9-5-24 [Intergrating cells into tissues] [Munmun]

Integrating Cells into Tissues

• Cell Biology GSBE 5302

Overview of Multicellular Organisms

• Multicellular organisms are made up of specialized cells organized into tissues.

• Four major classes of tissues:

  • Epithelial

  • Muscular

  • Connective

  • Nervous

• Tissues combine to form organs.

Cell-to-Cell Adhesion

• Cells contact with a complex network of secreted macromolecules known as the extracellular matrix (ECM).

• Direct cell-to-cell adhesions are mediated by cell adhesion molecules (CAMs).

• Cell Adhesion Functions:

  • Aggregates cells

  • Provides bidirectional communication among cells.

Types of Cell Adhesion

• Cell-Matrix Adhesion:

  • Indirect interaction via adhesion receptors binding to ECM.

• Cell-to-Cell Adhesion:

  • Direct adhesion between cells through CAMs.

Categories of Cell Adhesion

• Homotypic Adhesion:

  • Same cell type.

• Heterotypic Adhesion:

  • Different cell types.

• Homophilic Adhesion:

  • Same adhesive molecules.

• Heterophilic Adhesion:

  • Different adhesive molecules.

Major Families of CAMs

• Four major families:

  1. Cadherins

  2. Immunoglobulin (Ig) Superfamily

  3. Integrins

  4. Selectins

Generation of Cell-Cell Adhesions

• Cis (Lateral) Interaction:

  • Cells associate laterally, involving extracellular or cytosolic domains in the plasma membrane.

• Trans Interaction:

  • Cell binding through same or different CAMs on adjacent cells.

Specific Interaction of Adhesion Molecules

• Species-specific homotypic adhesion demonstrated in sponge studies (e.g., Microciona prolifera and Halichondra panicea).

• Adhesion Factor (AF): Protein that forms cross-links between cell membranes, enabling tissue formation.

Importance of Cell Adhesion

• Adhesion Functions:

  • Assembly into tissues

  • Maintains composition

  • Architecture definition

  • Functional properties

• Conservation of Adhesion Molecules:

  • Highly conserved proteins across species.

E-Cadherin and Calcium-Dependent Adhesion

• Mouse fibroblasts expressing E-cadherin show adhesion in Ca2+ presence but not without it.

Cell Junction Overview

• Junctions vital for tissue integrity:

  • Tight Junctions

  • Anchoring Junctions

  • Gap Junctions

Specialized Junctions

• Three major types define epithelial structure and function:

  1. Anchoring Junctions: Include adherens and desmosomes.

  2. Tight Junctions: Seal neighboring cells.

  3. Gap Junctions: Allow small molecule passage.

Proteins Mediating Tight Junctions

• Integral proteins include occludin and claudin which play roles in permeability and cell polarity maintenance.

Physiological Consequences of Tight Junction Disruption

• Genetic defects in claudin proteins can lead to various disorders, including hearing loss and renal issues.

Gap Junctions and Communication

• Comprised of connexins, allowing inter-cellular signaling.

Extracellular Matrix Functions

• ECM supports tissue structure, influences cell behavior, and regulates communication:

  1. Anchors cells for solid tissue structure

  2. Affects biomechanical properties

  3. Controls cell survival, proliferation, and migration.

Cell-Matrix Interactions in Development

• ECM plays a critical role in branching morphogenesis (e.g., organ development).

• Disruption of ECM can lead to severe developmental defects.

Specialized Basal Lamina

• Basal lamina anchors epithelial tissues using a network of collagen and laminin, critical for tissue regeneration.

Cancers and Cadherin Function

• Changes in cadherin expression, such as E-cadherin in cancer, affect adhesion and migration, influencing metastasis.

Questions and Quizzes

• Include key concepts for testing knowledge on tissue types, CAM families, adhesion mechanisms, and functions of ECM components.

Conclusion

• Understanding cell-to-cell and cell-matrix adhesion is essential for comprehending tissue formation, maintenance, and cellular communication.