Pah1p negatively regulates the expression of V-ATPase genes as well as vacuolar acidification.

In yeast, PAH1 plays an important role in cell homeostasis and lipid biosynthesis. PAH1 encodes for the PA phosphatase, Pah1p, which is responsible for de novo TAG and phospholipid synthesis. It has been suggested that the lack of Pah1p causes irregular vacuolar morphology and dysfunctional V-ATPase pump activity. However, the molecular connection between Pah1p and V-ATPase activity has remained unclear. Through real-time PCR, we have shown that PAH1 is maximally induced at the stationary stage in the presence of inositol. We also found that vacuoles were less fragmented when PAH1 is maximally expressed. Subsequently, we observed that vacuoles from pah1Δ cells were more acidic than those in WT cells. Furthermore, V-ATPase genes were upregulated in the absence of Pah1p. These results suggest that Pah1p plays an important role in vacuolar activity by negatively regulating the expression of V-ATPase genes. As such, we provide evidence to show the role of Pah1p in vacuolar acidification and fragmentation.

Myomaker, Regulated by MYOD, MYOG and miR-140-3p, Promotes Chicken Myoblast Fusion.

The fusion of myoblasts is an important step during skeletal muscle differentiation. A recent study in mice found that a transmembrane protein called Myomaker, which is specifically expressed in muscle, is critical for myoblast fusion. However, the cellular mechanism of its roles and the regulatory mechanism of its expression remain unclear. Chicken not only plays an important role in meat production but is also an ideal model organism for muscle development research. Here, we report that Myomaker is also essential for chicken myoblast fusion. Forced expression of Myomaker in chicken primary myoblasts promotes myoblast fusion, whereas knockdown of Myomaker by siRNA inhibits myoblast fusion. MYOD and MYOG, which belong to the family of myogenic regulatory factors, can bind to a conserved E-box located proximal to the Myomaker transcription start site and induce Myomaker transcription. Additionally, miR-140-3p can inhibit Myomaker expression and myoblast fusion, at least in part, by binding to the 3' UTR of Myomaker in vitro. These findings confirm the essential roles of Myomaker in avian myoblast fusion and show that MYOD, MYOG and miR-140-3p can regulate Myomaker expression.