All of the following genes are associated with establishment of left sidedness, EXCEPT:
Correct Answer: None of the above
Description: Left-right-sidedness, also established early in development, is orchestrated by a cascade of genes. When the primitive streak appears, fibroblast growth factor 8 (FGF8) is secreted by cells in the node and primitive streak and induces expression of Nodal but only on the left side of the embryo. Later, as the neural plate is induced, FGF8 maintains Nodal expression in the lateral plate mesoderm, as well as LEFTY-2, and both of these genes upregulate PITX2. PITX2 is a homeobox-containing transcription factor responsible for establishing left-sidedness. Also, it is expressed on the left side of the hea, stomach, and gut primordia, and, if expressed ectopically, it results in laterality defects. Simultaneously, LEFTY is expressed on the left side of the floor plate of the neural tube and may act as a barrier to prevent left-sided signals from crossing over. Sonic hedgehog (SHH) may also function in this role as well as serving as a repressor for left-sided gene expression on the right. Ref: Langman's embryology 11th edition Chapter 35.
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