete exon 2 sequence. Thus, the results suggest that positive selection has occurred in the PBRs and purifying selection in the non-PBRs and exon 2. Thirteen class Ⅱ B alleles were used to study the association between alleles and resistance to infection. Though not significant, alleles Cyse-DAB*0601, Cyse-DAB*0706, and Cyse-DBB*0101, Cyse-DBB*1301 were only found in surviving individuals and may represent alleles that have resistance against V. anguillarum infection. Alleles Cyse-DAB*0701 and Cyse-DAB*1301 were significantly more prevalent in dead individuals than in surviving ones and may represent alleles that are associated with increased susceptibility to V. anguillarum infection.     

角叉菜(Chondrus ocellatus Holm)原生质体分离、培养与再生的研究

从角叉菜(Chondrus ocellatus Holm)的孢子体和雌配子体中,分离了大量的成活原生质体。分离的最适条件为:纤维素酶3％,粉红鲍鱼酶8％,山梨醇1.2mol/dm~3,pH6.0,温度为15℃。细胞壁的完全解离,已用荧光增白剂的染色不着色和原生质体在低渗溶液中的易碎性证实。培养后再生的细胞,经均等分裂,随后发育成实心球状体;或出芽后不等分裂,发育成丝状体和愈伤组织状细胞团。在PES培养基中,经30～40d培养,部分球状体和愈伤组织状细胞团分化出完整植株,但丝状体未能分化。低浓度的IAA、6—FA和C—751对球状体和愈伤组织状细胞团的生长和分化都有促进作用。由原生质体培养获得完整的再生植株,这在真红藻纲(Florideophyceae)中为首例报道。