Apical constriction

Apical constriction is a fundamental process in morphogenesis that involves the narrowing of cell apexes to facilitate the bending of epithelial sheets. This process is crucial in the formation of various structures during embryogenesis, including the neural tube, the heart tube, and the gut tube.

Mechanism

The mechanism of apical constriction involves the contraction of actomyosin networks, which are located at the apical surface of the cell. This contraction is regulated by RhoA, a small GTPase, which activates Rho-associated protein kinase (ROCK). ROCK, in turn, phosphorylates myosin light chain (MLC), leading to the activation of myosin II and the subsequent contraction of the actomyosin network.

Role in Morphogenesis

Apical constriction plays a pivotal role in the morphogenesis of various tissues and organs. For instance, during gastrulation, apical constriction of cells in the blastopore region leads to the invagination of the endoderm and mesoderm. Similarly, in the formation of the neural tube, apical constriction of neuroepithelial cells results in the bending of the neural plate, leading to the formation of the neural groove and eventually the neural tube.

Regulation

The regulation of apical constriction is complex and involves various signaling pathways. Key regulators include planar cell polarity (PCP) pathway, Wnt signaling pathway, and Hedgehog signaling pathway. These pathways regulate the localization and activity of RhoA, thereby controlling the contraction of the actomyosin network.

Clinical Significance

Abnormalities in apical constriction can lead to various developmental disorders. For example, defects in neural tube closure due to impaired apical constriction can result in neural tube defects such as spina bifida and anencephaly.