gastrulaation

Gastrulaation is a term used in embryology to describe the morphogenetic stage during which the blastula reorganizes into a gastrula, establishing the three primary germ layers: ectoderm, mesoderm, and endoderm. The word is sometimes used interchangeably with gastrulation, though some sources reserve gastrulaation for the broader sequence of cellular movements that produces the germ layers and the basic body plan.

During gastrulaation, cells undergo coordinated movements such as invagination, involution, ingression, delamination, and epiboly. These movements result in the formation of the archenteron (the primitive gut) and the internalization and specification of the germ layers. Genetic control involves conserved networks of signaling pathways, including Nodal, BMP, and Wnt signals, and transcription factors that coordinate tissue specification and axis formation.

Modes vary among lineages: in amphibians, endoderm and mesoderm form through involution and archenteron formation; in birds and mammals, epiboly and the primitive streak reorganize cells to generate mesoderm and endoderm from the epiblast; some invertebrates and echinoderms rely more heavily on invagination. In all cases, gastrulaation yields a multilayer embryo with distinct germ layers and established body axes.

Gastrulaation is a central event in development because it establishes the foundations for organ formation and overall body plan organization. Disruptions can lead to major congenital anomalies.

Origin of the term: from gastrula, the stage that follows the blastula. Gastrulation remains the standard term in modern usage, while gastrulaation appears in some texts as an alternative spelling or umbrella concept.