Mutations in a specific mammalian signaling pathway result in early defects observed in the establishment or maintenance of midline structures, such as the notochord and the floor plate. Later defects include the absence of distal limb structures, ventral cell types within the neural tube, spinal column and most of the ribs, and cyclopia. Mutations in which one of the following signaling pathways is the most reported cause for these congenital defects?

Correct option is A

The correct answer is Sonic Hedgehog (Shh). The Sonic Hedgehog (Shh) signaling pathway is crucial for the development of midline structures in vertebrates, including the notochord, floor plate, and neural tube. Mutations in Shh result in a variety of congenital defects, including the absence of distal limb structures, defects in the spinal column, ribs, and neural tube defects. Cyclopia, where only one eye forms in the center of the face, is also a hallmark of Shh pathway mutations, highlighting its critical role in proper midline development.

Information Booster:

1. The Sonic Hedgehog (Shh) gene is a signaling molecule that plays a key role in early patterning and development of tissues during embryogenesis.
2. Shh is involved in the development of midline structures such as the notochord, floor plate, and neural tube.
3. Mutations in Shh signaling can lead to lateralization defects such as cyclopia (the formation of a single eye).
4. Shh signaling regulates the growth and differentiation of cells in the limb buds and the ventral neural tube.
5. Sonic Hedgehog signaling is crucial for the establishment of bilateral symmetry in vertebrate organisms.
6. Defects in Shh signaling can lead to conditions such as holoprosencephaly, where the brain fails to divide properly into two hemispheres, resulting in midline defects.

Additional Information:

• (b) Wingless: Incorrect — Wingless (Wnt) signaling is involved in cell differentiation, proliferation, and axis formation but is not primarily responsible for midline defects.
• (c) Notch: Incorrect — Notch signaling is crucial for cell fate determination, but it does not directly cause the specific midline patterning defects seen in Shh mutations.
• (d) Epidermal Growth Factor (EGF): Incorrect — EGF signaling is involved in cell growth and differentiation, but it is not linked to the specific defects associated with midline structure formation and cyclopia caused by Shh mutations.