Cellular Differentiation

Learning Objectives

• Understand how a complex organism develops from a single cell into various specialized cell types.

• Explore the process of cellular differentiation.

Cellular Differentiation

• Definition: Process by which unspecialized cells become specialized to perform distinct functions.

• Final morphology and physiology are determined through differentiation.

Stem Cells

• Definition: Unspecialized cells that can divide indefinitely and differentiate under certain conditions.

• Categories of Stem Cells:

  • Totipotent Stem Cells:

    • Origin: First embryonic cells from zygote division.

    • Potential: Can differentiate into any cell type necessary for organism development.

  • Pluripotent Stem Cells:

    • Derived from totipotent cells.

    • Potential: Can become any type of human tissue but cannot develop into a full organism.

  • Multipotent Stem Cells:

    • More specialized than pluripotent; can differentiate into various cell types within a specific lineage.

    • Examples: Red and white blood cells.

  • Oligopotent Stem Cells:

    • Limited to a few cell types. - eg Myeloblast

  • Unipotent Stem Cells:

    • Fully specialized, can only produce more of their specific type - eg T lymphocyte, Basophil, Neutrophil

Lifespan of Stem Cells

• Stem cells vary by developmental stage:

  • Embryonic Stem Cells: Present in embryos.

  • Fetal Stem Cells: Found in fetuses.

  • Adult Stem Cells: Exist in adults with various types performing specific functions.

Types of Adult Stem Cells

• Epithelial Stem Cells: Produce keratinocytes for skin layers.

• Hematopoietic Stem Cells:

  • Location: Adult bone marrow.

  • Function: Generate red and white blood cells and platelets.

• Endothelial Stem Cells: Form cells lining blood and lymph vessels.

• Mesenchymal Stem Cells: Differentiate into muscle cell types.

Hematopoiesis

• Definition: The process by which multipotent stem cells differentiate into blood and immune cells.

Everyday Connection: Stem Cell Research

• Research focuses on using stem cells for regenerating and repairing cellular damage.

• Stem cells' ability to maintain themselves and differentiate into specialized cells is crucial for tissue renewal.

• Differentiation induces changes in cell size, shape, metabolic activity, and function.

  • All cells contain the same DNA, but only read portions relevant to their function.

• Unique Genetic Expression:

  • Each cell type expresses different genes through transcription factors that activate or deactivate specific genes.

Transcription Factors and Gene Expression

• Transcription Factors:

  • Proteins that bind to specific DNA sequences to regulate gene expression by affecting RNA polymerase.

Stem Cell Classification by Origin

• Human Embryonic Stem Cells (hESCs):

  • Extracted from embryos; pluripotent.

• Adult Stem Cells:

  • Found in organs like bone marrow and skin; multipotent.

• Induced Pluripotent Stem Cells (iPSCs):

  • Created from adult stem cells; act like embryonic stem cells.

  • Potential for treating various diseases (e.g., diabetes, heart disease).

Cell-Based Therapy

• Defined as injecting induced stem cells into patients to repair damaged cells.

• Challenges:

  • Embryonic stem cells may be immunologically rejected; raise ethical/ legal issues due to embryo destruction.

Advantages of Adult vs. Embryonic Stem Cells

• Adult stem cells: not foreign to the patient's immune system, but have limited differentiation potential.

• Some choose to store cord blood or baby teeth for potential future therapeutic use.

• iPSCs present a promising solution, avoiding the issues associated with embryonic stem cells.

• Cellular Differentiation: Process by which unspecialized cells become specialized to perform distinct functions.

  • Final morphology and physiology are determined through differentiation.

• Types of Stem Cells:

  • Totipotent Stem Cells:

    • Origin: First embryonic cells from zygote division.

    • Potential: Can differentiate into any cell type necessary for organism development.

  • Pluripotent Stem Cells:

    • Derived from totipotent cells.

    • Potential: Can become any type of human tissue but cannot develop into a full organism.

  • Multipotent Stem Cells:

    • More specialized; can differentiate into various cell types within a specific lineage.

    • Examples: Red and white blood cells.

  • Oligopotent Stem Cells:

    • Limited to a few cell types.

  • Unipotent Stem Cells:

    • Fully specialized; can only produce more of their specific type.

• Lifespan of Stem Cells:

  • Vary by developmental stage:

    • Embryonic Stem Cells: Present in embryos.

    • Fetal Stem Cells: Found in fetuses.

    • Adult Stem Cells: Exist in adults with various types performing specific functions.

• Hematopoiesis: Process by which multipotent stem cells differentiate into blood and immune cells.

• Differential Gene Expression:

  • Determines specialization; involves transcription and translation processes.

  • Housekeeping genes: Expressed in virtually all cells for basic functions.

  • Unique proteins, such as hemoglobin, are specific to certain cell types.

• Functions of Stem Cells:

  • Renewal: Divide indefinitely under certain conditions, e.g., repair and replacement in tissues like skin and intestines.

• Transcription Factors:

  • Proteins that regulate gene expression; control which genes are turned on/off during specialization.