Cyclopia Research Paper

Cyclopia is a malformation that involves a lack of splitting of the single eye field into two bilateral eye fields and is typically accompanied by a non-functioning proboscis dorsal to the eye. This malformation is typically caused by a deficiency in midline shh signaling from the brain in which there is an incomplete cleavage of prosencephalon into the left and right hemispheres which occurs sometime between the 18th and 28th day of gestation. The primary defect is the lack of forebrain tissue which is impacted by a lack of sonic hedgehog signaling which causes the facial defects. During the 4th week of gestation, the neural tube gives rise to the three primary brain vesicles prosencephalon, mesencephalon, and rhombencephalon. In the 5th week of gestation, the prosencephalon divides into the telencephalon and …show more content…
Cyclopia is a part of holoprosencephaly disorders which result from the failure of the forebrain to develop properly. Cyclopia presents as alobar holoprosencephaly which is the most severe form and one characterization of such a disorder is the lack of midline structures. The lack or abundance of tissue in the midface, prevents the two nasal primordia from joining the midline. When shh is expressed by the prechordal plate and ventral midline of the diencephalon, it causes Pax-6 expression in the midline to become repressed causing the single eye field to split into two separate eye fields on either side of the diencephalon. Rax a retina and anterior neural fold homeobox and Six-3, another important transcription factor, protect the ability of the forebrain to express shh by suppressing Wnt signaling. When Wnt is active and not suppressed, it enabled the anterior region of the brain that is developing to become posteriorized and unable to secrete shh. The lack of Six-3 expression results in a loss of shh secretion which then stops the splitting of the eye fields causing one