Mechanism for the initiation of spliceosome disassembly.

Pre-mRNA splicing requires the assembly, remodeling, and disassembly of the multi-megadalton ribonucleoprotein complex called the spliceosome1. Recent studies have shed light on spliceosome assembly and remodeling for catalysis2-6, but the mechanism of disassembly remains unclear. Here, we report 2.6 to 3.2 Å resolution cryo-electron microscopy structures of nematode and human terminal intron-lariat spliceosomes along with biochemical and genetic data. Our results uncover how four disassembly factors and the conserved RNA helicase DHX15 initiate spliceosome disassembly. The disassembly factors probe large inner and outer spliceosome surfaces to detect the release of ligated mRNA. Two of these factors, TFIP11 and C19L1, and three general spliceosome subunits, SYF1, SYF2 and SDE2, then dock and activate DHX15 on the catalytic U6 snRNA to initiate disassembly. U6 thus controls both the start5 and end of pre-mRNA splicing. Taken together, our results explain the molecular basis of canonical spliceosome disassembly and provide a framework to understand general spliceosomal RNA helicase control and the discard of aberrant spliceosomes.

Adult neural stem cells and neurogenesis are resilient to intermittent fasting.

Intermittent fasting (IF) is a promising strategy to counteract ageing shown to increase the number of adult-born neurons in the dentate gyrus of mice. However, it is unclear which steps of the adult neurogenesis process are regulated by IF. The number of adult neural stem cells (NSCs) decreases with age in an activation-dependent manner and, to counteract this loss, adult NSCs are found in a quiescent state which ensures their long-term maintenance. We aimed to determine if and how IF affects adult NSCs in the hippocampus. To identify the effects of every-other-day IF on NSCs and all following steps in the neurogenic lineage, we combined fasting with lineage tracing and label retention assays. We show here that IF does not affect NSC activation or maintenance and, that contrary to previous reports, IF does not increase neurogenesis. The same results are obtained regardless of strain, sex, diet length, tamoxifen administration or new-born neuron identification method. Our data suggest that NSCs maintain homeostasis upon IF and that this intervention is not a reliable strategy to increase adult neurogenesis.