Missing western half of the Pacific Plate: Geochemical nature of the Izanagi-Pacific Ridge interaction with a stationary boundary between the Indian and Pacific mantles

The source mantle of the basaltic ocean crust on the western half of the Pacific Plate was examined using Pb–Nd–Hf isotopes. The results showed that the subducted Izanagi–Pacific Ridge (IPR) formed from both Pacific (180–∼80 Ma) and Indian (∼80–70 Ma) mantles. The western Pacific Plate becomes younger westward and is thought to have formed from the IPR. The ridge was subducted along the Kurile–Japan–Nankai–Ryukyu (KJNR) Trench at 60–55 Ma and leading edge of the Pacific Plate is currently stagnated in the mantle transition zone. Conversely, the entire eastern half of the Pacific Plate, formed from isotopically distinct Pacific mantle along the East Pacific Rise and the Juan de Fuca Ridge, largely remains on the seafloor. The subducted IPR is inaccessible; therefore, questions regarding which mantle might be responsible for the formation of the western half of the Pacific Plate remain controversial. Knowing the source of the IPR basalts provides insight into the Indian–Pacific mantle boundary before the Cenozoic. Isotopic compositions of the basalts from borehole cores (165–130 Ma) in the western Pacific show that the surface oceanic crust is of Pacific mantle origin. However, the accreted ocean floor basalts (∼80–70 Ma) in the accretionary prism along the KJNR Trench have Indian mantle signatures. This indicates the younger western Pacific Plate of IPR origin formed partly from Indian mantle and that the Indian–Pacific mantle boundary has been stationary in the western Pacific at least since the Cretaceous

Inducible deletion of microRNA activity in kidney mesenchymal cells exacerbates renal fibrosis

Abstract MicroRNAs (miRNAs) are sequence-specific inhibitors of post-transcriptional gene expression. However, the physiological functions of these non-coding RNAs in renal interstitial mesenchymal cells remain unclear. To conclusively evaluate the role of miRNAs, we generated conditional knockout (cKO) mice with platelet-derived growth factor receptor-β (PDGFR-β)-specific inactivation of the key miRNA pathway gene Dicer. The cKO mice were subjected to unilateral ureteral ligation, and renal interstitial fibrosis was quantitatively evaluated using real-time polymerase chain reaction and immunofluorescence staining. Compared with control mice, cKO mice had exacerbated interstitial fibrosis exhibited by immunofluorescence staining and mRNA expression of PDGFR-β. A microarray analysis showed decreased expressions of miR-9-5p, miR-344g-3p, and miR-7074-3p in cKO mice compared with those in control mice, suggesting an association with the increased expression of PDGFR-β. An analysis of the signaling pathways showed that the major transcriptional changes in cKO mice were related to smooth muscle cell differentiation, regulation of DNA metabolic processes and the actin cytoskeleton, positive regulation of fibroblast proliferation and Ras protein signal transduction, and focal adhesion-PI3K/Akt/mTOR signaling pathways. Depletion of Dicer in mesenchymal cells may downregulate the signaling pathway related to miR-9-5p, miR-344g-3p, and miR-7074-3p, which can lead to the progression of chronic kidney disease. These findings highlight the possibility for future diagnostic or therapeutic developments for renal fibrosis using miR-9-5p, miR-344g-3p, and miR-7074-3p

NG2-positive pericytes regulate homeostatic maintenance of slow-type skeletal muscle with rapid myonuclear turnover

Abstract Background Skeletal muscle comprises almost 40% of the human body and is essential for movement, structural support and metabolic homeostasis. Size of multinuclear skeletal muscle is stably maintained under steady conditions with the sporadic fusion of newly produced myocytes to compensate for the muscular turnover caused by daily wear and tear. It is becoming clear that microvascular pericytes (PCs) exhibit myogenic activity. However, whether PCs act as myogenic stem cells for the homeostatic maintenance of skeletal muscles during adulthood remains uncertain. Methods We utilized PC-fused myofibers using PC-specific lineage tracing mouse (NG2-CreERT/Rosa-tdTomato) to observe whether muscle resident PCs have myogenic potential during daily life. Genetic PC deletion mouse model (NG2-CreERT/DTA) was used to test whether PC differentiates to myofibers for maintenance of muscle structure and function under homeostatic condition. Results Under steady breeding conditions, tdTomato-expressing PCs were infused into myofibers, and subsequently, PC-derived nuclei were incorporated into myofibers. Especially in type-I slow-type myofibers such as the soleus, tdTomato+ myofibers were already observed 3 days after PC labeling; their ratio reached a peak (approximately 80%) within 1 month and was maintained for more than 1 year. Consistently, the NG2+ PC-specific deletion induced muscular atrophy in a slow-type myofiber-specific manner under steady breeding conditions. The number of myonucleus per volume of each myofiber was constant during observation period. Conclusions These findings demonstrate that the turnover of myonuclei in slow-type myofibers is relatively fast, with PCs acting as myogenic stem cells—the suppliers of new myonuclei under steady conditions—and play a vital role in the homeostatic maintenance of slow-type muscles

Additional file 1 of NG2-positive pericytes regulate homeostatic maintenance of slow-type skeletal muscle with rapid myonuclear turnover

Additional file 1: Fig. S1. Localization of NG2+ cells in adult skeletal muscle tissues. Circulating vessels in NG2-DsRed mice were visualized by intravenous injection of FITC-conjugated lectin. The lower limb skeletal muscles (gastrocnemius and soleus) were fixed and transparentized with RapiClear reagent. Microvessels, lectin-labeled endothelium tubes (lectin; green), and NG2+ cells (DsRed; red) within transparent muscles were visualized in a 3D view using confocal fluorescent microscopy. The nuclei were counterstained with DAPI. Scale bar = 50 µm. Fig. S2. NG2+ cell lineage tracing within the skeletal muscle. The tdTomato expression driven by the universal Rosa26 promoter was specifically induced in NG2+ cells using NG2-CreERT/Rosa-tdTomato mice. After five days of constitutive treatment with Tam, NG2+ cells were expressed. B. On day 1 of the observation period, tdTomato+ cells were observed only at perivascular sites, such as PCs. On day 21, tdTomato-expressing myofibers were observed in most muscle tissues. The ratio of tdTomato+ myofibers to total myofibers varied by muscle site, i.e., over 80% of tdTomato+ myofibers in the soleus and diaphragm and 20–30% in the gastrocnemius and rectus abdominal muscles. Scale bar = 200 µm. Fig. S3. Schematic diagram for the in vitro muscular differentiation assay. Myofibers were isolated from the soleus of NG2-CreERT/Rosa-tdTomato mice by using a collagenase-containing medium. Isolated myofibers were incubated in DMEM-containing 10% FBS and Tam (2 µM) for three days to label NG2+ PCs. The medium was then changed to a differentiation medium containing 2% horse serum. After six days of induction, the myogenesis of NG2+ PCs was observed. Fig. S4. In vitro myogenic potency of NG2+ PCs from soleus muscles. A. Myofibers isolated from the soleus of NG2-CreERT/Rosa-tdTomato mice, which were incubated in DMEM-containing hydroxy tamoxifen (Tam) for three days to label NG2+ PCs. After six days of differentiation induction, myogenesis was determined by immunostaining with myosin heavy chain (MyHC) and myosin heavy chain (MYH) isoform 2 and 7. Isolated soleus myofibers were used for control for immunostaining. Scale bars = 100 µm. Fig. S5. Tam treatment induces deletion of NG2+ cells. A. In vitro effects of 4-hydroxytamoxifen (4-HT) on NG2+ cells isolated from subcutaneous adipose tissues of NG2-CreERT/Rosa26-DTA mice. Cells at confluent were incubated in medium containing hydroxy-Tam for 5 days, and the number of cells were counted. B. Gene expression of NG2 in NG2+ cells with Tam was esteemed by qPCR. Fig. S6. Microarray enrichment analysis in response to PC deletion. After induction of NG2+ PC deletion for one month, microarray analysis of the soleus of PC-deletion and control mice was performed. The top 20 upregulated and downregulated pathway-related gene sets are listed