Gastrulation and Primitive Streak Formation Quiz

The primitive streak, a thickening along the epiblast, marks the beginning of gastrulation, not its end. Gastrulation is a complex process that involves the formation of germ layers and the establishment of the body axes. The primitive streak formation signifies the start of this crucial developmental event.

The primitive streak, visible as a narrow groove on the epiblast, can be observed in a 15- to 16-day embryo. This streak is a key feature of early embryonic development and provides the foundation for the formation of the three germ layers (ectoderm, mesoderm, and endoderm). As gastrulation progresses, the primitive streak elongates and shrinks, eventually disappearing.

Fibroblast growth factor 8 (FGF8) plays a crucial role in gastrulation by regulating cell migration and specification. It acts as a signaling molecule that directs cells to their appropriate locations during embryonic development. The specific mechanism involves the downregulation of cell adhesion proteins, allowing cells to detach and migrate.

The cephalic end of the primitive streak, the region that forms the anterior portion of the embryo, is known as the primitive node. This node serves as a signaling center, directing various developmental processes, including the formation of the notochord and the establishment of the body axes. The primitive node is a vital landmark during early embryonic development.

FGF8, a protein that acts as a signaling molecule, is crucial in controlling cell movements during gastrulation. It achieves this by downregulating cell adhesion proteins like E-cadherin, which normally keeps cells bound together. The reduction in E-cadherin allows cells to detach and migrate, following the FGF8 signaling gradient.