Characterization of a Novel Class II bHLH Transcription Factor from the Black Widow Spider,Latrodectus hesperus, with Silk-Gland Restricted Patterns of Expression

A screen for inducers of bHLH activity identifies pitavastatin as a regulator of p21, Rb phosphorylation and E2F target gene expression in pancreatic cancer

The average survival for patients with Pancreatic Ductal Adenocarcinoma (PDA) is merely 6 months, underscoring the need for new therapeutic approaches. During PDA progression, pancreatic acinar cells lose activity of the ClassI/II bHLH factors that regulate quiescence. We previously found that promoting transcriptional activity of the Class I bHLH factor E47 in highly aggressive PDA cells induced stable growth arrest in vitro and in vivo. To translate these findings for clinical utility, we developed a high throughput screening platform to identify small molecule inducers of Class I/II bHLH activity. A screen of 4,375 known drugs identified 70 bHLH activators. Prominent among the hits were members of the statin class of HMG-CoA reductase inhibitors, cholesterol lowering drugs that are also being evaluated in cancer. Studies with pitavastatin in primary patient derived tumor cells and established PDA lines, revealed dose dependent growth inhibition. At the molecular level, pitavastatin induced expression of the cyclin dependent kinase (CDK) inhibitor p21 in a cholesterol independent manner, blocked repressive phosphorylation of the Retinoblastoma tumor suppressor protein at CDK targeted sites, and reduced expression of E2F target genes required for progression through the G1/S boundary. Together, the data provide new insight into mechanisms by which statins constrain proliferation in cancer and establish the effectiveness of a novel screening platform to identify small molecules of clinical relevance in pancreatic cancer.

Multi-tissue transcriptomics of the black widow spider reveals expansions, co-options, and functional processes of the silk gland gene toolkit

Background

Spiders (Order Araneae) are essential predators in every terrestrial ecosystem largely because they have evolved potent arsenals of silk and venom. Spider silks are high performance materials made almost entirely of proteins, and thus represent an ideal system for investigating genome level evolution of novel protein functions. However, genomic level resources remain limited for spiders.

Results

We de novo assembled a transcriptome for the Western black widow (Latrodectus hesperus) from deeply sequenced cDNAs of three tissue types. Our multi-tissue assembly contained ~100,000 unique transcripts, of which > 27,000 were annotated by homology. Comparing transcript abundance among the different tissues, we identified 647 silk gland-specific transcripts, including the few known silk fiber components (e.g. six spider fibroins, spidroins). Silk gland specific transcripts are enriched compared to the entire transcriptome in several functions, including protein degradation, inhibition of protein degradation, and oxidation-reduction. Phylogenetic analyses of 37 gene families containing silk gland specific transcripts demonstrated novel gene expansions within silk glands, and multiple co-options of silk specific expression from paralogs expressed in other tissues.

Conclusions

We propose a transcriptional program for the silk glands that involves regulating gland specific synthesis of silk fiber and glue components followed by protecting and processing these components into functional fibers and glues. Our black widow silk gland gene repertoire provides extensive expansion of resources for biomimetic applications of silk in industry and medicine. Furthermore, our multi-tissue transcriptome facilitates evolutionary analysis of arachnid genomes and adaptive protein systems.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-365) contains supplementary material, which is available to authorized users.

Complex gene expression in the dragline silk producing glands of the Western black widow (Latrodectus hesperus)

Background

Orb-web and cob-web weaving spiders spin dragline silk fibers that are among the strongest materials known. Draglines are primarily composed of MaSp1 and MaSp2, two spidroins (spider fibrous proteins) expressed in the major ampullate (MA) silk glands. Prior genetic studies of dragline silk have focused mostly on determining the sequence of these spidroins, leaving other genetic aspects of silk synthesis largely uncharacterized.

Results

Here, we used deep sequencing to profile gene expression patterns in the Western black widow, Latrodectus hesperus. We sequenced millions of 3′-anchored “tags” of cDNAs derived either from MA glands or control tissue (cephalothorax) mRNAs, then associated the tags with genes by compiling a reference database from our newly constructed normalized L. hesperus cDNA library and published L. hesperus sequences. We were able to determine transcript abundance and alternative polyadenylation of each of three loci encoding MaSp1. The ratio of MaSp1:MaSp2 transcripts varied between individuals, but on average was similar to the estimated ratio of MaSp1:MaSp2 in dragline fibers. We also identified transcription of TuSp1 in MA glands, another spidroin family member that encodes the primary component of egg-sac silk, synthesized in tubuliform glands. In addition to the spidroin paralogs, we identified 30 genes that are more abundantly represented in MA glands than cephalothoraxes and represent new candidates for involvement in spider silk synthesis.

Conclusions

Modulating expression rates of MaSp1 variants as well as MaSp2 and TuSp1 could lead to differences in mechanical properties of dragline fibers. Many of the newly identified candidate genes likely encode secreted proteins, suggesting they could be incorporated into dragline fibers or assist in protein processing and fiber assembly. Our results demonstrate previously unrecognized transcript complexity in spider silk glands.

Recombinant production of spider silk proteins

Natural spider silk fibers combine extraordinary properties such as stability and flexibility which results in a toughness superseding that of all other fiber materials. As the spider's aggressive territorial behavior renders their farming not feasible, the biotechnological production of spider silk proteins (spidroins) is essential in order to investigate and employ them for applications. In order to accomplish this task, two approaches have been tested: firstly, the expression of partial cDNAs, and secondly, the expression of synthetic genes in several host organisms, including bacteria, yeast, plants, insect cells, mammalian cells, and transgenic animals. The experienced problems include genetic instability, limitations of the translational and transcriptional machinery, and low solubility of the produced proteins. Here, an overview of attempts to recombinantly produce spidroins will be given, and advantages and disadvantages of the different approaches and host organisms will be discussed.

Bombyx mori transcription factors: genome-wide identification, expression profiles and response to pathogens by microarray analysis

Transcription factors are present in all living organisms, and play vital roles in a wide range of biological processes. Studies of transcription factors will help reveal the complex regulation mechanism of organisms. So far, hundreds of domains have been identified that show transcription factor activity. Here, 281 reported transcription factor domains were used as seeds to search the transcription factors in genomes of Bombyx mori L. (Lepidoptera: Bombycidae) and four other model insects. Overall, 666 transcription factors including 36 basal factors and 630 other factors were identified in B. mori genome, which accounted for 4.56% of its genome. The silkworm transcription factors' expression profiles were investigated in relation to multiple tissues, developmental stages, sexual dimorphism, and responses to oral infection by pathogens and direct bacterial injection. These all provided rich clues for revealing the transcriptional regulation mechanism of silkworm organ differentiation, growth and development, sexual dimorphism, and response to pathogen infection.

Molecular cloning and characterization of homologs of achaete-scute and hairy-enhancer of split in the olfactory organ of the spiny lobster Panulirus argus

The olfactory organ of the Caribbean spiny lobster Panulirus argus maintains lifelong proliferation and turnover of olfactory receptor neurons (ORNs). Towards examining the molecular basis of this adult neurogenesis, we search for expression of homologs of proneural, neurogenic, and pre-pattern genes in this olfactory organ. We report here a homolog of the proneural Achaete-Scute family, called splash (spiny lobster achaete-scute homolog), and a homolog of the pre-pattern and neurogenic hairy-enhancer of split family, called splhairy (spiny lobster hairy). Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) indicates a molt stage dependence of the levels of expression of splash and splhairy mRNA in the olfactory organ, with higher expression in premolt than in postmolt or intermolt animals, which is positively correlated with rates of neurogenesis. splash and splhairy mRNA are expressed not only in the olfactory organ but also in other tissues, albeit at lower levels, irrespective of molt stage. We conclude that the expression of achaete-scute and hairy-enhancer of split in the proliferation zone of the olfactory organ of spiny lobsters and their enhanced expression in premolt animals suggest that they play a role in the proliferation of ORNs and that their expression in regions of the olfactory organ populated by mature ORNs and in other tissues suggests that they have additional functions.

Blueprint for a high-performance biomaterial: full-length spider dragline silk genes

Spider dragline (major ampullate) silk outperforms virtually all other natural and manmade materials in terms of tensile strength and toughness. For this reason, the mass-production of artificial spider silks through transgenic technologies has been a major goal of biomimetics research. Although all known arthropod silk proteins are extremely large (>200 kiloDaltons), recombinant spider silks have been designed from short and incomplete cDNAs, the only available sequences. Here we describe the first full-length spider silk gene sequences and their flanking regions. These genes encode the MaSp1 and MaSp2 proteins that compose the black widow's high-performance dragline silk. Each gene includes a single enormous exon (>9000 base pairs) that translates into a highly repetitive polypeptide. Patterns of variation among sequence repeats at the amino acid and nucleotide levels indicate that the interaction of selection, intergenic recombination, and intragenic recombination governs the evolution of these highly unusual, modular proteins. Phylogenetic footprinting revealed putative regulatory elements in non-coding flanking sequences. Conservation of both upstream and downstream flanking sequences was especially striking between the two paralogous black widow major ampullate silk genes. Because these genes are co-expressed within the same silk gland, there may have been selection for similarity in regulatory regions. Our new data provide complete templates for synthesis of recombinant silk proteins that significantly improve the degree to which artificial silks mimic natural spider dragline fibers.