Developmental Changes of the Notochord and its Inductive Effects on the Adjacent Embryonic Germ Layers with Regard to the Role of Glycoconjugates

Notochord is an axial structure derived of embryonic mesoderm and in addition to structural supporting role in inducing nearby germinal layers, it has a basic role in formation of organs such as vertebral column, axial vessels, neural tube and primitive gut. This organ undergoes essential changes during the development process. First, arises from the primitive node and terms notochordal process, while containing a central canal. Then, transforms to notochordal plate and thereafter, changes to a cord called definitive notochord. Finally, it degenerates in centra and remains in intervertebral discs and makes its nucleus pulposus. Glycoconjugates are macromolecules containing carbohydrates that interfere in some biological phenomena such as cell proliferation, differentiation, migration and apoptosis during the development of numerous organs. The terminal sugars of carbohydrate chains are mainly responsible for these duties.  These sugars are identifiable by using some polypeptides derived from plants and animals sources termed lectins. Lectins are linked exclusively to these sugars and the applied technique is called lectin histochemistry. Investigation of the developmental changes of notochord using this technique has shown that different glycoconjugates with divers terminal sugars such as N-acetylgalactoseamine (GalNac), N-acetylclucoseamine (GlcNac), galactose (Gal), fucose (Fuc), mannose (Man) and neuraminic acid (NeuAc) and also Gal-GalNac and GalGlcNac disaccharides are expressed during morphogenesis period in this organ of different animal species. Review of extensive studies carried out on development of notochord and its inductive role on nearby tissues has revealed that it is a highly glycosylated tissue and diverse glycoconjugates with different terminal sugars are expressed in it. Some of these molecules are probably involved in morphological changes of notochord while, the others are present in secreted substances from it and play key roles in its inductive effects on the nearby tissues.