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The vertebrate body is made by progressive addition of new tissue from progenitors at the posterior embryonic end. Axial extension involves different mechanisms that produce internal organs in the trunk but not in the tail. We show that Gdf11 signaling is a major coordinator of the trunk-to-tail transition. Without Gdf11 signaling, the switch from trunk to tail is significantly delayed, and its premature activation brings the hindlimbs and cloaca next to the forelimbs, leaving extremely short trunks. Gdf11 activity includes activation of Isl1 to promote formation of the hindlimbs and cloaca-associated mesoderm as the most posterior derivatives of lateral mesoderm progenitors. Gdf11 also coordinates reallocation of bipotent neuromesodermal progenitors from the anterior primitive streak to the tail bud, in part by reducing the retinoic acid available to the progenitors. Our findings provide a perspective to understand the evolution of the vertebrate body plan.

Schistosomiasis is a water-borne parasitic illness caused by neoophoran trematodes of the genus Schistosoma. Using classical histological techniques and whole-mount preparations, the present work describes the embryonic development of Schistosoma mansoni eggs in the murine host and compares it with eggs maintained under in vitro conditions. Two pre-embryonic stages occur inside the female worm: the prezygotic stage is characterized by the release of mature oocytes from the female ovary until its fertilization. The zygotic stage encompasses the migration of the zygote through the ootype, where the eggshell is formed, to the uterus. Fully formed eggs are laid still undeveloped, without having suffered any cleavage. In the outside environment, eight embryonic stages can be defined: stage 1 refers to early cleavages and the beginning of yolk fusion. Stage 2 represents late cleavage, with the formation of a stereoblastula and the onset of outer envelope differentiation. Stage 3 is defined by the elongation of the embryonic primordium and the onset of inner envelope formation. At stage 4, the first organ primordia arise. During stages 5 to 7, tissue and organ differentiation occurs (neural mass, epidermis, terebratorium, musculature, and miracidial glands). Stage 7 is characterized by the nuclear condensation of neurons of the central neural mass. Stage 8 refers to the fully formed larva, presenting muscular contraction, cilia, and flame-cell beating. This staging system was compared to a previous classification and could underlie further studies on egg histoproteomics (morphological localizome). The differentiation of embryonic structures and their probable roles in granulomatogenesis are discussed herein.

Vertebrates exhibit a remarkably broad variation in trunk and tail lengths. However, the evolutionary and developmental origins of this diversity remain largely unknown. Posterior Hox genes were proposed to be major players in trunk length diversification in vertebrates, but functional studies have so far failed to support this view. Here we identify the pluripotency factor Oct4 as a key regulator of trunk length in vertebrate embryos. Maintaining high Oct4 levels in axial progenitors throughout development was sufficient to extend trunk length in mouse embryos. Oct4 also shifted posterior Hox gene-expression boundaries in the extended trunks, thus providing a link between activation of these genes and the transition to tail development. Furthermore, we show that the exceptionally long trunks of snakes are likely to result from heterochronic changes in Oct4 activity during body axis extension, which may have derived from differential genomic rearrangements at the Oct4 locus during vertebrate evolution.

Faecal exams are widely used for the diagnosis of intestinal helminth infections because microscopic findings of parasitic structures typically assure reliable and accurate identification of the parasites. Although several types of qualitative and quantitative methods exist for stool examination (Lutz 1919, Hastings-Willis 1921, Faust & Melency 1924, Hoffman et al. 1934, Stoll 1946, Ritchie 1948, Sapero et al. 1951, Kato & Miura 1954, Blagg et al. 1955, Bell 1963, Katz et al. 1972, some of these techniques have operational limitations, including high cost, complexity, low sensitivity and/or reproducibility. These limitations may restrict their respective uses in large-scale surveys in the field.A method commonly used in epidemiological studies due to its relative simplicity and low cost is the quantitative Kato-Katz faecal smear technique (Katz et al. 1972). Katz et al. (1970) showed the limit of sensitivity for this method to be 20 eggs per gram of faeces by recovering Schistosoma mansoni eggs that were added to negative human faecal samples. This exam is considered to be the gold standard for diagnosing schistosomiasis mansoni as per the World Health Organization (WHO 1993). Although this method is widely used, the Kato-Katz test might lack sensitivity in situations of low worm burden, low endemicity and in cases of evaluation post treatment (Ferrari et al. 2003). To overcome these limitations, it is necessary to increase the number of stool samples, which may increase costs and possibly cause logistic difficulties in epidemiological surveys (Enk et al. 2008).Alternative approaches based on antibody, antigen and DNA detection are of potential application, but when the financial and infrastructural difficulties of most endemic countries are taken into consideration, these techniques become unsatisfactory (WHO 2006b). Perhaps as an opposite effect of successful control programs worldwide, the diagnosis of schistosomiasis still needs a more sensitive and low-cost tool for detecting light infections in the field (WHO 2006a). Recently, two novel methods have been proposed. Teixeira et al. (2007) developed a highly sensitive method (named Helmintex) for identifying S. mansoni eggs in large amounts of faeces. Faecal samples of 30 g were processed through a sequence of spontaneous sedimentation, sieving and the Ritchie method and then incubated with or without lectins. This was followed by isolation through interaction with paramagnetic beads and microscopic inspection. The other method consists of a hatching device containing a collecting container for the detection of miracidia (Jurberg et al. 2008). Although hatching methods are highly sensitive, they have an obvious limitation because the faecal samples must be fresh at the moment of the exam. On the other hand, the miracidia suspension fixed in 10% formaldehyde solution could be examined for at least 15 days after the fixation without a statistically significant loss of the miracidia number.In an attempt to develop more sensitive diagnostic tools for schistosomia...

Extension of the vertebrate body results from the concerted activity of many signals in the posterior embryonic end. Among them, Wnt3a has been shown to play relevant roles in the regulation of axial progenitor activity, mesoderm formation and somitogenesis. However, its impact on axial growth remains to be fully understood. Using a transgenic approach in the mouse, we found that the effect of Wnt3a signaling varies depending on the target tissue. High levels of Wnt3a in the epiblast prevented formation of neural tissues, but did not impair axial progenitors from producing different mesodermal lineages. These mesodermal tissues maintained a remarkable degree of organization, even within a severely malformed embryo. However, from the cells that failed to take a neural fate, only those that left the epithelial layer of the epiblast activated a mesodermal program. The remaining tissue accumulated as a folded epithelium that kept some epiblast-like characteristics. Together with previously published observations, our results suggest a dose-dependent role for Wnt3a in regulating the balance between renewal and selection of differentiation fates of axial progenitors in the epiblast. In the paraxial mesoderm, appropriate regulation of Wnt/β-catenin signaling was required not only for somitogenesis, but also for providing proper anterior-posterior polarity to the somites. Both processes seem to rely on mechanisms with different requirements for feedback modulation of Wnt/β-catenin signaling, once segmentation occurred in the presence of high levels of Wnt3a in the presomitic mesoderm, but not after permanent expression of a constitutively active form of β-catenin. Together, our findings suggest that Wnt3a/β-catenin signaling plays sequential roles during posterior extension, which are strongly dependent on the target tissue. This provides an additional example of how much the functional output of signaling systems depends on the competence of the responding cells.

It is still imperative to develop a parasitological

S U M M A R YWe have observed that when cercariae penetrate the skin of mice, there is influx into their tissues of Lucifer Yellow and certain labelled molecules of up to 20 kDa molecular weight. This observation was made using a variety of fluorescent membrane-impermeant compounds injected into the skin before the application of cercariae. This unexpected phenomenon was investigated further by transforming cercariae in vitro in the presence of the membrane-impermeant compounds and examining the distribution by microscopy. In schistosomula derived from this procedure, the nephridiopore and surface membrane were labelled while the pre-and post-acetabular glands were not labelled. The region associated with the oesophagus within the pharyngeal muscle clearly contained the fluorescent molecules, as did the region adjacent to the excretory tubules and the germinal mass. We used cercariae stained with carmine to aid identification of regions labelled with Lucifer Yellow. Although the mechanism of this influx is unclear, the observation is significant. From it, we can suggest an hypothesis that, during skin penetration, exposure of internal tissues of the parasite to external macromolecules represents a novel host-parasite interface.