While the majority of cells contain a single nucleus, cell types such as trophoblasts, osteoclasts, and skeletal myofibers require multinucleation. One advantage of multinucleation can be the assignment of distinct functions to different nuclei, but comprehensive interrogation of transcriptional heterogeneity within multinucleated tissues has been challenging due to the presence of a shared cytoplasm. Here, we utilized single-nucleus RNA-sequencing (snRNA-seq) to determine the extent of transcriptional diversity within multinucleated skeletal myofibers. Nuclei from mouse skeletal muscle were profiled across the lifespan, which revealed the presence of distinct myonuclear populations emerging in postnatal development as well as aging muscle. Our datasets also provided a platform for discovery of genes associated with rare specialized regions of the muscle cell, including markers of the myotendinous junction and functionally validated factors expressed at the neuromuscular junction. These findings reveal that myonuclei within syncytial muscle fibers possess distinct transcriptional profiles that regulate muscle biology.

Skeletal muscle adapts to external stimuli such as increased work. Muscle progenitors (MPs) control muscle repair due to severe damage, but the role of MP fusion and associated myonuclear accretion during exercise are unclear. While we previously demonstrated that MP fusion is required for growth using a supra-physiological model (Goh and Millay, 2017), questions remained about the need for myonuclear accrual during muscle adaptation in a physiological setting. Here, we developed an 8 week high-intensity interval training (HIIT) protocol and assessed the importance of MP fusion. In 8 month-old mice, HIIT led to progressive myonuclear accretion throughout the protocol, and functional muscle hypertrophy. Abrogation of MP fusion at the onset of HIIT resulted in exercise intolerance and fibrosis. In contrast, ablation of MP fusion 4 weeks into HIIT, preserved exercise tolerance but attenuated hypertrophy. We conclude that myonuclear accretion is required for different facets of exercise-induced adaptive responses, impacting both muscle repair and hypertrophic growth.

The poor prognosis of patients with pancreatic ductal adenocarcinoma (PDAC) is partially attributed to the invasive and metastatic behavior of this disease. Laminin subunit beta-3 (LAMB3) encodes one of the three subunits of LM-332, an extracellular matrix protein secreted by cultured human keratinocytes. In addition, LAMB3 is involved in the invasive and metastatic abilities of some types of cancer, including colon, pancreas, lung, cervix, stomach, and prostate cancer, but the role and mechanism of LAMB3 in PDAC have not been previously determined. Herein, we tentatively investigated the role of LAMB3 in the malignant biological behavior of PDAC. In this study, we demonstrated that LAMB3 is upregulated in PDAC. Inhibition of LAMB3 abrogated the tumorigenic outcomes of PI3K/Akt signaling pathway activation, including those involving cell cycle arrest, cell apoptosis, proliferation, invasion and migration in vitro, and tumor growth and liver metastasis in vivo. Our results showed that LAMB3 could mediate cell cycle arrest and apoptosis in PDAC cells and alter the proliferative, invasive, and metastatic behaviors of PDAC by regulating the PI3K/Akt signaling pathway. LAMB3 may be a novel therapeutic target for the treatment of PDAC in the future.

Background: Accumulating evidence demonstrates the essential role of long non-coding RNA (lncRNA) in various types of cancers, including pancreatic cancer. However, the functions and regulation mechanism of lncRNA PMSB8-AS1 in pancreatic cancer are largely unclear. Methods: Quantitative reverse transcription PCR (qRT-PCR) is used to examine the expression of PMSB8-AS1 in PC tissues and PC cell lines. The effect of PMSB8-AS1 on the proliferation of PC cells was detected using CCK8 assay, colony assay, and flow cytometry. The effect of PMSB8-AS1 on the migration and invasion of pancreatic cancer cells was detected using a wound-healing assay and transwell migration assay. Bioinformatic analysis, double luciferase reporting assay, western blot, and rescue experiments were used to detect the regulatory relationship between PMSB8-AS1, miR-382-3p, STAT1, and PD-L1. Results: PMSB8-AS1 expression was upregulated in PC tissues and cell lines and positively associated with the worst survival in patients with PC. The in vitro and in vivo assays demonstrated that overexpression of PMSB8-AS1 significantly promoted pancreatic cancer cell proliferation, migration, and invasion, whereas knockdown of PMSB8-AS1 suppressed cell proliferation, migration, invasion, and EMT, and decreased apoptosis of PC cells. Besides, PMSB8-AS1 directly bound to miR-382-3p downregulated its expression. Besides, PMSB8-AS1 reversed the effect of miR-382-3p on the growth and metastasis of PC cells, which might be targeted on STAT1. Furthermore, STAT1 is the transcriptional factor that activates the expression of PD-L1. Conclusion: lncRNA PMSB8-AS1 promotes pancreatic cancer progression via STAT1 by sponging miR-382-3p involving regulation PD-L1.