Penaeus monodon Tudor staphylococcal nuclease preferentially interacts with N-terminal domain of Argonaute-1

RNA interference (RNAi) plays a crucial role as an antiviral defense in several organisms including plants and invertebrates. An understanding of RNAi machineries especially protein components of the RNA-induced silencing complex (RISC) is essential for prior to applying RNAi as a tool for viral protective immunity in shrimp. Tudor staphylococcal nuclease (TSN) is an evolutionarily conserved protein and is one of the RISC components. In previous study, suppression of Penaeus monodon TSN (PmTSN) by double-stranded RNA (dsRNA) resulted in decreasing dsRNA-mediated gene silencing activity. To elucidate the functional significance of PmTSN in shrimp RNAi pathway, interactions between PmTSN and three Argonaute proteins (PmAgo) were characterized by yeast two-hybrid and in vitro pull-down assays. The results demonstrated that PmTSN interacted with PmAgo1, but not with PmAgo2 or PmAgo3. The interaction between PmAgo and PmTSN was mediated through the N-terminal domain of PmAgo1 and the SN1-2 domains of PmTSN. Analysis of the nuclease activity of the recombinant PmTSN indicated that PmTSN possessed calcium-dependent nuclease activity specific to single-stranded RNA (ssRNA), but not dsRNA and DNA. Knockdown of PmAgo1 and PmTSN diminished the ability of dsRNA-Rab7 to knockdown PmRab7 expression, indicating the involvement of PmAgo1 and PmTSN in shrimp RNAi pathway. Taken together, the results imply that PmTSN is one of the components of PmAgo1-RISC, thus providing new insights in the RNAi-based mechanism in shrimp.     

Structural design and characterization of a channel-forming peptide

A 16-residue polypeptide model with the sequence acetyl-YALSLAATLLKEAASL-OH was derived by rational de novo peptide design. The designed sequence consists of amino acid residues with high propensity to adopt an alpha helical conformation, and sequential order was arranged to produce an amphipathic surface. The designed sequence was chemically synthesized using a solid-phase method and the polypeptide was purified by reverse-phase liquid chromatography. Molecular mass analysis by electro-spray ionization mass spectroscopy confirmed the correct designed sequence. Structural characterization by circular dichroism spectroscopy demonstrated that the peptide adopts the expected alpha helical conformation in 50% acetonitrile solution. Liposome binding assay using Small Unilamellar Vesicle (SUV) showed a marked release of entrapped glucose by interaction between the lipid membrane and the tested peptide. The channel-forming activity of the peptide was revealed by a planar lipid bilayer experiment. An analysis of the conducting current at various applied potentials suggested that the peptide forms a cationic ion channel with an intrinsic conductance of 188 pS. These results demonstrate that a simple rational de novo design can be successfully employed to create short peptides with desired structures and functions.     

A plasmid encoding a combination of mosquito-larvicidal genes from Bacillus thuringiensis subsp. israelensis and Bacillus sphaericus confers toxicity against a broad range of mosquito larvae when expressed in Gram-negative bacteria

A recombinant plasmid harboring cry4A, cry4B and cry11A from Bacillus thuringiensis subsp. israelensis and binary toxin genes from Bacillus sphaericus has been constructed. The three cry genes were placed under the control of the cry4B promoter whereas the binary toxin gene was controlled by its native promoter. The expression of toxins in Escherichia coli harboring the resulting plasmid, p4BDA-5142, was investigated. Cry4B expression was highest compared to other toxins. Although the level of toxin expression was low compared with E. coli expressing single toxins, the recombinant E. coli strain harboring p4BDA-5142 exhibited broad range mosquito-larvicidal activity against all Aedes, Culex and Anopheles larvae. This work has shown that the development of the recombinant plasmid can be used to broaden the host range spectrum of the appropriate bacterial host for mosquito control.     

Secretion of Pem-CMG,a peptide in the CHH/MIH/GIH family of Penaeus monodon,in Pichia pastoris is directed by secretion signal of the alpha-mating factor from Saccharomyces cerevisiae

The CHH/MIH/GIH peptide family of black tiger prawn (Paneaus monodon) is important in shrimp reproduction and growth enhancement. In this study, the cDNA that encodes the complete peptide that is related to the CHH/MIH/GIH family (so-called, Pem-CMG) in the eyestalk of P. monodon was successfully expressed in a methylotrophic yeast Pichia pastoris under the control of an alcohol oxidase promoter. In order to obtain the secreted Pem-CMG, a secretion signal of either the Saccharomyces cerevisiae alpha-factor or Pem-CMG was employed. The results demonstrated that alphaPem-CMG, either with (alpha2EACMG) or without (alphaCMG) the Glu-Ala repeats, was secreted into the medium, while Pem-CMG with its own secretion signal failed to be secreted. The total protein amount that was secreted from the transformant that contained either alpha2EACMG or alphaMG was approximately 60 mg/l and 150 mg/l, respectively. The N-terminus of the Pem-CMG peptide of both alpha2EACMG and alphaCMG was correctly processed. This produced the mature Pem-CMG peptide.     

High variation in repetitive DNA fragment length for white spot syndrome virus (WSSV) isolates in Thailand

White spot syndrome virus (WSSV) presently causes the most serious losses to shrimp farmers worldwide. Earlier reports of high DNA sequence homology among isolates from widely separated geographical regions suggested that a single virus was the cause. However, we have found surprisingly high variation in the number of 54 bp DNA repeats in ORF94 (GenBank AF369029) from 55 shrimp ponds (65 shrimp samples) experiencing WSSV outbreaks in Thailand in 2000 and 2002. These were detected by PCR amplification using primers ORF94-F and ORF94-R flanking the repeat region. Altogether, 12 different repeat groups were found (from 6 to 20 repeats) with 8 repeats being most frequent (about 32%). Extracts prepared from individual shrimp in the same outbreak pond belonged to the same repeat group while those collected at the same time from separate WSSV outbreak ponds, or from the same ponds at different times, usually belonged to different repeat groups. This suggested that different outbreaks were caused by different WSSV isolates. In contrast to the highly variable numbers of repeats, sequence variation within the repeat region was confined to either T or G at Position 36. These variations may be useful for epidemiological studies on the local and global movement of WSSV, since there is high variation in the number of repeats (good for local studies) but little sequence change (good for global studies).     

Propagation of infectious yellow head virus particles prior to cytopathic effect in primary lymphoid cell cultures of Penaeus monodon

Yellow head virus is a highly pathogenic agent that can cause a fatal disease in several species of penaeid shrimps. Using a primary cell culture and an in vitro quantal assay (TCID50), this study sought to determine the propagation profile of yellow head virus after inoculation at a low multiplicity of infection in the lymphoid tissue (oka organ) of Penaeus monodon. Detectable levels of virus were present as early as 24 h post-inoculation. Maximal viral yields were reached by 4 d post-infection, approximately 24 h after the onset of a detectable cytopathic effect, which was normally observable at 3 d post-inoculation. The methodology provides a useful tool for studying yellow head virus-host-cell interactions.     

Induction of Ovarian Maturation and Spawning in <Emphasis Type="Italic">Penaeus monodon</Emphasis> Broodstock by Double-Stranded RNA

Ovarian maturation in crustacean is under the control of gonad-inhibiting hormone (GIH); a neuropeptide secreted from X-organ sinus gland complex in eyestalks. Unilateral eyestalk ablation that partially destroys GIH source is therefore a general practice in Penaeus monodon hatchery to induce ovarian maturation and spawning. Our previous report showed that silencing of GIH expression by GIH-specific double-stranded RNA (GIH-dsRNA) resulted in an increased expression level of vitellogenin in P. monodon, thus suggesting that GIH-dsRNA could be an alternative method to induce ovarian maturation in female P. monodon broodstock. In this study, we further demonstrated that a single injection of GIH-dsRNA into previtellogenic female P. monodon at the concentration of 3 μg GIH-dsRNA per gram body weight of shrimp was able to inhibit GIH expression for a minimum of 30 days. This dsRNA-mediated GIH silencing led to ovarian maturation and eventual spawning in both domesticated and wild female broodstock, particularly with a comparable effect to eyestalk ablation in wild shrimp. This is the first report that demonstrates a potential strategy to induce ovarian maturation in female P. monodon broodstock by GIH-dsRNA and thus provides a possible substitute for the cruel and detrimental eyestalk ablation practice.