ホメオティック遺伝子
Segmentation in the hind-brain and paraxial mesoderm is highly regulated by the expression of the Hox gene. Hox genes encode helix-turn-helix transcription factors and play the major role in specifying the positional identities for tissues along the anterior-posterior axis (A-P axis) during the developmental phase. Humans, like other vertebrates have a total of 39 Hox genes organized into four different clusters. The property of Hox genes called colinearity, whereby the gene arrangement, timing and the boundaries of expression on the A-P axis are correlated, is instrumental in the development of ordered domains of expression. The Hox gene expression leads to the development of unique combination codes for the different segments that specify their distinct identity. Even though the development of segmentation in the hind-brain and paraxial mesoderm are distinct, the Hox expression in both system are coordinated with the process of morphological segmentation.