Holocentric Chromosomes of Luzula elegans Are Characterized by a Longitudinal Centromere Groove, Chromosome Bending, and a Terminal Nucleolus Organizer Region

The structure of holocentric chromosomes was analyzed in mitotic cells of Luzula elegans. Light and scanning electron microscopy observations provided evidence for the existence of a longitudinal groove along each sister chromatid. The centromere-specific histone H3 variant, CENH3, colocalized with this groove and with microtubule attachment sites. The terminal chromosomal regions were CENH3-negative. During metaphase to anaphase transition, L. elegans chromosomes typically curved to a sickle-like shape, a process that is likely to be influenced by the pulling forces of microtubules along the holocentric axis towards the corresponding microtubule organizing regions. A single pair of 45S rDNA sites, situated distal to Arabidopsis-telomere repeats, was observed at the terminal region of one chromosome pair. We suggest that the 45S rDNA position in distal centromere-free regions could be required to ensure chromosome stability. Copyright (C) 2011 S. Karger AG, Base

Rasl11b Knock Down in Zebrafish Suppresses One-Eyed-Pinhead Mutant Phenotype

The EGF-CFC factor Oep/Cripto1/Frl1 has been implicated in embryogenesis and several human cancers. During vertebrate development, Oep/Cripto1/Frl1 has been shown to act as an essential coreceptor in the TGFβ/Nodal pathway, which is crucial for germ layer formation. Although studies in cell cultures suggest that Oep/Cripto1/Frl1 is also implicated in other pathways, in vivo it is solely regarded as a Nodal coreceptor. We have found that Rasl11b, a small GTPase belonging to a Ras subfamily of putative tumor suppressor genes, modulates Oep function in zebrafish independently of the Nodal pathway. rasl11b down regulation partially rescues endodermal and prechordal plate defects of zygotic oep−/− mutants (Zoep). Rasl11b inhibitory action was only observed in oep-deficient backgrounds, suggesting that normal oep expression prevents Rasl11b function. Surprisingly, rasl11b down regulation does not rescue mesendodermal defects in other Nodal pathway mutants, nor does it influence the phosphorylation state of the downstream effector Smad2. Thus, Rasl11b modifies the effect of Oep on mesendoderm development independently of the main known Oep output: the Nodal signaling pathway. This data suggests a new branch of Oep signaling that has implications for germ layer development, as well as for studies of Oep/Frl1/Cripto1 dysfunction, such as that found in tumors

Prediction of the Consolidation Delay in Blockchain-based Applications

In the last years, blockchains have become a popular technology to store immutable data validated in a peer-To-peer way. Software systems can take advantage of blockchains to publicly store data (organised in transactions) which is immutable by design. The most important consensus algorithm in public blockchains is the proof-of-work in which miners invest a huge computational power to consolidate new data in a ledger. Miners receive incentives for their work, i.e., a fee decided and paid for each transaction. Rational miners aim to maximise the profit generated by the mining activity, and thus choose the transactions offering the highest fee per byte for their consolidation. In this paper, we propose a queueing model to study the relation between the fee offered by a transaction and its expected consolidation time, i.e., the time required to be added to the blockchain by the miners. The solution of the queueing model, although approximate, is computationally and numerically efficient and software systems can use it online to analyse the trade-off between costs and response times. Indeed, a static configuration of the model would not account for the high variations in the blockchain workload and fees offered by other users. The model takes into account the dropping of transactions caused by timeouts or finite capacity transaction pools. We validate our results with data extracted from the Bitcoin blockchain and with discrete event simulations