cell cell interactions

Cell-Cell Interactions

Preparation for Biology

Plant Cells

  • Plant cells are encased by a thick cell wall.

    • Functions:

      • Provides protection.

      • Regulates water uptake.

      • Determines cell shape.

    • Organizational Structure:

      • Primary Cell Wall (1o): Present in young plants, softer and more flexible.

      • Middle Lamella: Composed of sticky polysaccharides such as pectin; holds the cell walls of adjacent cells together.

      • Secondary Cell Wall (2o): Strong and durable, formed after the primary wall.

Animal Cells

  • Animal cells lack a cell wall.

  • The Extracellular Matrix (ECM) is secreted by the cell, serving multiple functions:

    • Provides mechanical and structural support.

    • Facilitates communication among cells (referring to Mina Bissell’s experiments).

    • Offers protection to the cells.

    • Serves as an anchor to cells.

  • Composition of ECM includes:

    • Glycoproteins: Secreted by cells, playing a key role in cell structure.

    • Proteoglycans: Present in connective tissues, providing hydration and structural support.

    • Collagen: The most abundant fibrous protein in ECM, constituting around 30% of the total protein mass.

    • Fibronectin: Binds to integrins and helps organize the ECM.

    • Integrins: Transmembrane proteins that connect cells to the ECM, playing an integral role in various cellular signaling processes.

Cell Adhesions and Junctions

  • In many animal tissues, the ECM separates the cells.

  • In contrast, in certain tissues, the plasma membranes of adjacent cells are in contact.

  • Questions to consider:

    • Why do cells need to be in contact?

    • What functions do these contacts provide?

    • How do cells communicate with one another?

    • Consider the relationship between structure and function relative to cell types and junctions present.

Types of Junctions

  • There are several types of cell junctions characterized by their distinct functions:

    • Tight Junctions

    • Anchoring Junctions

    • Communication Junctions

Tight Junctions

  • Definition: Occluding junctions that connect the plasma membranes of adjacent cells in sheets.

    • Function:

      • Acts as a barrier to prevent small molecules from leaking between the cells, maintaining tissue integrity and functionality.

Anchoring Junctions

  • Definition: Mechanically attach the cytoskeletons of adjacent cells to one another or to the ECM.

    • Significance:

      • These junctions resist mechanical stress, which is crucial in tissues subjected to stretching or pressure.

    • Components:

      • Adherens Junctions: Involve proteins such as cadherins and catenins.

      • Integrins also play a significant role in these junctions.

Communication Junctions

  • Definition: Also known as gap junctions in animals or plasmodesmata in plants.

    • Function:

      • Link the cytoplasm of neighboring cells, permitting the free passage of ions and small molecules between them.

      • Connexons: Specialized protein complexes that form gap junctions in animal cells, allowing communication.

Environmental and Intercellular Signaling

  • Cells receive signals from their environment and from each other, highlighting the importance of communication in cellular functions.

Extracellular Matrix in Mammary Glands

  • Components in Focus:

    • Myoepithelial Cells

    • Luminal Epithelial Cells

    • The acini of mammary glands are noted for their role in milk production.

ECM Staining

  • Staining Observations:

    • Identifies structures such as E-cadherin in cell junctions, significant for evaluating cell junction organization.

    • Quantitative Analysis:

      • The ẞ-Catenin/E-Cadherin Interaction Index highlights quantitative differences in arrangement without providing explicit values in the transcript.

      • Variations in integrin expression were noted between S1 and T4-2 cells.

        • S1 cells: Integrins primarily located on the basal side.

        • T4-2 cells: Higher integrin density (2.8 times more at the surface than in S1).

Investigating Integrin Role in Tissue Formation

  • Questions posed for further investigation include:

    • How would one test the role of integrins in tissue formation?

    • Observations relate to integrin functionality across different cell conditions.

Findings from Integrin Manipulation Experiments

  • Analysis of Cell Treatments:

    • Mock-treated and treated cells (particularly focusing on T4-2 cells under varying integrin conditions).

  • Conclusions drawn from these experimental conditions discuss:

    • Changes in tissue architecture depend critically on both cell identity and their extracellular environment.

    • Structural Adaptability: There is a relationship between structure and function throughout the tissue types.

    • Reversal mechanisms may exist that allow ECM signal alterations to inhibit malignant growth despite preexisting genetic defects.