Establishment and characterization of a novel cell line from midgut tissue of Helicoverpa armigera (Lepidoptera: Noctuidae)

The untapped potential of cell culture in disentangling insect-microbial relationships

Cell culture is a powerful technique for the investigation of molecular mechanisms fundamental to health and disease in a diverse array of organisms. Cell lines offer several advantages, namely their simplistic approach and high degree of reproducibility. One field where cell culture has proven particularly useful is the study of the microbiome, where cell culture has led to the illumination of microbial influences on host immunity, nutrition, and physiology. Thus far, researchers have focused cell culture work predominantly on humans, but the growing field of insect microbiome research stands to benefit greatly from its application. Insects constitute one of Earth's most diverse and ancient life forms and, just as with humans, possess microbiomes with great significance to their health. Insects, which play critical roles in supporting food security and ecological stability, are facing increasing threats from agricultural intensification, climate change, and pesticide use. As the microbiome is closely tied to host health, gaining a more robust understanding is of increasing importance. In this review, we assert that the cultivation and utilization of insect gut cell lines in microbiome research will bridge critical knowledge gaps essential for informing insect management practices in a world under pressure.

A database of crop pest cell lines

We have developed an online database describing the known cell lines from Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera that were developed from agricultural pests. Cell line information has been primarily obtained from previous compilations of insect cell lines. We conducted in-depth Internet literature searches and drew on Internet sources such as the Cellosaurus database (https://web.expasy.org/cellosaurus/), and inventories from cell line depositories. Here, we report on a new database of insect cell lines, which covers 719 cell lines from 86 species. We have not included cell lines developed from Drosophila because they are already known from published databases, such as https://dgrc.bio.indiana.edu/cells/Catalog. We provide the designation, tissue and species of origin, cell line developer, unique characteristics, its use in various applications, publications, and patents, and, when known, insect virus susceptibility. This information has been assembled and organized into a searchable database available at the link https://entomology.ca.uky.edu/aginsectcellsdatabase which will be updated on an ongoing basis.

Establishment and characterization of the Bactrocera dorsalis (Diptera: Tephritidae) embryonic cell line QAU-Bd-E-2

In this study, we successfully established a Bactrocera dorsalis (Diptera: Tephritidae) embryonic cell line, i.e., QAU-Bd-E-2, from the insect eggs. The cells have been stably passaged for more than 60 times in TNM-FH medium with 10% fetal bovine serum (FBS). QAU-Bd-E-2 cells are adherent cells. Most of the cells were round, spindle-shaped, and rod-shaped. Round cells accounted for 82.3%, with a diameter of 13.9 ± 2.6 µm; spindle-shaped cells accounted for 9.8%, with the size of 51.2 ± 11.2 µm × 10.3 ± 3.1 µm; the rod-shaped cells accounted for 7.9%, with the size of 35.2 ± 9.4 µm × 12.0 ± 2.5 µm. The mitochondrial cytochrome oxidase I subunit (CoI) gene from QAU-Bd-E-2 cells was amplified, and the 657 bp fragment had a 100% similarity with the CoI gene of B. dorsalis, suggesting that the cell line was derived from B. dorsalis. The chromosome number of QAU-Bd-E-2 cells was mostly 12, which is the same as the B. dorsalis chromosome number. The cell density of QAU-Bd-E-2 cells reached the maximum (3.4 × 10⁶ cells/mL) at 192 h, and the population doubling time was 31.9 h. Bactrocera dorsalis cripavirus (BdCV) could replicate in QAU-Bd-E-2 cells, suggesting that this cell line could be used for in-depth study of the relationship between virus and host.

Functional characterization and transcriptomic profiling of a spheroid-forming midgut cell line from Helicoverpa zea (Lepidoptera: Noctuidae)

Insect cell lines have been frequently used in insect science research in recent years. Establishment of cell lines from specialized tissues like the lepidopteran midgut is expected to facilitate research efforts towards the understanding of uptake and metabolic properties, as well as the design of assays for use in pesticide discovery. However, the number of available lines from specialized tissues of insects and the level of understanding of the biological processes taking place in insect cells is far behind mammalian systems. In this study we examine two established cell lines of insect midgut origin, investigate their growth parameters and amenability to transfection and genetic manipulation, and test their potential to form spheroid-like 3D structures. Our results indicate that a midgut-derived cell line from Helicoverpa zea, RP-HzGUT-AW1, is amenable to genetic manipulation by transfection with a standard insect expression vector and has excellent ability to form spheroids. To further investigate the differentiation status of this line, we examined for expression of several candidate marker genes from different midgut cell types, enterocytes (ECs), Goblet cells (GCs), enteroendocrine cells (EEs) and intestinal stem cells (ISCs), indicating that both certain ISC and certain differentiated cell markers were present. To acquire a more detailed perspective of the differentiation landscape of the specific cells, we performed an RNAseq analysis of RP-HzGUT-AW1 grown either in 2D or 3D cultures. We hypothesize that RP-HzGUT-AW1 are in an "arrested" developmental stage between ISC and terminal differentiation. Furthermore, an enrichment of stress response and oxidoreductase genes was observed in the spheroid samples while no significant difference was evident in differentiation markers between cells grown in 2D and 3D. These results render RP-HzGUT-AW1 as the most well-characterized insect gut derived cell line so far, and lay the groundwork for future work investigating midgut cell lines application potential.

Establishment and characterization of a new embryonic cell line from Helicoverpa armigera (Hübner)

Here, a new cell line, Ha168, was established from Helicoverpa armigera eggs and has been stably subcultured for over 30 passages in TNM-FH medium supplemented with 10% fetal bovine serum. The cell line consists of round and spindle-shaped cells and several giant cells. The round cells, with a cell diameter of 14.30 ± 2.804 μm, account for 77% of the cells. DNA amplification fingerprinting, random amplified polymorphic DNA analysis, and analysis of the mitochondrial cytochrome c oxidase subunit I gene confirmed that the Ha168 cells were derived from H. armigera. Karyotype analysis revealed the average chromosome number of Ha168 cells to be 71. Growth curves at passage 25 were determined and demonstrated that the cell population doubling time is 56.8 h. No mycoplasma contamination was detected in the cell line. Ha168 cells can be infected by recombinant baculovirus AcMNPV-EGFP, and exogenous protein expression level in this cell line is 70% of that in the Sf9 cell line.

Establishment of two midgut cell lines from the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Two cell lines were generated from larval midguts of Spodoptera frugiperda and have been 26 passaged over 50 times. The CT/BCIRL-SfMG1-0611-KZ line was established from 27 trypsinized, minced whole midgut tissues: the CT/BCIRL-SfMG-0617-KZ line from isolated 28 midgut muscle tissue (containing some residual epithelial cells). Additional midgut cultures were 29 generated from isolated epithelial cells; some passaged not more than three times, which grew 30 very slowly and survived longer than 1 year. The continuously replicating cell lines contain 31 firmly adhering cells with different morphologies, including elongated, spherical, and/or 32 rectangular. The mean diameters of these cell lines are 9.3 ± 4.0 μm (SfMG1-0611) and 9.2 ± 3.9 33 μm (SfMG-0617). Growth curves for the two lines have relatively lengthy doubling times of 73.9 34 h and 50.4 h for SfMG1-0611 and SfMG-0617, respectively. We confirmed the identity of these 35 lines using DNA amplification fingerprinting (DAF-PCR) and noted that the DNA patterns for 36 each cell line were similar to their host tissues but distinctly different from other cell lines or 37 tissues from different insect species. Amplification of genomic DNA with species-specific 38 primers yielded DNA fragments of the expected sizes and with sequences nearly identical to 39 those from the S. frugiperda genome. Both cell lines were exposed to selected Bt Cry proteins 40 with minimal impact. These lines are currently available to researchers worldwide.

Cell lines from diamondback moth exhibiting differential susceptibility to baculovirus infection and expressing midgut genes

Six new cell lines were established from embryonic tissues of the diamondback moth, Plutella xylostella (L.). The cell lines showed differential characteristics, including growth in attachment or in suspension, susceptibility to a baculovirus infection and expression of genes involved in the glucosinolate detoxification pathway in P. xylostella larvae. Five of the cell lines grew attached to the culture flask and one cell line grew unattached as a suspension cell line. The cell lines had population doubling times ranging from 18 to 23 h. Among five of the P. xylostella cell lines examined for infection of a nucleopolyhedrovirus from Autographa californica, AcMNPV, four cell lines were highly susceptible to AcMNPV infection, but one was only semi-permissive to AcMNPV infection. The production of two recombinant proteins, a β-galactosidase of bacterial origin and a secreted alkaline phosphatase of eukaryotic origin, in the P. xylostella cell lines was examined in comparison with that in the cell line Sf9 which is commonly used for recombinant protein production. In the P. xylostella cell lines, expression of three important midgut genes involved in the glucosinolate detoxification pathway, including the glucosinolate sulfatase genes GSS1 and GSS2 and the sulfatase modifying factor gene SUMF1, was detected. The P. xylostella cell lines developed in this study could be useful in in vitro research systems for studying insec-virus interactions and complex molecular mechanisms in glucosinolate detoxification and insect-plant interactions.