Sperm motility initiation and duration in a euryhaline fish, medaka (Oryzias latipes)

The medaka, Oryzias latipes, is a well-recognized fish model for biomedical research. An understanding of gamete characteristics is necessary for experimental manipulations such as artificial fertilization and sperm cryopreservation. The goal of this study was to investigate sperm characteristics of motility initiation, duration, and retention in medaka. First, motility was initiated by osmolality values ranging from 25 to 686 mOsm/kg, which included deionized water and hypotonic, isotonic, and hypertonic Hanks’ balanced salt solution. The percentage of motile sperm was >80% when osmolality was <315 mOsm/kg and decreased as osmolality increased. This is different from most fish with external fertilization in which sperm motility can be initiated by hypotonic (for freshwater fish) or hypertonic (for marine fish) solutions or by altering the concentration of specific ions such as potassium (e.g., in salmonids). Second, upon activation, the sperm remained continuously motile, with reserve capacity, for as long as 1 wk during storage at 4 °C. This was also different from other externally fertilizing fish, in which motility is typically maintained for seconds to several minutes. Third, after changing the osmolality to 46 to 68 mOsm/kg by adding deionized water, the motility of sperm held at 274 to 500 mOsm/kg was higher than the original motility (P ≤ 0.035) after 24, 48, and 72 h of storage at 4 °C. Fourth, the addition of glucose had no effect on maintaining sperm motility during refrigerated storage. To our knowledge, this combination of sperm motility characteristics is reported for the first time in fish and may be unique to medaka or may represent an undescribed modality of sperm behavior within euryhaline fish.     

Evaluation of cryoprotectant and cooling rate for sperm cryopreservation in the euryhaline fish medaka Oryzias latipes

Medaka Oryzias latipes is a well-recognized biomedical fish model because of advantageous features such as small body size, transparency of embryos, and established techniques for gene knockout and modification. The goal of this study was to evaluate two critical factors, cryoprotectant and cooling rate, for sperm cryopreservation in 0.25-ml French straws. The objectives were to: (1) evaluate the acute toxicity of methanol, 2-methoxyethanol (ME), dimethyl sulfoxide (Me₂SO), N,N-dimethylacetamide (DMA), N,N-dimethyl formamide (DMF), and glycerol with concentrations of 5%, 10%, and 15% for 60 min of incubation at 4 °C; (2) evaluate cooling rates from 5 to 25 °C/min for freezing and their interaction with cryoprotectants, and (3) test fertility of thawed sperm cryopreserved with selected cryoprotectants and associated cooling rates. Evaluation of cryoprotectant toxicity showed that methanol and ME (5% and 10%) did not change the sperm motility after 30 min; Me₂SO, DMA, and DMF (10% and 15%) and glycerol (5%, 10% and 15%) significantly decreased the motility of sperm within 1 min after mixing. Based on these results, methanol and ME were selected as cryoprotectants (10%) to evaluate with different cooling rates (from 5 to 25 °C/min) and were compared to Me₂SO and DMF (10%) (based on their use as cryoprotectants in previous publications). Post-thaw motility was affected by cryoprotectant, cooling rate, and their interaction (P ? 0.000). The highest post-thaw motility (50 ± 10%) was observed at a cooling rate of 10 °C/min with methanol as cryoprotectant. Comparable post-thaw motility (37 ± 12%) was obtained at a cooling rate of 15 °C/min with ME as cryoprotectant. With DMF, post-thaw motility at all cooling rates was ?10% which was significantly lower than that of methanol and ME. With Me₂SO, post-thaw motilities were less than 1% at all cooling rates, and significantly lower compared to the other three cryoprotectants (P ? 0.000). When sperm from individual males were cryopreserved with 10% methanol at a cooling rate of 10 °C/min and 10% ME with a rate of 15 °C/min, no difference was found in post-thaw motility. Fertility testing of thawed sperm cryopreserved with 10% methanol at a rate of 10 °C/min showed average hatching of 70 ± 30% which was comparable to that of fresh sperm (86 ± 15%). Overall, this study established a baseline for high-throughput sperm cryopreservation of medaka provides an outline for protocol standardization and use of automated processing equipment in the future.     

Sorgoleone,a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20 μg mL⁻¹. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25 μg mL⁻¹. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5 μg mL⁻¹ and 99% of Anabaena affinis Lemmermann at 4 μg mL⁻¹. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16 μg mL⁻¹ sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1 μg mL⁻¹ during the test period. The no observed effect concentration (NOEC) value was 1.5 μg mL⁻¹ for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.     

Functional lysophosphatidic acid receptors expressed in Oryzias latipes

Lysophosphatidic acid (LPA) signaling is known to play biological and pathophysiological roles in many types of animals. Medaka (Oryzias latipes) is an experimental fish that can be easily maintained, propagated, and analyzed, and whose genome has been completely sequenced. However, there is limited information available regarding medaka LPA receptors. Here, using information from the medaka genome database, we examine the genomic structures, expression, and functions of six LPA receptor genes, Lpar1–Lpar6. Our analyses reveal that the genomic structures of Lpar1 and Lpar4 are different from those deduced from the database. Functional analyses using a heterologous expression system demonstrate that all medaka LPA receptors except for LPA_5b respond to LPA treatment with cytoskeletal changes. These findings provide useful information on the structure and function of medaka LPA receptor genes, and identify medaka as a useful experimental model for exploration of the biological significance of LPA signaling.     

Sexually dimorphic expression of the sex chromosome-linked genes cntfa and pdlim3a in the medaka brain

In vertebrates, sex differences in the brain have been attributed to differences in gonadal hormone secretion; however, recent evidence in mammals and birds shows that sex chromosome-linked genes, independent of gonadal hormones, also mediate sex differences in the brain. In this study, we searched for genes that were differentially expressed between the sexes in the brain of a teleost fish, medaka (Oryzias latipes), and identified two sex chromosome genes with male-biased expression, cntfa (encoding ciliary neurotrophic factor a) and pdlim3a (encoding PDZ and LIM domain 3 a). These genes were found to be located 3–4 Mb from and on opposite sides of the Y chromosome-specific region containing the sex-determining gene (the medaka X and Y chromosomes are genetically identical, differing only in this region). The male-biased expression of both genes was evident prior to the onset of sexual maturity. Sex-reversed XY females, as well as wild-type XY males, had more pronounced expression of these genes than XX males and XX females, indicating that the Y allele confers higher expression than the X allele for both genes. In addition, their expression was affected to some extent by sex steroid hormones, thereby possibly serving as focal points of the crosstalk between the genetic and hormonal pathways underlying brain sex differences. Given that sex chromosomes of lower vertebrates, including teleost fish, have evolved independently in different genera or species, sex chromosome genes with sexually dimorphic expression in the brain may contribute to genus- or species-specific sex differences in a variety of traits.     

Modulation of ethanol toxicity by Asian ginseng (Panax ginseng) in Japanese ricefish (Oryzias latipes) embryogenesis

Alcohol consumption by women during pregnancy often induces fetal alcohol spectrum disorder (FASD) in children who have serious central nervous system (CNS), cardiovascular, and craniofacial defects. Prevention of FASD, other than women abstaining from alcohol drinking during pregnancy, is not known. A limitation of the use of synthetic anti-alcoholic drugs during pregnancy led us to investigate herbal products. In particular, many plants including Asian ginseng (Panax ginseng) have therapeutic potential for the treatment of alcoholism. We used Japanese ricefish (medaka) (Oryzias latipes), an animal model of FASD, for identifying herbal medicines that can attenuate ethanol toxicity. Fertilized eggs in standard laboratory conditions were exposed to ginseng (PG) root extract (0–2 mg/mL) either 0–2 (group A) or 1–3 (group B) day post fertilization (dpf) followed by maintenance in a clean hatching solution. The calculated IC₅₀ as determined 10 dpf in A and B groups were 355.3 ± 1.12 and 679.7 ± 1.6 μg/mL, respectively. Simultaneous exposure of embryos in sub-lethal concentrations of PG (50–200 μg/mL) and ethanol (300 mM) for 48 h disrupted vessel circulation and enhanced mortality. However, PG (100 μg/mL) may partially protect trabecular cartilage (TC) deformities in the neurocranium in B group embryos induced by ethanol (300 mM). To understand the mechanism, embryonic ethanol concentration was measured at 2 dpf and adh5, adh8, aldh2, aldh9a, catalase, GST, and GR mRNAs were analyzed at 6 dpf. It was observed that although ethanol is able to reduce adh8 and GST mRNA contents, the simultaneous addition of PG was unable to alter ethanol level as well as mRNA contents in these embryos. Therefore, antagonistic effects of PG on ethanol toxicity are mediated by a mechanism which is different from those regulating ethanol metabolism and oxidative stress.     

Molecular cloning and characterization of rat LC3A and LC3B--two novel markers of autophagosome

Rat microtubule-associated protein light chain 3 (LC3) is a homologue of yeast Atg8, an essential component of autophagy. Following synthesis, the C-terminus of rat LC3 is cleaved by a cysteine protease-Atg4, to produce LC3-I, which is located in cytosolic fraction. LC3-I can be converted to LC3-II through the processing by Atg7 (E1-like enzyme) and Atg3 (E2-like enzyme). LC3-II is modified by phosphatidylethanolamine on C-terminus and binds tightly to autophagosomal membrane. Here we reported the cloning of two novel variants of rat LC3, named LC3A and LC3B, respectively, and LC3B is an alternative splicing variant of LC3. LC3A, LC3B, and LC3 showed different expression patterns in rat tissues, suggesting a functional divergence among these proteins. When LC3A and LC3B were overexpressed, both exhibited two forms (18 and 16 kDa, representing types of I and II, separately), which might be due to post-translational modification including the characteristic C-terminal cleavage at these two proteins as similar to that found in rat LC3 and yeast Atg8. Subcellular localization demonstrated that both LC3A and LC3B are colocalized with LC3 and associated with the autophagic membranes. Mutation analysis further revealed that the conserved Gly120 residues of LC3A and LC3B are essential for their characteristic C-terminal cleavage and localization to autophagic membranes. Present data suggested that LC3A and LC3B could also be used as two novel autophagosomal markers.     

Nile Tilapia Neu3 sialidases: Molecular cloning,functional characterization and expression in Oreochromis niloticus

Mammalian Neu3 is a ganglioside specific sialidase. Gangliosides are involved in various physiological events such as cell growth, differentiation and diseases. Significance of Neu3 and gangliosides is still unclear in aquaculture fish species. To gain more insights of fish Neu3 sialidases, molecular cloning and characterization were carried out in tilapia (Oreochromis niloticus). A tilapia genome-wide search for orthologues of human NEU1, NEU2, NEU3 and NEU4 yielded eight putative tilapia sialidases, five of which were neu3-like and designated as neu3a, neu3b, neu3c, neu3d and neu3e. Among five neu3 genes, neu3a, neu3d and neu3e were amplified by PCR from adult fish brain cDNA with consensus sequences of 1227 bp, 1194 bp and 1155 bp, respectively. Multiple alignments showed conserved three Asp-boxes (SXDXGXTW), YRIP and VGPG motifs. The molecular weights for Neu3a, Neu3d and Neu3e were confirmed using immunoblotting analysis as 45.9 kDa, 44.4 kDa and 43.6 kDa, respectively. Lysate from neu3 genes transfected HEK293 cells showed sialidase activity in Neu3a towards ganglioside mix optimally at pH 4.6. Using pure gangliosides as substrates, highest sialidase activity for Neu3a was observed towards GD3 followed by GD1a and GM3, but not GM1. On the other hand, sialidase activities were not observed in Neu3d and Neu3e towards various sialoglycoconjugates. Indirect immunofluorescence showed that tilapia Neu3a and Neu3d are localized at the plasma membrane, while most Neu3e showed a cytosolic localization. RT-PCR analyses for neu3a showed significant expression in the brain, liver, and spleen tissues, while neu3d and neu3e showed different expression patterns. Based on these results, tilapia Neu3 exploration is an important step towards full understanding of a more comprehensive picture of Neu3 sub-family of proteins in fish.     

Fish cell culture: Establishment of two fibroblast-like cell lines (OL-17 and OL-32) from fins of the medaka,Oryzias latipes

Summary Two fibroblast-like cell lines were obtained from fins of adults of the medaka,Oryzias latipes, and serially cultured at 27° C. One cell line, which was derived from a fish of the orange-red variety, reached to population doubling level (PDL) 434 on Day 840 by 120 passages. The other, which was derived from a fish of the inbred strain HB32C, reached to PDL 294 on Day 551 by 80 passages. Any symptom of crisis was not detected. The cell lines were named OL-17 and OL-32, respectively. Population doubling time was 29 h for OL-17 cells, and 32 h for OL-32 cells. Density-dependent inhibition of growth was clear in OL-32 cells, but not so obvious in OL-17 cells. Modal chromosome number of OL-17 cells was 50, and that of OL-32 cells was 47 (2N=48). Plating efficiency of OL-17 cells was about 10%, whereas that of OL-32 cells was about 5%. The use of conditioned medium (80% concentration) increased the plating efficiency of OL-32 cells to more than 25%.     

Molecular phylogeny of the Pycnonotus sinensis and Pycnonotus taivanus in Taiwan based on sequence variations of nuclear CHD and mitochondrial cytochrome b genes

Sequences of the partial 293-bp nuclear Z-chromosome-linked chromo-helicase binding protein (CHD-Z) and 729-bp mitochondrial cytochrome b (cyt b) genes were obtained from two species of the same family Pycnonotidae of Pycnonotus sinensis (P. sinensis, Chinese Bulbul) and Pycnonotus taivanus (P. taivanus, Taiwan Bulbul) distributed in Taiwan. A panel of 10 individuals (n = 5 for each) with unknown relationship was used to characterize single nucleotide polymorphisms (SNPs) of these genes. We identified 2 and 10 SNPs in CHD-Z and cyt b loci, respectively. Frequency of SNPs was 10 per every 1465- and 729-bp on average. Pairwise nucleotide divergences of CHD-Z and cyt b genes among 10 specimens ranged from 0 to 0.0034 and 0 to 0.0055, respectively. Phylogenetic analysis suggested that the P. taivanus group assignment based on the CHD-Z and cyt b sequences is obviously very similar to P. sinensis.     

Molecular characterization and antigenic properties of a novel Babesia gibsoni glutamic acid-rich protein (BgGARP)

Identification and molecular characterization of Babesia gibsoni proteins with potential antigenic properties are crucial for the development and validation of the serodiagnostic method. In this study, we isolated a cDNA clone encoding a novel B. gibsoni 76-kDa protein by immunoscreening of the parasite cDNA library. Computer analysis revealed that the protein presents a glutamic acid-rich region in the C-terminal. Therefore, the protein was designated as B. gibsoni glutamic acid-rich protein (BgGARP). A BLASTp analysis of a translated BgGARP polypeptide demonstrated that the peptide shared a significant homology with a 200-kDa protein of Babesia bigemina and Babesia bovis. A truncated BgGARP cDNA (BgGARPt) encoding a predicted 13-kDa peptide was expressed in Escherichia coli (E. coli), and mouse antisera against the recombinant protein were used to characterize a corresponding native protein. The antiserum against recombinant BgGARPt (rBgGARPt) recognized a 140-kDa protein in the lysate of infected erythrocytes, which was detectable in the cytoplasm of the parasites by confocal microscopic observation. In addition, the specificity and sensitivity of enzyme-linked immunosorbent assay (ELISA) with rBgGARPt were evaluated using B. gibsoni-infected dog sera and specific pathogen-free (SPF) dog sera. Moreover, 107 serum samples from dogs clinically diagnosed with babesiosis were examined using ELISA with rBgGARPt. The results showed that 86 (80.4%) samples were positive by rBgGARPt-ELISA, which was comparable to IFAT and PCR as reference test. Taken together, these results demonstrate that BgGARP is a suitable serodiagnostic antigen for detecting antibodies against B. gibsoni in dogs.     

Structural and biochemical characterization of the broad substrate specificity of Bacteroides thetaiotaomicron commensal sialidase

Sialidases release the terminal sialic acid residue from a wide range of sialic acid-containing polysaccharides. Bacteroides thetaiotaomicron, a symbiotic commensal microbe, resides in and dominates the human intestinal tract. We characterized the recombinant sialidase from B. thetaiotaomicron (BTSA) and demonstrated that it has broad substrate specificity with a relative activity of 97, 100 and 64 for 2,3-, 2,6- and 2,8-linked sialic substrates, respectively. The hydrolysis activity of BTSA was inhibited by a transition state analogue, 2-deoxy-2,3-dehydro-N-acetyl neuraminic acid, by competitive inhibition with a K_i value of 35 μM. The structure of BSTA was determined at a resolution of 2.3 Å. This structure exhibited a unique carbohydrate-binding domain (CBM) at its N-terminus (a.a. 23–190) that is adjacent to the catalytic domain (a.a. 191–535). The catalytic domain has a conserved arginine triad with a wide-open entrance for the substrate that exposes the catalytic residue to the surface. Unlike other pathogenic sialidases, the polysaccharide-binding site in the CBM is near the active site and possibly holds and positions the polysaccharide substrate directly at the active site. The structural feature of a wide substrate-binding groove and closer proximity of the polysaccharide-binding site to the active site could be a unique signature of the commensal sialidase BTSA and provide a molecular basis for its pharmaceutical application.     

Molecular cloning,characterization and expression of a gene encoding phosphoketolase from Termitomyces clypeatus

A phosphoketolase (pk) gene from the fungus Termitomyces clypeatus (TC) was cloned and partially characterized. Oligonucleotide primers specific for the phosphoketolase gene (pk) were designed from the regions of homologies found in the primary structure of the enzyme from other fungal sources related to TC, using multiple sequence alignment technique. The cDNA of partial lengths were amplified, cloned and sequenced in three parts by 3′ and 5′ RACE and RT-PCR using these oligonucleotide primers. The full length ds cDNA was constructed next by joining these three partial cDNA sequences having appropriate overlapping regions using Overlap Extension PCR technique. The constructed full length cDNA exhibited an open reading frame of 2487 bases and 5′ and 3′ UTRs. The deduced amino acid sequence, which is of 828 amino acids, when analyzed with NCBI BLAST, showed high similarities with the phosphoketolase enzyme (Pk) superfamily with expected domains. The part of the TC genomic DNA comprising of the pk gene was also amplified, cloned and sequenced and was found to contain two introns of 68 and 74 bases that interrupt the pk reading frame. The coding region of pk cDNA was subcloned in pKM260 expression vector in correct frame and the protein was expressed in Escherichia coli BL21 (DE3) transformed with this recombinant expression plasmid. The recombinant protein purified by His-tag affinity chromatography indicated the presence of a protein of the expected size. In vivo expression studies of the gene in presence of different carbon sources indicated synthesis of Pk specific mRNA, as expected. Phylogenetic studies revealed a common ancestry of the fungal and bacterial Pk. The TC is known to secrete several industrially important enzymes involved in carbohydrate metabolism. However, the presence of Pk, a key enzyme in pentose metabolism, has not been demonstrated conclusively in this organism. Cloning, sequencing and expression study of this gene establishes the functioning of this gene in T. clypeatus. The Pk from TC is a new source for commercial exploitation.