Cyclin B3 implements timely vertebrate oocyte arrest for fertilization.

To ensure successful offspring ploidy, vertebrate oocytes must halt the cell cycle in meiosis II until sperm entry. Emi2 is essential to keep oocytes arrested until fertilization. However, how this arrest is implemented exclusively in meiosis II and not prematurely in meiosis I has until now remained enigmatic. Using mouse and frog oocytes, we show here that cyclin B3, an understudied B-type cyclin, is essential to keep Emi2 levels low in meiosis I. Direct phosphorylation of Emi2 at an evolutionarily highly conserved site by Cdk1/cyclin B3 targets Emi2 for degradation. In contrast, Cdk1/cyclin B1 is inefficient in Emi2 phosphorylation, and this provides a molecular explanation for the requirement of different B-type cyclins for oocyte maturation. Cyclin B3 degradation at exit from meiosis I enables Emi2 accumulation and thus timely arrest in meiosis II. Our findings illuminate the evolutionarily conserved mechanisms that control oocyte arrest for fertilization at the correct cell-cycle stage, which is essential for embryo viability.

Mass transport characteristics of alkyl amines in a water/n-decane system.

Water-in-decane emulsions can be applied as reaction system for the precipitation of nanoparticles. Herein the precipitation reaction is induced once an oil as well as water soluble compound (here: alkyl amines) diffuses from the continuous oil phase into a water based droplet, loaded with the reaction partner. Thus, the mass transfer and adsorption characteristics of the alkyl amine at the interface are key parameters to understand particle formation in emulsion droplets. For this reason, the effective diffusion coefficients and the interfacial tension of different alkyl amines in a water/n-decane system were estimated. Furthermore, emulsifiers necessary for the stability of the emulsion might represent a diffusion barrier. In order to determine its influence, diffusion experiments were also conducted in the presence of emulsifier. The effective diffusion coefficients were measured using an adapted photometric method. To identify relevant adsorption characteristics of the water/n-decane/alkyl amine systems, the interfacial tension was studied with the pendant drop technique. According to the results, we can draw three conclusions: First, the effective diffusion coefficient depends on the molecular structure of the amines. Second, regarding our materials, the surface activity and surface coverage proved to be a governing parameter to describe differences in the transport mechanism. And third, the presence of additional surface active compounds leads to a decrease of the effective diffusion coefficient.

A large-scale RNAi screen identifies Deaf1 as a regulator of innate immune responses in Drosophila.

Innate immune signalling pathways are evolutionarily conserved between invertebrates and vertebrates. The analysis of NF-kappaB signalling in Drosophila has contributed important insights into how organisms respond to infection. Nevertheless, significant gaps remain in our understanding of how the activation of intracellular signalling elicits specific transcriptional programs. Here we report a genome-wide RNA interference survey for transcription factors that are required for Toll-dependent immune responses. In addition to the NF-kappaB homologs Dif, Dorsal and factors of the general transcription machinery, we identified Deformed Epidermal Autoregulatory Factor 1 (Deaf1) to be required for the expression of the Toll target gene Drosomycin in cultured cells and in Drosophila in vivo. We show that Deaf1 is required for the survival of flies after fungal, but not E. coli, infection. We determine that Deaf1 acts downstream of the NF-kappaB factors Dorsal and Dif. These results indicate that Deaf1 is an important contributor to innate immune responses in vivo.