BIOS 1700 Chapter 10 Pt. 3

Embryo Development and Cell Types

  • Early experiments with embryos involved manipulating cell structures intentionally.

    • Plunging and rolling embryos to encourage mixing of different cell types.

    • Observations showed a tendency for cells to associate with one another, leading to distinct layers:

    • Epidermal cells on the outside.

    • Neural cells inside, forming complex arrangements.

Cell Adhesion Molecules (CAMs)

  • Description of CAMs

    • Proteins on the cell surface that promote adhesion between cells or to the extracellular matrix (ECM).

    • Not just cell-to-cell interactions; also connect to structures outside the cell (ECM).

    • Abbreviated as ECM throughout the lecture.

    • Breakdown of ECM terminology:

    • "Extra" refers to outside.

    • "Matrix" refers to structures surrounding cells.

  • Structure of Adhesion Molecules

    • Three domains in adhesion proteins:

    • Cytoplasmic domain (interacts with the cell's interior).

    • Transmembrane domain (hydrophobic; spans the membrane).

    • Extracellular domain (interacts with other cells or ECM).

    • Functionality is calcium-dependent; calcium is essential for adhesion processes.

Importance of Calcium

  • Functions of calcium in the body

    • Essential for muscle contractions.

    • Critical for maintaining tissue integrity and other biological processes.

    • Common misconception explained through the necessity of calcium in various bodily functions.

Types of Cadherins

  • Cadherin Types

    • E-cadherins: specific to epithelial cells; bind exclusively to other E-cadherins.

    • N-cadherins: found in neuronal cells; bind only to other N-cadherins.

    • Cells expressing both can connect with all types, indicating flexibility in cell communication.

Cell-to-Cell and Cell-to-Extracellular Matrix Interactions

  • Types of adhesion interactions highlighted

    • Adherens Junctions: connect cells through cadherins and actin filaments.

    • Often described as a button-like structure for cell reinforcement.

    • Desmosomes: connect cells through cadherins and intermediate filaments.

    • Provide mechanical stability to tissues.

    • Hemidesmosomes: use integrins to connect cells to the ECM.

    • Incorporate intermediate filaments internally, anchoring the cell to the ECM.

    • Tight Junctions: serve as barriers to regulate passage between cells.

    • Gap Junctions: facilitate communication between cells via direct connections for signal exchange.

Epithelial Tissue Connections

  • Description of epithelial tissue

    • Lines external and internal surfaces in the body (e.g., skin, digestive tract, blood vessels).

    • Anchored to the basal lamina: a non-cellular layer rich in collagen providing structural support.

    • Regions of epithelial cells:

    • Apical region: closest to the environment.

    • Basolateral region: sides connecting to the basal lamina.

  • Epithelial cell junctions location

    • Tight Junctions: at the apical surface to control permeability.

    • Adherens Junctions: located below tight junctions; they link to actin for cell shape maintenance.

    • Desmosomes: provide strength through mechanical connections with adjacent cells.

    • Hemidesmosomes: connect cells to the basal lamina, interacting with ECM.

    • Gap Junctions: allow for intercellular communication, enabling direct sharing of signaling molecules.

Comparison of Plant and Animal Cell Connections

  • Plant cell connections

    • Use plasmodesmata for communication; gaps through plasma membranes between plant cells.

    • Middle lamella acts as a cement between cell walls, rich in carbohydrates.

    • Structure of cell walls:

    • Primary cell wall: primarily composed of cellulose.

    • Secondary cell wall: added for structure, influenced by age and plant type.

  • Differences in ECM across cell types

    • Plant ECM is mainly the cell wall, while animal ECM consists of material between cells.

    • Collagen as a common protein in animal ECM; provides strength through fibers arranged in bundles.

Health and Disease Implications

  • Ehlers-Danlos Syndrome: a condition related to problems with collagen structure.

    • Presents differently depending on the collagen type affected.

  • Role of integrins in cancer metastasis

    • Cancer cells adapt integrins to migrate through ECM, enabling metastasis to distant sites.

    • Specialized enzymes in cancer cells break down ECM components, facilitating movement through tissues.

Research and Future Directions

  • Continuing focus on ECM and cytoskeleton in various diseases, including neurodegenerative disorders like Parkinson's Disease.

    • Instability of cytoskeleton linked to disease progression.

    • Integrins not only assist in physical connections but also signal changes within cells that affect behavior.