Question

MicroRNA 122a (miRNA122a) is highly expressed in the liver and is a major regulator of the gene Klf6 in the liver. If miRNA122a itself was inactivated in a liver cell, which of the following effects on Klf6 would you expect to observe?

	A.	Levels of Klf6 mRNA would increase, and levels of Klf6 protein would decrease.
	B.	Levels of Klf6 protein would decrease.
	C.	There would be no change in levels of Klf6 mRNA or protein.
	D.	Levels of Klf6 protein would increase.

Answer 1

MicroRNAs are used to degrade specific RNA in the cell. MicroRNAs are transcribed in the nucleus as pri-mRNAs. They are then processed to pre-miRNAs in the nucleus by DROSHA and Pasha/DGCR8 (double stranded binding protein). They are then exported to the cytoplasm where they are acted upon by DICER. Single stranded miRNA will then bind to RISC complex to form mature miRNA. The miRNA has a complementary sequence to the target mRNA and can bind to it. The RISC complex then degrades the mRNA that is bound by the miRNA.

In liver cells, miRNA122a will therefore degrade the Klf6 mRNA, if expressed. When the miRNA122a is inactivated, it cannot bind to the KLf6 mRNA and degrade it. Hence, Klf6 mRNA is no longer degraded and can undergo translation to produce Klf6 protein. Thus, Klf6 protein levels increase in the cell.

Klf6 protein would increase and not decrease if miRNA122a is inhibited as translation is occurring due to increased stability of Klf6 mRNA. Presence of miRNA122a would normally have hampered it in the cells in normal conditions,         

Right choice: D. Levels of Klf6 protein would increase.