BCA lecture 2 Flashcards
Morphogenesis
a process which regulates how the cells move or change
epithelial and mesenchymal
Epithelial
Function:
Specialized cells:
To cover surfaces of sheets of tubes
Morphology:
- Adhesive to one another
- Static
Mesenchymal
Function:
Not a defined function (yet)
Morphology:
- Not necessarily adhesive to other cells
- Can migrate individually or collectively
juxtacrine signalling
direct cell to cell signalling. Through proteins that are secreted from a cell and designed to communicate a response in another cell that is generally referred to as signalling proteins, or ligands, while the proteins within a membrane that function to bind either other membrane-associated proteins or signalling proteins are called receptors.
experimental analysis of morphogenesis arguably began in 1955 when Townes and Holtfreter
this experiment explains the different cell affinities towards each other. They mixed dissociated epithelial cells and neural plate cells resulting in segregation of both cells forming 2 different tissues. The same also happened with other types of cells concluding that selective affinities change during development. For development to occur, cells must interact differently with other cell populations at specific times. Such changes in cell affinity are extremely important in the processes of morphogenesis.
Cadherin and catenin
calcium-dependent adhesion molecules. Transmembrane proteins that interact with other cadherins on adjacent cells
Keep Cadherin anchored inside the cells
proteoglycans and fibronectins
both are ECMs that are crucial for cell to cell interactions
proteoglycans are large extracellular proteins that have sugars attached to them. they are essential to presenting paracrine factors to cell surface
fibronectins are very large proteins which aggregate forming fibrils. It function as intermediary adhesive molecule
integrins
Receptors for extracellular matrix molecules. They have a quaternary structure made of two subunits: α- and β- subunit. Intracellularly, they bind with two proteins that connect with actin cytoskeleton: α-Actinin and Talin
EMT
a process in which epithelial cells lose their cell-cell adhesion and polarity and acquire a mesenchymal phenotype, characterized by increased mobility and the ability to invade surrounding tissues.
what are the 2 major EMT transcription factors?
twist and snail. Both when activated causing the downregulation of cell adhesion molecules such as cadherins and the upregulation of of proteases, such as the matrix metalloproteinases MMP2 and MMP9, thus enhancing ECM protein degradation and enabling invasion
how are the 2 major transcription factors in EMT is ùsed in cancers?
twist and snail is activated in an uncontrolled manner causing the cancer cells to be able to migrate and invade surrounding or other tissues (metastasis)
paracrine signalling
a type of cell signalling in which a cell secretes signalling molecules (such as cytokines, growth factors, and neurotransmitters) that diffuse locally and affect nearby target cells. Cells can be also relatively distant from each other, in this case, communication is mediated by a so-called long-range distance signalling (ligands binding to a specific receptor).
explain the primary embryonic induction experiment by Spemann-mangold
they transplanted an ‘‘organizer’’ from a donor embryo into another embryo, resulting in the formation of another head, asking the question How can neural cells arise where skin cells are supposed to be? this is 1st example to show that development occurs through a cascade of cell-cell interactions (Paracrine signaling)
mention the molecules that are secreted by the organizer during early development
organizer secrets morphogens (genes that works during morphogenesis) such as chordin, noggin, etc which inhibits BMP4 (causing different cell fate)
explain the french flag model of pattern formation
a concept in developmental biology that describes how different levels of morphogen concentration can result in different cell fates in a developing organism. The threshold refers to a specific concentration of the morphogen above which a certain developmental outcome is triggered
explain C. elegans vulva development with a regard towards both juxtacrine and paracrine signalling
the vulva development starts from the 6 vulva precursor cells (p3-8). the paracrine signalling refers to the Lin3 ligands that are expressed by the anchor cell and received by LET23 receptor in the VPCs in a way that the cells had different fates (refer to french flag model, P6.p always acquire a primary fate. P5.p and P7.p always a secondary fate, while P3.p, P4.p and P8.p always acquire a tertiary fate). Lin3 binding towards LET23 causing Ras/MAPK pathway to be activated.
in regards to juxtacrine signalling, after the Lin3 is recognized by the LET23 the cells activate alternative signalling which expresses delta proteins that are received by notch proteins from other cells causing the inhibition of Ras/MAPK pathway resulting in the activation of is RGL-1/RAL1 pathway stimulating the secondary fate formation
