No abstract

A Bub1–Mad1 interaction targets the Mad1–Mad2 complex to unattached kinetochores to initiate the spindle checkpoint.

Neuropil is a fundamental form of tissue organization within brains 1 . In neuropils, densely packed neurons synaptically interconnect into precise circuit architecture 2 , 3 , yet the structural and developmental principles governing this nanoscale precision remain largely unknown 4 , 5 . Here, we use diffusion condensation, an iterative data coarse-graining algorithm 6 , to identify nested circuit structures within the C. elegans neuropil (called the nerve ring). We show that the nerve ring neuropil is largely organized into four strata composed of related behavioral circuits. The stratified architecture of the neuropil is a geometrical representation of the functional segregation of sensory information and motor outputs, with specific sensory organs and muscle quadrants mapping onto particular neuropil strata. We identify groups of neurons with unique morphologies that integrate information across strata and that create neural structures that cage the strata within the nerve ring. We use high resolution light-sheet microscopy 7 , 8 , coupled with lineage-tracing and cell-tracking algorithms 9 , 10 , to resolve the developmental sequence and reveal principles of cell position, migration and outgrowth that guide stratified neuropil organization. Our results uncover conserved structural design principles underlying nerve ring neuropil architecture and function, and a pioneer-neuron-based, temporal progression of outgrowth that guides the hierarchical development of the layered neuropil. Our findings provide a systematic blueprint for using structural and developmental approaches to understand neuropil organization within brains.

SUMMARY During M-phase entry in metazoans with open mitosis, the concerted action of mitotic kinases disassembles nuclei and promotes assembly of kinetochores—the primary microtubule attachment sites on chromosomes. At M-phase exit, these major changes in cellular architecture must be reversed. Here, we show that the conserved kinetochore-localized nucleoporin MEL-28/ELYS docks the catalytic subunit of protein phosphatase 1 (PP1c) to direct kinetochore disassembly-dependent chromosome segregation during oocyte meiosis I, and nuclear assembly during the transition from M-phase to interphase. During oocyte meiosis I, MEL-28-PP1c disassembles kinetochores in a timely manner to promote elongation of the acentrosomal spindles that segregate homologous chromosomes. During nuclear assembly, MEL-28 recruits PP1c to the periphery of decondensed chromatin where it directs formation of a functional nuclear compartment. Thus, a pool of phosphatase activity associated with a kinetochore-localized nucleoporin contributes to two key events that occur during M-phase exit in metazoans: kinetochore disassembly and nuclear reassembly.

Endosomes are emerging as specialized signaling compartments that endow receptors with distinct signaling properties. The diversity of endosomal signaling pathways and their contribution to various biological responses is still unclear. CD158d is an endosome-resident, killer cell Ig-like receptor (KIR2DL4) in natural killer cells that stimulates release of a unique set of pro-inflammatory and pro-angiogenic mediators in response to soluble HLA-G. We identify here the CD158d signaling cascade. In response to soluble agonist antibody or soluble HLA-G, signaling by CD158d was dependent on activation of NF-κB and Akt. CD158d associated with DNA-PKcs, promoted Akt recruitment to endosomes, and induced DNA-PKcs-dependent Akt phosphorylation. The sequential requirement for DNA-PKcs, Akt, and NF-κB in signaling by receptor CD158d delineates a new endosomal signaling pathway for a pro-inflammatory response.

In early C. elegans embryos, the kinetochore-localized BUB- 1/BUB-3 complex promotes anaphase onset independently of its roles in spindle checkpoint signaling and chromosome alignment.

Highlights d The spindle checkpoint protein Mad2 has a conserved role in the G2-to-M transition d Mad2's role in G2-to-M requires Mad1 but is independent of kinetochores d Mad2 enables cyclin B accumulation by restraining its degradation by APC/C-Cdc20 d Mad2 and Cdk phosphorylation act in parallel to inhibit APC/ C-Cdc20 in G2

Selenocysteine insertion during decoding of eukaryotic selenoprotein mRNA requires several trans-acting factors and a cis-acting selenocysteine insertion sequence (SECIS) usually located in the 39 UTR. A second cis-acting selenocysteine codon redefinition element (SRE) has recently been described that resides near the UGA-Sec codon of selenoprotein N (SEPN1). Similar phylogenetically conserved elements can be predicted in a subset of eukaryotic selenoprotein mRNAs. Previous experimental analysis of the SEPN1 SRE revealed it to have a stimulatory effect on readthrough of the UGA-Sec codon, which was not dependent upon the presence of a SECIS element in the 39 UTR; although, as expected, readthrough efficiency was further elevated by inclusion of a SECIS. In order to examine the nature of the redefinition event stimulated by the SEPN1 SRE, we have modified an experimentally tractable in vitro translation system that recapitulates efficient selenocysteine insertion. The results presented here illustrate that the SRE element has a stimulatory effect on decoding of the UGA-Sec codon by both the methylated and unmethylated isoforms of Sec tRNA [Ser]Sec , and confirm that efficient selenocysteine insertion is dependent on the presence of a 39-UTR SECIS. The variation in recoding elements predicted near UGA-Sec codons implies that these elements may play a differential role in determining the amount of selenoprotein produced by acting as controllers of UGA decoding efficiency.