ABSTRACT
<p><b>OBJECTIVE</b>To investigate the time course of let-7a microRNA expression in the cell cycle of HeLa cells.</p><p><b>METHODS</b>HeLa cells were synchronized in G(1), S and G(2)/M phases using double-thymidine block, and the cell cycle phases were defined by flow cytometry. Real-time quantitative RT-PCR was used to examine the expression of let-7a in HeLa cells in different cell cycle phases.</p><p><b>RESULTS</b>The synchronization rates of G(1), S and G(2)/M phases were 84.81%, 83.65% and 77.69%, respectively. Let-7a was constitutively expressed throughout the cell cycle in HeLa cells, but the expression levels in G(1) and S phases were lower than those in G(2)/M phase.</p><p><b>CONCLUSIONS</b>Cell cycle can significantly influence the expression level of let-7a, which may provide new clues to the understanding of the cell cycle control mechanisms.</p>