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The adult Hydra polyp continually renews all of its cells using three separate stem cell populations, but the genetic pathways enabling this homeostatic tissue maintenance are not well understood. We sequenced 24,985 Hydra single-cell transcriptomes and identified the molecular signatures of a broad spectrum of cell states, from stem cells to terminally differentiated cells. We constructed differentiation trajectories for each cell lineage and identified gene modules and putative regulators expressed along these trajectories, thus creating a comprehensive molecular map of all developmental lineages in the adult animal. In addition, we built a gene expression map of the Hydra nervous system. Our work constitutes a resource for addressing questions regarding the evolution of metazoan developmental processes and nervous system function.

During embryogenesis, cells acquire distinct fates by transitioning through transcriptional states. To uncover these transcriptional trajectories during zebrafish embryogenesis, we sequenced 38,731 cells and developed URD, a simulated diffusion-based computational reconstruction method. URD identified the trajectories of 25 cell types through early somitogenesis, gene expression along them, and their spatial origin in the blastula. Analysis of Nodal signaling mutants revealed that their transcriptomes were canalized into a subset of wild-type transcriptional trajectories. Some wild-type developmental branch points contained cells that express genes characteristic of multiple fates. These cells appeared to trans-specify from one fate to another. These findings reconstruct the transcriptional trajectories of a vertebrate embryo, highlight the concurrent canalization and plasticity of embryonic specification, and provide a framework with which to reconstruct complex developmental trees from single-cell transcriptomes.

Many, if not most, embryos begin development with extremely short cell cycles that exhibit unusually rapid DNA replication and no gap phases. The commitment to the cell cycle in the early embryo appears to preclude many other cellular processes that only emerge as the cell cycle slows just prior to gastrulation at a major embryonic transition known as the mid-blastula transition (MBT). As reviewed here, genetic and molecular studies in Drosophila have identified changes that extend S phase and introduce a post-replicative gap phase, G2, to slow the cell cycle. Although many mysteries remain about the upstream regulators of these changes, we review the core mechanisms of the change in cell cycle regulation and discuss advances in our understanding of how these might be timed and triggered. Finally, we consider how the elements of this program may be conserved or changed in other organisms.

para-Substitution reactions on C6F5 rings of Lewis acids have been exploited to achieve triply substituted derivatives. The reaction of B(C6F5)3 with P(SiMe3)3 ultimately affords the Lewis acid B(C6F4P(SiMe3)2)31. This species binds Lewis bases affording the adducts LB(C6F4P(SiMe3)2)3 (L = MeCN 2, OPEt33, PMe34, PBu35) and reacts with LiMe to give the salt [Li][MeB(C6F4P(SiMe3)2)3]·3THF 6. It also reacts with H2O to give (L)B(C6F4PH2)3 (L = H2O 7, MeCN 8). In an analogous fashion, [(C6F5)3PF][B(C6F5)4] was converted to [FP(C6F4P(SiMe3)2)3] [B(C6F5)4] 9 and subsequently to [(MeO)P(C6F4PH2)3][B(C6F5)4] 10. [ABSTRACT FROM AUTHOR]

BackgroundIn Drosophila embryos, the midblastula transition (MBT) dramatically remodels the cell cycle during the 14(th) interphase. Before the MBT, each cycle is composed of only a short S phase and mitosis. At the MBT, S phase is dramatically lengthened by the onset of late replication, and a G2 phase is introduced. Both changes set the stage for gastrulation and require downregulation of Cdc25 phosphatase, which was previously attributed to the elimination of its transcripts at the MBT.ResultsPremature removal of cdc25 transcripts by RNAi did not affect progression to the MBT. Instead, an antibody against the Cdc25 isoform Twine showed that Twine protein was abundant and stable until the MBT, when it was destabilized and rapidly eliminated. Persistence of pre-MBT levels of Twine was sufficient to prevent cell-cycle slowing. Twine protein destruction was timed by the nucleocytoplasmic ratio and depended on the activation of zygotic transcription at the MBT, including expression of the gene tribbles, whose activity was sufficient to trigger Twine destruction and was required for prompt Twine disappearance.ConclusionsWe propose that the developmentally regulated destruction of Twine protein is a critical switch that contributes to the cell-cycle change at the MBT, including the addition of a G2 phase and onset of late replication. Moreover, we show that this destruction is triggered by the nucleocytoplasmic ratio-dependent onset of zygotic transcription of tribbles and other unknown genes.

Cyclins are key cell cycle regulators, yet few analyses test their role in timing the events that they regulate. We used RNA interference and real-time visualization in embryos to define the events regulated by each of the three mitotic cyclins of Drosophila melanogaster, CycA, CycB, and CycB3. Each individual and pairwise knockdown results in distinct mitotic phenotypes. For example, mitosis without metaphase occurs upon knockdown of CycA and CycB. To separate the role of cyclin levels from the influences of cyclin type, we knocked down two cyclins and reduced the gene dose of the one remaining cyclin. This reduction did not prolong interphase but instead interrupted mitotic progression. Mitotic prophase chromosomes formed, centrosomes divided, and nuclei exited mitosis without executing later events. This prompt but curtailed mitosis shows that accumulation of cyclin function does not directly time mitotic entry in these early embryonic cycles and that cyclin function can be sufficient for some mitotic events although inadequate for others.

The effect of the residual signal energy level in sample-matrix-inversion (SMI) estimators of the optimum linear minimum-mean-square-error/linearly constrained-minimum-variance (MMSE/LCMV) filter is examined. The iterative decision-directed filter has displayed average normalized output signal-to-interference-plus-noise ratio (SINR) performance.

Herein we devise and execute a new synthesis of a pristine boron‐doped nanographene. Our target boron‐doped nanographene was designed based on DFT calculations to possess a low LUMO energy level and a narrow band gap derived from its precise geometry and B‐doping arrangement. Our synthesis of this target, a doubly B‐doped hexabenzopentacene (B2‐HBP), employs six net C−H borylations of an alkene, comprising consecutive hydroboration/electrophilic borylation/dehydrogenation and BBr3/AlCl3/2,6‐dichloropyridine‐mediated C−H borylation steps. As predicted by our calculations, B2‐HBP absorbs strongly in the visible region and emits in the NIR up to 1150 nm in o‐dichlorobenzene solutions. Furthermore, B2‐HBP possesses a very low LUMO level, showing two reversible reductions at −1.00 V and −1.17 V vs. Fc+/Fc. Our methodology is surprisingly selective despite its implementation of unfunctionalized precursors and offers a new approach to the synthesis of pristine B‐doped polycyclic aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Utilizing Pd‐catalyzed [5+2] annulation a series of heptagon‐extended corannulenes could be synthesized from a borinic acid precursor furnished by C−H borylation strategy. Single‐crystal X‐ray analysis revealed the presence of two conformational enantiomers crystallizing in a racemic mixture. Through their embedded five‐ and seven‐membered rings these polycyclic aromatic hydrocarbons (PAHs) exhibit both negative and positive curvature and UV/Vis/NIR absorption spectroscopy as well as cyclic voltammetry experiments provided insights into the influence of larger flanking aromatic systems and electron‐donating substituents encompassing the heptagonal ring. Through [5+2] annulation of acenaphthylene an azulene‐containing PAH with intriguing optoelectronical properties including a very small bandgap and absorption over the whole visible spectrum could be obtained. Theoretical calculations were employed to elucidate the long‐wavelength absorption and aromaticity. [ABSTRACT FROM AUTHOR]

A new strategy is demonstrated for the synthesis of warped, negatively curved, all‐sp2‐carbon π‐scaffolds. Multifold C−C coupling reactions are used to transform a polyaromatic borinic acid into a saddle‐shaped polyaromatic hydrocarbon (2) bearing two heptagonal rings. Notably, this Schwarzite substructure is synthesized in only two steps from an unfunctionalized alkene. A highly warped structure of 2 was revealed by X‐ray crystallographic studies and pronounced flexibility of this π‐scaffold was ascertained by experimental and computational studies. Compound 2 exhibits excellent solubility, visible range absorption and fluorescence, and readily undergoes two reversible one‐electron oxidations at mild potentials. [ABSTRACT FROM AUTHOR]