Question

Explain the roles of phosphatidylinositol, small monomeric GTPases, phospholipase C, and PI3K in the determination of polar movement of a mammalian cell. Specifically, note how phospholipid gradients are established, where you might find Cdc42, RhoA, and Rac1 during polarized cell movement (e.g. in response to a chemoattractant), and how PLC and PI3K compete to determine these gradients.

Answer 1

The role of phosphatidylinositol,small monomeric GTPases,phospholipase C and PI3K:

• The phosphatidylinositol is localised in the inner half of the plasma membrane.Although it is a minor component,it plays important role in cell signalling during the polar movement in mammalian cells.
• These small monomeric GTPases are involved in endocytosis or exocytosis in mammalian cells.These are also actively involved in the mammalian cell shape,polarity and movement.
• The role of Phospholipase C is,it cleaves an inositol in the cytosolic monolayer of the plasma membrane to generate two fragments.One of the fragment is useful in the activation of kinease C.
• The Pi3K is activated in response to the extracellular signals and help to recruit specific intracellular signalling proteins.
• The mechanism of phospholipids transport occurs between organelles via through a spontaneous membrane diffusion.Thus the phospholipid gradient is established.
• In mammals,Rho GTPase is consisting of 32 members which can be divided into 8 subgroups.In the group of 8 is the Cdc42,Rac1,RhoA.These promote the growth of actin.These are found in the polarised cell during chemotaxis and when a cell determines the direction of signal pathway.
• The chemotaxis is achieved by coupling gradient sensing to basic cell movement.PLC and PI3K are not mediators of chemotaxis.But the PLC mediates the regulation of activity of PI3K.