Ch18

Chapter 18: Genes & Development

18.1 Genetic Basis of Development

• Zygote: Totipotent; can develop into any cell type.

• Inner Cell Mass: In humans, cells remain totipotent, forming inner cell mass in the blastocyst.

• Pluripotent Cells: Daughter cells can become many, but not all, cell types (e.g., gastrula can form ectoderm, mesoderm, or endoderm).

• Multipotent Cells: More restricted; can only form a limited number of cell types (e.g., blood stem cells differentiate into various blood cell types).

18.2 Hierarchical Control

• Overview of Development Control: Development is hierarchical; early gene expression regulates subsequent expression.

• Model Organism: Drosophila serves as model for studying genotype, development, and phenotype.

• Gene mutations in embryos affect larval/adult phenotype.

18.2.1 Maternal Effect Genes

• Bicoid Gene: Genotype of the mother hooks into RNA/protein synthesis before fertilization; mutations lead to larvae without heads.

• Nanos Gene: Regulates tail development; similar translational regulation applies.

• Consequences of Maternal Effects: Maternal proteins (Bicoid and Nanos) regulate translations of zygotic genes like caudal and hunchback.

18.2.2 Localization and Translation Regulation

• Bicoid mRNA: More concentrated in the anterior, translated post-fertilization; crucial for anterior development.

• Nanos mRNA: Concentrated in the posterior and required for tail development.

18.2.3 Zygotic Gene Regulation

• Hierarchical Regulation: After fertilization, various maternal-effect proteins regulate zygotic genes leading to organized development.

• Caudal and Hunchback Proteins: Both are transcription factors regulated by their respective maternal proteins.

18.2.4 Progressive Regionalization

• Gene Regulation Sequence: Maternal-effect genes lead to zygotic gap genes which determine further cell fate.

• Homeotic Genes (Hox Genes): Involved in segmental identity; mutations cause misexpression resulting in developmental anomalies.

18.3 Master Regulators

• Eye Development: Eyes exhibit morphological diversity; all utilize similar developmental proteins.

• Pax6 Master Regulator: Activates genes essential for eye formation; mutations lead to abnormal eyes.

• Retinal Development: Involves the precise arrangement of photoreceptor cells, influenced by various signaling pathways, including those regulated by Pax6.

• Signaling Pathways: These pathways coordinate the development of the retina, ensuring proper cellular interactions and the establishment of functional retinal architecture.

Core Concepts + Learning Objectives

• Cell Type Definitions:

  • Totipotent: Capable of becoming any cell type.

  • Pluripotent: Many cell types, not all.

  • Multipotent: Limited cell types.

  • Stem Cells: Undifferentiated cells with potential to become specialized.

  • Induced Pluripotent Stem Cells: Adult cells reprogrammed to pluripotent state.

• Gene Regulation in Development:

  • Maternal effect genes control early development.

  • Understanding gene interaction through mRNA and protein distribution.

  • Definition and function of homeotic genes.