Neural crest stem cells undergo multilineage differentiation in developing peripheral nerves to generate endoneurial fibroblasts in addition to Schwann cells

Neural crest stem cells (NCSCs) persist in peripheral nerves throughout late gestation but their function is unknown. Current models of nerve development only consider the generation of Schwann cells from neural crest, but the presence of NCSCs raises the possibility of multilineage differentiation. We performed Cre-recombinase fate mapping to determine which nerve cells are neural crest derived. Endoneurial fibroblasts, in addition to myelinating and non-myelinating Schwann cells, were neural crest derived, whereas perineurial cells, pericytes and endothelial cells were not. This identified endoneurial fibroblasts as a novel neural crest derivative, and demonstrated that trunk neural crest does give rise to fibroblasts in vivo, consistent with previous studies of trunk NCSCs in culture. The multilineage differentiation of NCSCs into glial and non-glial derivatives in the developing nerve appears to be regulated by neuregulin, notch ligands, and bone morphogenic proteins, as these factors are expressed in the developing nerve, and cause nerve NCSCs to generate Schwann cells and fibroblasts, but not neurons, in culture. Nerve development is thus more complex than was previously thought, involving NCSC self-renewal, lineage commitment and multilineage differentiation

A game theoretic model of kleptoparasitism with strategic arrivals and departures of beetles at dung pats

Dung beetles Onthophagus taurus lay their eggs in brood balls within dung pats. The dung that is used must be sufficiently fresh, and so beetles must keep moving from pat to pat to find fresh dung. If another beetle finds a brood ball it will usually eat the egg inside and lay its own egg in the brood ball instead of constructing its own ball. Thus, beetles will often stay near their eggs to guard them. We model a population of beetles where the times of arrival and departure from pats are strategic choices, and investigate optimal strategies depending upon environmental conditions, which can be reduced to two key parameters, the cost of brood ball construction and the ease of finding balls to parasitise. We predict that beetles should follow one of three distinct behaviors; stay in patches for only short periods, arrive late and be purely parasitic, remain in pats for longer periods in order to guard their brood balls. Under different conditions populations can consist of the first of these types only, a combination of the first and second types, or a combination of all three types

First report of Crumillospongia (Demospongea) from the Cambrian of Europe (Murero biota, Spain)

The demosponge genus Crumillospongia, originally described from the Burgess Shale (middle Cambrian of Canada), has only been cited from lower and middle Cambrian localities of North America and China. The taxon is now also described from uppermost lower Cambrian rocks of the Murero Lagerstätte (Zaragoza Province, NE Spain). Crumillospongia mureroensis sp. nov. is a small to medium sized sack-shaped to elongate demosponge characterized by the presence of densely packed pores of three sizes, considerably larger than those in any other species of the genus. The Spanish material represents a link in the chronostratigraphical gap between the Chinese and North American material.Peer reviewe

Studio del processo di macinazione meccanica di un acciaio per lavorazioni a caldo

Gli acciai per lavorazioni a caldo sono caratterizzati da buona tenacità ed elevata durezza a caldo.La metallurgia delle polveri, grazie alla produzione di materiali con microstruttura più fine,consente di migliorare entrambe queste caratteristiche. In questo lavoro, una polvere di AISI H13atomizzata in gas è stata macinata meccanicamente in modo da ridurre sia la dimensione delleparticelle che la dimensione della grana cristallina. I risultati mostrano che dopo 1000 minuti dimacinazione in un mulino planetario a sfere la dimensione del grano può essere ridotta in modosignificativo fino a 15nm. L’elevato grado di deformazione introdotto nelle particelle attiva ilprocesso di sinterizzazione e di conseguenza la polvere può essere sinterizzata a temperature e pertempi inferiori. Per produrre campioni ad alta densità e per mantenere la dimensione della granafine (<1?m) la polvere è stata sinterizzata tramite Spark Plasma Sintering. La microstruttura e ladurezza dei campioni prodotti da polvere macinata sono state investigate e confrontate con quelle diun materiale prodotto con polvere atomizzata

A tissue-specific knockout reveals that Gata1 is not essential for Sertoli cell function in the mouse

The transcription factor Gata1 is essential for the development of erythroid cells. Consequently, Gata1 null mutants die in utero due to severe anaemia. Outside the haematopoietic system, Gata1 is only expressed in the Sertoli cells of the testis. To elucidate the function of Gata1 in the testis, we made a Sertoli cell-specific knockout of the Gata1 gene in the mouse. We deleted a normally functioning 'floxed' Gata1 gene in pre-Sertoli cells in vivo through the expression of Cre from a transgene driven by the Desert Hedgehog promoter. Surprisingly, Gata1 null testes developed to be morphologically normal, spermatogenesis was not obviously affected and expression levels of putative Gata1 target genes, and other Gata factors, were not altered. We conclude that expression of Gata1 in Sertoli cells is not essential for testis development or spermatogenesis in the mouse

150 años del descubrimiento del yacimiento cámbrico de Murero (Cadenas Ibéricas, NE España).

The lower-middle Cambrian palaeontological site of Murero (Cadenas Ibéricas, NE Spain) is a classical locality of the Cambrian in Europe. The site was first reported by the French geologist Edouard de Verneuil in 1862, and now it achieves 150 years of geological works contributing to a better knowledge of the Cambrian Period. Murero is an exceptional Lagerstätte because the coexistence of both skeletal and soft-bodied groups along a continuous record of ca. 8 million years, which is subdivided into 14 trilobite zones. Murero was the first palaeontological site in Spain to obtain the highest protection figure (Bien de Interés Cultural, BIC) from the Spanish Administration in 1997. Since then, the educational and social projection of the site is continuously increasing

Combinatorial Markov chains on linear extensions

We consider generalizations of Schuetzenberger's promotion operator on the set L of linear extensions of a finite poset of size n. This gives rise to a strongly connected graph on L. By assigning weights to the edges of the graph in two different ways, we study two Markov chains, both of which are irreducible. The stationary state of one gives rise to the uniform distribution, whereas the weights of the stationary state of the other has a nice product formula. This generalizes results by Hendricks on the Tsetlin library, which corresponds to the case when the poset is the anti-chain and hence L=S_n is the full symmetric group. We also provide explicit eigenvalues of the transition matrix in general when the poset is a rooted forest. This is shown by proving that the associated monoid is R-trivial and then using Steinberg's extension of Brown's theory for Markov chains on left regular bands to R-trivial monoids.Comment: 35 pages, more examples of promotion, rephrased the main theorems in terms of discrete time Markov chain

Evolution and mutagenesis of the mammalian excision repair gene ERCC-1

The human DNA excision repair protein ERCC-1 exhibits homology to the yeast RADIO repair protein and its longer C-terminus displays similarity to parts of the E.coli repair proteins uvrA and uvrC. To study the evolution of this 'mosaic' ERCC-1 gene we have isolated the mouse homologue. Mouse ERCC-1 harbors the same pattern of homology with RAD10 and has a comparable C-terminal extension as its human equivalent. Mutation studies show that the strongly conserved C-terminus is essential in contrast to the less conserved N-terminus which is even dispensible. The mouse ERCC-1 amino acid sequence is compatible with a previously postulated nuclear location signal and DNA-binding domain. The ERCC-1 promoter harbors a region which is highly conserved in mouse and man. Since the ERCC-1 promoter is devoid of all classical promoter elements this region may be responsible for the low constitutive level of expression in all mouse tissues and stages of embryogenesis examined