Comparison of Bombyx mori and Helicoverpa armigera cytoplasmic actin genes provides clues to the evolution of actin genes in insects

The intronic promoter of Actin4 mediates high-level transgene expression mainly in the wing and epidermis of silkworms

The cytoplasmic actin gene Actin4 (A4) in silkworm (Bombyx mori) was isolated 20 years ago and has a distal promoter upstream of the first exon and a proximal promoter within the first intron; however, how the promoter regulates gene expression has yet to be fully elucidated. Here, we characterized the function and expression of the proximal promoter (named A4IP) by analyzing transgenic Gal4/UAS silkworms, A4IP-Gal4/UAS-EGFP. We demonstrated that A4IP drives the expression of Gal4 and thereby activates UAS-linked EGFP in transgenic silkworms beginning in day-3 embryos through adults. Further detection revealed that EGFP was expressed at a low level in tissues including the trachea, fat body and midgut but was highly expressed in the wing disks/wings and inner epidermis of transgenic silkworms. No EGFP signals were detected in other tissues by western blot assay. Interestingly, EGFP fluorescence had a spot-like distribution on the epidermis of transgenic larvae. These observations are quite different from those in transgenic silkworms driven by the promoter of Actin3 (A3), another cytoplasmic actin gene in B. mori. These findings reveal the expression profiles of the A4IP promoter and provide new insights into the regulatory mechanism of cytoplasmic actin genes in silkworms.

Structural and functional characterization of the actin-1 gene promoter from the Antheraea pernyi (Lepidoptera: Saturniidae)

The Chinese oak silkworm, Antheraea pernyi, is an economically important insect of the Saturniidae family. In this study, genome walking was performed to obtain an A. pernyi actin promoter, which can be employed in transgenic or stable cell line expression systems. The putative promoter was analyzed by the online promoter analysis programs at the Berkeley Drosophila Genome Project and the Web Promoter Scan Service, which led to the recognition of several functional elements. With respect to these elements, a series of actin A1 promoter fragments with 5'-deletions were generated that were then used to construct different vectors expressing Green Fluorescent Protein (GFP). The plasmids were transfected into Sf9 cells and GFP expression was determined by observing GFP fluorescence in cells and by measuring GFP mRNA levels with real-time polymerase chain reaction. Sequence comparisons indicated that the sequence cloned from A. pernyi was the actin A1 promoter. The basic function of the promoter was verified by constructing expression vectors and observing GFP expression. In addition, real-time polymerase chain reaction revealed a strong inhibitory element may exist upstream of the TATA box, which downregulated gene expression. The actin A1 promoter is an ideal candidate for use in A. pernyi transgenic systems.

Genomic sequencing and analyses of HearMNPV--a new Multinucleocapsid nucleopolyhedrovirus isolated from Helicoverpa armigera

Background

HearMNPV, a nucleopolyhedrovirus (NPV), which infects the cotton bollworm, Helicoverpa armigera, comprises multiple rod-shaped nucleocapsids in virion(as detected by electron microscopy). HearMNPV shows a different host range compared with H. armigera single-nucleocapsid NPV (HearSNPV). To better understand HearMNPV, the HearMNPV genome was sequenced and analyzed.

Methods

The morphology of HearMNPV was observed by electron microscope. The qPCR was used to determine the replication kinetics of HearMNPV infectious for H. armigera in vivo. A random genomic library of HearMNPV was constructed according to the “partial filling-in” method, the sequence and organization of the HearMNPV genome was analyzed and compared with sequence data from other baculoviruses.

Results

Real time qPCR showed that HearMNPV DNA replication included a decreasing phase, latent phase, exponential phase, and a stationary phase during infection of H. armigera. The HearMNPV genome consists of 154,196 base pairs, with a G + C content of 40.07%. 162 putative ORFs were detected in the HearMNPV genome, which represented 90.16% of the genome. The remaining 9.84% constitute four homologous regions and other non-coding regions. The gene content and gene arrangement in HearMNPV were most similar to those of Mamestra configurata NPV-B (MacoNPV-B), but was different to HearSNPV. Comparison of the genome of HearMNPV and MacoNPV-B suggested that HearMNPV has a deletion of a 5.4-kb fragment containing five ORFs. In addition, HearMNPV orf66, bro genes, and hrs are different to the corresponding parts of the MacoNPV-B genome.

Conclusions

HearMNPV can replicate in vivo in H. armigera and in vitro, and is a new NPV isolate distinguished from HearSNPV. HearMNPV is most closely related to MacoNPV-B, but has a distinct genomic structure, content, and organization.

Sequence analysis and quantification of transposase cDNAs of transposon TCp3.2 in Cydia pomonella larvae

The Tc1-like transposable element TCp3.2 was previously found to be horizontally transferred from the genome of Cydia pomonella to the C. pomonella granulovirus (CpGV). In this study, the transcription of transposase genes of endogenous TCp3.2 copies in the insect host genome was investigated. Cloning and sequencing of cDNAs prepared from TCp3.2 transposase transcripts resulted in the identification of a 199-bp-long intron. Sequence heterogeneities among different cDNA clones suggested that multiple copies of the transposase are transcribed, but that a part of these copies encode a defective transposase. The actin gene of C. pomonella was cloned and sequenced, and used to standardise quantitative real time PCR on prepared cDNA of the TCp3.2 transposase. Comparison of cDNA levels of TCp3.2 transposase prepared from mock and CpGV-infected C. pomonella larvae did not provide evidence that CpGV infection influenced the transcription level of TCp3.2 transposase.

Hypervariable and Highly Divergent Intron?Exon Organizations in the Chordate Oikopleura dioica

Oikopleura dioica is a pelagic tunicate with a very small genome and a very short life cycle. In order to investigate the intron-exon organizations in Oikopleura, we have isolated and characterized ribosomal protein EF-1alpha, Hox, and alpha-tubulin genes. Their intron positions have been compared with those of the same genes from various invertebrates and vertebrates, including four species with entirely sequenced genomes. Oikopleura genes, like Caenorhabditis genes, have introns at a large number of nonconserved positions, which must originate from late insertions or intron sliding of ancient insertions. Both species exhibit hypervariable intron-exon organization within their alpha-tubulin gene family. This is due to localization of most nonconserved intron positions in single members of this gene family. The hypervariability and divergence of intron positions in Oikopleura and Caenorhabditis may be related to the predominance of short introns, the processing of which is not very dependent upon the exonic environment compared to large introns. Also, both species have an undermethylated genome, and the control of methylation-induced point mutations imposes a control on exon size, at least in vertebrate genes. That introns placed at such variable positions in Oikopleura or C. elegans may serve a specific purpose is not easy to infer from our current knowledge and hypotheses on intron functions. We propose that new introns are retained in species with very short life cycles, because illegitimate exchanges including gene conversion are repressed. We also speculate that introns placed at gene-specific positions may contribute to suppressing these exchanges and thereby favor their own persistence.

Gene structure and hemocyanin isoform HtH2 from the mollusc Haliotis tuberculata indicate early and late intron hot spots

We have cloned and sequenced cDNAs coding for the complete primary structure of HtH2, the second hemocyanin isoform of the marine gastropod Haliotis tuberculata. The deduced protein sequence comprises 3399 amino acids, corresponding to a molecular mass of 392 kDa. It shares only 66% of structural identity with the previously analysed first isoform HtH1, and according to a molecular clock, the two isoforms of Haliotis hemocyanin separated ca. 320 million years ago. By genomic polymerase chain reaction and 5' race, we have also sequenced the complete gene of HtH2 (18,598 bp), except of the 5' region in front of the secreted protein. It encompasses 15 exons and 14 introns and shows several microsatellite-rich regions. It mirrors the modular structure of the encoded hemocyanin subunit, with a linear arrangement of eight different functional units separated and bordered by seven phase 1 'linker introns'. In addition, within regions encoding three of the functional units, the HtH2 gene contains six 'internal introns'. Comparison to previously sequenced genes of Octopus dofleini hemocyanin and Haliotis hemocyanin isoform (HtH1) suggests Precambrian and Palaeocoic hot spot of intron gains, followed by 320 million years of absolute stasis.

Extrachromosomal transposition of the transposable element Minos in embryos of the cricket Gryllus bimaculatus

Effective germline transformation of insects has been shown to depend on the right choice of transposon system and selection marker. In this study the promoter region of a Gryllus cytoplasmic actin (GbA3/4) gene was isolated and characterized, and was used to drive the expression of Minos transposase in embryos of the cricket Gryllus bimaculatus. Active Minos transposase was produced in these embryos as monitored through established transposon excision and interplasmid transposition assays. In contrast, Drosophila melanogaster hsp70 promoter, previously used to express Minos transposase in a number of insect species and insect cell lines, failed to produce any detectable Minos transposase activity, as recorded by using the very sensitive transposon excision assay. In addition, the GbA3/4 promoter was found to drive expression of enhanced green fluorescent protein (eGFP) predominantly in vitellophages of the developing Gryllus eggs when a plasmid carrying a GbA3/4 promoter-eGFP fusion gene was transiently injected into embryos. These results strongly support the use of Minos transposons marked with the GbA3/4 promoter-eGFP for the genetic transformation of this emerging model insect species.

Use of beta-actin gene intron 2 as a phylogenetic marker in fish taxonomy

Intron 2 of the beta-actin genes from several fish species was sequenced and aligned with a Clustal W program for maximum similarity. From the maximum similarity and phylip data, it was noted that the intron 2 sequences would be useful for establishing a molecular phylogenetic tree and in elucidating the gene flow through evolution, especially at the family level.

The current state of insect molecular systematics: a thriving Tower of Babel

Insect molecular systematics has undergone remarkable recent growth. Advances in methods of data generation and analysis have led to the accumulation of large amounts of DNA sequence data from most major insect groups. In addition to reviewing theoretical and methodological advances, we have compiled information on the taxa and regions sequenced from all available phylogenetic studies of insects. It is evident that investigators have not usually coordinated their efforts. The genes and regions that have been sequenced differ substantially among studies and the whole of our efforts is thus little greater than the sum of its parts. The cytochrome oxidase I, 16S, 18S, and elongation factor-1 alpha genes have been widely used and are informative across a broad range of divergences in insects. We advocate their use as standards for insect phylogenetics. Insect molecular systematics has complemented and enhanced the value of morphological and ecological data, making substantial contributions to evolutionary biology in the process. A more coordinated approach focused on gathering homologous sequence data will greatly facilitate such efforts.