The strength of SMAD1/5 activity determines the mode of stem cell division in the developing spinal cord

The different modes of stem cell division are tightly regulated to balance growth and differentiation during organ development and homeostasis. However, the mechanisms controlling such events are not fully understood. We have developed markers that provide the single cell resolution necessary to identify the three modes of division occurring in a developing nervous system: self-expanding, self-renewing, and self-consuming. Characterizing these three modes of division during interneuron generation in the developing chick spinal cord, we demonstrated that they correlate to different levels of activity of the canonical bone morphogenetic protein effectors SMAD1/5. Functional in vivo experiments showed that the premature neuronal differentiation and changes in cell cycle parameters caused by SMAD1/5 inhibition were preceded by a reduction of self-expanding divisions in favor of self-consuming divisions. Conversely, SMAD1/5 gain of function promoted self-expanding divisions. Together, these results lead us to propose that the strength of SMAD1/5 activity dictates the mode of stem cell division during spinal interneuron generation.     

Orthologs of key vertebrate neural genes are expressed during neurogenesis in the annelid Platynereis dumerilii

SUMMARY The molecular mechanisms underlying the formation and patterning of the nervous system are relatively poorly understood for lophotrochozoans (like annelids) as compared with ecdysozoans (especially Drosophila ) and deuterostomes (especially vertebrates). Therefore, we have undertaken a candidate gene approach to study aspects of neurogenesis in a polychaete annelid Platynereis dumerilii . We determined the spatiotemporal expression for Platynereis orthologs of four genes ( SoxB, Churchill, prospero / Prox , and SoxC) known to play key roles in vertebrate neurogenesis. During Platynereis development, SoxB is expressed in the neuroectoderm and its expression switches off when committed neural precursors are formed. Subsequently, Prox is expressed in all differentiating neural precursors in the central and peripheral nervous systems. Finally, SoxC and Churchill are transcribed in patterns consistent with their involvement in neural differentiation. The expression patterns of Platynereis SoxB and Prox closely resemble those in Drosophila and vertebrates—this suggests that orthologs of these genes play similar neurogenic roles in all bilaterians. Whereas Platynereis SoxC , like its vertebrate orthologs, plays a role in neural cell differentiation, related genes in Drosophila do not appear to be involved in neurogenesis. Finally, conversely to Churchill in Platynereis , vertebrate orthologs of this gene are expressed during neuroectoderm formation, but not later during nerve cell differentiation; in the insect lineage, homologs of these genes have been secondarily lost. In spite of such instances of functional divergence or loss, the present study shows conspicuous similarities in the genetic control of neurogenesis among bilaterians. These commonalities suggest that key features of the genetic program for neurogenesis are ancestral to bilaterians.     

Atx1-like chaperones and their cognate P-type ATPases: copper-binding and transfer

Copper is an essential yet toxic metal ion. To satisfy cellular requirements, while, at the same time, minimizing toxicity, complex systems of copper trafficking have evolved in all cell types. The best conserved and most widely distributed of these involve Atx1-like chaperones and P_1B-type ATPase transporters. Here, we discuss current understanding of how these chaperones bind Cu(I) and transfer it to the Atx1-like N-terminal domains of their cognate transporter.     

Advantages of Task-Specific Multi-Objective Optimisation in Evolutionary Robotics

The application of multi-objective optimisation to evolutionary robotics is receiving increasing attention. A survey of the literature reveals the different possibilities it offers to improve the automatic design of efficient and adaptive robotic systems, and points to the successful demonstrations available for both task-specific and task-agnostic approaches (i.e., with or without reference to the specific design problem to be tackled). However, the advantages of multi-objective approaches over single-objective ones have not been clearly spelled out and experimentally demonstrated. This paper fills this gap for task-specific approaches: starting from well-known results in multi-objective optimisation, we discuss how to tackle commonly recognised problems in evolutionary robotics. In particular, we show that multi-objective optimisation (i) allows evolving a more varied set of behaviours by exploring multiple trade-offs of the objectives to optimise, (ii) supports the evolution of the desired behaviour through the introduction of objectives as proxies, (iii) avoids the premature convergence to local optima possibly introduced by multi-component fitness functions, and (iv) solves the bootstrap problem exploiting ancillary objectives to guide evolution in the early phases. We present an experimental demonstration of these benefits in three different case studies: maze navigation in a single robot domain, flocking in a swarm robotics context, and a strictly collaborative task in collective robotics.     

Polypyrimidine Tract Binding Protein Prevents Activity of an Intronic Regulatory Element That Promotes Usage of a Composite 3��-Terminal Exon

Alternative splicing of 3′-terminal exons plays a critical role in gene expression by producing mRNA with distinct 3′-untranslated regions that regulate their fate and their expression. The Xenopus α-tropomyosin pre-mRNA possesses a composite internal/3′-terminal exon (exon 9A9′) that is differentially processed depending on the embryonic tissue. Exon 9A9′ is repressed in non-muscle tissue by the polypyrimidine tract binding protein, whereas it is selected as a 3′-terminal or internal exon in myotomal cells and adult striated muscles, respectively. We report here the identification of an intronic regulatory element, designated the upstream terminal exon enhancer (UTE), that is required for the specific usage of exon 9A9′ as a 3′-terminal exon in the myotome. We demonstrate that polypyrimidine tract binding protein prevents the activity of UTE in non-muscle cells, whereas a subclass of serine/arginine rich (SR) proteins promotes the selection of exon 9A9′ in a UTE-dependent way. Morpholino-targeted blocking of UTE in the embryo strongly reduced the inclusion of exon 9A9′ as a 3′-terminal exon in the endogenous mRNA, demonstrating the function of UTE under physiological circumstances. This strategy allowed us to reveal a splicing pathway that generates a mRNA with no in frame stop codon and whose steady-state level is translation-dependent. This result suggests that a non-stop decay mechanism participates in the strict control of the 3′-end processing of the α-tropomyosin pre-mRNA.     

A comparison of ferric-chelate reductase and chlorophyll and growth ratios as indices of selection of quince,pear and olive genotypes under iron deficiency stress

Quince (Cydonia oblonga Mill.), pear (Pyrus communis L.) and olive (Olea europaea L.) genotypes were evaluated for their tolerance to iron deficiency stress by growing young plants in three types of aerated nutrient solutions: (1) with iron, (2) without iron or (3) low in iron and with 10 mM bicarbonate. Plants were obtained either from rooted softwood cuttings or from germination of seeds. The degree of tolerance was evaluated with several indices: (1) the chlorophyll content, (2) the root Fe³⁺ reducing capacity and (3) the whole plant relative growth. Fifteen hours before Fe³⁺ reducing capacity determination, iron was applied to the roots of plants with iron-stress, since this method resulted in increasing the reductase activity. All quince and pear genotypes increased the root Fe³⁺ reducing capacity when grown in the treatments for iron-stress, in relation to control plants of the same genotypes. In olive cultivars, the Fe³⁺ reducing capacity was lower in the iron-stress treatments than in the control one. Studying the relationship between relative growth and chlorophyll content for each genotype under iron-stress, in relation to both indices in control plants, a classification of species and genotypes was established. According to that, most olive cultivars and some pear rootstocks and cultivars appear more iron-efficient than quince rootstocks. Our study shows that in some woody species, determining root Fe³⁺ reducing capacity is not the best method to establish tolerance to iron deficiency stress.