The Roles of Cell to Cell Communication in Development Lange BIOL 370 – Developmental Biology Topic #3

Morphogenesis is one of the major outstanding problems in the biological sciences. It concerns the fundamental question of how biological form and structure are generated. Morphogenesis encompasses a broad scope of biological processes. It concerns adult as well as embryonic tissues, and includes an understanding of the maintenance, degeneration, and regeneration of tissues and organs as well as their formation.

Reaggregation of cells from amphibian neurulae A study that illustrates that even in this early stage, the presumptive cells have already differentiated in ways that allows them to segregate following experimental disaggregation.

Sorting out and reconstruction of spatial relationships in aggregates of embryonic amphibian cells In this classic study by Townes and Holtfreter (1955), it is shown that a variety of different disaggregated cells lines will display enough differentiation to segregate into separate structural cell groupings.

Aggregates formed by mixing 7-day chick embryo neural retina cells with pigmented retina cells This experimental mixture shows how the segregation can visibly begin to be seen after even just 5 hours (B) and is very obvious and clear after 19 hours (C).

In physics, the dyne is a unit of force. One dyne is equal to 10 µN (micronewtons). Equivalently, the dyne is defined as "the force required to accelerate a mass of one gram at a rate of one centimetre per second squared. In developmental biology, “dynes per centimeter” are units traditionally used to measure surface tension. For example, the surface tension of distilled water is 72 dyn/cm at 25 °C (77 °F). Water displays cohesion (surface tension), but this cohesion varies based upon other physical factors such as solute concentrations and temperature.

Hierarchy of cell sorting in order of decreasing surface tensions In this segregation series, cells that aggregate more towards the interior have a greater surface tension score (dyne/cm) than do the cells in the outer later. These differences in surface tension suggest one mechanism by which differentiation may proceed.

Cell junctions can impact adhesion relationships between tissues as well. For developmental effects, cadherins can play an especially crucial role. Interlocking junctional proteins Intercellular space Intercellular space Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Plaque Linker glycoproteins (cadherins) Intermediate filament (keratin) Intercellular space Channel between cells (connexon) (a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space. (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. (c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication.

Cadherin-mediated cell adhesion

Importance of the amount of cadherin for correct morphogenesis

Importance of the amount of cadherin for correct morphogenesis (Part 1)

Importance of the amount of cadherin for correct morphogenesis (Part 2)

Importance of the types of cadherin for correct morphogenesis

Importance of the types of cadherin for correct morphogenesis (Part 1)

Importance of the types of cadherin for correct morphogenesis (Part 2)

Ventral furrow formation during Drosophila gastrulation internalizes the cells that will become the mesoderm

Getting mesodermal cells inside the embryo during Drosophila gastrulation by regulation of the cytoskeleton

Tracheal development in Drosophila

Schematic diagram of induction of the mouse lens (Part 1)

Schematic diagram of induction of the mouse lens (Part 2)

Schematic diagram of induction of the mouse lens (Part 3)

Genetic specificity of induction in amphibians

Sonic Hedgehog is one of three proteins in the mammalian signaling pathway family called hedgehog. It plays a key role in regulating vertebrate organogenesis, such as in the growth of digits on limbs and organization of the brain and neural pathways.

Hedgehog signal transduction pathway

Hedgehog signal transduction pathway (Part 1)

Hedgehog signal transduction pathway (Part 2)

(A) Sonic hedgehog expression is shown by in situ hybridization in the nervous system, gut, and limb bud of a chick embryo. (B) Head of a cyclopic lamb

Apoptosis pathways in nematodes and mammals Apoptosis – programed cell death that is needed for many types of organ development. The mammalian brain is an especially well known instance of widespread apoptosis.

Disruption of normal brain development by blocking apoptosis

C. elegans vulval precursor cells and their descendants (Part 1)

C. elegans vulval precursor cells and their descendants (Part 2)

Model for the generation of two cell types from two equivalent cells in C. elegans

Extracellular matrices in the developing embryo

Role of the extracellular matrix in cell differentiation

Basement membrane-directed gene expression in mammary gland tissue

Basement membrane-directed gene expression in mammary gland tissue (Part 1)

Basement membrane-directed gene expression in mammary gland tissue (Part 2)

End.