Introduction

• Amoeba is a genus of protozoa that can be found in freshwater environments.
• They possess pseudopodia, which are used for motility.
• The pseudopodia can be extended and retracted to move in any direction.
• Understanding the molecular mechanisms that underlie pseudopodial extension and retraction is crucial for understanding the physiology of amoeboid cells.

Actin Cytoskeleton

• The actin cytoskeleton is a key component in the molecular basis of pseudopodial extension and retraction in amoeba.
• Actin filaments are polymerized at the leading edge of the pseudopodia and depolymerized at the trailing edge.
• This process is regulated by the coordinated activity of actin-binding proteins, such as actin-related protein 2/3 complex (Arp2/3) and formins.
• Arp2/3 complex nucleates the formation of new actin filaments at the leading edge, while formins promote the elongation of existing actin filaments.

Membrane Protrusion and Retraction

• The movement of the plasma membrane is closely linked to the actin cytoskeleton during pseudopodial extension and retraction in amoeba.
• The protrusion of the plasma membrane is driven by the actin-dependent formation of a cup-like invagination called a phagosome.
• Retraction of the plasma membrane is driven by the actin-dependent formation of a tubular structure called a pseudopod retraction fiber.
• The coordinated activity of phosphoinositide-dependent kinase 1 (PDK1) and the Rho-family GTPase, Rac1, regulates the formation of phagosomes and pseudopod retraction fibers.

Conclusion

• The molecular basis of pseudopodial extension and retraction in amoeba is controlled by the actin cytoskeleton and the coordination of actin-binding proteins such as Arp2/3 and formins.
• The protrusion and retraction of the plasma membrane is driven by the actin-dependent formation of phagosomes and pseudopod retraction fibers, respectively.
• Understanding these molecular mechanisms can provide insight into the physiology of amoeboid cells and the mechanisms of cell motility in general.