Molecular phylogeny of silk-producing insects based on 16S ribosomal RNA and cytochrome oxidase subunit I genes

A comprehensive review of recent advances in silk sericin: Extraction approaches, structure, biochemical characterization, and biomedical applications

Silks are natural polymers that have been widely used for centuries. Silk consists of a filament core protein, termed fibroin, and a glue-like coating substance formed of sericin (SER) proteins. This protein is extracted from the silkworm cocoons (particularly Bombyx mori) and is mainly composed of amino acids like glycine, serine, aspartic acid, and threonine. Silk SER can be obtained using numerous methods, including enzymatic extraction, high-temperature, autoclaving, ethanol precipitation, cross-linking, and utilizing acidic, alkali, or neutral aqueous solutions. Given the versatility and outstanding properties of SER, it is widely fabricated to produce sponges, films, and hydrogels for further use in diverse biomedical applications. Hence, many authors reported that SER benefits cell proliferation, tissue engineering, and skin tissue restoration thanks to its moisturizing features, antioxidant and anti-inflammatory properties, and mitogenic effect on mammalian cells. Remarkably, SER is used in drug delivery depending on its chemical reactivity and pH-responsiveness. These unique features of SER enhance the bioactivity of drugs, facilitating the fabrication of biomedical materials at nano- and microscales, hydrogels, and conjugated molecules. This review thoroughly outlines the extraction techniques, biological properties, and respective biomedical applications of SER.

Silk fibroin scaffolds with muscle-like elasticity support in vitro differentiation of human skeletal muscle cells

Human adult skeletal muscle has a limited ability to regenerate after injury and therapeutic options for volumetric muscle loss are few. Technologies to enhance regeneration of tissues generally rely upon bioscaffolds to mimic aspects of the tissue extracellular matrix (ECM). In the present study, silk fibroins from four Lepidoptera (silkworm) species engineered into three-dimensional scaffolds were examined for their ability to support the differentiation of primary human skeletal muscle myoblasts. Human skeletal muscle myoblasts (HSMMs) adhered, spread and deposited extensive ECM on all the scaffolds, but immunofluorescence and quantitative polymerase chain reaction analysis of gene expression revealed that myotube formation occurred differently on the various scaffolds. Bombyx mori fibroin scaffolds supported formation of long, well-aligned myotubes, whereas on Antheraea mylitta fibroin scaffolds the myotubes were thicker and shorter. Myotubes were oriented in two perpendicular layers on Antheraea assamensis scaffolds, and scaffolds of Philosamia/Samia ricini (S. ricini) fibroin poorly supported myotube formation. These differences were not caused by fibroin composition per se, as HSMMs adhered to, proliferated on and formed striated myotubes on all four fibroins presented as two-dimensional fibroin films. The Young's modulus of A. mylitta and B. mori scaffolds mimicked that of normal skeletal muscle, but A. assamensis and S. ricini scaffolds were more flexible. The present study demonstrates that although myoblasts deposit matrix onto fibroin scaffolds and create a permissive environment for cell proliferation, a scaffold elasticity resembling that of normal muscle is required for optimal myotube length, alignment, and maturation. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd. StartCopTextStartCopText© 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

The complete mitochondrial genome of Rondotia menciana (Lepidoptera: Bombycidae)

The mulberry white caterpillar, Rondotia menciana Moore (Lepidoptera: Bombycidae) is a species with closest relationship with Bombyx mori and Bombyx mandarina, and the genetic information of R. menciana is important for understanding the diversity of the Bombycidae. In this study, the mitochondrial genome (mitogenome) of R. menciana was amplified by polymerase chain reaction and sequenced. The mitogenome of R. menciana was determined to be 15,301 bp, including 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, 22 transfer RNA genes, and an AT-rich region. The A+T content (78.87%) was lower than that observed for other Bombycidae insects. All PCGs were initiated by ATN codons and terminated with the canonical stop codons, except for coxII, which was terminated by a single T. All the tRNA genes displayed a typical clover-leaf structure of mitochondrial tRNA. The length of AT-rich region (360 bp) of R. menciana mitogenome is shorter than that of other Bombycidae species. Phylogenetic analysis showed that the R. menciana was clustered on one branch with B. mori and B. mandarina from Bombycidae.

Characterization of the complete mitochondrial genome of the giant silkworm moth, Eriogyna pyretorum (Lepidoptera: Saturniidae)

The complete mitochondrial genome (mitogenome) of Eriogyna pyretorum (Lepidoptera: Saturniidae) was determined as being composed of 15,327 base pairs (bp), including 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and a control region. The arrangement of the PCGs is the same as that found in the other sequenced lepidopteran. The AT skewness for the E. pyretorum mitogenome is slightly negative (-0.031), indicating the occurrence of more Ts than As. The nucleotide composition of the E. pyretorum mitogenome is also biased toward A + T nucleotides (80.82%). All PCGs are initiated by ATN codons, except for cytochrome c oxidase subunit 1 and 2 (cox1 and cox2). Two of the 13 PCGs harbor the incomplete termination codon by T. All tRNA genes have a typical clover-leaf structure of mitochondrial tRNA, with the exception of trnS1(AGN) and trnS2(UCN). Phylogenetic analysis among the available lepidopteran species supports the current morphology-based hypothesis that Bombycoidea, Geometroidea, Notodontidea, Papilionoidea and Pyraloidea are monophyletic. As has been previously suggested, Bombycidae (Bombyx mori and Bombyx mandarina), Sphingoidae (Manduca sexta) and Saturniidae (Antheraea pernyi, Antheraea yamamai, E. pyretorum and Caligula boisduvalii) formed a group.

Silk fibroin protein from mulberry and non-mulberry silkworms: cytotoxicity, biocompatibility and kinetics of L929 murine fibroblast adhesion

Silks fibers and films fabricated from fibroin protein of domesticated mulberry silkworm cocoon have been traditionally utilized as sutures in surgery and recently as biomaterial films respectively. Here, we explore the possibility of application of silk fibroin protein from non-mulberry silkworm cocoon as a potential biomaterial aid. In terms of direct inflammatory potential, fibroin proteins from Antheraea mylitta and Bombyx mori are immunologically inert and invoke minimal immune response. Stimulation of murine peritoneal macrophages and RAW 264.7 murine macrophages by these fibroin proteins both in solution and in the form of films assayed in terms of nitric oxide and TNFalpha production showed comparable stimulation as in collagen. Kinetics of adhesion of L929 murine fibroblasts, for biocompatibility evaluation, monitored every 4 h from seeding and studied over a period of 24 h, reveal A. mylitta fibroin film to be a better substrate in terms of rapid and easier cellularization. Cell viability studies by MTT assay and flow cytometric analyses indicate the ability of fibroin matrices to support cell growth and proliferation comparable to collagen for long-term culture. This matrix may have potential to serve in those injuries where rapid cellularization is essential.

WildSilkbase: an EST database of wild silkmoths

Background

Functional genomics has particular promise in silkworm biology for identifying genes involved in a variety of biological functions that include: synthesis and secretion of silk, sex determination pathways, insect-pathogen interactions, chorionogenesis, molecular clocks. Wild silkmoths have hardly been the subject of detailed scientific investigations, owing largely to non-availability of molecular and genetic data on these species. As a first step, in the present study we generated large scale expressed sequence tags (EST) in three economically important species of wild silkmoths. In order to make these resources available for the use of global scientific community, an EST database called 'WildSilkbase' was developed.

Description

WildSilkbase is a catalogue of ESTs generated from several tissues at different developmental stages of 3 economically important saturniid silkmoths, an Indian golden silkmoth, Antheraea assama, an Indian tropical tasar silkmoth, A. mylitta and eri silkmoth, Samia cynthia ricini. Currently the database is provided with 57,113 ESTs which are clustered and assembled into 4,019 contigs and 10,019 singletons. Data can be browsed and downloaded using a standard web browser. Users can search the database either by BLAST query, keywords or Gene Ontology query. There are options to carry out searches for species, tissue and developmental stage specific ESTs in BLAST page. Other features of the WildSilkbase include cSNP discovery, GO viewer, homologue finder, SSR finder and links to all other related databases. The WildSilkbase is freely available from .

Conclusion

A total of 14,038 putative unigenes was identified in 3 species of wild silkmoths. These genes provide important resources to gain insight into the functional and evolutionary study of wild silkmoths. We believe that WildSilkbase will be extremely useful for all those researchers working in the areas of comparative genomics, functional genomics and molecular evolution in general, and gene discovery, gene organization, transposable elements and genome variability of insect species in particular.

Silkworm nucleotide databases--current trends and future prospects

The domesticated silkworm, Bombyx mori serves as an ideal representative of lepidopteran species for a variety of scientific studies. As a result, databases have been created to organize information pertaining to the silkworm genome that is subject to constant updating. Of these, four main databases are important for store nucleotide information in the form of genomic data, ESTs and microsatelites. These databases also store data related to other lepidoptera and important insects, which help in insect biological research. Though a considerable amount of nucleotide data is currently available, there is a paucity of data related to silkworm and other lepidopteran proteins. Hence, the focus of this article is to present the current status of nucleotide databases of silkworm, avenues for improvement and possibilities for databases that could be created in the future.