To meet the high demands of actively proliferating cells, it was previously reported that the 3’- untranslated region (3’-UTR) of specific transcripts would be shortened in these cell types. As the 3’-UTR harbors regulatory sites such as microRNA and RNA-binding protein binding sites, shortening of the 3’-UTR would affect the transcripts’ susceptibility to negative regulation and, in turn, increase protein output. The shortening of the 3’-UTR was suggested to be regulated by the shielding of proximal polyadenylation site (PAS) by poly(A) binding protein nuclear 1 (PABPN1) and the abundance of cleavage and polyadenylation specificity factor (CPSF) protein available. We wish to investigate whether this process also occurs in muscle stem cells.

Muscle stem cells, also known as satellite c...[ Read more ]

To meet the high demands of actively proliferating cells, it was previously reported that the 3’- untranslated region (3’-UTR) of specific transcripts would be shortened in these cell types. As the 3’-UTR harbors regulatory sites such as microRNA and RNA-binding protein binding sites, shortening of the 3’-UTR would affect the transcripts’ susceptibility to negative regulation and, in turn, increase protein output. The shortening of the 3’-UTR was suggested to be regulated by the shielding of proximal polyadenylation site (PAS) by poly(A) binding protein nuclear 1 (PABPN1) and the abundance of cleavage and polyadenylation specificity factor (CPSF) protein available. We wish to investigate whether this process also occurs in muscle stem cells.

Muscle stem cells, also known as satellite cells (SCs), are primarily quiescent in resting muscle. Upon injury, SCs will activate, proliferate, and subsequently differentiate to repair the damaged muscle. Quiescence is a tightly regulated process; dysregulation results in depletion of the stem cell pool and impairment of muscle regeneration. As previous reports only focused on the levels of CPSF during alternative polyadenylation, here we investigate the role of PABPN1 on PAS selection and propose that alternative polyadenylation is an important post-transcriptional regulator of stem cell quiescence. We confirmed that 3’-UTR shortening indeed occurs during SC activation. In addition, the expression of PABPN1 is highly up-regulated during satellite cell activation. Knockdown experiments were also performed to investigate the effect of PABPN1 on satellite cell numbers and proliferation. To understand the role of PABPN1 in vivo, Pabpn1 conditional knockout mice were utilized to study the changes in alternative polyadenylation and the proteome. The results of this project will shed light on how alternative polyadenylation regulates muscle stem cell function.