Cell Cycle Regulation of Stem Cells by MicroRNAs
The cell cycle is divided into four phases in eukaryotes: Gap 1 (G1), Synthesis (S), Gap 2 (G2), and Mitosis (M). During G1, also known as the first interphase, the cell synthesizes necessary proteins for DNA replication and continuous growth. This is followed by DNA replication which occurs in the S phase. The DNA integrity is then checked in the G2 phase, or second interphase, and at this point the cell is growing and preparing for cell division. Finally, during the M phase, the cell divides into two daughter cells. After division the cell can either reenter the G1 phase or go into the quiescent state. This state of reversible cell cycle arrest is known as the G0 phase and helps maintain cellular homeostasis.
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A non-coding RNA (ncRNA) is an RNA molecule that is not translated into a protein. MicroRNAs (miRNAs) are a class of small non-coding RNA molecules involved in the regulation of gene expression. They play a role in the fine-tuning of essential biological processes such as proliferation, differentiation, and apoptosis in many types of cells. It has been postulated that several miRNAs target transcripts that directly or indirectly coordinate the progression of the cell cycle within stem cells. Furthermore, past studies have shown that altered expression levels of miRNAs can contribute to pathological conditions, such as cancer, due to the loss of cell cycle regulation. However, the exact mechanism by which miRNAs control the cell cycle within stem cells is still incompletely understood. In this review, we will discuss current knowledge of the regulatory role of miRNAs in the progression of the cell cycle within stem cells and how specific miRNAs may control cell cycle associated molecules in embryonic and somatic stem cells
