A periodic pattern generator for dental diversity

© 2008 Fraser et al; licensee BioMed Central Ltd. The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1741-7007/6/32DOI:10.1186/1741-7007-6-22Background: Periodic patterning of iterative structures is a fundamental process during embryonic organization and development. Studies have shown how gene networks are employed to pattern butterfly eyespots, fly bristles and vertebrate epithelial appendages such as teeth, feathers, hair and mammary glands. Despite knowledge of how these features are organized, little is known about how diversity in periodic patterning is generated in nature. We address this problem through the molecular analysis of oral jaw dental diversity in Lake Malawi cichlids, where closely related species exhibit from 1 to 20 rows of teeth, with total teeth counts ranging from around 10 to 700. Results: We investigate the expression of conserved gene networks (involving bmp2, bmp4, eda, edar, fgf8, pax9, pitx2, runx2, shh and wnt7b) known to pattern iterative structures and teeth in other vertebrates. We show that spatiotemporal variation in expression pattern reflects adult morphological diversity among three closely related Malawi cichlid species. Combinatorial epithelial expression of pitx2 and shh appears to govern the competence both of initial tooth sites and future tooth rows. Epithelial wnt7b and mesenchymal eda are expressed in the inter-germ and inter-row regions, and likely regulate the spacing of these shh-positive units. Finally, we used chemical knockdown to demonstrate the fundamental role of hedgehog signalling and initial placode formation in the organization of the periodically patterned cichlid dental programme. Conclusion: Coordinated patterns of gene expression differ among Malawi species and prefigure the future-ordered distribution of functional teeth of specific size and spacing. This variation in gene expression among species occurs early in the developmental programme for dental patterning. These data show how a complex multi-rowed vertebrate dentition is organized and how developmental tinkering of conserved gene networks during iterative pattern formation can impact upon the evolution of trophic novelty

A etnografia como extensão da guerra por outros meios: notas sobre a pesquisa com militares

Este artigo pretende abordar resultados e consequências da realização de pesquisas etnográficas com militares. Partindo de uma discussão mais ampla sobre a ideia de antropólogos trabalhando "com militares", pretendo posteriormente situar os resultados de uma etnografia realizada no Exército brasileiro, tomada a partir de sintomas e/ou efeitos colaterais ocorridos durante e depois da pesquisa de campo. Ao retomar a relação estabelecida, e também a que não foi estabelecida, foi possível constatar a centralidade dos conceitos de "amigo" e "inimigo", para definir um amplo escopo de ligações entre o universo militar e o "mundo de fora". Tais conceitos, de início tomados como relações derivadas de uma noção nativa de guerra, em certa medida projetam-se nas relações entre militares e pesquisadores, o que levou a tratar a etnografia, neste caso específico, em continuidade com uma noção antropológica (posteriormente transformada) de guerra: guerra como relação. A partir dessa premissa relacional, pretende-se pensar algumas consequências metodológicas para uma antropologia deste tipo de objeto de pesquisa.<br>This article investigates the results and consequences of carrying out ethnographic research with the military. Beginning with a wide-ranging discussion of the idea of anthropologists working "with the military", I then seek to situate the results of an ethnography carried out with the Brazilian Army through the symptoms and/or collateral effects that were visible both during and after my research. By taking up the relationship that was established, and also that which was not, it was possible to observe the centrality of the concepts of "friend" and "enemy" in the definition of a wide range of ties between the military world and the "outside world". These concepts, which were initially understood to be relationships derived from a native notion of warfare, project themselves, to some extent, upon the relationships between military men and researchers, which, in this specific case, led me to approach ethnography in continuity with a, formerly transformed, anthropological notion of warfare: warfare as relation. From this relational premise, I will investigate certain methodological consequences of an anthropology of this sort of research object

Skeletogenesis and sequence heterochrony in rodent evolution, with particular emphasis on the African striped mouse, Rhabdomys pumilio (Mammalia)

Data documenting skeletal development in rodents, the most species-rich ‘order’ of mammals, are at present restricted to a few model species, a shortcoming that hinders exploration of the morphological and ecological diversification of the group. In this study we provide the most comprehensive sampling of rodent ossification sequences to date, with the aim of exploring whether heterochrony is ubiquitous in rodent evolution at the onset of skeletal formation. The onset of ossification in 17 cranial elements and 24 postcranial elements was examined for eight muroid and caviomorph rodent species. New data are provided for two non-model species. For one of these, the African striped mouse, Rhabdomys pumilio, sampling was extended by studying 53 autopodial elements and examining intraspecific variation. The Parsimov method of studying sequence heterochrony was used to explore the role that changes in developmental timing play in early skeletal formation. Few heterochronies were found to diagnose the muroid and caviomorph clades, suggesting conserved patterning in skeletal development. Mechanisms leading to the generation of the wide range of morphological diversity encapsulated within Rodentia may be restricted to later periods in development than those studied in this work. Documentation of skeletogenesis in Rhabdomys indicates that intraspecifc variation in ossification sequence pattern is present, though not extensive. Our study suggests that sequence heterochrony is neither pivotal nor prevalent during early skeletal formation in rodents