Stem Cell Specialization and Potency

Introduction

• Analogy: Stem cells are like babies full of potential whose specialization narrows as they age.
• Main Point: Stem cells go from unspecialized to specialized as they mature.

Zygote and Early Development

• Zygote: Origin of stem cells; formed when sperm and egg fuse.
• Blastocyst Stage: Cells divide by mitosis forming a blastocyst (hollow ball of cells).
• Inner Cell Mass (ICM): Special group of cells within blastocyst; becomes embryo.
• Pluripotent Stem Cells: Cells that can specialize into several cell types (pluri = several, potent = ability to differentiate).
• Embryonic Stem Cells (ESCs): Found in developmental structures like the ICM.

Two Main Types of Mammalian Stem Cells

1. Embryonic Stem Cells: From early development, can differentiate into any cell type.
2. Somatic Stem Cells: Found in adult organisms, act as a repair system.

Somatic Stem Cells

• Skin Cells: Continually replaced by epidermal stem cells.
  • Epidermal Stem Cells: Divide and replace outer skin layer cells.
  • Shedding Rate: 40,000 skin cells per hour, complete skin renewal in a month.
• Key Differences: Mature cells are specialized for specific functions, while stem cells are unspecialized but can renew and give rise to specialized cells.

Properties of Stem Cells

• Two Main Properties:
  1. Self-renewal: Ability to continually divide, with at least one daughter cell remaining a stem cell.
  2. Potency: Ability to differentiate into specialized cells.
• Types of Potency:
  • Unipotent: Can only produce one cell type (e.g., epithelial stem cells).
  • Multipotent: Can produce multiple cell types within a family (e.g., hematopoietic stem cells).

Examples of Multipotent Stem Cells

• Hematopoietic Stem Cells: Located in bone marrow; produce blood cells.
  • Red Blood Cells: Life span of ~4 months; constantly replaced.
  • White Blood Cells: Key to immune system.
• Clinical Use: Bone marrow transplants for diseases like leukemia.
• Other Examples:
  • Neural Stem Cells: Produce neurons and supporting cells.
  • Mesenchymal Stem Cells: Produce bone, cartilage, and fat cells.

Stem Cell Maintenance Mechanisms

• Obligate Asymmetric Replication: One stem cell remains undifferentiated, one becomes specialized.
• Stochastic Differentiation: If both daughter cells differentiate, another stem cell divides to produce two new stem cells.

Induced Pluripotent Stem Cells (IPS Cells)

• Definition: Specialized cells reprogrammed to become pluripotent stem cells.
• Relevance: Core of regenerative medicine; potential to replace damaged tissues.
• Clinical Implications: Creation of organs from a patient's own cells; no immune rejection.

Trigger for Differentiation

• Regulation: Stem cells express genes that prevent differentiation.
• Environmental Signals: Specific chemical signals cause stem cells to differentiate.

Cord Blood

• Source: Blood taken from placenta and umbilical cord post-birth.
• Significance: Contains multipotent and sometimes pluripotent stem cells; used to be discarded.

Conclusion

• Stem Cells: Crucial for development, repair, and potential future medical treatments.