Molecular and Physiological Characterization of Two Novel Multirepeat β-Thymosins from Silkworm, Bombyx mori

β-Thymosin is an essential regulator of stem cell proliferation and neuron regeneration in planarian (Dugesia japonica)

β-Thymosin is a multifunctional peptide ubiquitously expressed in vertebrates and invertebrates. Many studies have found β-thymosin is critical for wound healing, angiogenesis, cardiac repair, hair regrowth, and anti-fibrosis in vertebrates, and plays an important role in antimicrobial immunity in invertebrates. However, whether β-thymosin participates in the regeneration of organisms is still poorly understood. In this study, we identified a β-thymosin gene in Dugesia japonica which played an important role in stem cell proliferation and neuron regeneration during the tissue repair process in D. japonica. Sequencing analysis showed that β-thymosin contained two conserved β-thymosin domains and two actin-binding motifs, and had a high similarity with other β-thymosins of invertebrates. In situ or fluorescence in situ hybridization analysis revealed that Djβ-thymosin was co-localized with DjPiWi in the neoblast cells of intact adult planarians and the blastema of regenerating planarians, suggesting Djβ-thymosin has a potential function of regeneration. Disruption Djβ-thymosin by RNA interference results in a slightly curled up head of planarian and stem cell proliferation defects. Additionally, we found that, upon amputation, Djβ-thymosin RNAi-treated animals had impaired regeneration ability, including impaired blastema formation, delayed eyespot formation, decreased brain area, and disrupted central CNS formation, implying Djβ-thymosin is an essential regulator of stem cell proliferation and neuron regeneration.

Cloning, Expression and Effects of P. americana Thymosin on Wound Healing

The American cockroach (Periplaneta americana) is a medicinal insect. Its extract is used clinically to promote wound healing and tissue regeneration, but the effective medicinal components and mechanisms are not yet clear. It has been reported that human thymosin beta 4 (Tβ4) may accelerate skin wound healing, however, the role of P. americana thymosin (Pa-THYs) is still poorly understood. In the present study, we identify and analyze the DNA sequences of Pa-THYs by bioinformatics analysis. Then we clone, express, and purify the Pa-THYs proteins and evaluate the activity of recombinant Pa-THYs proteins by cell migration and proliferation assays in NIH/3T3 cells. To elucidate the role of Pa-THYs in wound healing, a mouse model is established, and we evaluate wound contraction, histopathological parameters, and the expressions of several key growth factors after Pa-THYs treatment. Our results showed that three THY variants were formed by skipping splicing of exons. Pa-THYs could promote fibroblast migration, but have no effect on fibroblast proliferation. In wound repair, Pa-THYs proteins could effectively promote wound healing through stimulating dermal tissue regeneration, angiogenesis, and collagen deposition. On the molecular mechanism, Pa-THYs also stimulated the expression of several key growth factors to promote wound healing. The data suggest that Pa-THYs could be a potential drug for promoting wound repair.

Vacuolar protein sorting 4 is required for silkworm metamorphosis

Vacuolar protein sorting 4 (Vps4) not only functions with its positive regulator vacuolar protein sorting 20-associated 1 (Vta1) in the multivesicular body (MVB) pathway but also participates alone in MVB-unrelated cellular processes. However, its physiological roles at the organism level remain rarely explored. We previously identified their respective homologues Bombyx mori Vps4 (BmVps4) and BmVta1 from the silkworm, a model organism for insect research. In this study, we performed fluorescence quantitative real-time PCR and Western blot to globally characterize the transcription and protein expression profiles of BmVps4 and BmVta1 during silkworm development and in different silkworm tissues and organs. The results showed that they were significantly up-regulated in metamorphosis, adulthood and embryogenesis relative to larval stages, and displayed a roughly similar tissue-and-organ specificity for transcriptions in silkworm larvae. Importantly, BmVps4 was down-regulated during the early period of the fifth instar, reaching the lowest level of transcription on Day 6, then up-regulated from Day 7 to the wandering, spinning and pupal stages, and down-regulated again in adulthood. Moreover, knocking down BmVps4 by RNA interference significantly inhibited silk gland growth, shortened spinning time, prolonged pupation, reduced pupal size and weight, and increased moth wing defects. Together, our data demonstrate the critical and broad requirements for BmVps4 in silkworm metamorphosis.

Thymosin participates in antimicrobial immunity in zebrafish

Thymosin hormones, which were shown to be involved in immune system development and differentiation in previous studies, have antimicrobial functions in different animals. Zebrafish are a useful model for immunology research. Although thymosin has been reported to be involved in the embryonic development of zebrafish, it is necessary to uncover the antimicrobial function of thymosin in zebrafish. In this study, we expressed thymosin β (Tβ) in zebrafish in vitro and studied its antimicrobial function. The Tβ protein consists of 45 amino acids and is conserved among its family members, especially the actin-binding motif (LKKTET). Tβ was expressed in all tested tissues and was highly expressed in the brain, liver and hindgut. After Aeromonas hydrophila challenge, the Tβ transcript level increased in the skin, liver, kidney, spleen, thymus, foregut, gills and midgut. Purified recombinant thymosin β (rTβ) protein was used to study the antimicrobial mechanism. rTβ could inhibit the growth of Staphylococcus aureus, Aeromonas hydrophila, Vibrio anguillarum, Pseudomonas aeruginosa and Klebsiella pneumoniae. rTβ also binds to and agglutinates certain bacteria. Further study showed that rTβ could combine with the polysaccharides from gram-negative and gram-positive bacterial walls. All results suggested that the Tβ of zebrafish plays a significant role in innate antibacterial immune responses.

Identification and Characterization of BmVta1, a Bombyx mori (Lepidoptera: Bombycidae) Homologue for Vta1 That is Up-Regulated in Development

Vps20-associated 1 (Vta1) positively regulates Vacuolar protein sorting 4 (Vps4) to disassemble endosomal sorting complex required for transport III (ESCRT-III) for repeated uses in multivesicular body (MVB) pathway, virus budding and other processes. Currently, these proteins have mainly been studied in yeast and mammalian cells, while identities of them in insects remain largely unknown. We previously identified BmVps4, a Vps4 homologue from Bombyx mori. Here, we report the identification of a homologue for Vta1, designated as BmVta1. The BmVta1 cDNA contains an open reading frame of 933 bp and encodes a protein of 311 amino acid residues. We cloned BmVta1, expressed it in Escherichia coli, and prepared mouse polyclonal antibodies. Like BmVps4, BmVta1 is well conserved as shown by sequence analysis. Both proteins are localized in cytoplasm as revealed by subcellular location analysis. Interestingly, as revealed by semi-quantitative reverse transcription polymerase chain reaction (sqRT-PCR), transcriptions of BmVta1 and BmVps4 are highly up-regulated during silkworm metamorphosis and embryogenesis but down-regulated during larva stages, and are of higher levels in head, silk gland and testis than in Malpighian tube, fat body and ganglion, indicating important and similar roles of them in silkworm development and in silkworm tissues and organs. However, compared to BmVps4, the transcription of BmVta1 changes less drastically during development and is of much higher levels in midgut, ovary and hemolymph, suggesting the existence of distinct requirements of them in silkworm development and in certain tissues and organs.

IDENTIFICATION AND EXPRESSION ANALYSIS OF TWO 14-3-3 PROTEINS IN THE MOSQUITO Aedes aegypti, AN IMPORTANT ARBOVIRUSES VECTOR

The 14-3-3 proteins are evolutionarily conserved acidic proteins that form a family with several isoforms in many cell types of plants and animals. In invertebrates, including dipteran and lepidopteran insects, only two isoforms have been reported. 14-3-3 proteins are scaffold molecules that form homo- or heterodimeric complexes, acting as molecular adaptors mediating phosphorylation-dependent interactions with signaling molecules involved in immunity, cell differentiation, cell cycle, proliferation, apoptosis, and cancer. Here, we describe the presence of two isoforms of 14-3-3 in the mosquito Aedes aegypti, the main vector of dengue, yellow fever, chikungunya, and zika viruses. Both isoforms have the conserved characteristics of the family: two protein signatures (PS1 and PS2), an annexin domain, three serine residues, targets for phosphorylation (positions 58, 184, and 233), necessary for their function, and nine alpha helix-forming segments. By sequence alignment and phylogenetic analysis, we found that the molecules correspond to Ɛ and ζ isoforms (Aeae14-3-3ε and Aeae14-3-3ζ). The messengers and protein products were present in all stages of the mosquito life cycle and all the tissues analyzed, with a small predominance of Aeae14-3-3ζ except in the midgut and ovaries of adult females. The 14-3-3 proteins in female midgut epithelial cells were located in the cytoplasm. Our results may provide insights to further investigate the functions of these proteins in mosquitoes.

Thymosin From Bombyx mori Is Down-Regulated in Expression by BmNPV Exhibiting Antiviral Activity

Thymosins have been highly conserved during evolution. These hormones exist in many animal species and play an essential role in many biological events. However, little is known regarding the physiological function of silkworm Bombyx mori thymosin (BmTHY). In this study, we investigated the expression pattern of BmTHY in a Bombyx mori larval ovarian cell line (BmN) challenged with Bombyx mori nuclear polyhydrosis virus (BmNPV) and the antiviral effect of recombinant BmTHY (rBmTHY) for Bombyx mori against BmNPV. Western-blot assay and qRT-PCR analysis revealed that the level of BmTHY protein expression and transcription decreased over time when BmN cells were infected by BmNPV. Treatment with endotoxin-free rBmTHY led to a significant reduction in viral titer in the supernatant of BmN cells challenged with BmNPV. The results from antiviral tests performed in vitro and in vivo showed that endotoxin-free rBmTHY improved the survival rate of Bombyx mori infected with BmNPV. These findings suggest that BmTHY exerts immunomodulatory effects on Bombyx mori, rendering them resistant to viral infection.