NODAL

Role in the organism:

Although the human body on the outside looks bilaterally symmetrical, many of our internal organs are lateralized (either on the left or on the right). For example, the heart, liver, digestive organs and spleen are all on one side, and the lungs have different numbers of lobes on each side of the body (the lungs do not have the same number of lobes). Since we all originate from a single cell, then there must be a point in embryonic development when the human embryo first shows signs of left to right asymmetry. The first physical sign is the asymmetrical position of the heart. Prior to this, however, several genes are expressed either on the left or right side of the embryo, including NODAL, which is only expressed on the left side of the embryo. The NODAL gene encodes a signaling protein that activates certain transcription factors, activating the transcription of genes whose expression they control - but only on the left side of the embryo.

Role in the disorder (state):

Mutations in the NODAL gene alternate with the lateral organization of the organ, a condition known as situs ambiguus. Mutations in other genes, including the LEFTA and LEFTB genes (on chromosome 1), also cause situs disorders by altering the expression pattern of the NODAL gene. This indicates that the function of LEFTA and LEFTB proteins is to establish expression of the NODAL gene in the embryo.