Protocol for automated multivariate quantitative-image-based cytometry analysis by fluorescence microscopy of asynchronous adherent cells

Here, we present a protocol for multivariate quantitative-image-based cytometry (QIBC) analysis by fluorescence microscopy of asynchronous adherent cells. We describe steps for the preparation, treatment, and fixation of cells, sample staining, and imaging for QIBC. We then detail image analysis with our open source Fiji script developed for QIBC and present multiparametric data visualization. Our QIBC Fiji script integrates modern artificial-intelligence-based tools, applying deep learning, for robust automated nuclei segmentation with minimal user adjustments, a major asset for efficient QIBC analysis. For complete details on the use and execution of this protocol, please refer to Besse et al. (2023).1.

A pulse-chase strategy combining click-EdU and photoconvertible fluorescent reporter: tracking Golgi protein dynamics during the cell cycle

Imaging or quantifying protein synthesis in cellulo through a well-resolved analysis of the cell cycle (also defining G1 subcompartments) is a methodological challenge. Click chemistry is the method of choice to reveal the thymidine analogue 5-ethynyl-2'-deoxyuridine (EdU) and track proliferating nuclei undergoing DNA synthesis. However, the click reaction quenches fluorescent proteins. Our challenge was to reconcile these two tools. A robust protocol based on a high-resolution cytometric cell cycle analysis in tobacco (Nicotiana tabacum) BY2 cells expressing fluorescent Golgi markers has been established. This was broadly applicable to tissues, cell clusters, and other eukaryotic material, and compatible with Scale clearing. EdU was then used with the photoconvertible protein sialyl transferase (ST)-Kaede as a Golgi marker in a photoconversion pulse-chase cytometric configuration resolving, in addition, subcompartments of G1. Quantitative restoration of protein fluorescence was achieved by introducing acidic EDTA washes to strip the copper from these proteins which were then imaged at neutral pH. The rate of synthesis of this Golgi membrane marker was low during early G1, but in the second half of G1 (30% of cycle duration) much of the synthesis occurred. Marker synthesis then persisted during S and G2. These insights into Golgi biology are discussed in terms of the cell's ability to adapt exocytosis to cell growth needs.

Multiple functions of Kip-related protein5 connect endoreduplication and cell elongation

Despite considerable progress in our knowledge regarding the cell cycle inhibitor of the Kip-related protein (KRP) family in plants, less is known about the coordination of endoreduplication and cell differentiation. In animals, the role of cyclin-dependent kinase (CDK) inhibitors as multifunctional factors coordinating cell cycle regulation and cell differentiation is well documented and involves not only the inhibition of CDK/cyclin complexes but also other mechanisms, among them the regulation of transcription. Interestingly, several plant KRPs have a punctuated distribution in the nucleus, suggesting that they are associated with heterochromatin. Here, one of these chromatin-bound KRPs, KRP5, has been studied in Arabidopsis (Arabidopsis thaliana). KRP5 is expressed in endoreduplicating cells, and loss of KRP5 function decreases endoreduplication, indicating that KRP5 is a positive regulator of endoreduplication. This regulation relies on several mechanisms: in addition to its role in cyclin/CDK kinase inhibition previously described, chromatin immunoprecipitation sequencing data combined with transcript quantification provide evidence that KRP5 regulates the transcription of genes involved in cell wall organization. Furthermore, KRP5 overexpression increases chromocenter decondensation and endoreduplication in the Arabidopsis trithorax-related protein5 (atxr5) atxr6 double mutant, which is deficient for the deposition of heterochromatin marks. Hence, KRP5 could bind chromatin to coordinately control endoreduplication and chromatin structure and allow the expression of genes required for cell elongation.

Assessment of mitochondria as a compartment for phosphatidylinositol synthesis in Solanum tuberosum

The outer mitochondrial membrane is particularly rich in phosphatidylinositol (PtdIns), a phospholipid found in different amounts in all eukaryotic membranes, but not synthesized in situ by all. PtdIns is therefore subjected to traffic from the synthesizing membranes to the non-synthesizing ones. The contribution of mitochondria to the cell PtdIns pool has never been the focus of a specific study in plants, whereas in yeast, the presence of the enzyme responsible for synthesis, PtdIns synthase (PIS, cytidine 5'-diphospho-1,2-diacyl-sn-glycerol:myo-inositol 3-phosphatidyltransferase, EC 2.7.8.11), has clearly been demonstrated in mitochondria. As these organelles have now been shown to be responsible for the synthesis of several lipids, the present work aimed at evaluating mitochondria as a compartment for the synthesis of PtdIns in plants. The sub-cellular localization of PIS was studied in Solanum tuberosum L. by membrane fractionation, enzymatic analysis and by confocal microscopy in living cells. In potato, beside the endoplasmic reticulum, the activity of PIS was found to be tightly associated to mitochondria. Using a fluorescent reporter fusion, the enzyme was also found to be associated to these organelles. The enzyme was not present at the plasma membrane. A comparison of the localization in other cell systems suggests that the mitochondrial localization could be regulated.

Exploring plant endomembrane dynamics using the photoconvertible protein Kaede

Photoactivatable and photoconvertible fluorescent proteins capable of pronounced light-induced spectral changes are a powerful addition to the fluorescent protein toolbox of the cell biologist. They permit specific tracking of one subcellular structure (organelle or cell subdomain) within a differentially labelled population. They also enable pulse-chase analysis of protein traffic. The Kaede gene codes for a tetrameric protein found in the stony coral Trachyphyllia geoffroyi, which emits green fluorescence that irreversibly shifts to red following radiation with UV or violet light. We report here the use of Kaede to explore the plant secretory pathway. Kaede versions of the Golgi marker sialyl-transferase (ST-Kaede) and of the vacuolar pathway marker cardosin A (cardA-Kaede) were engineered. Several optical devices enabling photoconversion and observation of Kaede using these two constructs were assessed to optimize Kaede-based imaging protocols. Photoconverted ST-Kaede red-labelled organelles can be followed within neighbouring populations of non-converted green Golgi stacks, by their gradual development of orange/yellow coloration from de novo synthesis of Golgi proteins (green). Results highlight some aspects on the dynamics of the plant Golgi. For plant bio-imaging, the photoconvertible Kaede offers a powerful tool to track the dynamic behaviour of designated subpopulations of Golgi within living cells, while visualizing the de novo formation of proteins and structures, such as a Golgi stack.

Gene therapy of rat medullary thyroid cancer by naked nitric oxide synthase II DNA injection

BACKGROUND

Nitric oxide (NO), produced by NO synthase II (NOS II), is the main mediator of the tumoricidal action of activated macrophages. In the present study we examined the potential of the NOS II gene as a suicide gene for medullary thyroid cancer (MTC) therapy.

METHODS

We orthotopically transplanted rMTC 6-23 cells into the inbred strain of Wag/Rij rats and constructed a plasmid carrying the NOS II gene under the control of the cytomegalovirus (CMV) promoter.

RESULTS

Successive injections of tumor cells (Day 0) and naked DNA (Day 2) caused strong inhibition of tumor growth (50%, p < 0.05). Plasmid injection into established tumors (14-day tumors) resulted in the development of large cavities due to tumor cell destruction, with a significant reduction in tumor tissue volume (35%, p < 0.05). Adjacent quiescent tissues were unaffected. Cell death occurred by apoptosis as demonstrated by specific labeling. Macrophages and CD4+ lymphocytes were recruited in the treated tumors. However, tumor-specific T lymphocytes were undetectable in the spleen of treated rats. In control experiments using Lac Z as a reporter gene, expression of beta-galactosidase was detected in only 1% of the tumor cells.

CONCLUSIONS

Despite a low gene transfer efficiency, NOS II plasmid produced a strong anti-tumor action resulting from its marked 'bystander' effect mainly due to NO production and diffusion. Therefore the NOS II gene appears to be a promising suicide gene therapy of human cancer.

Treatment of medullary thyroid carcinoma by combined expression of suicide and interleukin-2 genes

Inherited medullary thyroid carcinomas (MTC) are aggressive and resistant to conventional chemo- and radiotherapies. We evaluated a novel strategy for treatment of MTC, combining "suicide" and interleukin-2 (IL-2) gene therapies. Tumors were produced in Wag/Rij rats by orthotopic injection of the rMTC 6-23 cell line, and/or derivatives expressing the herpes simplex virus 1 thymidine kinase (HSV1-TK) gene (rMTC-TK). Ganciclovir, a nucleoside analog selectively transformed to a toxic metabolite by HSV1-TK, totally eradicated rMTC-TK tumors in 60% of the animals. 1:1 rMTC and rMTC-TK mixed tumors were also strongly inhibited by ganciclovir (P < 0.05), indicating the occurrence of an efficient "bystander" effect in vivo. Double labelling of rMTC cell membranes and apoptotic nuclei revealed that, as with the TK+ cells, some TK- cells died by apoptosis. A 1:1 mixture of rMTC and rMTC-TK cells was administered to produce established tumors and then rMTC cells, transfected to express the IL-2 gene (rMTC-IL2), were inoculated. Combined ganciclovir and IL-2 treatment improved the inhibition of tumor growth compared to that following ganciclovir alone (86% compared to 54%, P < 0.05). This treatment also significantly enhanced macrophage activation and tumor infiltration by CD8+ and CD4+ T lymphocytes. These results open an avenue for combining suicide and immunoregulatory gene therapies for MTC management in man.