Dual epithelial origin of vertebrate oral teeth

The oral cavity of vertebrates is generally thought to arise as an ectodermal invagination. Consistent with this, oral teeth are proposed to arise exclusively from ectoderm, contributing to tooth enamel epithelium, and from neural crest derived mesenchyme, contributing to dentin and pulp. Yet in many vertebrate groups, teeth are not restricted only to the oral cavity, but extend posteriorly as pharyngeal teeth that could be derived either directly from the endodermal epithelium, or from the ectodermal epithelium that reached this location through the mouth or through the pharyngeal slits. However, when the oropharyngeal membrane, which forms a sharp ecto/endodermal border, is broken, the fate of these cells is poorly known. Here, using transgenic axolotls with a combination of fate-mapping approaches, we present reliable evidence of oral teeth derived from both the ectoderm and endoderm and, moreover, demonstrate teeth with a mixed ecto/endodermal origin. Despite the enamel epithelia having a different embryonic source, oral teeth in the axolotl display striking developmental uniformities and are otherwise identical. This suggests a dominant role for the neural crest mesenchyme over epithelia in tooth initiation and, from an evolutionary point of view, that an essential factor in teeth evolution was the odontogenic capacity of neural crest cells, regardless of possible 'outside-in' or 'inside-out' influx of the epithelium.     

The first hominin of Europe

The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins.     

A photosynthetic alveolate closely related to apicomplexan parasites

Many parasitic Apicomplexa, such as Plasmodium falciparum, contain an unpigmented chloroplast remnant termed the apicoplast, which is a target for malaria treatment. However, no close relative of apicomplexans with a functional photosynthetic plastid has yet been described. Here we describe a newly cultured organism that has ultrastructural features typical for alveolates, is phylogenetically related to apicomplexans, and contains a photosynthetic plastid. The plastid is surrounded by four membranes, is pigmented by chlorophyll a, and uses the codon UGA to encode tryptophan in the psbA gene. This genetic feature has been found only in coccidian apicoplasts and various mitochondria. The UGA-Trp codon and phylogenies of plastid and nuclear ribosomal RNA genes indicate that the organism is the closest known photosynthetic relative to apicomplexan parasites and that its plastid shares an origin with the apicoplasts. The discovery of this organism provides a powerful model with which to study the evolution of parasitism in Apicomplexa.     

Biodegradable zinc-iron alloys: Complex study of corrosion behavior,mechanical properties and hemocompatibility

Zn-Fe alloys have been extensively investigated in this study with a view to their application as biodegradable bone implants. Biogenic element zinc is a very appropriate metal because of the ideal degradation rate compared to those of Mg and Fe. Studied alloys were made by compressing metallic powders in a content ratio of 100% Zn,Zn-1% Fe, Zn-2% Fe, Zn-5% Fe and Zn-10% Fe and sintering at 350°C for 1 h. Prepared samples were examined by optical microscopy, SEM and XRD. Corrosion behavior, mechanical testing and hemocompatibility were observed subsequently. The electrochemical performance of such materials was studied in the simulated body fluids. The enhanced corrosion rate was observed for all samples after iron addition due to the micro-galvanic effect between the pure Zn and Zn_(11)Fe intermetallic phase. The corrosion rate of the Zn-5% Fe alloyed sample was more than 20-times higher(2.89 mmpy) compared to the pure Zn. However, alloying with more than 5 wt %of iron diminished the mechanical performance of the material. Therefore, the performed mechanical and hemocompatibility tests showed acceptable biocompatibility of zinc and Zn-1% Fe and Zn-2% Fe samples.     

AN AUTOMATED REFERENCE POINT-LIKE APPROACH FOR MULTICRITERIA SHORTEST PATH PROBLEMS

1. Introduction Nowadays the exponential and convergent development of informatics and telecommunications, including Internet, makes that, in many communication networks, important decisions of technical nature have to be made in short time periods or even in real-time. This is particularly relevant in the context of routing models involving the calculation and selection of routes (corresponding to loopless paths) for node to node traffic flows, which seek to optimize certain metric(s) while s…     

A Cretaceous terrestrial snake with robust hindlimbs and a sacrum

It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.     

Assembly of the inner rod determines needle length in the type III secretion injectisome

Assembly of multi-component supramolecular machines is fundamental to biology, yet in most cases, assembly pathways and their control are poorly understood. An example is the type III secretion machine, which mediates the transfer of bacterial virulence proteins into host cells. A central component of this nanomachine is the needle complex or injectisome, an organelle associated with the bacterial envelope that is composed of a multi-ring base, an inner rod, and a protruding needle. Assembly of this organelle proceeds in sequential steps that require the reprogramming of the secretion machine. Here we provide evidence that, in Salmonella typhimurium, completion of the assembly of the inner rod determines the size of the needle substructure. Assembly of the inner rod, which is regulated by the InvJ protein, triggers conformational changes on the cytoplasmic side of the injectisome, reprogramming the secretion apparatus to stop secretion of the needle protein.     

Organizational Model Design for Small Coffee Farmers in the Municipality of Viotá - Colombia Case Study: Creo en el Agro

Systemic Practice and Action Research - An organizational design proposal is made for Creo en el Agro, an organization made up of small coffee growers who were victims of the armed conflict in the...