Ribosome biogenesis takes place in the nucleolus, the size of which is often coordinated with cell growth and development. However, how metazoans control nucleolar size remains largely unknown. Caenorhabditis elegans provides a good model to address this question owing to distinct tissue distribution of nucleolar sizes and a mutant, ncl-1, which exhibits larger nucleoli than wild-type worms. Here, through a series of loss-of-function analyses, we report that the nucleolar size is regulated by a circuitry composed of microRNA let-7, translation repressor NCL-1, and a major nucleolar pre-rRNA processing protein FIB-1/fibrillarin. In cooperation with RNA binding proteins PUF and NOS, NCL-1 suppressed the translation of FIB-1/fibrillarin, while let-7 targeted the 3’UTR of ncl-1 and inhibited its expression. Consequently, the abundance of FIB-1 is tightly controlled and correlated with the nucleolar size. Together, our findings highlight a novel genetic cascade by which post-transcriptional regulators interplay in developmental control of nucleolar size and function.
Magnetic properties of vortex nucleation, annihilation, and switching field distribution (SFD) in NiFe disk arrays, where the elements are with 300nm diameter and different degrees of asymmetry, were investigated through measurements and simulations of hysteresis loop. The nucleation and annihilation of vortex state show strong dependences on the asymmetry. More interestingly, the width of SFD, the crucial factor for high-density storage application, oscillating with the degree of asymmetry is observed. The simulation results agree well with the experimental data.
An asymmetric disk achieves control over the clockwise and counterclockwise vortex states in a magnetic disk with an in-plane magnetic field. In this study, the influence of different geometric asymmetry on the vortex motion in 800nm disks has been studied. The excised angle, defined as half of the center angle corresponding to the excised arc, is flatted varying from 15° to 90°. For each asymmetric degree disk, the vortex motion is investigated through anisotropic magnetoresistance measurement and hysteresis loops recorded by focused magneto-optic Kerr effect magnetometry. The vortex nucleation and annihilation fields show strong dependence and different sensitivity on the asymmetry of disk. An interestingly evident switching mode change is also observed at particular excised angle. Numerical simulations, corresponding to realistically identical system, are calculated and agree well with the experimental results.
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