Analysis of xanthophore and pterinosome biogenesis in zebrafish using methylene blue and pteridine autofluorescence

We have identified two simple methods to analyse xanthophore and pterinosome biogenesis in zebrafish. The first uses methylene blue (methylthionium chloride), a redox dye which specifically labels xanthophores and pterinosomes, while the second uses autofluorescence to detect pteridine levels; these methods may be used to detect the number, location and shape of xanthophores and pterinosomes. These assays were applied to two zebrafish mutants--brie and yobo--and revealed that both mutants have pterinosome biogenesis and pteridine synthesis defects. Additionally, using capillary electrophoresis, we provide evidence that sepiapterin is responsible for the yellow colour and blue-light induced fluorescence in zebrafish embryos.     

In ovo transplantation of enteric nervous system precursors from vagal to sacral neural crest results in extensive hindgut colonisation

The enteric nervous system (ENS) is derived from vagal and sacral neural crest cells (NCC). Within the embryonic avian gut, vagal NCC migrate in a rostrocaudal direction to form the majority of neurons and glia along the entire length of the gastrointestinal tract, whereas sacral NCC migrate in an opposing caudorostral direction, initially forming the nerve of Remak, and contribute a smaller number of ENS cells primarily to the distal hindgut. In this study, we have investigated the ability of vagal NCC, transplanted to the sacral region of the neuraxis, to colonise the chick hindgut and form the ENS in an experimentally generated hypoganglionic hindgut in ovo model. Results showed that when the vagal NC was transplanted into the sacral region of the neuraxis, vagal-derived ENS precursors immediately migrated away from the neural tube along characteristic pathways, with numerous cells colonising the gut mesenchyme by embryonic day (E) 4. By E7, the colorectum was extensively colonised by transplanted vagal NCC and the migration front had advanced caudorostrally to the level of the umbilicus. By E10, the stage at which sacral NCC begin to colonise the hindgut in large numbers, myenteric and submucosal plexuses in the hindgut almost entirely composed of transplanted vagal NCC, while the migration front had progressed into the pre-umbilical intestine, midway between the stomach and umbilicus. Immunohistochemical staining with the pan-neuronal marker, ANNA-1, revealed that the transplanted vagal NCC differentiated into enteric neurons, and whole-mount staining with NADPH-diaphorase showed that myenteric and submucosal ganglia formed interconnecting plexuses, similar to control animals. Furthermore, using an anti-RET antibody, widespread immunostaining was observed throughout the ENS, within a subpopulation of sacral NC-derived ENS precursors, and in the majority of transplanted vagal-to-sacral NCC. Our results demonstrate that: (1) a cell autonomous difference exists between the migration/signalling mechanisms used by sacral and vagal NCC, as transplanted vagal cells migrated along pathways normally followed by sacral cells, but did so in much larger numbers, earlier in development; (2) vagal NCC transplanted into the sacral neuraxis extensively colonised the hindgut, migrated in a caudorostral direction, differentiated into neuronal phenotypes, and formed enteric plexuses; (3) RET immunostaining occurred in vagal crest-derived ENS cells, the nerve of Remak and a subpopulation of sacral NCC within hindgut enteric ganglia.     

Negative effect of Hox gene expression on the development of the neural crest-derived facial skeleton

Diencephalic, mesencephalic and metencephalic neural crest cells are skeletogenic and derive from neural folds that do not express Hox genes. In order to examine the influence of Hox gene expression on skull morphogenesis, expression of Hoxa2, Hoxa3 and Hoxb4 in conjunction with that of the green fluorescent protein has been selectively targeted to the Hox-negative neural folds of the avian embryo prior to the onset of crest cell emigration. Hoxa2 expression precludes the development of the entire facial skeleton. Transgenic Hoxa2 embryos such as those from which the Hox-negative domain of the cephalic neural crest has been removed have no upper or lower jaws and no frontonasal structures. Embryos subjected to the forced expression of Hoxa3 and Hoxb4 show severe defects in the facial skeleton but not a complete absence of facial cartilage. Hoxa3 prevents the formation of the skeleton derived from the first branchial arch, but allows the development (albeit reduced) of the nasal septum. Hoxb4, by contrast, hampers the formation of the nasal bud-derived skeleton, while allowing that of a proximal (but not distal) segment of the lower jaw. The combined effect of Hoxa3 and Hoxb4 prevents the formation of facial skeletal structures, comparable with Hoxa2. None of these genes impairs the formation of neural derivatives of the crest. These results suggest that over the course of evolution, the absence of Hox gene expression in the anterior part of the chordate embryo was crucial in the vertebrate phylum for the development of a face, jaws and brain case, and, hence, also for that of the forebrain.     

Interactions between Hox-negative cephalic neural crest cells and the foregut endoderm in patterning the facial skeleton in the vertebrate head

The vertebrate face contains bones that differentiate from mesenchymal cells of neural crest origin, which colonize the median nasofrontal bud and the first branchial arches. The patterning of individual facial bones and their relative positions occurs through mechanisms that remained elusive. During the early stages of head morphogenesis, an endodermal cul-de-sac, destined to become Sessel's pouch, underlies the nasofrontal bud. Reiterative outpocketings of the foregut then form the branchial pouches. We have tested the capacity of endoderm of the avian neurula to specify the facial skeleton by performing ablations or grafts of defined endodermal regions. Neural crest cells that do not express Hox genes respond to patterning cues produced regionally in the anterior endoderm to yield distinct skeletal components of the upper face and jaws. However, Hox-expressing neural crest cells do not respond to these cues. Bone orientation is likewise dependent on the position of the endoderm relative to the embryonic axes. Our findings thus indicate that the endoderm instructs neural crest cells as to the size, shape and position of all the facial skeletal elements, whether they are cartilage or membrane bones.     

Initial activation of cyclin-B1-cdc2 kinase requires phosphorylation of cyclin B1

At the G₂/M transition of the cell cycle, the cdc25c phosphatase dephosphorylates inhibitory residues of cdc2, and cyclin-B–cdc2 kinase (MPF) is activated. Phosphorylation of cyclin B1 induces its nuclear accumulation, and, since cdc25c is also believed to accumulate and activate shortly before G₂/M in the nucleus, it has been proposed that this induces cyclin-B1–cdc2 kinase activation. We demonstrate that cyclin B1 phosphorylation has another essential function in vivo: it is required for cdc25c and MPF activation, which does not require nuclear accumulation of cyclin B1, and occurs in the cytoplasm.     

New N-pyridinyl(methyl)-indole-2- and 3-(alkyl)carboxamides and derivatives acting as systemic and topical inflammation inhibitors

A series of novel N-substituted-(indol-2-yl)carboxamides (12-18) and (indol-3-alkyl)carboxamides (25-31) were synthesized and evaluated as inhibitors of the inflammation process. Pharmacomodulation at the level of the amidic nitrogen by incorporation of the previously described pharmacophoric moieties 6-aminolutidine, beta-picolylamine, 4-aminopyridine and piperazine was investigated; only two compounds (12) and (31) exhibited significant (approximately 40%) inhibitory effect in the carrageenan-induced rat paw edema after oral administration of a dose of 0.1 mM kg(-1). Replacement of the indole core by indazole failed to increase activity. Incorporation of an alkyl chain spacer led to more efficient compounds (46-52) especially in the indolepropanamide sub-series. Determination of the efficiency of the most active compounds on topical inflammation, by measuring reduction of ear thickness in the acute tetradecanoyl phorbol acetate (TPA)-induced mouse ear swelling assay, confirmed the high potency of propanamides (49) and (51) after oral administration: ID50 = 0.041 +/- 0.013 and 0.042 +/- 0.016 mM kg(-1) respectively. The less toxic propanamide (51) exerted a high level of inhibitory activity after topical application of 2 x 100 microg/ear: 78 +/- 2%.     

Synthesis and antileishmanial activity of 3-(alpha-azolylbenzyl)indoles

The goal of the present study was to evaluate several azolyl-substituted indoles as new antileishmanial agents. Ten 3-(alpha-azolylbenzyl)indoles have been synthesized using Friedel-Crafts acylation as a key-step. All the target compounds were found to display high levels of activity when tested against Leishmania mexicana promastigotes in vitro. The most active compounds, showing an IC50 < 1 microM, were 5-bromo-1-ethyl-3-[(2,4-dichlorophenyl)(1H-imidazol-1-yl)methyl]-1H-indole 15 and its triazole analogue 17. Four representative compounds 15, 17, 22 and, 23 were also tested against intracellular amastigotes of L. mexicana using ketoconazole and meglumine antimoniate as reference compounds, the results of which are discussed.     

New in vivo and ex vivo models for the experimental study of sheep scrapie: development and perspectives

Sheep scrapie is a prototypical transmissible spongiform encephalopathy (TSE), and the most widespread of these diseases. Experimental study of TSE infectious agents from sheep and other species essentially depends on bioassays in rodents. Transmission of natural sheep scrapie to conventional mice commonly requires one or two years. In an effort to develop laboratory models in which investigations on the sheep TSE agent would be facilitated, we have established mice and cell lines that were genetically engineered to express ovine PrP protein and examined their susceptibility to the infection. A series of transgenic mice lines (tgOv) expressing the high susceptibility allele (VRQ) of the ovine PrP gene from different constructs was expanded. Following intracerebral inoculation with natural scrapie isolates, all animals developed typical TSE neurological signs and accumulated abnormal PrP in their brain. The survival time in the highest expressing tgOv lines ranged from 2 to 7 months, depending on the isolate. It was inversely related to the brain PrP content, and essentially unchanged on further passaging. Ovine PrP transgene expression thus enhanced scrapie disease transmission from sheep to mice. Such tgOv mice may bring new opportunities for analysing the natural variation of scrapie strains and measuring infectivity. As no relevant cell culture models for agents of naturally-occurring TSE exist, we have explored various strategies in order to obtain stable cell lines that would propagate the sheep agent ex vivo without prior adaptation to rodent. In one otherwise refractory rabbit epithelial cell line, a regulable expression of ovine PrP was achieved and found to enable an efficient replication of the scrapie agent in inoculated cultures. Cells derived from sheep embryos or from tgOv mice were also used in an attempt to establish permissive cell lines derived from the nervous system. Cells engineered to express PrP proteins of a specified sequence may thus represent a promising strategy to further explore, at the cellular level, various aspects of TSE diseases.     

Solubility and diffusion of nitrogen in maltodextrin/protein tablets

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history-dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.