Classical experiments performed half a century ago demonstrated the immense self-organizing capacity of vertebrate cells. Even after complete dissociation, cells can reaggregate and reconstruct the ...original architecture of an organ. More recently, this outstanding feature was used to rebuild organ parts or even complete organs from tissue or embryonic stem cells. Such stem cell-derived three-dimensional cultures are called organoids. Because organoids can be grown from human stem cells and from patient-derived induced pluripotent stem cells, they have the potential to model human development and disease. Furthermore, they have potential for drug testing and even future organ replacement strategies. Here, we summarize this rapidly evolving field and outline the potential of organoid technology for future biomedical research.
Human brain development exhibits several unique aspects, such as increased complexity and expansion of neuronal output, that have proven difficult to study in model organisms. As a result, in vitro ...approaches to model human brain development and disease are an intense area of research. Here we describe a recently established protocol for generating 3D brain tissue, so-called cerebral organoids, which closely mimics the endogenous developmental program. This method can easily be implemented in a standard tissue culture room and can give rise to developing cerebral cortex, ventral telencephalon, choroid plexus and retinal identities, among others, within 1-2 months. This straightforward protocol can be applied to developmental studies, as well as to the study of a variety of human brain diseases. Furthermore, as organoids can be maintained for more than 1 year in long-term culture, they also have the potential to model later events such as neuronal maturation and survival.
The ability of cells to divide asymmetrically is essential for generating diverse cell types during development. The past 10 years have seen tremendous progress in our understanding of this important ...biological process. We have learned that localized phosphorylation events are responsible for the asymmetric segregation of cell fate determinants in mitosis and that centrosomes and microtubules play important parts in this process. The relevance of asymmetric cell division for stem cell biology has added a new dimension to the field, and exciting connections between asymmetric cell division and tumorigenesis have begun to emerge.
Stem cells self-renew but also give rise to daughter cells that are committed to lineage-specific differentiation. To achieve this remarkable task, they can undergo an intrinsically asymmetric cell ...division whereby they segregate cell fate determinants into only one of the two daughter cells. Alternatively, they can orient their division plane so that only one of the two daughter cells maintains contact with the niche and stem cell identity. These distinct pathways have been elucidated mostly in
Drosophila. Although the molecules involved are highly conserved in vertebrates, the way they act is tissue specific and sometimes very different from invertebrates.
The historical reliance of biological research on the use of animal models has sometimes made it challenging to address questions that are specific to the understanding of human biology and disease. ...But with the advent of human organoids - which are stem cell-derived 3D culture systems - it is now possible to re-create the architecture and physiology of human organs in remarkable detail. Human organoids provide unique opportunities for the study of human disease and complement animal models. Human organoids have been used to study infectious diseases, genetic disorders and cancers through the genetic engineering of human stem cells, as well as directly when organoids are generated from patient biopsy samples. This Review discusses the applications, advantages and disadvantages of human organoids as models of development and disease and outlines the challenges that have to be overcome for organoids to be able to substantially reduce the need for animal experiments.
The adult Drosophila midgut is maintained by intestinal stem cells (ISCs) that generate both self-renewing and differentiating daughter cells. How this asymmetry is generated is currently unclear. ...Here, we demonstrate that asymmetric ISC division is established by a unique combination of extracellular and intracellular polarity mechanisms. We show that Integrin-dependent adhesion to the basement membrane induces cell-intrinsic polarity and results in the asymmetric segregation of the Par proteins Par-3, Par-6, and aPKC into the apical daughter cell. Cell-specific knockdown and overexpression experiments suggest that increased activity of aPKC enhances Delta/Notch signaling in one of the two daughter cells to induce terminal differentiation. Perturbing this mechanism or altering the orientation of ISC division results in the formation of intestinal tumors. Our data indicate that mechanisms for intrinsically asymmetric cell division can be adapted to allow for the flexibility in lineage decisions that is required in adult stem cells.
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► Par complex segregates asymmetrically in dividing Drosophila intestinal stem cells ► Par complex inhibition leads to tumor-like intestinal stem cell overproliferation ► aPKC overactivation alters levels of Notch activity, causing stem cell loss ► Integrins regulate spindle orientation and Par protein localization
This paper extends the role of Par proteins in asymmetric cell division to an adult stem cell lineage—the Drosophila intestinal stem cell—and implicates integrins in regulating Par asymmetry in this context.
Human tissues in a dish Bredenoord, Annelien L.; Clevers, Hans; Knoblich, Juergen A.
Science (American Association for the Advancement of Science),
01/2017, Volume:
355, Issue:
6322
Journal Article
Peer reviewed
The ability to generate human tissues in vitro from stem cells has raised enormous expectations among the biomedical research community, patients, and the general public. These organoids enable ...studies of normal development and disease and allow the testing of compounds directly on human tissue. Organoids hold the promise to influence the entire innovation cycle in biomedical research. They affect fields that have been subjects of intense ethical debate, ranging from animal experiments and the use of embryonic or fetal human tissues to precision medicine, organoid transplantation, and gene therapy. However, organoid research also raises additional ethical questions that require reexamination and potential recalibration of ethical and legal policies. In this Review, we describe the current state of research and discuss the ethical implications of organoid technology.
The current understanding of neurological diseases is derived mostly from direct analysis of patients and from animal models of disease. However, most patient studies do not capture the earliest ...stages of disease development and offer limited opportunities for experimental intervention, so rarely yield complete mechanistic insights. The use of animal models relies on evolutionary conservation of pathways involved in disease and is limited by an inability to recreate human-specific processes. In vitro models that are derived from human pluripotent stem cells cultured in 3D have emerged as a new model system that could bridge the gap between patient studies and animal models. In this Review, we summarize how such organoid models can complement classical approaches to accelerate neurological research. We describe our current understanding of neurodevelopment and how this process differs between humans and other animals, making human-derived models of disease essential. We discuss different methodologies for producing organoids and how organoids can be and have been used to model neurological disorders, including microcephaly, Zika virus infection, Alzheimer disease and other neurodegenerative disorders, and neurodevelopmental diseases, such as Timothy syndrome, Angelman syndrome and tuberous sclerosis. We also discuss the current limitations of organoid models and outline how organoids can be used to revolutionize research into the human brain and neurological diseases.
Three-dimensional cell culture models have either relied on the self-organizing properties of mammalian cells or used bioengineered constructs to arrange cells in an organ-like configuration. While ...self-organizing organoids excel at recapitulating early developmental events, bioengineered constructs reproducibly generate desired tissue architectures. Here, we combine these two approaches to reproducibly generate human forebrain tissue while maintaining its self-organizing capacity. We use poly(lactide-co-glycolide) copolymer (PLGA) fiber microfilaments as a floating scaffold to generate elongated embryoid bodies. Microfilament-engineered cerebral organoids (enCORs) display enhanced neuroectoderm formation and improved cortical development. Furthermore, reconstitution of the basement membrane leads to characteristic cortical tissue architecture, including formation of a polarized cortical plate and radial units. Thus, enCORs model the distinctive radial organization of the cerebral cortex and allow for the study of neuronal migration. Our data demonstrate that combining 3D cell culture with bioengineering can increase reproducibility and improve tissue architecture.
Stem cells are highly abundant during early development but become a rare population in most adult organs. The molecular mechanisms causing stem cells to exit proliferation at a specific time are not ...well understood. Here, we show that changes in energy metabolism induced by the steroid hormone ecdysone and the Mediator initiate an irreversible cascade of events leading to cell-cycle exit in Drosophila neural stem cells. We show that the timely induction of oxidative phosphorylation and the mitochondrial respiratory chain are required in neuroblasts to uncouple the cell cycle from cell growth. This results in a progressive reduction in neuroblast cell size and ultimately in terminal differentiation. Brain tumor mutant neuroblasts fail to undergo this shrinkage process and continue to proliferate until adulthood. Our findings show that cell size control can be modified by systemic hormonal signaling and reveal a unique connection between metabolism and proliferation in stem cells.
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•Changes in energy metabolism can profoundly change cell fate•Stem cells can exit proliferation by uncoupling growth from cell division•Mediator complex is crucially involved in steroid hormone signaling•Reduced oxidative phosphorylation can extend life span in stem cells
A change in energy metabolism induced by steroid hormone signaling is responsible for cell-cycle exit in Drosophila neural stem cells. The unexpected connection between metabolism and cell fate could also be relevant for the immortalization of tumor cells.
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