Human Fetal Tissue Research Articles

A Letter to President Biden and Secretary Designate of HHS Xavier Becerra: Remove Barriers to Federal Funding of Human Embryo and Fetal Tissue Research.

Human fetal tissue (HFT) has been used in biomedical research for nearly a century and has led to extraordinarily valuable discoveries that have benefitted humankind. Politicization of the use of HFT over recent years has led to the creation of numerous obstacles to scientific progress in this field. In July 2019, the imposition of redundant ethics policies was supplemented with the creation of the Human Fetal Tissue Ethics Advisory Board, which withheld funding of 13 out of 14 NIH grants that were favorably peer reviewed in the Summer of 2020. We believe that these new sets of restrictions are harmful to the goals of scientific progress and call upon the new administration of our government to allow peer review, not politics, to determine scientific merit and to reinstitute the previously existing ethics policies that were more than adequate to assure the appropriateness of human fetal tissue research.

Fetal brain tissue characterization at 1.5 T using STrategically Acquired Gradient Echo (STAGE) imaging

To estimate human fetal brain MRI tissue properties including apparent T1 (T1app) and apparent proton density (PDapp) by using a rapid multi-contrast acquisition protocol called STrategically Acquired Gradient Echo (STAGE) imaging. STAGE data were collected using two flip angles (15° and 60°, with a TR = 600 ms) for 30 pregnant women at 1.5 T (15 healthy controls: gestational age (GA) range 19 + 1/7 weeks to 34 + 5/7 weeks; 11 abnormal subjects with ventriculomegaly: GA range 21 + 5/7 weeks to 31 + 5/7 weeks; 4 subjects with other abnormalities). Both T1app and PDapp maps of the fetal brain were calculated from the STAGE data. A region-of-interest-based approach was used to measure T1app and PDapp in the subplate/intermediate zone (SP/IZ), cortical plate (CP), and cerebrospinal fluid (CSF) in the fetal brain. The ratios of T1appSP/IZ/T1appCP and PDappSP/IZ/PDappCP were larger than unity while T1appSP/IZ/T1appCSF and PDappSP/IZ/PDappCSF were both less than unity. STAGE imaging provides a potential practical approach to estimate multi-parametric properties of the human fetal brain. • STAGE is feasible in measuring fetal brain tissue properties. • Water content in cortical plate and subplate/intermediate zone approaches that of cerebrospinal fluid in early gestational ages.

Human and Animal Studies in Craniofacial Embryology Enrich Human Postnatal Craniofacial Insight Differently

Objectives: To compare results obtained since 1970 from craniofacial embryological studies on human fetal tissues with results from similar studies performed on animal tissues and focus on how the different tissue types and methods can enrich the human postnatal craniofacial research. There are three sections: i) research on normal and pathological human fetal material, ii) animal experimental research performed on different species, and iii) comparisons of the results obtained. Human Material: On human prenatal material, normal and pathological developmental processes in the mandible, maxilla, nasal cavity, body axis, cranial base, vomeronasal organs, pituitary gland and nervous system were related to postnatal findings. Specific focus was given to pre/postnatal bridging of observations on holoprosencephaly, cleft lip/palate, Down syndrome, myelomeningocele/spina bifida, Kallmann syndrome, Turner syndrome and Fragile X syndrome. Demarcations of pathological regions in Cri du chat, Velo-cardio-Facial syndrome and Crouzon syndrome were mapped. Animal Material: Animal experimental results from studies on the notochord, gastrulation, neural crest, hindbrain, rhombomere, homeobox genes and experimentally induced malformation were presented. Comparing materials: The educational background of the scientists performing human and animal research, their postnatal clinical experience, the research materials used and the methods available for research are compared. Furthermore, the obtained findings result in a “pro et contra list” indicating what is positive and what is negative for improving postnatal human diagnostics. Conclusion: Human and animal studies in craniofacial embryology enrich human postnatal craniofacial insight differently. Future cooperation between human and animal research cultures is recommended.

Two distinct trophectoderm lineage stem cells from human pluripotent stem cells

The trophectoderm layer of the blastocyst-stage embryo is the precursor for all trophoblast cells in the placenta. Human trophoblast stem (TS) cells have emerged as an attractive tool for studies on early trophoblast development. However, the use of TS cell models is constrained by the limited genetic diversity of existing TS cell lines and restrictions on using human fetal tissue or embryos needed to generate additional lines. Here we report the derivation of two distinct stem cell types of the trophectoderm lineage from human pluripotent stem cells. Analogous to villous cytotrophoblasts in vivo, the first is a CDX2- stem cell comparable with placenta-derived TS cells—they both exhibit identical expression of key markers, are maintained in culture and differentiate under similar conditions, and share high transcriptome similarity. The second is a CDX2+ stem cell with distinct cell culture requirements, and differences in gene expression and differentiation, relative to CDX2- stem cells. Derivation of TS cells from pluripotent stem cells will significantly enable construction of in vitro models for normal and pathological placental development.

COVID-19 and Vertical Transmission: Assessing the Expression of ACE2 / TMPRSS2 in the Human Fetus and Placenta to Assess the Risk of SARS-CoV-2 Infection

Background: While pregnant women have been identified as a potentially at-risk group concerning COVID-19 infection, little is known regarding the susceptibility of the fetus to infection. Co-expression of ACE2 and TMPRSS2 has been identified as a pre-requisite for infection, and expression across different tissues is known to vary between children and adults. However, the expression of these proteins in the fetus is unknown.Methods: We performed a retrospective analysis of single cell data repositories. This data was then validated at both gene and protein level by performing qRT-PCR and two-colour immunohistochemistry on a library of second-trimester human fetal tissues.Findings: TMPRSS2 is present at both gene and protein level in the predominantly epithelial fetal tissues analysed. ACE2 is present at significant levels, only in the fetal intestine and kidney and is not expressed in the fetal lung. The placenta is also negative for the two proteins both during development and at term.Interpretation: This dataset indicates that the lungs are unlikely to be a viable route of SARS-CoV2 fetal infection. The fetal kidney, despite presenting both the proteins required for the infection, is anatomically protected from the exposure to the virus. However, the GI tract is likely to be susceptible to infection due to its high co-expression of both proteins, as well as its exposure to potentially infected amniotic fluid.Funding Information: This work was made possible by an MRC / UKRI COVID-19 Rapid response initiative grant (MR/V028480/1).Declaration of Interests: The authors declare no conflicts of interest related to this work or its developments. DC is founder, shareholder, and consultant of Next Generation Diagnostic SRL.Ethics Approval Statement: Human fetal tissues were obtained with consent through the Human Developmental Biology Resource (HDBR; REC 18/LO/0822 – IRAS 244325; Project ID 2000478). Placental samples were obtained at delivery of an uncomplicated, full-term pregnancy (median 39 weeks PCW [Range 38+1 -39+4] for 6 patients recruited through the EVERREST Prospective Study as normal controls (National Research Ethics reference 13/LO/1254), NCT02097667 registered 31st October 2013[10].

Isolation and Propagation of Primary Human and Rodent Embryonic Neural Progenitor Cells and Cortical Neurons.

The research on human neural progenitor cells holds great potential for the understanding of the molecular programs that control differentiation of cells of glial and neuronal lineages, as well as pathogenetic mechanisms of neurological diseases. Stem cell technologies also provide opportunities for the pharmaceutical industry to develop new approaches for regenerative medicine. Here, we describe the protocol for the isolation and maintenance of neural progenitor cells and cortical neurons using human fetal brain tissue. This protocol can be successfully adapted for the preparation of rodent neural and oligodendrocyte progenitor cells. While several methods for isolating neural and oligodendrocyte progenitors from rodent brain tissue have been described, including techniques utilizing gene transfer and magnetic resonance beads, few methods are specifically focused on deriving human oligodendrocyte progenitor cells. Development of the human cultures provides the most physiologically relevant system for investigating mechanisms which regulate the function of oligodendrocytes, specifically of human origin.

A SCID mouse-human lung xenograft model of SARS-CoV-2 infection.

SARS-CoV-2 infection, which is responsible for the current COVID-19 pandemic, can cause life-threatening pneumonia, respiratory failure and even death. Characterizing SARS-CoV-2 pathogenesis in primary human target cells and tissues is crucial for developing vaccines and therapeutics. However, given the limited access to clinical samples from COVID-19 patients, there is a pressing need for in vitro/in vivo models to investigate authentic SARS-CoV-2 infection in primary human lung cells or tissues with mature structures. The present study was designed to evaluate a humanized mouse model carrying human lung xenografts for SARS-CoV-2 infection in vivo.Methods: Human fetal lung tissue surgically grafted under the dorsal skin of SCID mice were assessed for growth and development after 8 weeks. Following SARS-CoV-2 inoculation into the differentiated lung xenografts, viral replication, cell-type tropism and histopathology of SARS-CoV-2 infection, and local cytokine/chemokine expression were determined over a 6-day period. The effect of IFN-α treatment against SARS-CoV-2 infection was tested in the lung xenografts.Results: Human lung xenografts expanded and developed mature structures closely resembling normal human lung. SARS-CoV-2 replicated and spread efficiently in the lung xenografts with the epithelial cells as the main target, caused severe lung damage, and induced a robust pro-inflammatory response. IFN-α treatment effectively inhibited SARS-CoV-2 replication in the lung xenografts.Conclusions: These data support the human lung xenograft mouse model as a useful and biological relevant tool that should facilitate studies on the pathogenesis of SARS-CoV-2 lung infection and the evaluation of potential antiviral therapies.

Balancing Scientific Advice with Political Realities during the Campaign to Pass California's Ballot Proposition 14.

Balancing Scientific Advice with Political Realities during the Campaign to Pass California's Ballot Proposition 14.

Evaluation of TH-Cre knock-in cell lines for detection and specific targeting of stem cell-derived dopaminergic neurons

The focal and progressive degeneration of dopaminergic (DA) neurons in ventral midbrain has made Parkinson's disease (PD) a particularly interesting target of cell-based therapies. However, ethical issues and limited tissue availability have so far hindered the widespread use of human fetal tissue in cell-replacement therapy. DA neurons derived from human pluripotent stem cells (hPSCs) offer unprecedented opportunities to access a renewable source of cells suitable for PD therapeutic applications. To better understand the development and functional properties of stem-cell derived DA neurons, we generated targeted hPSC lines with the gene coding for Cre recombinase knocked into the TH locus. When combined with flexed GFP, they serve as reporter cell lines able to identify and isolate TH+ neurons in vitro and after transplantation in vivo. These TH-Cre lines provide a valuable genetic tool to manipulate DA neurons useful for the design of more precise DA differentiation protocols and the study of these cells after transplantation in pre-clinical animal models of PD.

Production of Functional Hepatobiliary Organoids from Human Pluripotent Stem Cells.

The research on human hepatobiliary development and disorders has been constrained by minimal access to human fetal tissue, and low accuracy of animal models. To overcome this problem, we have established a system for the differentiation of human pluripotent stem cells (hPSCs) into functional hepatobiliary organoids (HBOs). We have previously reported that our 45-d approach closely mimics key stages of hepatobiliary development, starting with the differentiation of hiPSC into endoderm and a small part of mesoderm, and subsequently into hepatoblast-like cells, followed by the parallel generation of hepatocyte-like cells and cholangiocyte-like cells, formation of immature HBO expressing early hepatic and biliary markers, and mature HBO displaying hepatobiliary functionality. In this study, we present an updated version of our previous protocol, which only needs 35 days to achieve maturation in vitro. Furthermore, a hepatobiliary culture medium is developed to functionally maintain the HBOs for more than 1.5 months. The capacity of this approach for producing large amounts of functional HBOs and enabling long-term culture in vitro holds promise for applications on developmental research, disease modeling, as well as screening of therapeutic agents.

Chronological study in microanatomy of human foetal pancreatic tissue

Introduction: The name of pancreas derives from the Greek’ word. The pancreas involves in diseases like diabetes mellitus and pancreatic cancer. It is contains Endocrine cells or Islets of Langerhans that secrete insulin, glucagon and somatostatin, which regulate blood glucose levels.1 The exocrine pancreatic acini secretes pancreatic enzymes and alpha fetoprotein which change the expression level during development and influences development and differentiation of pancreas.2 Endocrine disease causes diabetes which affects at least 200 million people worldwide, and this number is to be doubled by 2025.1 The exocrine part leads to pancreatic cancer causing about 65,000 deaths in European countries which is virtually incurable. Aims: The purpose of the current study was to investigate microanatomy (Histogenesis) of Pancreas in aborted fresh human foetuses without any congenital abnormality. So the present study was conducted to know the development of acini and islets and their clinical correlation. Materials and Methods: Foetuses aged between 12 to 40 weeks of gestational age and they were collected from Obstetrics and Gynaecology department of Kamineni Institute of Medical Sciences, Narkatpally, Nalgonda (Dt), Telangana, (India) and Kamineni Academy of Medical Sciences and Research centre, L.B. Nagar, Hyderabad. The histogenic procedures were employed at all gestational ages and were discussed with the available literature because various studies have proved that the islets of pancreas are necessary for the transplantation of pancreas, but very few studies showed the importance of pancreatic acini. Results and Conclusion: In the early weeks (12-18 weeks) the parenchyma forms primitive tubules with small lobes and lobules of acini and small spherical islets. As the age advances (18-24 weeks) the size and number of Islets are increased with encapsulation and proliferation of acinar cells. To conclude, at the age of 18-24 weeks the fetal pancreas is suitable for organ transplantation in patients with diabetes mellitus and pancreatic cancer. Keywords: Histogenesis, Gestational period, Pancreas, Serous acini, Islets of Langerhans, Microanatomy, Ducts, Alpha fetoprotein (AFP).

Effect of Intrauterine Smoke Exposure on microRNA-15a Expression in Human Lung Development and Subsequent Asthma Risk.

Background: In utero smoke (IUS) exposure is associated with asthma susceptibility. Objective: We sought to test the hypothesis that changes in miRNA expression by IUS exposure during human lung development is associated with asthma susceptibility. Methods: Gene expression was profiled from 53 IUS unexposed and 51 IUS exposed human fetal lung tissues. We tested for the differential expression of miRNAs across post-conception age and by IUS using linear models with covariate adjustment. We tested the IUS-associated miRNAs for association with their gene expression targets using pair-wise inverse correlation. Using our mouse model, we investigated the persistence of the IUS-associated miRNA signature using RT-PCR from the lungs of mouse pups with and without IUS at postnatal day 14. MiRNAs were then tested for association with asthma and exacerbations using whole blood gene expression profiles from Asthma BRIDGE. Results: Five miRNAs were differentially expressed across post-conception age (adjusted p < 0.0002) including two that were differentially expressed by IUS exposure in human fetal lung (p < 0.05). MiR-15a was differentially expressed by post-conception age (p = 0.00002), IUS exposure in human fetal lung (p = 0.005), and in the post-natal mouse lung (p = 0.01). MiR-15a was also associated with the in utero expression of GSDMB (adjusted p = 0.0002), a known childhood asthma gene and with asthma exacerbations (p = 0.0009) in Asthma BRIDGE. Thus, miR-15a is expressed during human lung development, is impacted by IUS exposure, regulates the intrauterine expression of asthma genes, and is associated with asthma severity. Conclusions: These results provide evidence for the role of miR-15a in the fetal origin of asthma.

Cisplatin and carboplatin result in similar gonadotoxicity in immature human testis with implications for fertility preservation in childhood cancer

BackgroundClinical studies indicate chemotherapy agents used in childhood cancer treatment regimens may impact future fertility. However, effects of individual agents on prepubertal human testis, necessary to identify later risk, have not been determined. The study aimed to investigate the impact of cisplatin, commonly used in childhood cancer, on immature (foetal and prepubertal) human testicular tissues. Comparison was made with carboplatin, which is used as an alternative to cisplatin in order to reduce toxicity in healthy tissues.MethodsWe developed an organotypic culture system combined with xenografting to determine the effect of clinically-relevant exposure to platinum-based chemotherapeutics on human testis. Human foetal and prepubertal testicular tissues were cultured and exposed to cisplatin, carboplatin or vehicle for 24 h, followed by 24–240 h in culture or long-term xenografting. Survival, proliferation and apoptosis of prepubertal germ stem cell populations (gonocytes and spermatogonia), critical for sperm production in adulthood, were quantified.ResultsCisplatin exposure resulted in a significant reduction in the total number of germ cells (− 44%, p < 0.0001) in human foetal testis, which involved an initial loss of gonocytes followed by a significant reduction in spermatogonia. This coincided with a reduction (− 70%, p < 0.05) in germ cell proliferation. Cisplatin exposure resulted in similar effects on total germ cell number (including spermatogonial stem cells) in prepubertal human testicular tissues, demonstrating direct relevance to childhood cancer patients. Xenografting of cisplatin-exposed human foetal testicular tissue demonstrated that germ cell loss (− 42%, p < 0.01) persisted at 12 weeks. Comparison between exposures to human-relevant concentrations of cisplatin and carboplatin revealed a very similar degree of germ cell loss at 240 h post-exposure.ConclusionsThis is the first demonstration of direct effects of chemotherapy exposure on germ cell populations in human foetal and prepubertal testis, demonstrating platinum-induced loss of all germ cell populations, and similar effects of cisplatin or carboplatin. Furthermore, these experimental approaches can be used to determine the effects of established and novel cancer therapies on the developing testis that will inform fertility counselling and development of strategies to preserve fertility in children with cancer.

Human Fetal Tissue Regulation. Impact on Pediatric and Adult Respiratory-related Research.

Human Fetal Tissue Regulation. Impact on Pediatric and Adult Respiratory-related Research.

Methadone Suppresses Neuronal Function and Maturation in Human Cortical Organoids.

Accumulating evidence has suggested that prenatal exposure to methadone causes multiple adverse effects on human brain development. Methadone not only suppresses fetal neurobehavior and alters neural maturation, but also leads to long-term neurological impairment. Due to logistical and ethical issues of accessing human fetal tissue, the effect of methadone on brain development and its underlying mechanisms have not been investigated adequately and are therefore not fully understood. Here, we use human cortical organoids which resemble fetal brain development to examine the effect of methadone on neuronal function and maturation during early development. During development, cortical organoids that are exposed to clinically relevant concentrations of methadone exhibited suppressed maturation of neuronal function. For example, organoids developed from 12th week till 24th week have an about 7-fold increase in AP firing frequency, but only half and a third of this increase was found in organoids exposed to 1 and 10 μM methadone, respectively. We further demonstrated substantial increases in INa (4.5-fold) and IKD (10.8-fold), and continued shifts of Na+ channel activation and inactivation during normal organoid development. Methadone-induced suppression of neuronal function was attributed to the attenuated increase in the densities of INa and IKD and the reduced shift of Na+ channel gating properties. Since normal neuronal electrophysiology and ion channel function are critical for regulating brain development, we believe that the effect of prolonged methadone exposure contributes to the delayed maturation, development fetal brain and potentially for longer term neurologic deficits.

Establishment of a Novel Human Fetal Adrenal Culture Model that Supports de Novo and Manipulated Steroidogenesis.

Disorders affecting adrenal steroidogenesis promote an imbalance in the normally tightly controlled secretion of mineralocorticoids, glucocorticoids, and androgens. This may lead to differences/disorders of sex development in the fetus, as seen in virilized girls with congenital adrenal hyperplasia (CAH). Despite the important endocrine function of human fetal adrenals, neither normal nor dysregulated adrenal steroidogenesis is understood in detail. Due to significant differences in adrenal steroidogenesis between human and model species (except higher primates), we aimed to establish a human fetal adrenal model that enables examination of both de novo and manipulated adrenal steroidogenesis. Human adrenal tissue from 54 1st trimester fetuses were cultured ex vivo as intact tissue fragments for 7 or 14 days. Model validation included examination of postculture tissue morphology, viability, apoptosis, and quantification of steroid hormones secreted to the culture media measured by liquid chromatography-tandem mass spectrometry. The culture approach maintained cell viability, preserved cell populations of all fetal adrenal zones, and recapitulated de novo adrenal steroidogenesis based on continued secretion of steroidogenic intermediates, glucocorticoids, and androgens. Adrenocorticotropic hormone and ketoconazole treatment of ex vivo cultured human fetal adrenal tissue resulted in the stimulation of steroidogenesis and inhibition of androgen secretion, respectively, demonstrating a treatment-specific response. Together, these data indicate that ex vivo culture of human fetal adrenal tissue constitutes a novel approach to investigate local effects of pharmaceutical exposures or emerging therapeutic options targeting imbalanced steroidogenesis in adrenal disorders, including CAH.

Abstract 12937: Single-cell Transcriptomic Analysis Reveals Developmentally Impaired Endocardial Population in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is one of the most challenging forms of congenital heart diseases. Previous studies were mainly focused on intrinsic defects in myocardium. However, this does not sufficiently explain the abnormal development of the cardiac valve, septum, and vasculature, known to originate from the endocardium. Here, using single-cell transcriptomic profiling, induced pluripotent stem cells (iPSC) derived endocardial cells (iEECs), human fetal heart tissue with underdeveloped left ventricle, as well as a Xenopus model, we identified a developmentally impaired endocardial population in HLHS. The intrinsic endocardial deficits contributed to abnormal endothelial to mesenchymal transition, NOTCH signaling, and extracellular matrix organization, all of which are key factors in valve formation. Consequently, in an endocardium-myocardium co-culture system, we found that endocardial abnormalities conferred reduced proliferation and maturation of iPSC derived cardiomyocyte (iPSC-CMs) judged by Ki67 staining, contractility, sarcomere organization, and related gene expressions through a disrupted fibronectin (FN1)-integrin interaction. Several recently described HLHS de novo mutations such as ETS1 and CHD7 showed reduced binding to FN1 promoter and enhancer in HLHS vs. control iEECs based on ChIP-qPCR analysis. Additionally, we found that suppression of the ETS1 in Xenopus caused reduced endocardial FN1 expression and impaired heart development. Supplementation of FN1 or ETS1 over-expression in HLHS iEECs could rescue dysfunctions in both endocardium and myocardium in HLHS. Our studies reveal a critical role of endocardial abnormality in causing HLHS, and provide a rationale for improving endocardial function in future regenerative strategies. Schematic illustration of the endocardial and myocardial defects in HLHS.

Multimerization of Zika Virus-NS5 Causes Ciliopathy and Forces Premature Neurogenesis.

Zika virus (ZikV) is a flavivirus that infects neural tissues, causing congenital microcephaly. ZikV has evolved multiple mechanisms to restrict proliferation and enhance cell death, although the underlying cellular events involved remain unclear. Here we show that the ZikV-NS5 protein interacts with host proteins at the base of the primary cilia in neural progenitor cells, causing an atypical non-genetic ciliopathy and premature neuron delamination. Furthermore, in human microcephalic fetal brain tissue, ZikV-NS5 persists at the base of the motile cilia in ependymal cells, which also exhibit a severe ciliopathy. Although the enzymatic activity of ZikV-NS5 appears to be dispensable, the amino acids Y25, K28, and K29 that are involved in NS5 oligomerization are essential for localization and interaction with components of the cilium base, promoting ciliopathy and premature neurogenesis. These findings lay the foundation for therapies that target ZikV-NS5 multimerization and prevent the developmental malformations associated with congenital Zika syndrome.

Single-cell RNA sequencing of human fetal epicardium reveals novel markers and regulators of EMT

Abstract Background The heart is covered by the epicardium, consisting of epithelial cells and a mesenchymal layer. The epicardium has been shown to be essential during cardiac development by contributing cells through epithelial-to-mesenchymal transition (EMT) and the secretion of paracrine factors. In the adult, the epicardium conveys a cardioprotective response after myocardial infarction, albeit suboptimal compared to the epicardial contribution to heart development. Although the developing epicardium has been characterised in mice and zebrafish, knowledge on the human fetal epicardium derives mostly from cell culture models. Therefore, direct analysis of the human fetal epicardium is vital as it provides new insights into the cellular and biochemical interactions within the developing heart, which can potentially contribute to enhancing the post-injury response. Aim To study the human fetal epicardium using single-cell RNA sequencing (scRNA seq) in order to determine its cellular compositionThe data are further explored to e.g.identify regulators of epicardial EMT. Methods Epicardial layers were isolated from four fetal human hearts (14–15 weeks gestation, obtained under informed consent and according to local ethical approval). Tissue was digested, and single live cells were sorted into 384-wells plates and sequenced. Data analysis was performed using R-packages RaceID3 and StemID2. Findings were validated using qPCR and immunohistochemistry. Results Analysis of 2024 cells reveals a clear clustering of the epicardial epithelium and the mesenchymal population. Importantly, we found that “classical” markers, such as Wilms' Tumor 1 and T-box transcription factor 18, are not specific enough to reliably identify the epicardium, but our analysis has provided markers that do allow for robust identification of the epicardium. Additionally, we were able to identify epicardial subpopulations based on their expression profile, and we are currently investigating these using immunohistochemistry in human fetal and adult heart tissue sections. To establish the regulation of epicardial activation we are focussing on the process of EMT within our dataset using RaceID2. From our analysis, several regulators of epicardial EMT are proposed that will be followed up on in vitro. Conclusions We identify various novel markers of the fetal epithelial epicardium, as well as characterizing markers of the mesenchymal layer. We also identified novel factors involved in epicardial EMT, and these are currently being validated in our cell-culture model. These data can provide new insights into the post-injury response in the adult heart. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Dutch Heart Foundation

Limitations and Promise of Retinal Tissue From Human Pluripotent Stem Cells for Developing Therapies of Blindness.

The self-formation of retinal tissue from pluripotent stem cells generated a tremendous promise for developing new therapies of retinal degenerative diseases, which previously seemed unattainable. Together with use of induced pluripotent stem cells or/and CRISPR-based recombineering the retinal organoid technology provided an avenue for developing models of human retinal degenerative diseases “in a dish” for studying the pathology, delineating the mechanisms and also establishing a platform for large-scale drug screening. At the same time, retinal organoids, highly resembling developing human fetal retinal tissue, are viewed as source of multipotential retinal progenitors, young photoreceptors and just the whole retinal tissue, which may be transplanted into the subretinal space with a goal of replacing patient’s degenerated retina with a new retinal “patch.” Both approaches (transplantation and modeling/drug screening) were projected when Yoshiki Sasai demonstrated the feasibility of deriving mammalian retinal tissue from pluripotent stem cells, and generated a lot of excitement. With further work and testing of both approaches in vitro and in vivo, a major implicit limitation has become apparent pretty quickly: the absence of the uniform layer of Retinal Pigment Epithelium (RPE) cells, which is normally present in mammalian retina, surrounds photoreceptor layer and develops and matures first. The RPE layer polarize into apical and basal sides during development and establish microvilli on the apical side, interacting with photoreceptors, nurturing photoreceptor outer segments and participating in the visual cycle by recycling 11-trans retinal (bleached pigment) back to 11-cis retinal. Retinal organoids, however, either do not have RPE layer or carry patches of RPE mostly on one side, thus directly exposing most photoreceptors in the developing organoids to neural medium. Recreation of the critical retinal niche between the apical RPE and photoreceptors, where many retinal disease mechanisms originate, is so far unattainable, imposes clear limitations on both modeling/drug screening and transplantation approaches and is a focus of investigation in many labs. Here we dissect different retinal degenerative diseases and analyze how and where retinal organoid technology can contribute the most to developing therapies even with a current limitation and absence of long and functional outer segments, supported by RPE.