Neurula

[2] In addition to development of the neural tube, other processes occur in a neurula stage embryo depending on the species.

[8] The point at which the embryo reaches the neurula stage differs among species, while for oviparous organisms, the length of neurulation is additionally affected by incubation temperature.

Reptiles, including crocodiles, lizards, and turtles, tend to spend a longer time in the neurula stage.

Somites, in turn, give rise to vertebrae, ribs, skeletal muscle, cartilage, tendons, and skin.

Following involution at the mid-gastrula stage, the IMZ undergoes convergent extension, in which the lateral regions narrow and move towards the midline and the anterior end lengthens.

The NIMZ, which does not involute, simultaneously extends in the opposite direction and at a greater rate to cover regions no longer occupied by the IMZ.

The convergent extension of the IMZ and NIMZ begins in the second half of gastrulation and continues into the late neurula stage.

Notochordal cells become arranged in a formation representing a stack of coins in a process termed circumferential intercalation.

Additionally, within the reptilian neurula, tissues of the brain begin to differentiate and the heart and blood vessels start to form.

[2] Mouse neurula tissues divide rapidly, with an average cell cycle lasting 8–10 hours.

Proteoglycans in the extracellular matrix (ECM) of neurula-stage cells play an important role in promoting functional cranial neurulation and neural fold elevation; hyaluronic acid (HA) is synthesized and becomes accumulated, while the cell maintains a low level of sulfated glycosaminoglycans (GAGs).

Signaling molecules such as Wnts, FGFs, and BMFs along with the transcription factors that include Msx, Snails, Sox8/9/10, and Pax3/7 genes play key roles in neural crest formation.

[7] In mouse embryos Pax3 blocks the tumor suppressor gene p53, which is necessary for controlled proliferation and genomic stability, is expressed in all cells of the neurula.

[7] Neural crest defects were found to occur in mouse and human Pax3 mutants, indicating an importance of functionality.

[14] The gene Apolipoprotein B, which is involved in transporting and metabolizing fat soluble molecules in the blood, is expressed in the yolk sac and fetal liver.