Golgi apparatus (GA) and centrosome reposition toward cell leading end during directional cell migration in a coupling way, thereby determining cell polarity by transporting essential factors to the ...proximal plasma membrane. The study provides mechanistic insights into how GA repositioning (GR) is regulated, and how GR and centrosome repositioning (CR) are coupled. Our previous published works reveals that PRMT5 methylates HURP at R122 and the HURP m122 inhibits GR and cell migration by stabilizing GA‐associated acetyl‐tubulin and then rigidifying GA. The current study further shows that the demethylase JMJD6‐guided demethylation of HURP at R122 promotes GR and cell migration. The HURP methylation mimicking mutant 122 F blocks JMJD6‐induced GR and cell migration, suggesting JMJD6 relays GR stimulating signal to HURP. Mechanistic studies reveal that the HURP methylation deficiency mutant 122 K promotes GR through NF‐κB‐induced CR and subsequently CR‐dependent Cdc42 upregulation, where Cdc42 couples CR to GR. Taken together, HURP methylation statuses provide a unique opportunity to understand how GR is regulated, and the GA intrinsic mechanism controlling Golgi rigidity and the GA extrinsic mechanism involving NF‐κB‐CR‐Cdc42 cascade collectively dictate GR.
Nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record. However, bulk sedimentary nitrogen isotope ratios, which can be determined ...routinely and at minimal cost, may be altered during burial and early sedimentary diagenesis, particularly outside of continental margin settings. The causes and detailed mechanisms of isotopic alteration are still under investigation. Case studies of the Mediterranean and South China Seas underscore the complexities of investigating isotopic alteration. In an effort to evaluate the evidence for alteration of the sedimentary N isotopic signal and try to quantify the net effect, we have compiled and compared data demonstrating alteration from the published literature. A >100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that, at sites located off of the continental margins, an increase in sediment 15N/14N occurs during early burial, likely at the seafloor. The extent of isotopic alteration appears to be a function of water depth. Depth‐related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of N isotopic alteration. Moreover, the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global N cycle.
Key Points
Use of sedimentary nitrogen isotopes is examined
On average, sediment 15N/14N increases approx. 2 per mil during early burial
Isotopic alteration scales with water depth
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