practical 1 - morphogenesis Flashcards
what are the 2 type of molecules that help mediate connections between cells?
1) Cell-cell adhesion molecules
2) Cell-matrix adhesion molecules
what is the property of the cell membrane that prevents cells from spontaneously attaching to each other?
The cell membrane has a negative net charge which acts as a repelling force when 2 cells get near each other, pushing them away from one another. This prevents cells from spontaneously fusing into one large mass of cells
Cells simply do not fuse their membranes together because of the hydrophobic core of the phospholipid bilayer, which is thermodynamically unstable. Fusing membranes together would cost energy.
what are the 3 main types of cell-cell adhesion connections?
1) ADHERENS JUNCTIONS: mediated by cadherins that adhere to each other, allowing membranes to align. Inside the cell, cadherin is connected to catenin (in the cytoplasm), which connects to the actin bundles of the cytoskeleton. They are dependent on concentration of Ca present in the cell.
2) DESMOSOMES - also mediated by cadherins in a similar fashion. The difference is that cadherins are now bound to intermediate filaments such as keratin. They are also Ca dependent and are stronger than adherens junctions.
3) Ca - INDEPENDENT ADHESIONS - use protein such as those from the immunoglobulin superfamily such as neural cell-adhesion molecule (N-CAM). They have an intracellular and an extracellular domain
What are other types of cell-cell connections?
GAP JUNCTIONS, TIGHT JUNCTIONS
How does cell shape change through the establishment of cell-cell interactions during compaction?
Cells are not amorphous entities. They have certain shapes that change.
Outer side = apical side experiences less or no cell-cell contact
More inside = Basal side experiences many cell-cell contacts
What is the role of the actomyosin network in regulating cell shape?
The actomyosin network has contractile properties, which allow for the bending of tissues. It can contract and make the circumference of the cell at one end smaller. This process is basically called apical constriction.
How does the Hippo pathway work in regulating polarization of cells?
The Hippo pathway acts as a mechanosensing system that transmits effects of forces to the cell’s transcriptional machinery. It is activated by high surface tension.
Cells have developed a polarity. Depending on the cleavage plane, daughter cells inherit more or less of the apical cortex. This creates differences in surface tension and cell-cell interaction between daughter cells.
Cells with higher surface tension will switch on the Hippo pathway, which leads to degradation of Yap/Taz transcriptional effector and Cdx2 is not expressed, while Oct4 is expressed inside.
what happens during EMT? (epithelia-to-mesecnchymal transition)
The adherens junctions must change: their strength must decrease in order to go from epithelium to mesenchyme (cells in mesenchyme are more loosely connected)
what is the difference between CONVERGENT EXTENSION and EPIBOLY?
CONVERGENT EXTENSION = intercalation of cells in a direction perpendicular to the direction in which the structure lengthens
EPIBOLY = intercalation of cells underneath the layer; the top layer is spread in all directions
