Morphogenesis Flashcards
What are the characteristics of epithelial cells in an embryo?
- Cellularity: they are tightly packed and form a continious layer, creating a barrier between the interior, exterior environment
- Polarity: they have distinct atypical and baso/ateral domains which specialized structures and functions at each end
- Cell-Cell adhesion: epithelial cells are held together by tight junction, adhesion junctions and desmosomes, maintaining the integrity of epithelial layer
What are the typical cell behaviour of an animal (early) embryo?
- Direction and number of cell division
- Cell shape changes
- Cell migration
- Cell growth
- Cell death
- Changes in composition of the cell membrane and secreted products
Do Cadherins and Catenin creare bounderies between tissues?
Yes, Cadherins and Catenin are cell adhesion moleculas what will create boundaries between tissues
Name the 2 cell to cell communication in an Animal Embryo
- Juxtacrine signaling: Direct contact via receptor binding, or binding with ECM. This happens with either homophilic binding (2 receptors that are the same) or heterophilic binding (2 receptors that are different)
- Paracrine signaling: Signaling from a distant
Catenin is internal of the cell; where is Cadherins located?
Cadherins use Catenin as an anchor so Cadherins are located outside of the cell, but are transmembrane molecules, so they go through the membrane
Name the functions of Cadherins
- Their external domains serve to adhere cells togehter
- Catherins link to and help assemble the actin cytoskeleton, thereby providing the mechanical forces for forming sheets and tubes
- Cadherins can initiate and transduce signals that can lead to changes in a cell gene expression
How can the ECM and the corresponding proteins process the developmental signals
ECM: Has 2 important proteins:
1. Proteoglycans: Essential to presenting paracrine factors to cell surface
2. Fribronectin: Is connected to subunit of integrin
Integrins: transmembrane proteins; they bind with 2 proteins that connect with actin (in the cell); alpha actinin and Talin.
Intracellular adaptor proteins: Vinculin, Talin and alpha-actinin –> integrate external signals onto cytoskeleton. This signal might lead to cell adhesion, cell migration and formation of the epithelial sheets
What is the marker for Mesenchymal cells?
Vinculin, because this protein makes the cell move which is also a characteristic of Mesenchymal cells
What is the Spemann organizer?
A region of the embryo which, if transplanted, is able to organize in a secundary twinned body axis Wnt signaling plays a crucial role in generating the Spemann organizer
What is the molecular mechanism in the Organizer that drives development?
Cells on the ventral (left side) of the blastula secrete a variety of proteins such as BMP4. These induce the ectoderm to become epidermis. If their action is blocked, the ectoderm cells are allowed to follow their defult pathway, which is to become nerve tissue. The spemann organizer block BMP4 by secreting Chordin and Noggin. Both these molecules are able to bind BMP4 to inhibit it.
Explain the development of vulva in the C. elegans
You have the Anchor cell (on top) and beneath you have 6 cells. Straight under the Anchor cell, you have P6-p. On the left of P6-p, there is P5-p and on the right of P6-p, there is the P7-p cell. There are also 3 outer cells. On the right side of P7-p, you have P8p, and on the left of P5p, you have P4p and P3p. The anchor cell secretes LIN-3 what will activate P6p, and over gradient also the other cells.
What happens when the Wnt signaling pathway is OFF VS ON?
Wnt signal pathway off: If the Wnt protein doesnot bind on the receptors Frizzled and LRP’s, the protein Dishevelled will not get activated, and the APC domain will stay activated. If the APC is activated, beta-catenin will gets ubiquitiled and degraded which will not lead to gene expression
Wnt signal pathway on: A Wnt protein binds to the frizlled receptor, and the receptor LRP will bind to the frizzled. Due to phosphorylation, Dishevelled protein will bind, which will lead to the construction of APC complex and part of that structure will bind to the activated receptors Frizzled and LRP. Beta-catenin will not be degraded, which will translocate to the nucleus. One in the nucleus, it will bind to the TF and the inhibitor protein Groucho will leave. Now the Wnt target proteins will get expressed. These genes are important for cell proliferation, cell migration, cell polarization
What happens if APC is not present in the cell (or mutated)?
Too much proliferation when it shouldn’t
What is morphologenesis?
Process by which the many individual cells within developing embryo move around and organize themselves to eventually form the specialized and complex structures/organs/systems that make up that organism
