ABSTRACT
Cell fate decisions occur through the switch-like, irreversible activation of fate-specifying genes. These activation events are often assumed to be tightly coupled to changes in upstream transcription factors, but could also be constrained by cis-epigenetic mechanisms at individual gene loci. Here, we studied the activation of Bcl11b, which controls T-cell fate commitment. To disentangle cis and trans effects, we generated mice where two Bcl11b copies are tagged with distinguishable fluorescent proteins. Quantitative live microscopy of progenitors from these mice revealed that Bcl11b turned on after a stochastic delay averaging multiple days, which varied not only between cells but also between Bcl11b alleles within the same cell. Genetic perturbations, together with mathematical modeling, showed that a distal enhancer controls the rate of epigenetic activation, while a parallel Notch-dependent trans-acting step stimulates expression from activated loci. These results show that developmental fate transitions can be controlled by stochastic cis-acting events on individual loci.
Subject(s)
Cell Differentiation , Epigenesis, Genetic , Repressor Proteins/biosynthesis , T-Lymphocytes/physiology , Transcription, Genetic , Tumor Suppressor Proteins/biosynthesis , Animals , Genes, Reporter , Intravital Microscopy , Luminescent Proteins/analysis , Luminescent Proteins/genetics , Mice , Models, Theoretical , Staining and Labeling , Time FactorsABSTRACT
Leiodermatolide is an antimitotic macrolide isolated from the marine sponge Leiodermatium sp. whose potentially novel tubulin-targeting mechanism of action makes it an exciting lead for anticancer drug discovery. In pursuit of a sustainable supply, we report a highly stereocontrolled total synthesis (3.2% yield) based on a convergent sequence of palladium-mediated fragment assembly and macrolactonization. Boron-mediated aldol reactions were used to configure the three key fragments 2, 5, and 6 by employing the appropriate enantiomer of the lactate-derived ketone 7.
Subject(s)
Antimitotic Agents/chemical synthesis , Macrolides/chemical synthesis , Porifera/chemistry , Animals , Antimitotic Agents/chemistry , Macrolides/chemistry , Molecular Conformation , StereoisomerismABSTRACT
Four decades since Mukaiyama's first reports on the successful application of silicon and boron enolates in directed aldol reactions, the ability of this highly controlled carbon-carbon bond-forming method to simultaneously define stereochemistry, introduce complexity, and construct the carbon skeleton with a characteristic 1,3-oxygenation pattern has made it a powerful tool for natural product synthesis. This Minireview highlights a number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction and discusses the underlying mechanistic rationale that determines the stereochemical outcomes.
