6. During development homing of cell is mediated by
   (1) Integrin (2) Laminin
   (3) Cadherin (4) Selectin

Introduction: What Is Cell Homing?

Cell homing is the highly regulated process by which cells migrate to and engraft at their appropriate locations during embryonic development and tissue repair. This step is critical for the effective organization of tissues and organs, ensuring each cell reaches its functional destination.​

Integrins: The Key Players in Cell Homing

Integrins are transmembrane receptors that connect the inside of a cell with the extracellular matrix (ECM). They play a central role in the later stages of homing by mediating firm adhesion and transmigration of cells across vessel walls, as well as anchoring cells to their proper tissue niches. The most studied integrin in homing is VLA-4 (α4β1α4β1), which binds to VCAM-1 on endothelial cells, facilitating cell adhesion and entry into tissues.​

• Integrins are required for the migration, stable adhesion, and tissue anchoring of homing cells.​

• Blocking integrin function impairs the homing and engraftment of stem cells, demonstrating their necessity.​

Selectins and Other Molecules: Supporting Roles

Selectins assist in the very first contact by mediating the rolling or tethering of cells along the endothelium, but do not provide the strong adhesion required for transmigration and tissue integration. Cadherins are more critical for later cell-cell adhesion within tissues, and laminin is a major ECM component rather than a direct mediator of homing itself.​

• Selectins facilitate initial rolling, but integrins are required for subsequent arrest and migration.​

• Laminin serves as an ECM ligand for certain integrins but is not the adhesive molecule directly responsible for homing.​

Cell Homing Steps

1. Tethering and Rolling: Selectins mediate the initial loose interactions as cells roll along blood vessel surfaces.​

2. Activation: Chemokines activate integrins on the migrating cells.

3. Arrest and Firm Adhesion: Integrins bind to their ligands (such as VCAM-1), causing cells to halt and adhere firmly.​

4. Transmigration: Cells migrate through the vessel wall using integrin-mediated interactions.​

5. Tissue Migration and Engraftment: Integrins continue to guide cells as they anchor to their tissue niches in response to the ECM.​

Key Table: Role of Molecules in Homing

Conclusion

• Integrin is the essential molecule responsible for mediating the homing of cells during development through firm adhesion, transmigration, and anchoring at target sites.​

• Selectins, cadherins, and laminin play supporting or different roles in adhesion processes but are not the main mediators of homing during embryogenesis and tissue formation.​