Preferential interaction of loach DNA polymerase delta with DNA duplexes containing single-stranded gaps

We studied the interaction of DNA polymerase delta (pol delta) purified from the eggs of the teleost fish Misgurnus fossilis (loach) with DNA duplexes containing single-stranded gaps of 1-13 nucleotides (nt). In the absence of processivity factors (PCNA, RF-C, and ATP), pol delta elongated primers on single-stranded DNA templates in a distributive manner. However, the enzyme was capable of processive synthesis by filling gaps of 5-9 nt in DNA duplexes. These data suggest that, upon filling a small gap, pol delta interacts with the 5'-terminus downstream of the gap as well as with the 3'-terminus of the primer. Interaction of pol delta with the proximal 5'-terminus restricting the gap was confirmed by electrophoretic mobility shift assay. Analysis of the enzyme binding to DNA duplexes containing gaps of various sizes showed a much higher affinity of pol delta for duplexes with gaps of about 10 nt than for DNA substrates with primers annealed to single-stranded templates. The most efficient pol delta binding was observed in experiments with DNA substrates containing unpaired 3'-tails in primers. The data obtained suggest that DNA molecules with small gaps and single-stranded tails may serve as substrates for direct action of pol delta in the course of DNA repair.

Isogenic transgenic homozygous fish induced by artificial parthenogenesis

As a model system for vertebrate transgenesis, fish have many attractive advantages, especially with respect to the characteristics of eggs, allowing us to produce isogenic, transgenic, homozygous vertebrates by combining with chromosome-set manipulation. Here, we describe the large-scale production of isogenic transgenic homozygous animals using our experimental organism, the mud loach Misgurnus mizolepis, by the simple process of artificial parthenogenesis in a single generation. These isogenic fish have retained transgenic homozygous status in a stable manner during the subsequent 5 years, and exhibited increased levels of transgene expression. Furthermore, their isogenic nature was confirmed by cloned transgenic homozygous offspring produced via another step of parthenogenic reproduction of the isogenic homozygous transgenic fish. These results demonstrate that a combination of transgenesis and artificial parthenogenesis will make the rapid utilization of genetically pure homozygous transgenic system in vertebrate transgenesis possible.

Electroporated sperm mediation of a gene transfer system for finfish and shellfish

We investigated gene transfer in finfish and shellfish via electroporated sperm. The mobility of sperm, the fertilization rate, the hatching rate, gene transfer rate, and abnormality rate of derived embryos were primarily dependent on the voltage level and concentration of DNA during electroporation. Optimal conditions for sperm of each species of aquatic animals can be reached. Genome of the electroporated sperm was analyzed by PCR, and it was shown that an expected-sized product was amplified, corresponding to that of the transgene's amplification. Southern blotting also showed that a positive band located at the same position as the DNA fragment used for the transfer was found in the electroporated sperm after DNase treatment. When the genome isolated from embryos, larvae, juvenile, and adult individuals, all derived from sperm electroporated with foreign DNA molecules, was analyzed by PCR, the existence of foreign DNA was detected in some samples. The integration of the transferred DNA into the genome of transgenic samples was also shown by Southern blot analysis. There was a mosaic distribution of exogenous DNA in a wide variety of tissues analyzed. In addition to CAT activity being positive for the experimental larvae, the transferred GH gene was functional in transgenic finfish and shellfish and resulted in fast-growing transgenic varieties. The overall evidence strongly suggests that the use of electroporated sperm is the simplest yet most efficient approach to perform mass gene transfer in aquacultural animals, including marine mollusks.

[The chromosome mapping of PdSox8 and PdSox9 in two kinds of loaches]

With the Dig-labelled PdSox8 and PdSox9 as probes, the chromosome mapping of Sox8 and Sox9 in Paramisgurnus dabryanus and Misgurnus anguillicaudatus were analyzed by chromosome in situ hybridization technique. In P. dabryanus, the PdSox8 and PdSox9 were successfully localized in the No. 4 and No. 2 telocentric chromosome respectively, the relative distance to centromere is 40.2% and 67.5%; In M. anguillicaudatus, they were localized in the No. 9 and No. 6 telocentric chromosome respectively, the relative distance to centromere is 58.3% and 30.8%.

Genomic organization and sequence of the mud loach (Misgurnus mizolepis) growth hormone gene: a comparative analysis of teleost growth hormone genes

The mud loach (Misgurnus mizolepis) growth hormone (GH) gene was cloned and a comparative analysis on its genomic organization was performed. Based on Southern analysis using various kinds of restriction endonucleases, the GH gene proved to exist as a single-copy gene in the mud loach. The complete nucleotide sequences of a 5.1 kb SacI/EcoRI genomic fragment containing the mud loach GH gene and its 5' flanking sequences as well as a mud loach GH cDNA obtained by rapid amplification of a reverse transcriptase-PCR have been determined. The GH gene spans 2.0 kb from the start codon to the polyadenylation signal, and contains five exons and four introns similar to those of carps and mammals. The evolutionary relation of the mud loach GH gene, inferred by comparative analyses of gene structures and sequences in each exon and intron of representative teleost GH genes, reflects the major phylogenetic groupings of teleost.

Protein kinase C and casein kinase 2 phosphorylate in vitro proteins of the annexin family from eggs of loach Misgurnus fossilis

A mixture of proteins of the annexin family was obtained from the cytoplasm of mature eggs of loach Misgurnus fossilis (by reprecipitation with acid phospholipids in the presence of Ca2+). This mixture comprised five proteins with molecular weights of 58, 38, 36, 35, and 31 kD. Polyclonal rabbit antibodies against the major 31-kD protein were obtained. Western blot analysis showed that the obtained antibodies exhibit a high specificity towards the 31-kD protein from eggs and other tissues of loach and zebrafish (Brachydanio rerio). The analysis of cDNA corresponding to the 31-kD protein by screening the zebrafish cDNA library confirmed that this protein belongs to the annexin family. Phosphorylation of the obtained annexins in vitro was studied. It is shown that the 58-kD protein is phosphorylated by casein kinase 2 (CK2), whereas the 38-, 36-, 35-, and 31-kD proteins are phosphorylated by protein kinase C (PKC).

[Expression of the CMV-lacZ- and RSV-lacZ-genes in transgenic fish and mouse embryos]

The bacterial gene for beta-galactosidase under the control of LTR from either human cytomegalovirus (CMV-lacZ) or the Rous sarcoma virus (RSV-lacZ) was injected into fertilized eggs of Misgurnus fossilis L. loaches and F1 hybrid mice (CBA x C57Bl). Expression of the CMV-lacZ was observed in almost 100% of the loach embryos and larvae for two months following the first day of embryonic development. In some cases, expression points were located only on either the right or the left side of a fish. The spectrum of tissues expressing CMV-lacZ was decreased during embryonic development: CMV-lacZ was expressed only in fin and body muscles of 6- to 8-week-old loaches. In mice, the RSV-lacZ gene was expressed in ectoderm- and mesoderm-derived tissues of a 13-day-old embryo, and the CMV-lacZ gene was expressed in tissues derived from various blastophylli of a 14-day-old embryo. Distribution of transgene expression is discussed with regard to authors' and published data.

Genes encoding giant danio and golden shiner ependymin

Ependymin (EPN) is a brain glycoprotein that functions as a neurotrophic factor in optic nerve regeneration and long-term memory consolidation in goldfish. To date, true epn genes have been characterized in one order of teleost fish, Cypriniformes. In the study presented here, polymerase chain reactions were used to analyze the complete epn genes, gd (1480 bp), and sh (2071 bp), from Cypriniformes giant danio and shiner, respectively. Southern hybridizations demonstrated the existence of one copy of each gene per corresponding haploid genome. Each gene was found to contain six exons and five introns. Gene gd encodes a predicted 218-amino acid (aa) protein GD 93 percent conserved to goldfish EPN, while sh encodes a predicted 214-aa protein SH 91 percent homologous to goldfish. Evidence is presented classifying proteins previously termed "EPNs" into two major categories: true EPNs and non-EPN cerebrospinal fluid glycoproteins. Proteins GD and SH contain all the hallmark, features of true EPNs.

Comparative study of DNA adducts levels in white sucker fish (Catostomus commersoni) from the basin of the St. Lawrence River (Canada)

The levels of DNA adducts in the hepatic tissue of the white sucker fish species Catostomus commersoni were determined by 32P-postlabelling. The fish were caught at four sites: two sites near the city of Windsor (Québec, Canada) on the St. François River, a downstream tributary of the St. Lawrence River, and two sites in the St. Lawrence River itself, near the city of Montréal (Québec, Canada). The latter sites are known to be contaminated by many pollutants including polycyclic aromatic hydrocarbons. Total adduct levels in all fish ranged from 25.1-178.0 adducts per 10(9) nucleotides. White sucker from the selected sites of the St. Lawrence River had a significantly higher mean level of DNA adducts than those of the St. François River (129.4 vs 56.8, respectively). These results suggest that the effluents of many heavy industries (e.g. from a Soderberg aluminium plant) flowing in the St. Lawrence River are more likely to produce genotoxic damage to fish than those released in one of its tributary, and mainly associated to the activities of a small town and a nearby pulp and paper mill.

[Analysis of expression of the RSV-lacZ-gene in transgenic embryos of the loach Misgurnus fossilis L. during different variations of injection]

Several series of microinjection of the RSV-lacZ gene (the Escherichia coli beta-galactosidase gene under the control of the long terminal repeat of the Raus sarcoma virus) into fertilized mud loach eggs were carried out. The expression of the transgene in 3-5 day-old fry was shown to depend neither upon the stage of fry development at which the RSV-lacZ gene was introduced (early blastodisc, late blastodisc, 2-blastomere embryo) nor upon the region of transgene injection (blastodisc cytoplasm or egg yolk). Additionally, when injected into yolk, a smaller number of transgene expression points were observed and their distribution was confined to the surface of the yolk sac. In some experimental series, transgene expression was observed in 100% of embryos. The presence of exogenous genetic material in one of the experimental series was proved for 100% of 5- to 6-week old juveniles, when injected into cytoplasm, and for 67% of juveniles, when injected into yolk. This work provides evidence of the possibility of 100% transfer and expression of exogenous DNA when transgenic loachs are generated by injection into embryos and fry at different stages of their development.

5S rRNA gene hybridizes to human chromosome 1 at two sites (1q42.11-->q42.13 and 1q43)

Hybridization of a loach (Misgurnus fossilis) oocyte 5S rRNA gene repeat with human chromosomes was carried out to refine the localization of the 5S RNA gene in the human genome. Preliminary in situ hybridization analysis showed that this repeat hybridized with human chromosome region 1q42-->q43, the same location previously reported for the human 5S rRNA gene. High-resolution banding revealed the presence of two sites of hybridization, with a main peak in chromosome region 1q42.1 and a second peak in 1q43. These results are consistent with our data on the existence in the human genome of different 5S rRNA gene clusters specified by BamHI and HindIII restriction sites in spacer DNA (Timofeeva et al., 1993) and suggest a multicluster organization of the human 5S rRNA genes.

The expression of different annexins in the fish embryo is developmentally regulated

The expression of annexins, a family of Ca2+/phospholipid-binding proteins, was analyzed by biochemical and immunological criteria in the fish Misgurnus fossilis (loach), which is a good model system to study embryonic events. Five different annexins (loach annexins A to E) are present as a maternal pool in the unfertilized eggs. Only annexin E is newly synthesized in the early embryo. Its synthesis, already apparent at mid-blastula, decreases in later stages when two additional annexins (F and G) appear. They are present among the newly synthesized polypeptides of mid-gastrula and later embryonic stages and are also found in loach larvae. The developmentally controlled expression of several annexins indicates a specific role of these proteins at certain embryonic stages.

Structure, function, and phylogeny of [Arg8]vasotocin receptors from teleost fish and toad

[Arg8]Vasotocin (AVT) is considered to be the most primitive known vertebrate neurohypophyseal peptide of the vasopressin/oxytocin hormone family and may thus be ancestral to all the other vertebrate peptide hormones. The molecular evolution of the corresponding receptor family has now been studied by cloning an AVT receptor, consisting of 435 amino acid residues, from the teleost fish, the white sucker Catostomus commersoni. Frog oocytes injected with the AVT receptor-encoding cRNA respond to the application of AVT, but not to its structural and functional counterpart isotocin, by an induction of membrane chloride currents indicating the coupling of the AVT receptor to the inositol phosphate/calcium pathway. The pharmacological properties of the expressed AVT receptor show that it represents, or is closely related to, an ancestral nonapeptide receptor: oxytocin, aspargtocin, mesotocin, and vasopressin activated the receptor, but other members of the vasopressin/oxytocin family tested showed little or no potency; antagonists of the mammalian vasopressin V1 and oxytocin receptors blocked the AVT response. Comparison of AVT receptor sequences spanning transmembrane domains two to five, deduced by cloning cDNAs from the Pacific salmon Oncorhynchus kisutch, the cave-dwelling fish Astyanax fasciatus, and the anuran Xenopus laevis, with those of their mammalian counterparts emphasizes amino acid residues that are involved in hormone binding. The presence of a 5.0-kb transcript in various teleost tissues (pituitary, liver, gills, swim bladder, and lateral line) points to a physiological role for the fish AVT receptor in metabolic, osmoregulatory, and sensory processes.

The evolution of copulatory organs, internal fertilization, placentae and viviparity in killifishes (Cyprinodontiformes) inferred from a DNA phylogeny of the tyrosine kinase gene X-src

Cyprinodontiforms are a diverse group of approximately 900 pantropical and temperate fishes, mostly found in freshwater. Whereas the vast majority of fishes lay eggs (i.e. are oviparous), this group is unusual in that four groups of cyprinodont fishes give birth to living young (i.e. are viviparous). A molecular phylogenetic hypothesis was based on partial DNA sequences of the tyrosine kinase gene X-src. The study included the major lineages of fishes of the suborder Cyprinodontoidei, order Cyprinodontiformes. Our phylogeny agrees with some but not all of the conclusions of a previous morphological cladistic analysis (Parenti (Bull. Am. Mus. nat. Hist. 168, 335 (1981)). The differences are: (i) the Profundulidae are the sister group to the Goodeidae, not the sister group to all other cyprinodontoids; (ii) Fundulidae are the sister group to the Profundulidae and Goodeidae; (iii) Cubanichthys and the Cyprinodontinae might not be sister taxa; (iv) Cubanichthys, and not the Profundulidae, might be the most basal member of the cyprinodontoids; and (v) the Anablepinae and Poeciliinae might be sister groups. The molecular phylogeny was used to reconstruct the evolution of major life-history traits such as internal fertilization, copulatory organs, livebearing and placentas. Internal fertilization, modifications of the male's anal fin to form a copulatory organ, and viviparity probably evolved independently three times in cyprinodontiform fishes: in the subfamilies Goodeinae, Anablepinae and Poeciliinae (sensu Parenti 1981). The evolution of bundled sperm, spermatozeugmata, is probably not a prerequisite for internal fertilization because at least one species with internal fertilization has free spermatozoa. Livebearing (viviparity), which takes the form of ovoviviparity (where embryos are nourished by their yolk sac only), evolved only in the subfamily Poeciliinae. Advanced forms of viviparity, in which the mother provides additional nourishment to the embryos through placenta-like structures, apparently evolved at least three times from egg-laying ancestors: in the subfamilies Goodeinae, Anablepinae, and more than once in the Poeciliinae.

Molecular analysis of ependymins from the cerebrospinal fluid of the orders Clupeiformes and Salmoniformes: no indication for the existence of an euteleost infradivision

Ependymins represent the predominant protein constituents in the cerebrospinal fluid of many teleost fish and they are synthesized in meningeal fibroblasts. Here, we present the ependymin sequences from the herring (Clupea harengus) and the pike (Esox lucius). A comparison of ependymin homologous sequences from three different orders of teleost fish (Salmoniformes, Cypriniformes, and Clupeiformes) revealed the highest similarity between Clupeiformes and Cypriniformes. This result is unexpected because it does not reflect current systematics, in which Clupeiformes belong to a separate infradivision (Clupeomorpha) than Salmoniformes and Cypriniformes (Euteleostei). Furthermore, in Salmoniformes the evolutionary rate of ependymins seems to be accelerated mainly on the protein level. However, considering these inconstant rates, neither neighbor-joining trees nor DNA parsimony methods gave any indication that a separate euteleost infradivision exists.

[Expression of the beta-galactosidase gene in transgenic embryos of the loach Misgurnus fossilis L]

In order to study the topological characteristics of transgene expression in individuals, early loach embryos were injected with recombinant plasmid fragment, containing lacZ gene under the control of Raus sarcoma virus LTR. The expression of RSV-lacZ construct was found out in 80% of twenty-hours' embryos, 100% 2-3 days' embryos and 40% of 6-8 days' frys. Point and dot expression was observes on the surface of the head, muscle segments, the yolk sac, in the yolk, on the caudal fin. The number, size and intensity of expression dots varied in different individuals and decreased in the course of embryo development. The presence of RSV-lacZ sequences was found in 57% of 19 days frys. The variegation causes of transgene expression are discussed.

The complete nucleotide sequence of the Crossostoma lacustre mitochondrial genome: conservation and variations among vertebrates

The complete mitochondrial (mt) genome of Crossostoma lacustre, a freshwater loach from mountain stream of Taiwan, has been cloned and sequenced. This fish mt genome, consisting of 16558 base-pairs, encodes genes for 13 proteins, two rRNAs, and 22 tRNAs, in addition to a regulatory sequence for replication and transcription (D-loop), is similar to those of the other vertebrates in both the order and orientation of these genes. The protein-coding and ribosomal RNA genes are highly homologous both in size and composition, to their counterparts in mammals, birds, amphibians, and invertebrates, and using essentially the same set of codons, including both the initiation and termination signals, and the tRNAs. Differences do exist, however, in the lengths and sequences of the D-loop regions, and in space between genes, which account for the variations in total lengths of the genomes. Our observations provide evidence for the first time for the conservation of genetic information in the fish mitochondrial genome, especially among the vertebrates.

Elucidation of cDNA sequences for metallothioneins from rainbow trout, stone loach and pike liver using the polymerase chain reaction

Metallothionein cDNAs were generated from the livers of three fish species and amplified by PCR. Two distinct coding sequences (A and B) were elucidated for rainbow trout metallothioneins but single isoforms were encoded by genes isolated from the stone loach and pike. Different sized transcripts were observed both with stone loach and pike but these were accounted for by altered lengths of 3' untranslated regions.

Molecular cloning of two distinct vasotocin precursor cDNAs from chum salmon (Oncorhynchus keta) suggests an ancient gene duplication

The structures of two different vasotocin precursors from chum salmon brain have been elucidated through the molecular cloning of their corresponding cDNAs. Although the predicted precursors, consisting respectively of 153 and 158 amino acids, have the same structural organisation, they show 35% amino acid sequence divergence, of which only approximately half are isofunctional substitutions. Remarkably, while the C terminal segments of both precursors resemble the glycopeptide moiety of the related mammalian vasopressin precursor, both salmon precursors lack consensus sequences for N-glycosylation.

Two isotocin genes are present in the white sucker Catostomus commersoni both lacking introns in their protein coding regions

Two genes each encoding a distinct precursor protein to the hormone isotocin and a neurophysin-related protein are present in the teleost fish Catostomus commersoni. These precursors are referred to as isotocin 1 and 2. As shown by the polymerase chain reaction technique, both genes lack introns in their protein-coding sequences. Both genes are transcribed giving rise to mRNAs of 920 (isotocin 1) and 1020 (isotocin 2) bases, respectively. Based on the nucleotide sequences, the predicted isotocin precursors contain, besides the hormone moiety, a neurophysin-like protein that, in contrast to its mammalian counterpart, is extended at its C-terminus by a peptide which includes a leucine-rich core segment. This segment shows similarities to the copeptin of the mammalian vasopressin precursor that is known to possess prolactin-releasing activity. The data imply that the mammalian copeptin sequence was initially part of a larger ancestral neurophysin molecule.

[Intragenomic polymorphism of the primary structure of 5S rRNA gene variants of the loach (Misgurnus fossilis L.). Determination of the transcriptional activity]

The primary structure of 12 cloned repeats of loach oocyte 5S rRNA genes was determined. The heterogeneity of nucleotide sequences was revealed in the coding regions and spacer of the genes. The results of the study on in vivo transcriptional activity of the cloned 5S rRNA gene variants are consistent with the localisation of site specific base substitutions in the coding part affecting the transcription. We have compared the nucleotide sequences of loach 5S rRNA gene variants and of Xenopus laevis, X. borealis and Bombyx mori 5S genes which can be actively transcribed in X. laevis oocyte nuclei. As a result we could propose a consensus nucleotide sequence in the internal control region (from 45-th up to 100-th nucleotide) of the eukaryotic 5S rRNA gene. This sequence comprises a RNA-polymerase III promotor and stretches interacting with transcriptional factors. We have considered the base substitutions in the nucleotide sequences of 5S gene variants exerted on the experimental model of loach 5S rRNA secondary structure. All base substitutions in actively transcribed genes do not influence the general double-stranded structures of the transcripts. However in 5S RNA transcripts from genes with low transcriptional activity base substitutions affecting the box c RNA-polymerase III promoter destroy hairpin II interacting with ribosomal proteins. We have concluded that two factors can restrict the divergency of 5S rRNA genes: (1) conservation of the nucleotide sequence in the gene internal control region, and (2) conservation of the general double stranded structures in 5S rRNA transcripts.

Multiple sex-chromosome system in a loach fish

This study shows an X1X1X2X2/X1X2Y type of multiple sex-chromosome system in the genus Cobitis (Pisces, Ostariophysi). Observation of C-banded male meioses revealed that one arm of the neo-Y always associates end-to-end with one of the X chromosomes. This finding implies that a mechanism might be present that has prevented crossing-over between the ancestral X and Y chromosomes without morphological differentiation. This is the first reported case of multiple sex chromosomes among cyprinoid fish.

[Foreign DNA in developing embryos of the loach Misgurnus Fossilis L]

The fate of pAT153 DNA microinjected into the embryos of loach was examined. At the earliest stages of development (2 h) the high molecular weight transgenome consisting of pAT153 sequences is formed. The transgenome replicates intensively during the course of early development (until the blastula--early gastrula stages), but later the replication slows down which results in the elimination of the transgenome from the majority of embryos at more advanced stages. The analyses of the transgenome structure with the help of restriction endonucleases have shown that, after microinjection of linear DNA, the high molecular weight transgenome is formed by stochastic ligation of the sticky ends of injected molecules. Our data suggest that the transgenome formation from circular or supercoil DNA occurs after its linearization by host endonuclease.