Need for communication Why to communicate/ cordinate 1……. 2……. 3…………. Communication levels Cellular level Tissue Organ level Environment

TYPES OF COMMUNICATION Cell’s direct signaling or intracellular communication Direct cell contacts Extra cellular communication or chemical signaling Paracrine Autocrine signaling Endocrine signaling Synaptic signaling

CELL TO CELL CONTACTS/ JUNCTIONS vertebrates, 3 Types 1. Anchoring Junctions (connect the cytoskeletons of adjacent cells) Desmosomes Hemidesmosomes Adherens Junctions 2. Communicating (GAP) junctions (permit small molecules to pass between cells) 3. Tight Junctions (occluding junctions), create sheets of cells

A: Anchoring Junctions VERTEBRATES A: Anchoring Junctions Anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighbouring cells as well as to proteins in the extracellular matrix . Junction Cytoskeletal Anchor Transmembrane Linker Ties Cell To Desmosomes Intermediate filaments Cadherin Other Cells Hemidesmosomes Intermediate Filaments Integrins EC Matrix Adherens junctions Actin Filaments Cadherin/Integrins Other Cells / the EC Matrix

VERTEBRATES B: Communicating (GAP) junctions Direct chemical communication between adjacent cellular cytoplasm through diffusion without contact of the extracellular fluid. Six connexin proteins, interacting to form a cylinder with a pore in the centre. 2 adjacent cell connexons interact, they form the gap junction channel. Connexon pores vary in size n polarity and therefore can be specific depending on the connexin proteins that constitute each individual connexon Heart muscle, brain, Retinal and skin cells

VERTEBRATES C: Tight junctions Branching network of sealing strands, each acting independently tissue, organ or cell specific combination of proteins of the claudin, occluding, tricellulin and JAM families. Beside transmembrane proteins , a number of cytoplasmatic associated adaptor proteins are present, that mediate the regulation and connection of the tight junctions with the actic cytoskeleton

Efficiency of the junction in preventing ion passage increases exponentially with the number of strands. Regulate the movement of water and solutes between epithelial layers. Tight epithelia like distal convoluted tubule, and the collecting duct part of the nephron in the kidney and the bile ducts ramifying through liver tissue. Leaky epithelia have less complex tight junctions. For instance, the tight junction in the kidney proximal tubule, a very leaky epithelium, has only two to three junctional strands, and these strands exhibit infrequent large slit breaks.

CELL TO CELL CONTACTS/ JUNCTIONS Invertebrates: junctions, for example septate junctions or the C. elegans apical junction. epithelial cells, barrier to solute diffusion through the intracellular space beneath the apical, lumenal surface of the intestinal cells

MULTICELLULAR PLANTS PLASMODESMATA portions of the endoplasmic reticulum are trapped across the middle lamella in newly dividing plant cells eventually becoming (primary plasmodesmata). wall is not thickened further, and depressions or thin areas known as pits are formed Alternatively, plasmodesmata can be inserted into existing cell walls between non-dividing cells (secondary plasmodesmata)