In-depth Notes on Developmental Biology - Origins of Cells and Tissues (Lecture 11)

Learning Objectives

  • Describe the early steps of human development
  • Label different cell types present in the blastocyst
  • Define gastrulation and name the three embryonic germ layers derived from it
  • Describe the defining properties of stem cells
  • Define pluripotent and multipotent stem cells with examples
  • Distinguish embryonic stem cells from induced pluripotent stem cells (iPS cells)
  • Understand potential uses of stem cells in biomedicine

Introduction to Developmental Biology

  • Focus on the origins of cells and tissues in the human body
  • Relates to previous lecture on meiosis and zygote formation

Phases of Early Human Development

  • Fertilization occurs in the fallopian tube when a haploid sperm merges with a diploid ovum, forming a diploid zygote.
  • Cleavage: Rapid cell division after fertilization leading to a morula (solid ball of cells).
  • Blastocyst Formation: Involves transformation into a hollow ball of cells by day 4-5, consisting of:
    • Inner Cell Mass: Source of embryonic stem cells
    • Trophoblast: Outer cells contributing to the placenta
    • Blastocoel: Fluid-filled cavity

Stages of Embryonic Development

  • Timeline for development:
    • Day 1: Zygote
    • Day 3: Morula (16 cells, compact ball)
    • Day 4-5: Blastocyst (0.1 mm in size) ready for implantation
    • Day 6-7: Implantation begins in the uterus
  • Inner Cell Mass differentiates into:
    • Epiblast: Forming the embryo proper
    • Hypoblast: Leading to formation of extraembryonic endoderm

Gastrulation

  • Critical stage characterized by:
    • Rapid cell movement and proliferation
    • Formation of the three germ layers:
    • Endoderm (inner layer)
    • Mesoderm (middle layer)
    • Ectoderm (outer layer)
  • Cells migrating through the primitive streak move to form new layers, displacing previous cells:
    • First wave: Endoderm forms by displacing hypoblast
    • Second wave: Mesoderm forms below ectoderm

Neurulation

  • Development of the neural tube from the ectoderm:
    • Neural Plate forms a groove, which folds to create the Neural Tube
    • Neural Crest Cells: Cells migrating from the neural tube to form structures in the body

Derivatives of the Germ Layers

  • Ectoderm: Forms skin, nervous system, and neural crest derivatives
  • Mesoderm: Forms muscle, skeletal structures, circulatory system, and connective tissues
  • Endoderm: Forms internal organs such as gut, respiratory tract, and glands

Stem Cells

  • Definition: Undifferentiated cells capable of self-renewal and differentiation into specialized cells.
  • Types of Stem Cells:
    • Embryonic Stem Cells (ES cells): Derived from inner cell mass, pluripotent, can generate any body cell type except placenta.
    • Induced Pluripotent Stem Cells (iPS cells): Adult cells reprogrammed back to a pluripotent state using specific factors (Yamanaka factors).
    • Multipotent Stem Cells: Can differentiate into multiple cell types but is limited compared to pluripotent.
    • Totipotent Stem Cells: Can develop into a complete organism (e.g., zygote).

Applications of Stem Cells in Biomedicine

  • Potential uses include treating conditions like:
    • Myocardial infarction, muscular dystrophy, spinal injuries, and drug screening
  • ES Cells: Derived from embryos; offers promise in regenerative medicine but involves ethical concerns.
  • iPS Cells: Avoids ethical issues by using a patient's own cells, allowing for personalized treatments.
  • Disease Modeling: Can model diseases, enable drug testing, and potentially cure conditions by creating patient-specific cells.

Conclusion

  • Understanding embryonic development phases, stem cell properties, and their applications forms the backbone of regenerative medicine and therapeutic strategies.
  • The evolution of stem cell research propels advancements in treating degenerative diseases and opens up new realms in biomedicine.

References

  • Suggested readings for further insight into stem cell research and applications.