A Pitx2-miRNA pathway modulates cell proliferation in myoblasts and skeletal-muscle satellite cells and promotes their commitment to a myogenic cell fate

The acquisition of a proliferating cell status from a quiescent state as well as the shift between proliferation and differentiation are key developmental steps in skeletal-muscle stem cells (satellite cells) to provide proper muscle regeneration. However, how satellite-cell proliferation is regulated, though, is not fully understood. Here, we report that the c-isoform of the transcription factor Pitx2 increases cell proliferation in myoblasts by down-regulating the miRNAs miR-15b, miR-23b, miR-106b, and miR-503. This Pitx2c-miRNA pathway also regulates cell proliferation in early-activated satellite cells, enhancing the Myf5+ satellite cells and thereby promoting their commitment to a myogenic cell fate. This study reveals unknown functions of several miRNAs in myoblast and satellite-cell behaviour and thus may have future applications in regenerative medicine. mirVana microarrays (Ambion) were used to profile microRNA signature at different Pitx2 overexpression conditions, namely two different doses (4 and 8 µg CMV-Pitx2c plasmid, respectively) after 24 hours of transfection in SOL8 skeletal myogenic cells. 20 µg of total RNA was used to hybridize two distinct microRNA microarrays on each condition analyzed.