lecture 03/03

Overview of Developmental Biology

• Developmental biology explores how a fertilized egg develops into an adult organism.

• It examines the processes that lead to the diversity of cell types and the organization of body structures.

Key Concepts

Fundamental Questions

• How does a fertilized egg give rise to an adult body?

• How does an adult body produce another entire body?

• How do cells differentiate into various cell types?

  • Example: Root cells vs. leaf cells - same genetic information but different functions.

• How do cells know their location within an embryo?

Developmental Processes

• Several key developmental processes are essential:

  • Cell Division: Involves mitosis and cytokinesis.

  • Cell Signaling: Communication between cells that influences development.

  • Cell Differentiation: Transition from unspecialized cells to specialized cell types.

  • Cell Movement: Cells migrate during organismal development.

  • Programmed Cell Death: Necessary for removing unneeded cells during development.

Experimental Approaches in Developmental Biology

Three Main Approaches

1. Find It

   • Goal: Determine if a specific protein is present in the right time and place during development.

   • Technique: Observing where and when proteins are expressed.

2. Lose It

   • Goal: Assess if a component is necessary for a function by removing it.

   • Process: Knock-out mutants or genetic mutations.

3. Move It

   • Goal: Test if a component is sufficient to drive development in a new context.

   • Process: Introducing a component to a different location within the organism to see if the expected process occurs.

Fluorescence In Situ Hybridization (FISH)

• A technique used to visualize the presence of specific mRNA transcripts in cells.

• Involves binding a fluorescent probe to complementary nucleic acid sequences in the target mRNA.

• Important for studying gene expression in developmental contexts but cannot be applied in living cells without permeabilization.

Cell Potency and Differentiation

Types of Cell Potency

• Totipotent: Cells that can develop into any cell type, including extraembryonic tissues.

• Pluripotent: Cells capable of developing into any cell type within an organism but not able to form extraembryonic tissue.

• Multipotent: Cells with the potential to differentiate into a limited variety of cell types.

• Differentiated Cells: Cells that have specialized and can perform specific functions.

Examples of Differentiated Cells

• Stem Cells: Have the ability to differentiate into various cell types; example includes blood stem cells that can become multiple types of blood cells.

• Plasma Cells: Fully differentiated cells involved in the immune response.

Lineage Tracing

• Refers to tracking the ancestry of specific cells back to their origin in the zygote.

• Important for understanding how cell types diversify during development.

Historical Context and Hypotheses in Cell Specialization

• Hypothesis 1: Cells lose part of their DNA as they specialize, limiting the genes that can be expressed.

• Hypothesis 2: All cells retain the same DNA, and specialization comes from selective gene expression.

Experimentation Support

• Experiment: Introduction of a mammary cell nucleus into an egg cell to determine if the cell could still develop into a full organism.

  • If Hypothesis 2 is supported, a normal organism (clone) would develop, demonstrating that the differentiated cell retains all genetic information necessary for development.

  • Successful cloning of Dolly the sheep supported Hypothesis 2, revealing challenges in reprogramming differentiated cells to achieve totipotency.

Conclusion

• Understanding cell differentiation and development is vital for research in genetics, biology, and medicine.

• The concepts laid out explain the complexity and dynamism of biological systems as they develop from a single fertilized egg into diverse forms.