Convergent extension

[1] This process plays a crucial role in shaping the body plan during embryogenesis and occurs during gastrulation, neurulation, axis elongation, and organogenesis in both vertebrate and invertebrate embryos.

[2] Convergent extension has been primarily studied in frogs and fish due to their large embryo size and their development outside of a maternal host (in egg clutches in the water, as opposed to in a uterus).

Elongation continues through the neurula and tailbud stages…As these involuted dorsal mesodermal tissues converge and extend on the inside of the gastrula, the presumptive posterior neural tissue converges and extends on the outside of the embryo, parallel to the underlying mesoderm, and then rolls up to form the neural tube, which later forms the hindbrain and spinal cord of the central nervous system".

[2] Should convergent extension be interrupted or incomplete, the resulting organism will have a short anteroposterior axis, wide notochord, and broad, open neural tube.

[1] In addition to the non-canonical Wnt and PCP pathways involvement in convergent extension, the down-regulation of certain cell-cell adhesion molecules, such as C-cadherin and fibronectin/integrin interactions, may also play a role.