Gene action in fish of tetraploid origin. IV. Ribosomal DNA amount in clupeoid and salmonoid fish

Phylogenetically tetraploid species of the fish order Isospondyli generally have twice the mean ribosomal gene content as closely related species on the phylogenetically diploid level. Considerable intraspecific variation of rDNA amount was observed. These findings are discussed in view of the hypothesis that selective loss of ribosomal genes may account for diminishing genic activity in phylogenetically tetraploid organisms.This work was supported by the Deutsche Forschungsgemeinschaft.     

Gene action in fish of tetraploid origin. V. Cellular RNA and protein content and enzyme activities in cyprinid,clupeoid, and salmonoid species

The ratio of cellular RNA and protein content is about 1:1 between phylogenetically diploid and tetraploid species of the teleost family Cyprinidae, but is roughly in proportion to ploidy in species of the teleost order Isospondyli. Enzyme activities do not unequivocally comply with this scheme. These findings are discussed in view of the hypothesis that a regulatory mechanism which reduces genic activity has evolved in the tetraploid cyprinids but not in the tetraploid species of the order Isopondyli.     

Isoenzyme polymorphism of the sorbitol dehydrogenase and the NADP-dependent isocitrate dehydrogenases in the fish family Cyprinidae

Among members of the fish family Cyprinidae , the existence of a diploid-tetraploid relationship is well established. The analysis of individual gene loci, using isoenzyme polymorphism as genetic markers, does not always confirm the expected gene duplication in the tetraploids. Of the markers used in this study, only the M-form of the NADP-dependent isocitrate dehydrogenase follows this expectation; the data suggest the existence of a single gene locus for the enzyme in diploids, while the observations on tetraploids were consistent with control by two distinct loci. For two other enzymes, the S-form of the NADP-dependent isocitrate dehydrogenase and sorbitol dehydrogenase, no difference seems to exist in the number of gene loci between diploids and tetraploids. A comparison between Cyprinid fish (order Ostariophysi ) and members of the order Isospondyli in which another diploid-tetraploid relationship was established, reveals that gene duplications are more frequently demonstrable within tetraploid Isospondyli than in tetraploid Cyprinidae. From this, it is concluded that polyploidization occurred earlier in evolution of Cyprinidae than of Isospondyli.     

Single-copy DNA relationships between diploid and tetraploid teleostean fish species

The degree of single-copy DNA relatedness among nine Salmonid, Osmerid, and Clupeid species (teleosts, order Isospondyli) was explored by interspecific DNA hybridization and the determination of the thermal stability of these hybrids. It is shown that the extent of base substitution and the amount of shared sequences is largely consistent with the systematic interrelationship of the species compared. A tentative estimate of the average base substitution rate is about 0.1–0.25% per million years, which is in the range typical for animal and plant nuclear genomes. The results are also discussed in view of the phylogenetically tetraploid state of the Salmonid genomes. A comparison of the amount of intra-genomic and inter-genomic divergence in the tetraploids suggests that a polyploidization event occurred recently in Salmonid evolution.     

Cross-reactivity to mammalian anti-H-Y antiserum in teleostean fish.

Anti-H-Y antiserum, raised in highly inbred rats, is absorbed by gonadal cells of various species of fish. This cross-reactivity proved to be restricted to the male sex in the cyprinodont species Lebistes and Xiphophorus, known to have the XX/XY mechanism of sex determination. In members of the more primitive fish orders Isospondyli and Ostariophysi, cross-reactivity was shown to occur as well, but the amount of antiserum absorbed was very similar in both sexes. An antigen cross-reacting with mammalian anti-H-Y antiserum is assumed to exist in fish similar to that found in higher vertebrates. If this is true, this antigen may have been shared originally by both sexes. However, during evolution, its expression has become restricted to the heterogametic sex.     

Gene action in fish of tetraploid origin. III. Ribosomal DNA amount in cyprinid fish

Phylogenetically diploid and tetraploid cyprinid fish species have cells of very similar volumes and protein contents. This finding has prompted us to postulate a regulatory system established during the evolution of the tetraploids leading to a diploid state of genic expression. It was proposed that this might be accounted for by a selective loss of ribosomal genes. RNA-DNA hybridization experiments, however, reveal a clear-cut 1:2 relationship of ribosomal DNA amounts between the diploid and the tetraploid species.This work was supported by the Deutsche Forschungsgemeinschaft.     

Gene action in fish of tetraploid origin. I. Cellular and biochemical parameters in cyprinid fish

In phylogenetically diploid and tetraploid Cyprinid fish species, erythrocyte volumes, protein contents, and mean activities of the enzymes LDH, 6PGD, and PGI per cell per active gene locus decline with increasing DNA contents. These findings are assumed to reflect an evolutionary tendency of polyploids to regulate their genic activity down to the level of the diploids.     

Regain of sex determination system and sexual reproduction ability in a synthetic octoploid male fish

Polyploids in vertebrates are generally associated with unisexual reproduction, but the direct consequences of polyploidy on sex determination system and reproduction mode remain unknown. Here, we synthesized a group of artificial octoploids between unisexual gynogenetic hexaploid Carassius gibelio and sexual tetraploid Carassius auratus. The synthetic octoploids were revealed to have more than 200 chromosomes, in which 50 chromosomes including the X/Y sex determination system were identified to transfer from sexual tetraploid C. auratus into the unisexual gynogenetic hexaploid C. gibelio. Significantly, a few synthetic octoploid males were found to be fertile, and one octoploid male was confirmed to regain sexual reproduction ability,which exhibits characteristics that are the same to sexual reproduction tetraploid males, such as 1:1 sex ratio occurrence, meiosis completion and euploid sperm formation in spermatogenesis, as well as normal embryo development and gene expression pattern during embryogenesis. Therefore, the current finding provides a unique case to explore the effect of sex determination system incorporation on reproduction mode transition from unisexual gynogenesis to sexual reproduction along with genome synthesis of recurrent polyploidy in vertebrates.     

Evidence for non-disomic inheritance in a Citrus interspecific tetraploid somatic hybrid between C. reticulata and C. limon using SSR markers and cytogenetic analysis

Artificial tetraploid somatic hybrids have been developed for sterile triploid citrus breeding by sexual hybridization between diploid and tetraploid somatic hybrids. The genetic structure of diploid gametes produced by tetraploid genotypes depends on the mode of chromosome association at meiosis. In order to evaluate tetraploid inheritance in a tetraploid interspecific somatic hybrid between mandarin and lemon, we performed segregation studies using cytogenetic and single sequence repeat molecular markers. Cytogenetic analysis of meiosis in the somatic hybrid revealed 11% tetravalents and 76% bivalents. Inheritance of the tetraploid hybrid was analyzed by genotyping the triploid progeny derived from a cross between a diploid pummelo and the tetraploid somatic hybrid, in order to derive genotypes of the meiospores produced by the tetraploid. A likelihood-based approach was used to distinguish between disomic, tetrasomic, and intermediate inheritance models and to estimate the double reduction rate. In agreement with expectations based the cytogenetic data, marker segregation was largely compatible with tetrasomic and inheritance intermediate between disomic and tetrasomic, with some evidence for preferential pairing of homoeologous chromosomes. This has important implications for the design of breeding programs that involve tetraploid hybrids, and underscores the need to consider inheritance models that are intermediate between disomic and tetrasomic.     

Amount of repeated and non-repeated DNA in the genomes of closely related fish species with varying genome sizes.

1. Within the teleostean family Cyprinidae, diploid species occur with wide variation in genome size. There also exist species which were anciently tetraploid. 2. The quantitative changes of DNA content in the diploids are primarily due to differences in the amount of intermediately repeated DNA. DNA sequence composition of the ancient tetraploid genomes suggests that the species derived from diploid ancestors of small genome size. 3. The average base composition and the base compositional heterogeneity are similar in all the species examined.     

不同倍性鱼的血细胞和精子DNA含量比较

我们以前的研究表明, 以红鲫 (2n=100) 为母本及湘江野鲤 (2n=100) 为父本的杂交后代的F1-F2 为二倍体 (2n= 100)。在二倍体 F2 个体中, 存在能分别产生二倍体卵子和二倍体精子的雌、雄个体, 二倍体卵子和二倍体精子结合, 形成了两性可育的四倍体鱼 (F3)。目前四倍体鲫鲤已连续繁殖了 12 代 (F3-F14), 形成了一个遗传性状稳定的四倍体鱼群体 (4n= 200) (Liu et al.,2001; 孙远东等, 2003)。雌性四倍体鲫鲤产生的二倍体卵子经紫外线照射的散鳞镜鲤精子激活后,无须染色体加倍处理, 可发育为全雌性二倍体雌核发育后代 (G1) (2n=10…     

The formation of the polyploid hybrids from different subfamily fish crossings and its evolutionary significance

This study provides genetic evidences at the chromosome, DNA content, DNA fragment and sequence, and morphological levels to support the successful establishment of the polyploid hybrids of red crucian carp x blunt snout bream, which belonged to a different subfamily of fish (Cyprininae subfamily and Cultrinae subfamily) in the catalog. We successfully obtained the sterile triploid hybrids and bisexual fertile tetraploid hybrids of red crucian carp (RCC) (female symbol) x blunt snout bream (BSB) (male symbol) as well as their pentaploid hybrids. The triploid hybrids possessed 124 chromosomes with two sets from RCC and one set from BSB; the tetraploid hybrids had 148 chromosomes with two sets from RCC and two sets from BSB. The females of tetraploid hybrids produced unreduced tetraploid eggs that were fertilized with the haploid sperm of BSB to generate pentaploid hybrids with 172 chromosomes with three sets from BSB and two sets from RCC. The ploidy levels of triploid, tetraploid, and pentaploid hybrids were confirmed by counting chromosomal number, forming chromosomal karyotype, and measuring DNA content and erythrocyte nuclear volume. The similar and different DNA fragments were PCR amplified and sequenced in triploid, tetraploid hybrids, and their parents, indicating their molecular genetic relationship and genetic markers. In addition, this study also presents results about the phenotypes and feeding habits of polyploid hybrids and discusses the formation mechanism of the polyploid hybrids. It is the first report on the formation of the triploid, tetraploid, and pentaploid hybrids by crossing parents with a different chromosome number in vertebrates. The formation of the polyploid hybrids is potentially interesting in both evolution and fish genetic breeding.     

水稻基因组加倍对籽粒大小调控基因表达的影响

水稻是最重要的粮食作物之一,提高水稻产量一直是育种的主要目标。水稻四倍体相对于二倍体具有籽粒变大、粒重增加的特点,研究基因组加倍后籽粒大小基因的调控模式,在育种应用方面具有十分重要的意义。本文以二倍体 -四倍体水稻为材料,分析6个控制籽粒大小基因在幼穗发育中的表达差异,同时结合转基因实验,探讨基因剂量增加对基因表达水平和籽粒大小的影响。结果发现：基因组加倍后,水稻的发育进程不变,但株高增加,叶片变宽,籽粒变大,增大后的籽粒在籼稻表现为长、宽均增加显著,而在粳稻中长度比宽度增加更为明显。进一步分析控制籽粒大小基因的表达差异情况,发现这些基因的表达不仅受发育时期的影响,在籼粳亚种间也明显不同,即受遗传背景的影响。在基因组加倍的情况下,正调控基因GS5、HGW的表达普遍高于对应的二倍体;负调控基因GS3在籼稻D9311中趋于下调或沉默,而在粳稻DBl中趋于上调,GW2在D9311中上调,而在DBl中趋于沉默。通过转基因实验分析负调控基因GW2在二倍体Bl中的表达趋势,发现其在基因剂量线性增加的情况下,表达水平高于二倍体和四倍体,导致其籽粒变小。本研究结果有助于了解水稻中控制籽粒大小的基因在二倍体和四倍体中的表达模式,为高产育种提供理论依据。     

Duplication of the LDH gene loci by polyploidization in the fish order Clupeiformes

Summary Within the order Clupeiformes, chromosome analysis and DNA measurements have indicated a diploid-tetraploid relationship among closely related species. To confirm the presence of polyploidization at single gene loci we studied the LDH isoenzyme system. The results obtained are in agreement with the hypothesis of polyploidization. While the diploid species show two gene loci for LDH, the tetraploid species exhibit four separate gene loci.In Duarte, supported in part by CA-05138 from the National Cancer Institute, U.S. Public Health Service.     

Cross-Reactivity to Mammalian Anti-H-Y Antiserum in Teleostean Fish

Anti-H-Y antiserum, raised in highly inbred rats, is absorbed by gonadal cells of various species of fish. This cross-reactivity proved to be restricted to the male sex in the cyprinodont species Lebistes and Xiphophorus, known to have the XX/XY mechanism of sex determination. In members of the more primitive fish orders Isospondyli and Ostariophysi, cross-reactivity was shown to occur as well, but the amount of antiserum absorbed was very similar in both sexes. An antigen cross-reacting with mammalian anti-H-Y antiserum is assumed to exist in fish similar to that found in higher vertebrates. If this is true, this antigen may have been shared originally by both sexes. However, during evolution, its expression has become restricted to the heterogametic sex.     

Glucosephosphate-isomerase expression in a tetrapioid fish,Moxostoma lachneri (Cypriniformes,Catostomidae): evidence for ‘retetraploidization’?

Glucosephosphate-isomerase isozymes in the tetraploid catostomid Moxostoma lachneri are controlled by four gene loci. The expression of two Gpi-A loci and two Gpi-B loci in this species contrasts with the expression of two Gpi-A loci and one Gpi-B locus in the remainder of the genus. The additional Gpi-B locus expressed in M. lachneri may be the result of a reactivation event or post-polyploidization tandem duplication rather than the continuous expression of originally duplicated loci.     

Gene expression analysis at the intersection of ploidy and hybridity in maize

Heterosis and polyploidy are two important aspects of plant evolution. To examine these issues, we conducted a global gene expression study of a maize ploidy series as well as a set of tetraploid inbred and hybrid lines. This gene expression analysis complements an earlier phenotypic study of these same materials. We find that ploidy change affects a large fraction of the genome, albeit at low levels; gene expression changes rarely exceed 2-fold and are typically not statistically significant. The most common gene expression profile we detected is greater than linear increase from monoploid to diploid, and reductions from diploid to triploid and from triploid to tetraploid, a trend that mirrors plant stature. When examining heterosis in tetraploid maize lines, we found a large fraction of the genome impacted but the majority of changes were not statistically significant at 2-fold or less. Non-additive expression was common in the hybrids, and the extent of non-additivity increased both in number and magnitude from duplex to quadruplex hybrids. Overall, we find that gene expression trends mirror observations from the phenotypic studies; however, obvious mechanistic connections remain unknown.     

Comparison of chemically induced chromosome loss in a diploid, triploid, and tetraploid strain of Saccharomyces cerevisiae.

Triploid and tetraploid strains of Saccharomyces cerevisiae were constructed and the spontaneous loss during mitosis of one, two or three copies of chromosome VII was determined. In one strain, a triploid (VM2) in which expression of the recessive alleles can be observed only after loss of two copies of chromosome VII (3N-2), the spontaneous frequency of chromosome loss was lower than in the diploid D61.M. In another strain, a tetraploid (VM4) that also requires the loss of two copies of chromosome VII for observation (4N-2) of the recessive alleles, the spontaneous frequency was slightly higher than in the diploid D61.M. The spontaneous frequency of other genetic events (that is, mutation, recombination or chromosome breakage) were lower by 2-3 orders of magnitude than in the diploid strain D61.M. Induction of chromosome loss and other genetic events by nocodazole, ethyl acetate, hydroxyurea and ethyl methanesulfonate was determined in D61.M, VM2, and VM4, and the results were compared. Nocodazole and ethyl acetate induced chromosome loss in both the triploid and the tetraploid strains at lower concentrations than required in the diploid. These compounds also induced elevated frequencies of other genetic events in both the triploid and the tetraploid strains but not in the diploid. Hydroxyurea induced elevated frequencies of chromosome loss in the diploid and the tetraploid. Frequencies of chromosome loss in the triploid treated with hydroxyurea, although elevated, are based on observation of very few colonies of the correct phenotype. Ethyl methanesulfonate failed to induce chromosome loss in any of the three strains. Hydroxyurea and ethyl methanesulfonate did, however, induce very high frequencies of other genetic events.