What does the gene “sonic hedgehog” do? What are the consequences of over and under-expression of the genes?
The correct answer and explanation is:
The Sonic Hedgehog (SHH) gene encodes a protein that plays a crucial role in embryonic development. It is part of the Hedgehog signaling pathway, which regulates cell growth, differentiation, and tissue patterning. SHH is especially important for the proper formation of the brain, spinal cord, limbs, and various organs.
During early development, SHH directs the organization of the neural tube, influencing the pattern of neurons along the dorsal-ventral axis. It also helps establish the left-right symmetry of the body and is vital for limb development by specifying the identity of digits (fingers and toes). The protein acts as a signaling molecule that binds to receptors on target cells, triggering genetic programs that guide development.
Consequences of under-expression or loss of SHH function can be severe. Insufficient SHH activity is linked to developmental disorders such as holoprosencephaly, a condition where the brain fails to properly divide into two hemispheres. This can cause severe facial deformities and neurological impairments. Under-expression can also result in limb malformations such as fewer digits or incomplete limb formation. In addition, impaired SHH signaling during development may lead to defects in the spinal cord and other organs.
Over-expression or excessive SHH signaling is associated with abnormal cell proliferation and can lead to cancer. For example, overactive SHH signaling has been found in basal cell carcinoma, the most common form of skin cancer, and medulloblastoma, a type of brain tumor. In these cases, too much SHH signaling causes cells to grow uncontrollably. Over-expression can also disrupt normal tissue patterning, causing developmental abnormalities.
In summary, the Sonic Hedgehog gene is essential for guiding embryonic development by controlling cell growth and organization. Both insufficient and excessive SHH expression can cause significant developmental defects or contribute to tumor formation. The precise regulation of this gene’s activity is critical for normal growth and health.