The regulation of Hox gene expression during animal development

Hox genes encode a family of transcriptional regulators that elicit distinct developmental programmes along the head-to-tail axis of animals. The specific regional functions of individual Hox genes largely reflect their restricted expression patterns, the disruption of which can lead to developmental defects and disease. Here, we examine the spectrum of molecular mechanisms controlling Hox gene expression in model vertebrates and invertebrates and find that a diverse range of mechanisms, including nuclear dynamics, RNA processing, microRNA and translational regulation, all concur to control Hox gene outputs. We propose that this complex multi-tiered regulation might contribute to the robustness of Hox expression during development

Protein import into the endosymbiotic organelles of apicomplexan parasites

The organelles of endosymbiotic origin, plastids, and mitochondria, evolved through the serial acquisition of endosymbionts by a host cell. These events were accompanied by gene transfer from the symbionts to the host, resulting in most of the organellar proteins being encoded in the cell nuclear genome and trafficked into the organelle via a series of translocation complexes. Much of what is known about organelle protein translocation mechanisms is based on studies performed in common model organisms; e.g., yeast and humans or Arabidopsis. However, studies performed in divergent organisms are gradually accumulating. These studies provide insights into universally conserved traits, while discovering traits that are specific to organisms or clades. Apicomplexan parasites feature two organelles of endosymbiotic origin: a secondary plastid named the apicoplast and a mitochondrion. In the context of the diseases caused by apicomplexan parasites, the essential roles and divergent features of both organelles make them prime targets for drug discovery. This potential and the amenability of the apicomplexan Toxoplasma gondii to genetic manipulation motivated research about the mechanisms controlling both organelles’ biogenesis. Here we provide an overview of what is known about apicomplexan organelle protein import. We focus on work done mainly in T. gondii and provide a comparison to model organisms

Reassessing the Role of Hox Genes during Vertebrate Development and Evolution

Since their discovery Hox genes have been at the core of the established models explaining the development and evolution of the vertebrate body plan as well as its paired appendages. Recent work brought new light to their role in the patterning processes along the main body axis. These studies show that Hox genes do not control the basic layout of the vertebrate body plan but carry out region-specific patterning instructions loaded on the derivatives of axial progenitors by Hox-independent processes. Furthermore, the finding that Hox clusters are embedded in functional chromatin domains, which critically impacts their expression, has significantly altered our understanding of the mechanisms of Hox gene regulation. This new conceptual framework has broadened our understanding of both limb development and the evolution of vertebrate paired appendages.info:eu-repo/semantics/publishedVersio

Time exponential splitting integrator for the Klein–Gordon equation with free parameters in the Hagstrom–Warburton absorbing boundary conditions

The Klein–Gordon equation on an infinite two dimensional strip is considered. Numerical computation is reduced to a finite domain by using the Hagstrom–Warburton (H–W) absorbing boundary conditions (ABCs) with free parameters in the formulation of the auxiliary variables. The spatial discretization is achieved by using fourth order finite differences and the time integration is made by means of an efficient and easy to implement fourth order exponential splitting scheme which was used in Alonso-Mallo and Portillo (2016) considering the fixed Padé parameters in the formulation of the ABCs. Here, we generalize the splitting time technique to other choices of the parameters. To check the timeintegrator we consider, on one hand, fourty peso ffixed parameters, the Newmann’s parameters, the Chebyshev’s parameters, the Padé’s parameters and optimal parameters proposed in Hagstrom et al. (2007) and, on the other hand, an adaptive scheme for the dynamic control of the order of absorption and the parameters. We study the efficiency of the splitting scheme by comparing with thefourth-order four-stage Runge–Kutta method.MTM2015-66837-P del Ministerio de Economía y Competitivida

Retinoic Acid Disturbs Mouse Middle Ear Development in a Stage-Dependent Fashion

AbstractThe mammalian middle ear contains a chain of three ossicles, the malleus, incus, and stapes, that transmit into the inner ear the vibrations produced in the tympanic membrane by aerial sound. I show here that retinoic acid interferes with the formation of the middle ear in a stage-specific fashion. The malformations produced are derived from a retinoic acid-induced inhibition of the formation and/or migration of the cranial neural crest that generates the middle ear skeletal elements and not from a respecification of neural crest identity to more posterior fates. I have used these effects of retinoic acid to analyze the temporal sequence of events involved in the morphogenesis of the middle ear. I show that the middle ear bones develop from several primordia that originate in a typical temporal sequence from Day 8 plus 4.5 hr to Day 8 plus 7.5 hr of pregnancy. Moreover, interactions between adjacent bones are not required for their proper formation. My results also suggest aHoxa-2-mediated patterning of the otic capsule in the region where the oval window is located

Evidentiary Support Needed for Successful Proof of Claim Against Affiliated Debtors

(Excerpt) According to title 11 of the United States Code (the “Bankruptcy Code) and the Federal Rules of Bankruptcy Procedure (the “Bankruptcy Rules”), a debtor must file schedules of the debtor’s assets and liabilities. A debtor’s schedules would include a list of all known claims against the debtor and list the claims as disputed, contingent or unliquidated. If an entity believes they have a claim against the debtor that the debtor has not included on a schedule, or the claim is disputed, contingent, or unliquidated, that party can file a proof of claim. A proof of claim in a bankruptcy case is the creditor’s statement as to the amount and character of their claim. A claimant will file the claim for purposes of distributions and voting on the reorganization plan. There are certain situations when a claimant must file multiple proofs of claim and there are certain situations when a creditor should not. Part I of this article deals primarily with the procedural nature of filing a proof of claim. Part II examines who has the burden of proof when a claimant files a proof of claim. Part III concludes by analyzing whether a claimant should file a proof of claim against multiple debtors in a bankruptcy proceeding for affiliated companies

Revisiting the involvement of signaling gradients in somitogenesis

During embryonic development, formation of individual vertebrae requires that the paraxial mesoderm becomes divided into regular segmental units known as somites. Somites are sequentially formed at the anterior end of the presomitic mesoderm (PSM) resulting from functional interactions between the oscillatory activity of signals promoting segmentation and a moving wavefront of tissue competence to those signals, eventually generating a constant flow of new somites at regular intervals. According to the current model for somitogenesis, the wavefront results from the combined activity of two opposing functional gradients in the PSM involving the Fgf, Wnt and retinoic acid (RA) signaling pathways. Here, I use published data to evaluate the wavefront model. A critical analysis of those studies seems to support a role for Wnt signaling, but raise doubts regarding the extent to which Fgf and RA signaling contribute to this process.Não existem patrocinadores ou projectos indicados no artigo

Development of Violence and Sectarianism in Lebanon

The pattern and acceptance of sectarianism and the resultant ethnic violence in Lebanon can be traced back to the mid-19th century as the result of European involvement in the Levant. Through the history of Lebanon in the 19th and 20th centuries, the modern sectarianism and ethnic violence can be better understood as results of international intervention and interference