Lecture 6: adult stem cells in the gut

* Understand model organisms in stem-cell biology. * Explain stem-cell niche maintenance. * Describe intestinal crypt structure and signalling gradients. * Explain CBC and Paneth cell roles in the gut niche. * Understand mini-gut generation and self-organisation. * Explain organoid applications in research and medicine.

Explain why developmental biology has improved understanding of adult stem cells.

Developmental biology has revealed mechanisms controlling stem-cell behaviour, including signalling pathways and niche interactions. Comparison with simple model organisms has helped explain how adult stem cells maintain tissues and contribute to disease and ageing.

Why are model organisms useful for understanding human stem-cell biology?

Model organisms have simpler and experimentally accessible systems that reveal conserved mechanisms controlling stem-cell maintenance, signalling and differentiation that also apply to humans.

Which model organism was repeatedly highlighted in this lecture and why?

Drosophila was highlighted because studies of stem-cell niches in Drosophila revealed important mechanisms controlling stem-cell behaviour that can be applied to mammalian systems.

What was learned from Drosophila gonads regarding stem-cell behaviour?

Stem-cell behaviour is strongly controlled by interactions between stem cells and surrounding niche cells through signalling pathways and cell adhesion mechanisms.

Describe the role of cadherins in stem-cell niches.

Cadherins mediate cell-cell adhesion between stem cells and niche cells, helping anchor stem cells and maintain interactions important for self-renewal.

Describe the role of integrins in stem-cell niches.

Integrins mediate interactions between stem cells and extracellular matrix components, helping maintain stem-cell positioning and signalling.

Explain why adhesion molecules are important beyond anchoring stem cells.

Adhesion molecules also regulate signalling, asymmetric division, cell competition, stem-cell ageing and maintenance of tissue organisation.

How can adhesion molecules influence asymmetric cell division?

Adhesion molecules influence cell polarity and positioning of cellular components during division, contributing to different daughter-cell fates.

How can adhesion molecules contribute to cell competition?

Cells receiving stronger self-renewal signals may remain attached to the niche while weaker cells differentiate and leave the niche.

How may ageing affect stem-cell interactions with the niche?

Ageing may alter adhesion molecules and niche interactions, reducing self-renewal and changing stem-cell behaviour.

Why are stem cells considered promising therapeutic tools?

Stem cells may repair damaged tissues and provide treatment options for diseases where current approaches mainly manage symptoms rather than cure disease.

Which stem-cell sources were discussed for current clinical applications?

Human pluripotent stem cells and mesenchymal stem cells derived from bone marrow, adipose tissue and umbilical cord tissue.

Name diseases or conditions mentioned as potential targets of stem-cell therapy.

Neurological disorders, pulmonary dysfunctions, metabolic and endocrine disorders, reproductive disorders, skin burns and cardiovascular disease.

Why is the intestinal crypt considered one of the best-defined adult stem-cell niches?

The intestinal crypt has a highly organised structure with clearly defined stem cells, supporting niche cells and signalling gradients.

Describe the overall structure of the intestinal crypt.

The crypt is a tube-like structure with stem-like cells at the distal end near the crypt base and differentiated cells at the proximal region moving toward the villus.

What are Crypt Base Columnar cells (CBC cells)?

CBC cells are intestinal stem cells located at the crypt base and identified through expression of Wnt target genes.

How are CBC stem cells identified experimentally?

CBC cells are identified by expression of Wnt target genes including Lgr5.

What is Lgr5?

Lgr5 is a marker and Wnt target gene expressed by intestinal crypt base columnar stem cells.

What role do Paneth cells play within the intestinal niche?

Paneth cells act as supporting niche cells and secrete signals including Wnt that maintain stem-cell behaviour.

Describe the relationship between Paneth cells and CBC stem cells.

Paneth cells secrete Wnt signals that activate nearby CBC stem cells and support maintenance of the stem-cell population.

Explain how signalling gradients regulate intestinal stem cells.

Signals vary along the crypt axis and create different environments that promote stem-cell maintenance at the crypt base and differentiation higher in the villus.

Describe the Wnt signalling gradient within the intestinal crypt.

Wnt signalling is highest near the crypt base where stem cells are maintained and decreases toward differentiated regions.

Describe the BMP signalling gradient within the intestinal crypt.

BMP signalling opposes stemness and increases away from the crypt base toward differentiated regions.

Which signalling pathways were described as essential for intestinal epithelial stemness?

Wnt, Notch and EGF signalling were described as important for maintaining intestinal stemness.

What effect does BMP signalling have on stem cells?

BMP signalling negatively regulates stemness and promotes differentiation.

What is the function of EphB signalling in mini-gut formation?

EphB signalling contributes to repulsive interactions that help organise tissue architecture and bud formation.

What technique was used to isolate intestinal stem cells?

Fluorescent activated cell sorting (FACS) was used to isolate single intestinal stem cells.

Describe how mini-guts are generated.

Single intestinal stem cells are isolated and cultured under conditions that support growth and self-organisation into organoid structures.

What is meant by a self-organising mini-gut?

A self-organising mini-gut is an organoid that spontaneously forms structures resembling intestinal tissue without external structural guidance.

Explain how Wnt activation contributes to mini-gut organisation.

Wnt activation promotes local proliferation and EphB expression, contributing to formation of organised budding structures.

What was observed after mini-guts were transplanted into recipient tissue?

Engrafted mini-guts regenerated epithelial patches that became indistinguishable from surrounding tissue and persisted for at least six months.

Why was persistence of transplanted mini-guts important?

Long-term persistence suggests mini-guts can function similarly to normal tissue and may have therapeutic potential.

Describe one use of mini-guts in understanding human biology.

Mini-guts can be used to study mutation effects and improve understanding of human tissue biology.

Describe one use of mini-guts in disease testing and drug discovery.

Patient-derived organoids can be tested against treatments to evaluate disease mechanisms and therapeutic responses.

Describe one use of mini-guts in regenerative medicine.

Mini-guts may be used in transplantation and tissue repair approaches.

Which inflammatory molecules were used in organoid experiments described in the lecture?

IL-1β, TNF-α and IL-6 were used as inflammatory signals in organoid experiments.

What was the overall take-home message from this lecture?

Model organisms and developmental biology have revealed mechanisms controlling adult stem-cell niches, while intestinal organoids provide important tools for studying human biology, disease and regenerative medicine.