10/16 - Early development in deuterostome invertebrates

Introduction to Echinoderms and Urochordates

  • Overview of animal groups discussed:

    • Drosophila (fruit flies)

    • Nematodes (roundworms)

    • Echinoderms (e.g., sea urchins)

    • Urochordates (e.g., acidians)

  • Explanation of Deuterostomes

    • Definition: Deuterostomes are a clade of animals that are the sister group to Protostomes.

    • Major clades included within deuterostomes:

    • Chordates

    • Echinoderms - characterized as spiny-skinned animals (e.g., sea urchins)

    • Hemichordates - e.g., acorn worms

    • Acidians

    • Cephalochordates - e.g., amphioxus

Sea Urchin Development

  • Focus on early development of sea urchins

    • Importance of small micromeres or Primary Mesenchyme Cells (PMCs)

    • PMCs play a crucial role in skeleton formation in sea urchins

PMCs and Their Functions

  • Definition: PMCs (Primary Mesenchyme Cells)

  • Characteristics and importance in sea urchin development:

    • High quantities of eggs produced (e.g., 1 million eggs per milliliter)

    • Researchers can harvest billions of eggs; synchronous embryo development observed (e.g., 30 billion embryos)

    • Sea urchin embryos are optically clear, easy to maintain in laboratories, and amenable to genetic manipulation

Experimental Foundations

  • Key experiments performed to understand PMC function:

    • Horstadius' early experiments elucidated the role of PMCs.

    • Nuclear localized beta-catenin as a critical molecule in PMC differentiation

    • Beta-catenin is essential for establishing embryo axes

Mechanism of Early Development

  • Importance of beta-catenin in the signaling pathways

  • Organization of the embryo: how beta-catenin establishes developmental fates

    • Experiments showing the influence of PMCs on neighboring cells

    • PMCs were shown to reorganize cells and induce developmental pathways

Regulatory Networks in Development

  • Internal input into development

  • Beta-catenin's role in gene regulatory networks and its participation in the Wnt signaling pathway

    • Functions of beta-catenin include transcription factor activity and cellular adhesion (via cadherins)

Manipulation of Development

  • Methods of manipulating embryos:

    • Truncation of cadherins to create a beta-catenin sponge

    • Demonstration of PMCs and their effects on neighboring cells through manipulation

    • Consequence of ectopic (misplaced) PMCs on embryo development:

    • Formation of double axes in embryos upon the introduction of additional PMCs

Significance of Experimentation

  • Importance of these experiments in understanding embryonic axes formation and cellular differentiation

    • Dipeptide results of experimental manipulation indicate active cellular communication and signaling networks

Acidians and Their Development

Overview of Acidians

  • Description of acidians as chordates and their features

  • Mention of the unique adaptive characteristics of acidians, such as predation techniques in Deep-water species

  • Importance of acidians in developmental biology research

Mechanisms in Acidian Development

  • The significance of yellow cytoplasm in cell specification:

    • Movement of yellow cytoplasm in response to fertilization, marking developmental axes

    • Fate of cells determined by the presence of yellow cytoplasm

Cellular Signals in Development

  • Role of signaling molecules such as FGF (Fibroblast Growth Factor) in subsequent cell differentiation

    • Comparison of anterior/posterior signaling and how it affects cell fate determination

    • Experimentation shows how removal or addition of cytoplasm influences developmental outcomes

Conclusion of the Lecture

  • Summary of key points:

    • Critical understanding of signaling pathways and cellular interactions in deuterostome development

Additional Topics: Morpholinos

Introduction to Morpholinos

  • Definition of morpholinos and their role in gene function manipulation

    • Comparison with siRNA regarding mechanism and stability in cellular context

Mechanism of Action

  • Mechanism of morpholinos to block translation or affect splicing

  • Overview of how morpholinos are used experimentally to manipulate gene expression and study embryo development

    • Challenges faced with delivery in vivo experiments versus in vitro experimentation

Trajectory of Future Research and Applications

  • Potential future implications of findings in embryonic development on genetics and regenerative medicine.

Questions and Clarifications

  • Open the floor to any further questions regarding topics that are not fully understood, or need further clarification concerning the lecture content.

This represents a comprehensive outline of the major themes and details covered in the lecture, encapsulating all aspects of the sea urchin and acidian developmental biology discussed, along with experimental methodologies and the implications for understanding developmental processes in deuterostomes.