Apical constriction

Apical_constriction

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  Apical constriction

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  Apical constriction figure 1

• Apical constriction mechanisms. Filamentous actin is represented in red, and myosin in orange.

• Apical constriction figure 2

Apical Constriction

Apical constriction is a cellular process that plays a crucial role in morphogenetic movements during embryonic development. It involves the contraction of the apical side of epithelial cells, leading to changes in cell shape and tissue structure. This process is essential for various developmental events, including gastrulation, neurulation, and the formation of the neural tube.

Mechanism

Apical constriction is driven by the actomyosin cytoskeleton, which consists of actin filaments and myosin motor proteins. The contraction of the actomyosin network at the apical surface of the cell leads to a reduction in the apical surface area. This is often regulated by signaling pathways that control the activity of myosin light chain kinase and other proteins involved in cytoskeletal dynamics.

The process begins with the recruitment of actin filaments to the apical cortex of the cell. Myosin II motors then interact with these filaments, generating contractile forces. The contraction is often pulsatile, with cycles of contraction and relaxation, which gradually lead to a permanent change in cell shape.

Biological Significance

Apical constriction is a key mechanism in several developmental processes:

• Gastrulation: During gastrulation, apical constriction helps drive the invagination of epithelial sheets, forming the primitive gut and establishing the three germ layers: ectoderm, mesoderm, and endoderm.

• Neurulation: In neurulation, apical constriction contributes to the bending of the neural plate, facilitating the closure of the neural tube, which will eventually form the central nervous system.

• Organogenesis: Apical constriction is also involved in the shaping of various organs and tissues, such as the formation of the optic cup and the inner ear.

Molecular Regulation

The regulation of apical constriction involves several signaling pathways and molecular players:

• Rho GTPases: These small GTP-binding proteins, such as RhoA, are critical regulators of the actin cytoskeleton and are involved in the activation of myosin II.

• Myosin Light Chain Kinase (MLCK): This enzyme phosphorylates the regulatory light chain of myosin II, enhancing its motor activity and promoting contraction.

• Adherens Junctions: These cell-cell junctions, composed of cadherins and catenins, provide mechanical linkage between cells and are important for coordinating apical constriction across a tissue.

Related Pages

• Gastrulation
• Neurulation
• Actin
• Myosin
• Rho GTPase