Context:

• Embryonic stem cells are capable of generating all the cell types that compose the organs and systems of the human body.
• Now, researchers at Pune’s National Centre for Cell Science (NCCS) have found a dual mechanism that keeps specific genes off, which helps the embryonic stem cells maintain pluripotency — their ability to give rise to all the cell types.
• The dual mechanism functions in such a way that even if one mechanism fails, the other can function as a back-up and help the embryonic stem cells maintain pluripotency.

About Embryonic stem cells:

• Embryonic stem cells contain multiple endocytosis-associated genes whose expression is suppressed unlike in the case of the specialised or differentiated cells.
• Some of the genes are directly responsible or regulate the transport of molecules which are present on the cell surface membrane to the interior of the cell.
• The precise mechanism by which the expression of endocytosis-associated genes are turned off in embryonic stem cells and the role of endocytosis (transport of molecules from the membrane surface to inside the cell) in maintaining pluripotency was not known.

Identification of different pathways

• The team identified two pathways — polycomb repressive complex (PRC2) and embryonic stem cell-specific cell cycle (ESCC) regulating microRNAs — that suppressed the expression of the endocytosis-associated genes in embryonic stem cells but not in cells that have already differentiated.
• While the expression of 50 endocytosis-associated genes is kept under check by one pathway (PRC2), the expression of a smaller subset of 12 genes is also reduced by the action of the second pathway (ESCC).
• Stem cells have a class of small non-coding microRNAs called the ESCC-family of microRNAs. The microRNAs work by binding to the complementary sites seen on messenger RNA (mRNA).
• “Of the 50 endocytosis-associated genes, 21 genes had complementary sites for the microRNA, indicating that these 21 could potentially be controlled by microRNAs.

Helpful:

• It will be helpful in regenerative medicine. Understanding the pathways and mechanism of endocytosis can now give us a handle to try and convert induced pluripotent stem (iPS) cells, which are pluripotent, into specialised cells such as neurons by altering the expression of the endocytosis-associated genes.

Source:TH