CONSTRUCTION OF THE VERTEBRATE HEAD
Role of neural crest
Are highly pluripotent cells
Plays a critical role in the development of vertebrate head
Facial mesenchyme (unlike other parts of the body) is derived from neural crest cells
Neural crest cells migrate throughout the embryo in four overlapping domains cephalic, trunk, sacral and cardiac.
Cephalic neural crest migrate from posterior midbrain and hindbrain into brachial arch system.
Neural crest cell interact with epithelial and mesodermal cell populations within the branchial arches
Formation of bones, cartilages, connective tissue
Axial level specific code exist
Genes are involved in these steps of embryogenesis as encoding a set of instructions or rules of assembly. Implementation of these rules via gene expression and protein interaction produces the three dimensional embryo (Thorogood and Ferretti, 1992)
Construction of Drosiphilia
Head, 3 thoracic segments, 8 abdominal segments and a tail.
Once these basic segments have been established a group of genes called HOMEOTIC GENES specify their characteristic structure.
HOMEOTIC GENES are characterised by the presence of a highly conserved 180 basepair sequence called the HOMEOBOX