Contribution of intraflagellar transport to compartmentalization and maintenance of the photoreceptor cell.

The first steps of vision take place in the ciliary outer segment compartment of photoreceptor cells. The protein composition of outer segments is uniquely suited to perform this function. The most abundant among these proteins is the visual pigment, rhodopsin, whose outer segment trafficking involves intraflagellar transport (IFT). Here, we report three major findings from the analysis of mice in which ciliary transport was acutely impaired by conditional knockouts of IFT-B subunits. First, we demonstrate the existence of a sorting mechanism whereby mislocalized rhodopsin is recruited to and concentrated in extracellular vesicles prior to their release, presumably to protect the cell from adverse effects of protein mislocalization. Second, reducing rhodopsin expression significantly delays photoreceptor degeneration caused by IFT disruption, suggesting that controlling rhodopsin levels may be an effective therapy for some cases of retinal degenerative disease. Last, the loss of IFT-B subunits does not recapitulate a phenotype observed in mutants of the BBSome (another ciliary transport protein complex relying on IFT) in which non-ciliary proteins accumulate in the outer segment. Whereas it is widely thought that the role of the BBSome is to primarily participate in ciliary transport, our data suggest that the BBSome has another major function independent of IFT and possibly related to maintaining the diffusion barrier of the ciliary transition zone.

Aberrant Splicing of INS Impairs Beta-Cell Differentiation and Proliferation by ER Stress in the Isogenic iPSC Model of Neonatal Diabetes.

One of the causes of diabetes in infants is the defect of the insulin gene (INS). Gene mutations can lead to proinsulin misfolding, an increased endoplasmic reticulum (ER) stress and possible beta-cell apoptosis. In humans, the mechanisms underlying beta-cell failure remain unclear. We generated induced pluripotent stem cells (iPSCs) from a patient diagnosed with neonatal diabetes mellitus carrying the INS mutation in the 2nd intron (c.188-31G>A) and engineered isogenic CRISPR/Cas9 mutation-corrected cell lines. Differentiation into beta-like cells demonstrated that mutation led to the emergence of an ectopic splice site within the INS and appearance of the abnormal RNA transcript. Isogenic iPSC lines differentiated into beta-like cells showed a clear difference in formation of organoids at pancreatic progenitor stage of differentiation. Moreover, MIN6 insulinoma cell line expressing mutated cDNA demonstrated significant decrease in proliferation capacity and activation of ER stress and unfolded protein response (UPR)-associated genes. These findings shed light on the mechanism underlying the pathogenesis of monogenic diabetes.

Flavoprotein miniSOG as a genetically encoded photosensitizer for cancer cells.

BACKGROUND: Genetically encoded photosensitizers are a promising optogenetic instrument for light-induced production of reactive oxygen species in desired locations within cells in vitro or whole body in vivo. Only two such photosensitizers are currently known, GFP-like protein KillerRed and FMN-binding protein miniSOG. In this work we studied phototoxic effects of miniSOG in cancer cells. METHODS: HeLa Kyoto cell lines stably expressing miniSOG in different localizations, namely, plasma membrane, mitochondria or chromatin (fused with histone H2B) were created. Phototoxicity of miniSOG was tested on the cells in vitro and tumor xenografts in vivo. RESULTS: Blue light induced pronounced cell death in all three cell lines in a dose-dependent manner. Caspase 3 activation was characteristic of illuminated cells with mitochondria- and chromatin-localized miniSOG, but not with miniSOG in the plasma membrane. In addition, H2B-miniSOG-expressing cells demonstrated light-induced activation of DNA repair machinery, which indicates massive damage of genomic DNA. In contrast to these in vitro data, no detectable phototoxicity was observed on tumor xenografts with HeLa Kyoto cell lines expressing mitochondria- or chromatin-localized miniSOG. CONCLUSIONS: miniSOG is an excellent genetically encoded photosensitizer for mammalian cells in vitro, but it is inferior to KillerRed in the HeLa tumor. GENERAL SIGNIFICANCE: This is the first study to assess phototoxicity of miniSOG in cancer cells. The results suggest an effective ontogenetic tool and may be of interest for molecular and cell biology and biomedical applications.

Human rod photoreceptor outer segments are supported by accessory inner segment structures.

The first steps in vision take place in photoreceptor cells, which are highly compartmentalized neurons exhibiting significant structural variation across species. The light-sensitive ciliary compartment, called the outer segment, is located atop of the cell soma, called the inner segment. In this study, we present an ultrastructural analysis of human photoreceptors, which reveals that, in contrast to this classic arrangement, the inner segment of human rods extends alongside the outer segment to form a structure hereby termed the "accessory inner segment". While reminiscent of the actin-based microvilli known as "calyceal processes" observed in other species, the accessory inner segment is a unique structure: (1) it contains an extensive microtubule-based cytoskeleton, (2) it extends far alongside the outer segment, (3) its diameter is comparable to that of the outer segment, (4) it contains numerous mitochondria, and (5) it forms electron-dense structures that likely mediate adhesion to the outer segment. Given that the spacing of extrafoveal human photoreceptors is more sparse than in non-primate species, with vast amounts of interphotoreceptor matrix present between cells, the closely apposed accessory inner segment likely provides structural support to the outer segment. This discovery expands our understanding of the human retina and directs future studies of human photoreceptor function in health and disease.

RNA Interference Effectors Selectively Silence the Pathogenic Variant GNAO1 c.607 G > A In Vitro.

RNA interference (RNAi)-based therapeutics hold the potential for dominant genetic disorders, enabling sequence-specific inhibition of pathogenic gene products. We aimed to direct RNAi for the selective suppression of the heterozygous GNAO1 c.607 G > A variant causing GNAO1 encephalopathy. By screening short interfering RNA (siRNA), we showed that GNAO1 c.607G>A is a druggable target for RNAi. The si1488 candidate achieved at least twofold allelic discrimination and downregulated mutant protein to 35%. We created vectorized RNAi by incorporating the si1488 sequence into the short hairpin RNA (shRNA) in the adeno-associated virus (AAV) vector. The shRNA stem and loop were modified to improve the transcription, processing, and guide strand selection. All tested shRNA constructs demonstrated selectivity toward mutant GNAO1, while tweaking hairpin structure only marginally affected the silencing efficiency. The selectivity of shRNA-mediated silencing was confirmed in the context of AAV vector transduction. To conclude, RNAi effectors ranging from siRNA to AAV-RNAi achieve suppression of the pathogenic GNAO1 c.607G>A and discriminate alleles by the single-nucleotide substitution. For gene therapy development, it is crucial to demonstrate the benefit of these RNAi effectors in patient-specific neurons and animal models of the GNAO1 encephalopathy.

Generation of an induced pluripotent stem cell line HPCASRi002-A from a patient with neonatal severe primary hyperparathyroidism caused by a compound heterozygous mutation in the CASR gene.

Neonatal severe primary hyperparathyroidism (NSHPT) is a rare autosomal recessive disorder of calcium homeostasis that manifests shortly after birth with hypercalcemia and bone disease. NSHPT, in most cases, is attributed to mutations in the calcium-sensing receptor (CASR) gene. We reprogrammed dermal fibroblasts derived from a patient with NSHPT carrying a compound heterozygous mutation in the CASR gene into induced pluripotent stem cells (iPSCs). The established iPSCs expressed pluripotency markers, maintained normal karyotype and differentiated into all three germ layers. This line is a valuable resource for modeling of hyperparathyroidism related to CASR mutations.

Generation of an induced pluripotent stem cell line MNDINSi001-A from a patient with neonatal diabetes caused by a heterozygous INS mutation.

Insulin gene (INS) mutations prove to be the second most common cause of permanent neonatal diabetes. Here, we report the generation of iPSC line from a patient, heterozygous for the intronic INS mutation that presumably leads to aberrant splicing. Dermal fibroblasts were reprogrammed using non-integrating RNA-based vector. Derivation and expansion of iPSCs were performed under feeder-free culture conditions. The iPSC line expressed pluripotency markers, had normal karyotype, could differentiate into three germ layers in vitro and retained the disease mutation. This line can be a powerful tool for modeling of diabetes and cell replacement therapy as well.

Intrinsic blinking of red fluorescent proteins for super-resolution microscopy.

Single-molecule localization microscopy relies on either controllable photoswitching of fluorescent probes or their robust blinking. We have found that blinking of monomeric red fluorescent proteins TagRFP, TagRFP-T, and FusionRed occurs at moderate illumination power and matches well with camera acquisition speed. It allows for super-resolution image reconstruction of densely labelled structures in live cells using various algorithms.

Protein labeling for live cell fluorescence microscopy with a highly photostable renewable signal.

We present protein-PAINT - the implementation of the general principles of PAINT (Point Accumulation for Imaging in Nanoscale Topography) for live-cell protein labeling. Our method employs the specific binding of cell-permeable fluorogenic dyes to genetically encoded protein tags. We engineered three mutants of the bacterial lipocalin Blc that possess different affinities to a fluorogenic dye and exhibit a strong increase in fluorescence intensity upon binding. This allows for rapid labeling and washout of intracellular targets on a time scale from seconds to a few minutes. We demonstrate an order of magnitude higher photostability of the fluorescence signal in comparison with spectrally similar fluorescent proteins. Protein-PAINT ensures prolonged super-resolution fluorescence microscopy of living cells in both single molecule detection and stimulated emission depletion regimes.

Fluorescence Imaging of Actin Fine Structure in Tumor Tissues Using SiR-Actin Staining.

BACKGROUND: The rearrangement of actin cytoskeleton is being increasingly considered a marker of cancer cell activity, but the fine structure and remodeling of microfilaments within tumor tissue still remains unclear. MATERIALS AND METHODS: We used the recently introduced silicon-rhodamine (SiR)-actin dye to visualize endogenous actin within tissues by confocal or total internal reflection fluorescence microscopy. We established imaging conditions for robust blinking of SiR-actin, which makes this dye applicable for super-resolution localization microscopy, as well as for an efficient background elimination. RESULTS: We studied tumor tissue samples in two mouse models at high resolution and revealed a complex network of thick curved bundles of actin in cancer cells in tumors. This actin pattern differed strongly from that in cancer cells in vitro and in normal tissues. CONCLUSION: Localization microscopy with SiR-actin provides an efficient way to visualize fine actin structure in tumor tissues. It is potentially applicable to a variety of biological and clinical samples.

Influence of mesenchymal stem cells on metastasis development in mice in vivo.

INTRODUCTION: In recent years, mesenchymal stem cells (MSCs) have been demonstrated to play an important role in carcinogenesis. However, the effect of MSCs on tumor and metastasis development and the mechanisms underlying the interaction of cancer and stem cells are not completely understood. This study investigated the effect of MSCs on breast cancer metastasis formation by using the methods of in vivo fluorescence and luminescence imaging. METHODS: MSCs were isolated from bone marrow of normal donors, characterized, and genetically labeled with luciferase (luc2). The effects of MSCs on MDA-MB-231 cancer cell proliferation were evaluated in conditioned medium from MSCs. To generate lung metastases, MDA-MB-231 cells stably expressing red fluorescent protein Turbo FP650 were injected intravenously into nude mice. On day 10 after the cancer cell injection, mice were injected via the tail vein with MSCs-luc2 cells (the MET+MSCs group). Animals that received the injection of MDA-MB-231-Turbo FP650 alone (the MET group) and no injections (the intact control group) served as controls. Fluorescence and bioluminescence imaging was performed for monitoring of the metastasis formation and MSC distribution in the recipient's body. RESULTS: We found that the proliferative activity of the cancer cells in the presence of MSC conditioned medium was lower than that of the cells grown in conventional culture medium. The metastasis formation in the MET+MSCs group was delayed in time as compared with the MET group. Macroscopic and histological examination of isolated lungs 8 weeks after cancer cell injection showed that the total number of metastases in animals of the MET+MSCs group was significantly lower. Using bioluminescence imaging in vivo, we found that MSCs-luc2 cells survived in the host animal for at least 7 weeks and re-migrated to the lung 6 to 7 weeks after injection. Immunohistochemical analysis revealed the presence of MSCs-luc2 in metastases and lung tissue. CONCLUSIONS: Long-term in vivo bioluminescence imaging of intravenously injected MSCs-luc2 cells showed distribution of MSCs to the lungs and abdominal organs within the first 2 to 3 weeks and re-migration to the lungs in weeks 6 to 7. It was found that MSCs reduced the proliferative activity of cancer cells in vitro and lung metastasis formation in mice.