1. Tissues
Chapter 13

2. Differential Cell Affinities
Cells alter cell surface during development to change affinities.
This allows different interactions and movements.
Cell surface interactions determine strength and specificity of cell-cell binding.
Also involves the cytoskeleton and extracellular matrix (ECM).

3. Remove different regions of embryo.
Dissociate cells using alkaline solution and mix together.
Cells sort out according to type.
Final position reflects original position

4. Thermodynamic Sorting ModelB
Thermodynamic Sorting Model
If A-A adhesion is stronger than A-B or B-B, A cells will be in the center with B on the outside.
If A-A is equal to A-B there will be no sorting out
If A-A and B-B are MUCH GREATER than A-B they will separate out.

5. Cells and Tissues Cells are arranged as tissues
Tissues are held together by cell adhesion molecules (CAMs).
Cadherins
IgSuperfamily CAMs
Integrins
All are transmembrane proteins

6. Cell Adhesion Molecules
Cadherins
IgSuperfamily CAMs
Appendix A.7
Integrins

7. Cell Adhesion Molecules Cadherins
Ca++-dependent adhesion molecules.
Single-pass transmembrane glycoproteins
Homophilic binding--bind to the same type on other cells
Cytoplasmic region interacts with the actin cytoskeleton via proteins called catenins.
Examples:
E cadherin– mainly epithelial
N cadherin– mainly neural
P cadherin-- placental

8. Integral Membrane Proteins

9. Cell Adhesion Molecules Ig Superfamily CAMs
Ca++-independent adhesion molecules.
Single-pass transmembrane glycoproteins; extracellular region has disulfide loops similar to Igs.
Many show homophilic binding
Example:
N CAM
L1 CAM

10. Cell Adhesion Molecules Integrins
Heterodimers of alpha and beta chains
Act as receptors for extracellular matrix (ECM) molecules
Associate with the cytoskeleton on the inside
Transmit information about the outside to the inside for a response (cell movement, cell shape, differentiation, etc.)

11. Cell Junctions Tight junctions Desmosomes and Adherens junctions
seal epithelial cells to prevent molecules moving between cells
polarize cells (apical and basal sides different)
Desmosomes and Adherens junctions
Include cadherins to hold cells together
Gap Junctions
Allow cell-cell communication

13. Epithelial Tissues
Sheets of cells with an underlying basement membrane (basal lamina)
Cells have polarity-- basal side by basement membrane and apical side opposite.
Tight junctions prevent leakage between cells and maintain membrane polarity
Adherens junctions and desmosomes contain CAMS to hold cells together.
Adherens junctions and hemidesmosomes also hold cells to basement membrane

14. Epithelial Tissues
Fig 13.1

15. Epithelial Tissues May be derived from any tissue layer
Most coverings are ectodermal
Epithelial linings such as intestines are endodermal
Some sheets of muscle are epithelial

16. Types of Epithelial Tissue
Fig 13.2

17. Types of Epithelial Tissue
Simple epithelial--single layer
Stratified- multiple layers
Pseudostratified-- looks like multiple layers but each cells extends from apical to basal

18. Types of Epithelial Cells
Cuboidal
Squamous-- flattened
Columnar

19. Types of Epithelial Tissue
Fig 13.2

20. Epithelial Glands Many epithelial tissues form glands
Glands may be simple or branched
Exocrine glands secrete into ducts
Endocrine glands secrete hormones into the bloodstream or surrounding tissue.
Examples?
Exocrine– sweat glands, salivary glands, mammary glands, liver—bile, pancreas—digestive enzymes into small intestine
Endocrine– hormones; adrenal glands, thyroid glands, pituitary, hypothalamus, etc.pancreas-- insulin

21. Connective Tissues
Consist mainly of fibroblast cells and the extracellular matrix they secrete (and sometimes other cells).
Most are of mesodermal origin
Dermis of the skin
Adipose tissues
Cartilage
Bone
Blood (sometimes considered separately)

22. Connective Tissues
Collagen is most common extracellular matrix of connective tissues
Also hyaluronan, fibronectins, elastins, and proteoglycans

23. Collagen Main component of ligaments and tendons
Great tensile strength and elasticity
Consists of woven fibers

24. Fibronectin
Fibronectin in the extracellular matrix binds to integrins which are associated with actin filaments of the cytoskeleton.

25. Muscle Tissues
Fig 13.3

26. Muscle Tissues Skeletal formed from myotome of somites
Consist of multinucleate myofibers formed from fusion of myocytes
Arranged as sarcomeres which appear striated
Voluntary muscles

27. Muscle Tissues Smooth Cardiac From lateral plate mesoderm
Surround blood vessels, intestines, ducts from some glands
Mononucleate cells, not arranged as sarcomere
Cardiac
Heart muscle, also from lateral plate
Consists of individual cells held together by junctions
Has myofibers and is striated.

28. Muscle Tissues
Fig 13.3

29. Neural Tissue

30. Neural Tissue
Neural tube is induced by notochord in the ectoderm and forms as a neuroepithelium.
Neural tube cells form neurons and glial cells
Neurons send impulses; glial cells are support cells
Neural crest cells migrate from the neural folds to form many different kinds of cells

31. Blood Vessels
Fig 13.4

32. Circulatory system Sometimes considered connective tissue
Hematopoietic stem cells produce many types of blood cells
Arteries and veins consist of
inner endothelial layer
a smooth muscle layer
Outer fibrous connective tissue layer
Capillaries are a single cell layer thick with endothelial cells and a basal lamina.

33. Examples of importance of change in cell adhesion
1º and 2º mesenchyme cells of sea urchins
Compaction
Formation of the neural tube

34. Examples of importance of change in cell adhesion
1º and 2º mesenchyme cells of sea urchins
1º lose affinity for hyaline and each other and gain affinity for ECM components
2º gain affinity for fibronectin
Compaction
Formation of the neural tube

35. Examples of importance of change in cell adhesion
1º and 2º mesenchyme cells of sea urchins
Compaction
Formation of the neural tube

36. Compaction involves rearrangement of CAMs (E Cadherins) to sites of cell-cell contact-- holds cells tightly together.

37. Examples of importance of change in cell adhesion
1º and 2º mesenchyme cells of sea urchins
Compaction
Formation of the neural tube

38. Neural tube separates out from the epidermis above it.

39. Neural tube tissue stops expressing E-cadherins and begins expressing N-CAMs and N-cadherins.
If expression of CAMs is experimentally manipulated, the tube will not sort out correctly.