Development of Plasmodium falciparum liver-stages in hepatocytes derived from human fetal liver organoid cultures.

Plasmodium falciparum (Pf) parasite development in liver represents the initial step of the life-cycle in the human host after a Pf-infected mosquito bite. While an attractive stage for life-cycle interruption, understanding of parasite-hepatocyte interaction is inadequate due to limitations of existing in vitro models. We explore the suitability of hepatocyte organoids (HepOrgs) for Pf-development and show that these cells permitted parasite invasion, differentiation and maturation of different Pf strains. Single-cell messenger RNA sequencing (scRNAseq) of Pf-infected HepOrg cells has identified 80 Pf-transcripts upregulated on day 5 post-infection. Transcriptional profile changes are found involving distinct metabolic pathways in hepatocytes with Scavenger Receptor B1 (SR-B1) transcripts highly upregulated. A novel functional involvement in schizont maturation is confirmed in fresh primary hepatocytes. Thus, HepOrgs provide a strong foundation for a versatile in vitro model for Pf liver-stages accommodating basic biological studies and accelerated clinical development of novel tools for malaria control.

In vitro grafting of hepatic spheroids and organoids on a microfluidic vascular bed.

With recent progress in modeling liver organogenesis and regeneration, the lack of vasculature is becoming the bottleneck in progressing our ability to model human hepatic tissues in vitro. Here, we introduce a platform for routine grafting of liver and other tissues on an in vitro grown microvascular bed. The platform consists of 64 microfluidic chips patterned underneath a 384-well microtiter plate. Each chip allows the formation of a microvascular bed between two main lateral vessels by inducing angiogenesis. Chips consist of an open-top microfluidic chamber, which enables addition of a target tissue by manual or robotic pipetting. Upon grafting a liver microtissue, the microvascular bed undergoes anastomosis, resulting in a stable, perfusable vascular network. Interactions with vasculature were found in spheroids and organoids upon 7 days of co-culture with space of Disse-like architecture in between hepatocytes and endothelium. Veno-occlusive disease was induced by azathioprine exposure, leading to impeded perfusion of the vascularized spheroid. The platform holds the potential to replace animals with an in vitro alternative for routine grafting of spheroids, organoids, or (patient-derived) explants.

Intestinal organoid cocultures with microbes.

Adult-stem-cell-derived organoids model human epithelial tissues ex vivo, which enables the study of host-microbe interactions with great experimental control. This protocol comprises methods to coculture organoids with microbes, particularly focusing on human small intestinal and colon organoids exposed to individual bacterial species. Microinjection into the lumen and periphery of 3D organoids is discussed, as well as exposure of organoids to microbes in a 2D layer. We provide detailed protocols for characterizing the coculture with regard to bacterial and organoid cell viability and growth kinetics. Spatial relationships can be studied by fluorescence live microscopy, as well as scanning electron microscopy. Finally, we discuss considerations for assessing the impact of bacteria on gene expression and mutations through RNA and DNA sequencing. This protocol requires equipment for standard mammalian tissue culture, or bacterial or viral culture, as well as a microinjection device.

Homeostatic mini-intestines through scaffold-guided organoid morphogenesis.

Epithelial organoids, such as those derived from stem cells of the intestine, have great potential for modelling tissue and disease biology1-4. However, the approaches that are used at present to derive these organoids in three-dimensional matrices5,6 result in stochastically developing tissues with a closed, cystic architecture that restricts lifespan and size, limits experimental manipulation and prohibits homeostasis. Here, by using tissue engineering and the intrinsic self-organization properties of cells, we induce intestinal stem cells to form tube-shaped epithelia with an accessible lumen and a similar spatial arrangement of crypt- and villus-like domains to that in vivo. When connected to an external pumping system, the mini-gut tubes are perfusable; this allows the continuous removal of dead cells to prolong tissue lifespan by several weeks, and also enables the tubes to be colonized with microorganisms for modelling host-microorganism interactions. The mini-intestines include rare, specialized cell types that are seldom found in conventional organoids. They retain key physiological hallmarks of the intestine and have a notable capacity to regenerate. Our concept for extrinsically guiding the self-organization of stem cells into functional organoids-on-a-chip is broadly applicable and will enable the attainment of more physiologically relevant organoid shapes, sizes and functions.

Studying Cryptosporidium Infection in 3D Tissue-derived Human Organoid Culture Systems by Microinjection.

Cryptosporidium parvum is one of the major causes of human diarrheal disease. To understand the pathology of the parasite and develop efficient drugs, an in vitro culture system that recapitulates the conditions in the host is needed. Organoids, which closely resemble the tissues of their origin, are ideal for studying host-parasite interactions. Organoids are three-dimensional (3D) tissue-derived structures which are derived from adult stem cells and grow in culture for extended periods of time without undergoing any genetic aberration or transformation. They have well defined polarity with both apical and basolateral surfaces. Organoids have various applications in drug testing, bio banking, and disease modeling and host-microbe interaction studies. Here we present a step-by-step protocol of how to prepare the oocysts and sporozoites of Cryptosporidium for infecting human intestinal and airway organoids. We then demonstrate how microinjection can be used to inject the microbes into the organoid lumen. There are three major methods by which organoids can be used for host-microbe interaction studies-microinjection, mechanical shearing and plating, and by making monolayers. Microinjection enables maintenance of the 3D structure and allows for precise control of parasite volumes and direct apical side contact for the microbes. We provide details for optimal growth of organoids for either imaging or oocyst production. Finally, we also demonstrate how the newly generated oocysts can be isolated from the organoid for further downstream processing and analysis.

Ongoing chromosomal instability and karyotype evolution in human colorectal cancer organoids.

Chromosome segregation errors cause aneuploidy and genomic heterogeneity, which are hallmarks of cancer in humans. A persistent high frequency of these errors (chromosomal instability (CIN)) is predicted to profoundly impact tumor evolution and therapy response. It is unknown, however, how prevalent CIN is in human tumors. Using three-dimensional live-cell imaging of patient-derived tumor organoids (tumor PDOs), we show that CIN is widespread in colorectal carcinomas regardless of background genetic alterations, including microsatellite instability. Cell-fate tracking showed that, although mitotic errors are frequently followed by cell death, some tumor PDOs are largely insensitive to mitotic errors. Single-cell karyotype sequencing confirmed heterogeneity of copy number alterations in tumor PDOs and showed that monoclonal lines evolved novel karyotypes over time in vitro. We conclude that ongoing CIN is common in colorectal cancer organoids, and propose that CIN levels and the tolerance for mitotic errors shape aneuploidy landscapes and karyotype heterogeneity.

Modelling Cryptosporidium infection in human small intestinal and lung organoids.

Stem-cell-derived organoids recapitulate in vivo physiology of their original tissues, representing valuable systems to model medical disorders such as infectious diseases. Cryptosporidium, a protozoan parasite, is a leading cause of diarrhoea and a major cause of child mortality worldwide. Drug development requires detailed knowledge of the pathophysiology of Cryptosporidium, but experimental approaches have been hindered by the lack of an optimal in vitro culture system. Here, we show that Cryptosporidium can infect epithelial organoids derived from human small intestine and lung. The parasite propagates within the organoids and completes its complex life cycle. Temporal analysis of the Cryptosporidium transcriptome during organoid infection reveals dynamic regulation of transcripts related to its life cycle. Our study presents organoids as a physiologically relevant in vitro model system to study Cryptosporidium infection.

Organoid culture systems to study host-pathogen interactions.

Recent advances in host-microbe interaction studies in organoid cultures have shown great promise and have laid the foundation for much more refined future studies using these systems. Modeling of Zika virus (ZIKV) infection in cerebral organoids have helped us understand its association with microcephaly. Similarly, the pathogenesis of bacterial (Helicobacter pylori, Clostridium difficile) and viral (Norovirus, Rotaviruses) infections have been precisely dissected in organoid cultures. Additionally, direct associations between microbial colonization of tissues and diseases like cancer have also been deciphered. Here we discuss the most recent and striking studies on host-microbe interactions in organoid cultures, highlighting various methods which can be used for developing microbe-organoid co-culture systems.

Disease Modeling in Stem Cell-Derived 3D Organoid Systems.

Organoids are 3D in vitro culture systems derived from self-organizing stem cells. They can recapitulate the in vivo architecture, functionality, and genetic signature of original tissues. Thus, organoid technology has been rapidly applied to understanding stem cell biology, organogenesis, and various human pathologies. The recent development of human patient-derived organoids has enabled disease modeling with precision, highlighting their great potential in biomedical applications, translational medicine, and personalized therapy. In light of recent breakthroughs using organoids, it is only apt that we appreciate the advantages and shortcomings of this technology to exploit its full potential. We discuss recent advances in the application of organoids in studying cancer and hereditary diseases, as well as in the examination of host cell-microorganism interactions.

Regional Cell Specific RNA Expression Profiling of FACS Isolated Drosophila Intestinal Cell Populations.

The adult Drosophila midgut is built of five distinct cell types, including stem cells, enteroblasts, enterocytes, enteroendocrine cells, and visceral muscles, and is divided into five major regions (R1 to R5), which are morphologically and functionally distinct from each other. This unit describes a protocol for the isolation of Drosophila intestinal cell populations for the purpose of cell type-specific transcriptome profiling from the five different regions. A method to select a cell type of interest labeled with green or yellow fluorescent protein (GFP, YFP) by making use of the GAL4-UAS bipartite system and fluorescent-activated cell sorting (FACS) is presented. Total RNA is isolated from the sorted cells of each region, and linear RNA amplification is used to obtain sufficient amounts of high-quality RNA for analysis by microarray, RT-PCR, or RNA sequencing. This method will be useful for quantitative transcriptome comparison across intestinal cell types in the different regions under normal and various experimental conditions.

Niche appropriation by Drosophila intestinal stem cell tumours.

Mutations that inhibit differentiation in stem cell lineages are a common early step in cancer development, but precisely how a loss of differentiation initiates tumorigenesis is unclear. We investigated Drosophila intestinal stem cell (ISC) tumours generated by suppressing Notch (N) signalling, which blocks differentiation. Notch-defective ISCs require stress-induced divisions for tumour initiation and an autocrine EGFR ligand, Spitz, during early tumour growth. On achieving a critical mass these tumours displace surrounding enterocytes, competing with them for basement membrane space and causing their detachment, extrusion and apoptosis. This loss of epithelial integrity induces JNK and Yki/YAP activity in enterocytes and, consequently, their expression of stress-dependent cytokines (Upd2, Upd3). These paracrine signals, normally used within the stem cell niche to trigger regeneration, propel tumour growth without the need for secondary mutations in growth signalling pathways. The appropriation of niche signalling by differentiation-defective stem cells may be a common mechanism of early tumorigenesis.

Regional Cell-Specific Transcriptome Mapping Reveals Regulatory Complexity in the Adult Drosophila Midgut.

Deciphering contributions of specific cell types to organ function is experimentally challenging. The Drosophila midgut is a dynamic organ with five morphologically and functionally distinct regions (R1-R5), each composed of multipotent intestinal stem cells (ISCs), progenitor enteroblasts (EBs), enteroendocrine cells (EEs), enterocytes (ECs), and visceral muscle (VM). To characterize cellular specialization and regional function in this organ, we generated RNA-sequencing transcriptomes of all five cell types isolated by FACS from each of the five regions, R1-R5. In doing so, we identify transcriptional diversities among cell types and document regional differences within each cell type that define further specialization. We validate cell-specific and regional Gal4 drivers; demonstrate roles for transporter Smvt and transcription factors GATAe, Sna, and Ptx1 in global and regional ISC regulation, and study the transcriptional response of midgut cells upon infection. The resulting transcriptome database (http://flygutseq.buchonlab.com) will foster studies of regionalization, homeostasis, immunity, and cell-cell interactions.

Dpp/Gbb signaling is required for normal intestinal regeneration during infection.

Maintaining tissue homeostasis is a critical process during infection and inflammation. Tissues with a high intrinsic turnover, such as the intestinal epithelium, must launch a rapid response to infections while simultaneously coordinating cell proliferation and differentiation decisions. In this study, we searched for genes required for regeneration of the Drosophila intestine, and thereby affecting overall organism survival after infection with pathogenic bacteria. We found that Dpp/Gbb (BMP) signaling is essential for normal midgut regeneration, and that infection induces the BMP signaling ligands Dpp and Gbb. We demonstrate that Dpp is induced in visceral muscle and required for signaling activation. Subsequently, Gbb is induced in enterocytes after oral infection. Loss-of Dpp signaling in ISCs and transient committed progenitors called enteroblasts (EBs), or in EBs alone, led to a blockage in EC differentiation or maturation. Furthermore, our data show that down-regulation of Dpp signaling in the precursor cells including EBs also resulted in an increased number of abnormally small Pdm1-positive cells, suggesting a role of Dpp/Gbb signaling in EC growth. In addition, we show that Dpp/Gbb signaling acted downstream or in parallel to the Notch pathway to promote EC differentiation and growth. Our results suggest that Dpp/BMP signaling plays an important role in EBs to maintain tissue integrity and homeostasis during pathogenic infections.

Escargot maintains stemness and suppresses differentiation in Drosophila intestinal stem cells.

Snail family transcription factors are expressed in various stem cell types, but their function in maintaining stem cell identity is unclear. In the adult Drosophila midgut, the Snail homolog Esg is expressed in intestinal stem cells (ISCs) and their transient undifferentiated daughters, termed enteroblasts (EB). We demonstrate here that loss of esg in these progenitor cells causes their rapid differentiation into enterocytes (EC) or entero-endocrine cells (EE). Conversely, forced expression of Esg in intestinal progenitor cells blocks differentiation, locking ISCs in a stem cell state. Cell type-specific transcriptome analysis combined with Dam-ID binding studies identified Esg as a major repressor of differentiation genes in stem and progenitor cells. One critical target of Esg was found to be the POU-domain transcription factor, Pdm1, which is normally expressed specifically in differentiated ECs. Ectopic expression of Pdm1 in progenitor cells was sufficient to drive their differentiation into ECs. Hence, Esg is a critical stem cell determinant that maintains stemness by repressing differentiation-promoting factors, such as Pdm1.

Fly-FUCCI: A versatile tool for studying cell proliferation in complex tissues.

One promising approach for in vivo studies of cell proliferation is the FUCCI system (fluorescent ubiquitination-based cell cycle indicator). Here, we report the development of a Drosophila-specific FUCCI system (Fly-FUCCI) that allows one to distinguish G1, S, and G2 phases of interphase. Fly-FUCCI relies on fluorochrome-tagged degrons from the Cyclin B and E2F1 proteins, which are degraded by the ubiquitin E3-ligases APC/C and CRL4(Cdt2), during mitosis or the onset of S phase, respectively. These probes can track cell-cycle patterns in cultured Drosophila cells, eye and wing imaginal discs, salivary glands, the adult midgut, and probably other tissues. To support a broad range of experimental applications, we have generated a toolkit of transgenic Drosophila lines that express the Fly-FUCCI probes under control of the UASt, UASp, QUAS, and ubiquitin promoters. The Fly-FUCCI system should be a valuable tool for visualizing cell-cycle activity during development, tissue homeostasis, and neoplastic growth.

RNA expression profiling from FACS-isolated cells of the Drosophila intestine.

This unit describes a protocol for the isolation of Drosophila intestinal cell populations for the purpose of cell type-specific transcriptome profiling. A method to select a cell type of interest labeled with green or yellow fluorescent protein (GFP, YFP) by making use of the GAL4-UAS bipartite system and fluorescent-activated cell sorting (FACS) is presented. Total RNA is isolated from the sorted cells and linear RNA amplification is used to obtain sufficient amounts of high-quality RNA for analysis by microarray, RT-PCR, or RNA sequencing. This method will be useful for quantitative transcriptome comparison across intestinal cell types under normal and various experimental conditions.