Intestine in the lung

The phenomenon of metaplasia, in which one tissue type is converted into another, is beginning to be explained in molecular terms. The transformation of lung to intestinal tissue has not previously been described, but it is now reported that it can be brought about by prolonged Wnt signaling in late development

Can There Be Too Much Specialization? Specialization in Specialized Courts

While modern society has embraced specialization, the federal judiciary continues to prize the generalist jurist. This disconnect is at the core of the growing debate on the optimal level of specialization in the judiciary. To date, this discussion has largely revolved around the creation of specialized courts. Opinion specialization, however, provides an alternative, underappreciated method to infuse specialization into the judiciary. In contrast to specialized courts, opinion specialization is understudied and undertheorized. This Article makes two contributions to the literature. First, this Article theorizes whether opinion specialization is a desirable practice. It argues that the practice’s costs and benefits are a function of whether the court itself is specialized. More specifically, this Article contends that while opinion specialization may be normatively desirable for generalist courts, it is likely not for specialized tribunals. Perhaps most concerning, this Article argues that opinion specialization in specialized courts increases the likelihood legal doctrine will reflect the idiosyncratic preferences of a few judges. Second, given the concerns associated with opinion specialization in specialized tribunals, this Article empirically tests the extent to which specialization occurs in these specialized courts. We approach this question by examining the process of opinion assignment in the U.S. Court of Appeals for the Federal Circuit, which is best known for its near-exclusive jurisdiction over patent appeals. Utilizing a novel, author-constructed database of Federal Circuit opinions issued between 2004 and 2018, we find that opinion specialization is a robust part of the Federal Circuit’s practice. This Article demonstrates that opinion specialization may have led to several highly criticized legal developments at the Federal Circuit, exploring mechanisms in which opinion specialization may be diminished, and examining the implications of our findings for the broader judiciary

An amphibian with ambition: a new role for Xenopus in the 21st century

Much of our knowledge about the mechanisms of vertebrate early development comes from studies using Xenopus laevis. The recent development of a remarkably efficient method for generating transgenic embryos is now allowing study of late development and organogenesis in Xenopus embryos. Possibilities are also emerging for genomic studies using the closely related diploid frog Xenopus tropicalis

Regeneration of neural crest derivatives in the Xenopus tadpole tail

<p>Abstract</p> <p>Background</p> <p>After amputation of the <it>Xenopus </it>tadpole tail, a functionally competent new tail is regenerated. It contains spinal cord, notochord and muscle, each of which has previously been shown to derive from the corresponding tissue in the stump. The regeneration of the neural crest derivatives has not previously been examined and is described in this paper.</p> <p>Results</p> <p>Labelling of the spinal cord by electroporation, or by orthotopic grafting of transgenic tissue expressing GFP, shows that no cells emigrate from the spinal cord in the course of regeneration.</p> <p>There is very limited regeneration of the spinal ganglia, but new neurons as well as fibre tracts do appear in the regenerated spinal cord and the regenerated tail also contains abundant peripheral innervation.</p> <p>The regenerated tail contains a normal density of melanophores. Cell labelling experiments show that melanophores do not arise from the spinal cord during regeneration, nor from the mesenchymal tissues of the skin, but they do arise by activation and proliferation of pre-existing melanophore precursors. If tails are prepared lacking melanophores, then the regenerates also lack them.</p> <p>Conclusion</p> <p>On regeneration there is no induction of a new neural crest similar to that seen in embryonic development. However there is some regeneration of neural crest derivatives. Abundant melanophores are regenerated from unpigmented precursors, and, although spinal ganglia are not regenerated, sufficient sensory systems are produced to enable essential functions to continue.</p

What is a stem cell?

The historical roots of the stem cell concept are traced with respect to its usage in embryology and in hematology. The modern consensus definition of stem cells, comprising both pluripotent stem cells in culture and tissue-specific stem cells in vivo, is explained and explored. Methods for identifying stem cells are discussed with respect to cell surface markers, telomerase, label retention and transplantability, and properties of the stem cell niche are explored. The CreER method for identifying stem cells in vivo is explained, as is evidence in favor of a stochastic rather than an obligate asymmetric form of cell division. In conclusion, it is found that stem cells do not possess any unique and specific molecular markers; and stem cell behavior depends on the environment of the cell as well as the stem cell's intrinsic qualities. Furthermore, the stochastic mode of division implies that stem cell behavior is a property of a cell population not of an individual cell. In this sense, stem cells do not exist in isolation but only as a part of multicellular system.</p

Virus-like particles: A flexible platform for universal influenza vaccine development

Human influenza remains a global public health threat, namely due to its evolutionary adaptability, which hinders effective prevention. Vaccination is currently the predominant tool in the prevention of infectious disease. However, current production methods for influenza vaccines are not only logistically inadequate in the face of a pandemic, but also rely on targeting two surface proteins on the influenza virus, which are prone to antigenic drift. As a consequence, a new vaccine needs to be developed for each new seasonal epidemic. Additionally, the vaccine strain needs to be selected around eight months prior to administration and can often be mismatched leaving the population unprotected. A ‘universal’ vaccine, effective irrespective of the surface proteins, would be desirable to offer cross-protectivity across strains. Tandem core virus-like particles (VLPs), expressed in methylotrophic yeast Pichia pastoris, are an exciting alternative to current manufacturing methods. VLPs, due to their inherent safety profile and advances in genetic engineering, have excellent potential both as standalone vaccines for the virus from which they are derived, or as platforms for the display of foreign antigens. The hepatitis B core antigen (HBcAg) is able to spontaneously self-assemble, forming icosahedral particles that are inherently immunogenic. Moreover, the HBcAg is capable of carrying antigen inserts in the major insertion region (MIR) which are displayed on the particle surface. In order for VLPs to be considered a viable alternative, their bioprocessing must be optimized. Currently, various issues are at play including problems with formation, solubility and immunogenicity, often clone dependent. In this work, two genetically linked HBcAg monomers, carrying different inserts in the MIR, were used to study the effects on fermentation efficiencies using two different induction strategies. Rationalizing an induction strategy would enable the development of an efficient process to produce and purify VLPs. Results indicate that increased biomass is not always synonymous with increased protein expression. Moreover, protein expression and solubility appear to be linked with the complexity of the inserts displayed on the VLP surface. The aim of this work is to improve the bioprocessing of VLPs in a microbial expression system, using tandem core technology. This proposed method is cheap and rapidly scalable, reduces the cost per dose and eliminates the long production timelines associated with current manufacturing. The very nature of VLPs and the comparable ease of production would enable this to be promoted as a platform process, for a myriad of disease targets

In vitro culture of embryonic mouse intestinal epithelium: cell differentiation and introduction of reporter genes

BACKGROUND: Study of the normal development of the intestinal epithelium has been hampered by a lack of suitable model systems, in particular ones that enable the introduction of exogenous genes. Production of such a system would advance our understanding of normal epithelial development and help to shed light on the pathogenesis of intestinal neoplasia. The criteria for a reliable culture system include the ability to perform real time observations and manipulations in vitro, the preparation of wholemounts for immunostaining and the potential for introducing genes. RESULTS: The new culture system involves growing mouse embryo intestinal explants on fibronectin-coated coverslips in basal Eagle's medium+20% fetal bovine serum. Initially the cultures maintain expression of the intestinal transcription factor Cdx2 together with columnar epithelial (cytokeratin 8) and mesenchymal (smooth muscle actin) markers. Over a few days of culture, differentiation markers appear characteristic of absorptive epithelium (sucrase-isomaltase), goblet cells (Periodic Acid Schiff positive), enteroendocrine cells (chromogranin A) and Paneth cells (lysozyme). Three different approaches were tested to express genes in the developing cultures: transfection, electroporation and adenoviral infection. All could introduce genes into the mesenchyme, but only to a small extent into the epithelium. However the efficiency of adenovirus infection can be greatly improved by a limited enzyme digestion, which makes accessible the lateral faces of cells bearing the Coxsackie and Adenovirus Receptor. This enables reliable delivery of genes into epithelial cells. CONCLUSION: We describe a new in vitro culture system for the small intestine of the mouse embryo that recapitulates its normal development. The system both provides a model for studying normal development of the intestinal epithelium and also allows for the manipulation of gene expression. The explants can be cultured for up to two weeks, they form the full repertoire of intestinal epithelial cell types (enterocytes, goblet cells, Paneth cells and enteroendocrine cells) and the method for gene introduction into the epithelium is efficient and reliable

Animal regeneration:Ancestral character or evolutionary novelty?

An old question about regeneration is whether it is an ancestral character which is a general property of living matter, or whether it represents a set of specific adaptations to the different circumstances faced by different types of animal. In this review, some recent results on regeneration are assessed to see if they can throw any new light on this question. Evidence in favour of an ancestral character comes from the role of Wnt and bone morphogenetic protein signalling in controlling the pattern of whole-body regeneration in acoels, which are a basal group of bilaterian animals. On the other hand, there is some evidence for adaptive acquisition or maintenance of the regeneration of appendages based on the occurrence of severe non-lethal predation, the existence of some novel genes in regenerating organisms, and differences at the molecular level between apparently similar forms of regeneration. It is tentatively concluded that whole-body regeneration is an ancestral character although has been lost from most animal lineages. Appendage regeneration is more likely to represent a derived character resulting from many specific adaptations.</p

Reprogramming of pancreatic exocrine cells towards a beta (β) cell character using Pdx1, Ngn3 and MafA

Pdx1 (pancreatic and duodenal homeobox 1), Ngn3 (neurogenin 3) and MafA (v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A) have been reported to bring about the transdifferentiation of pancreatic exocrine cells to beta (β) cells in vivo. We have investigated the mechanism of this process using a standard in vitro model of pancreatic exocrine cells, the rat AR42j-B13 cell line. We constructed a new adenoviral vector encoding all three genes, called Ad-PNM (adenoviral Pdx1, Ngn3, MafA construct). When introduced into AR42j-B13 cells, Ad-PNM caused a rapid change to a flattened morphology and a cessation of cell division. The expression of exocrine markers is suppressed. Both insulin genes are up-regulated as well as a number of transcription factors normally characteristic of beta cells. At the chromatin level, histone tail modifications of the Pdx1, Ins1 (insulin 1) and Ins2 (insulin 2) gene promoters are shifted in a direction associated with gene activity, and the level of DNA CpG methylation is reduced at the Ins1 promoter. The transformed cells secrete insulin and are capable of relieving diabetes in streptozotocin-treated NOD-SCID (non-obese diabetic severe combined immunodeficiency) mice. However the transformation is not complete. The cells lack expression of several genes important for beta cell function and they do not show glucose-sensitive insulin secretion. We conclude that, for this exocrine cell model, although the transformation is dramatic, the reprogramming is not complete and lacks critical aspects of the beta cell phenotype