Cerberus (protein)

Function

Cerberus is an inhibitor in the TGF beta signaling pathway secreted during the gastrulation phase of the embryogenesis. Cerberus (Cer) is a gene that encodes a cytokine (a secreted signaling protein) important for the induction of head formation of vertebrates. The Cerberus gene encodes a polypeptide that is 270 amino acids in length and is expressed in the anterior domain of a gastrula in the endoderm layer. Cerberus also plays a large role as an inhibitory molecule, which is important for proper head induction. Cerberus inhibits the proteins BMP4, Xnr1, and Xwnt8.

This gene encodes a cytokine member of the cystine knot superfamily, characterized by nine conserved cysteines and a cysteine knot region. The cerberus-related cytokines, together with Dan and DRM / Gremlin, represent a group of bone morphogenetic protein (BMP) antagonists that can bind directly to BMPs and inhibit their activity.

In human embryonic development, Cerberus and the protein coded by GREM3 inhibit NODAL in the Wnt signaling pathway during the formation of the germ layers. Specifically, Cerberus and GREM3 act as antagonists to Nodal in the anterior region of the developing embryo, blocking its expression and halting the progression of the primitive node. Orthologs of the gene that codes Cerberus (CER1) are conserved in other non-rodent mammals, indicating that Cerberus has similar functions in other vertebrates.

A Gene knock down experiment was conducted in Xenopus where the amount of Cerberus expressed was decreased by inhibiting translation. The proteins that Cerberus inhibits (BMP4, Xnr1, Xwnt8) concentrations were increased also. It was also shown that just the decrease of Cerberus translation alone was not enough to inhibit the formation of head structures. While the increase of just BMP4, Xnr1, Xwnt8 led to defects in the formation of the head. The increase of BMP4, Xnr1, Xwnt8 and the decrease of Cerberus together blocked the formation of the head. This gene knockdown experiment showed the necessity of Cerberus’ inhibitory functions in the formation of head structures. It quite possibly may be that although Cerberus is necessary for the induction of a head, its inhibitory actions may play a more significant role in ensuring the head is developed properly.

Overexpression or overabundance of Cerberus is associated with the development of ectopic heads. These additional head-like structures may contain varying characteristics of a normal head (eye or eyes, brain, notochord) depending on the ratio of overabundant Cerberus to other proteins associated with anterior development that Cerberus inhibits (Wnt, Nodal, and BMP). If only Nodal is blocked, a single head will still form but with abnormalities such as cyclopia. If both Nodal and BMP or Wnt and BMP are sufficiently inhibited, ectopic, abnormal head-like structures will form. Inhibition of all three proteins by Cerberus is required for the development of complete, ectopic heads.