Genome-Wide Role of HSF1 in Transcriptional Regulation of Desiccation Tolerance in the Anhydrobiotic Cell Line, Pv11

Membraneless and membrane-bound organelles in an anhydrobiotic cell line are protected from desiccation-induced damage

Anhydrobiotic species can survive virtually complete water loss by entering a reversible ametabolic glassy state that may persist for years in ambient conditions. The Pv11 cell line was derived from the egg mass of the anhydrobiotic midge, Polypedilum vanderplanki, and is currently the only available anhydrobiotic cell line. Our results demonstrate that the necessary preconditioning for Pv11 cells to enter anhydrobiosis causes autophagy and reduces mitochondrial respiration by over 70%. We speculate that reorganizing cellular bioenergetics to create and conserve energy stores may be valuable to successfully recover after rehydration. Furthermore, mitochondria in preconditioned cells lose their membrane potential during desiccation but rapidly restore it within 30 min upon rehydration, demonstrating that the inner mitochondrial membrane integrity is well-preserved. Strikingly, the nucleolus remains visible immediately upon rehydration in preconditioned cells while absent in control cells. In contrast, a preconditioning-induced membraneless organelle reformed after rehydration, demonstrating that membraneless organelles in Pv11 cells can be either stabilized or recovered. Staining the endoplasmic reticulum and the Golgi apparatus revealed that these organelles fragment during preconditioning. We hypothesize that this process reduces sheering stress caused by rapid changes in cellular volume during desiccation and rehydration. Additionally, preconditioning was found to cause the filamentous-actin (F-actin) network to disassemble significantly and reduce the fusion of adjacent plasma membranes. This study offers several exciting avenues for future studies in the animal model and Pv11 cell line that will further our understanding of anhydrobiosis and may lead to advancements in storing sensitive biologics at ambient temperatures for months or years.

A sodium-dependent trehalose transporter contributes to anhydrobiosis in insect cell line, Pv11

Pv11 is the only animal cell line that, when preconditioned with a high concentration of trehalose, can be preserved in the dry state at room temperature for more than one year while retaining the ability to resume proliferation. This extreme desiccation tolerance is referred to as anhydrobiosis. Here, we identified a transporter that contributes to the recovery of Pv11 cells from anhydrobiosis. In general, the solute carrier 5 (SLC5)-type secondary active transporters cotransport Na+ and carbohydrates including glucose. The heterologous expression systems showed that the transporter belonging to the SLC5 family, whose expression increases upon rehydration, exhibits Na+-dependent trehalose transport activity. Therefore, we named it STRT1 (sodium-ion trehalose transporter 1). We report an SLC5 family member that transports a naturally occurring disaccharide, such as trehalose. Knockout of the Strt1 gene significantly reduced the viability of Pv11 cells upon rehydration after desiccation. During rehydration, when intracellular trehalose is no longer needed, Strt1-knockout cells released the disaccharide more slowly than the parental cell line. During rehydration, Pv11 cells became roughly spherical due to osmotic pressure changes, but then returned to their original spindle shape after about 30 min. Strt1-knockout cells, however, required about 50 min to adopt their normal morphology. STRT1 probably regulates intracellular osmolality by releasing unwanted intracellular trehalose with Na+, thereby facilitating the recovery of normal cell morphology during rehydration. STRT1 likely improves the viability of dried Pv11 cells by rapidly alleviating the significant physical stresses that arise during rehydration.

Effective methods for immobilization of non-adherent Pv11 cells while maintaining their desiccation tolerance

Pv11 was derived from embryos of the sleeping chironomid Polypedilum vanderplanki, which displays an extreme form of desiccation tolerance known as anhydrobiosis. Pre-treatment with a high concentration of trehalose allows Pv11 cells to enter anhydrobiosis. In the dry state, Pv11 cells preserve transgenic luciferase while retaining its activity. Thus, these cells could be utilized for dry-preserving antibodies, enzymes, signaling proteins or other valuable biological materials without denaturation. However, Pv11 cells grow in suspension, which limits their applicability; for instance, they cannot be integrated into microfluidic devices or used in devices such as sensor chips. Therefore, in this paper, we developed an effective immobilization system for Pv11 cells that, crucially, allows them to maintain their anhydrobiotic potential even when immobilized. Pv11 cells exhibited a very high adhesion rate with both biocompatible anchor for membrane (BAM) and Cell-Tak coatings, which have been reported to be effective on other cultured cells. We also found that Pv11 cells immobilized well to uncoated glass if handled in serum-free medium. Interestingly, Pv11 cells showed desiccation tolerance when trehalose treatment was done prior to immobilization of the cells. In contrast, trehalose treatment after immobilization of Pv11 cells resulted in a significant decrease in desiccation tolerance. Thus, it is important to induce anhydrobiosis before immobilization. In summary, we report the successful development of a protocol for the dry preservation of immobilized Pv11 cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00592-0.

Chilo suppressalis heat shock proteins are regulated by heat shock factor 1 during heat stress

Heat shock factor 1 (HSF1) functions to maintain cellular and organismal homeostasis by regulating the expression of target genes, including those encoding heat shock proteins (HSPs). In the present study, the gene encoding HSF1 was cloned from the rice pest Chilo suppressalis, and designated Cshsf1. The deduced protein product, CsHSF1, contained conserved domains typical of the HSF1 family, including a DNA-binding domain, two hydrophobic heptad repeat domains, and a C-terminal transactivation domain. Real-time quantitative PCR showed that Cshsf1 was highly expressed in hemocytes. Expression analysis in different developmental stages of C. suppressalis revealed that Cshsf1 was most highly expressed in male adults. RNAi-mediated silencing of Cshsf1 expression reduced C. suppressalis survival at high temperatures. To investigate the regulatory interactions between Cshsf1 and Cshsps, the promoters and expression patterns of 18 identified Cshsps in C. suppressalis were analysed; four types of heat shock elements (HSEs) were identified in promoter regions including canonical, tail-tail, head-head, and step/gap. The expression of Cshsp19.0, Cshsp21.7B, Cshsp60, Cshsp70 and Cshsp90 was positively regulated by Cshsf1; however, Cshsp22.8, Cshsp702, Cshsp705 and Cshsp706 gene expression was not altered. This study provides a foundation for future studies of HSF1 in insects during thermal stress.

High quality genome assembly of the anhydrobiotic midge provides insights on a single chromosome-based emergence of extreme desiccation tolerance

Non-biting midges (Chironomidae) are known to inhabit a wide range of environments, and certain species can tolerate extreme conditions, where the rest of insects cannot survive. In particular, the sleeping chironomid Polypedilum vanderplanki is known for the remarkable ability of its larvae to withstand almost complete desiccation by entering a state called anhydrobiosis. Chromosome numbers in chironomids are higher than in other dipterans and this extra genomic resource might facilitate rapid adaptation to novel environments. We used improved sequencing strategies to assemble a chromosome-level genome sequence for P. vanderplanki for deep comparative analysis of genomic location of genes associated with desiccation tolerance. Using whole genome-based cross-species and intra-species analysis, we provide evidence for the unique functional specialization of Chromosome 4 through extensive acquisition of novel genes. In contrast to other insect genomes, in the sleeping chironomid a uniquely high degree of subfunctionalization in paralogous anhydrobiosis genes occurs in this chromosome, as well as pseudogenization in a highly duplicated gene family. Our findings suggest that the Chromosome 4 in Polypedilum is a site of high genetic turnover, allowing it to act as a 'sandbox' for evolutionary experiments, thus facilitating the rapid adaptation of midges to harsh environments.

Identification of Genomic Safe Harbors in the Anhydrobiotic Cell Line, Pv11

Genomic safe harbors (GSHs) provide ideal integration sites for generating transgenic organisms and cells and can be of great benefit in advancing the basic and applied biology of a particular species. Here we report the identification of GSHs in a dry-preservable insect cell line, Pv11, which derives from the sleeping chironomid, Polypedilum vanderplanki, and similar to the larvae of its progenitor species exhibits extreme desiccation tolerance. To identify GSHs, we carried out genome analysis of transgenic cell lines established by random integration of exogenous genes and found four candidate loci. Targeted knock-in was performed into these sites and the phenotypes of the resulting transgenic cell lines were examined. Precise integration was achieved for three candidate GSHs, and in all three cases integration did not alter the anhydrobiotic ability or the proliferation rate of the cell lines. We therefore suggest these genomic loci represent GSHs in Pv11 cells. Indeed, we successfully constructed a knock-in system and introduced an expression unit into one of these GSHs. We therefore identified several GSHs in Pv11 cells and developed a new technique for producing transgenic Pv11 cells without affecting the phenotype.

Chironomid midges (Diptera) provide insights into genome evolution in extreme environments

Extremophiles often undergo marked changes in genomic architecture, likely as a result of adaptation to the harsh environments they inhabit. These changes can involve gene duplications that affect subsequent gene evolution and the regulation of gene expression. Excellent examples of this are provided by two non-biting chironomid midges (Diptera, Chironomidae): Polypedilum vanderplanki, which in its larval form can withstand almost complete water loss, and Belgica antarctica, which exhibits freeze tolerance. This review presents recent studies on the molecular adaptations and evolutionary features of these and other extremophile chironomid genomes, as well as biotechnological applications of a cell line derived from P. vanderplanki that can survive air-drying. We highlight the importance of genomics in identifying molecular pathways and genomic modifications associated with adaptation to extreme environmental conditions.