Zebrafish Endzone Regulates Neural Crest-Derived Chromatophore Differentiation and Morphology

The development of neural crest-derived pigment cells has been studied extensively as a model for cellular differentiation, disease and environmental adaptation. Neural crest-derived chromatophores in the zebrafish (Danio rerio) consist of three types: melanophores, xanthophores and iridiphores. We have identified the zebrafish mutant endzone (enz), that was isolated in a screen for mutants with neural crest development phenotypes, based on an abnormal melanophore pattern. We have found that although wild-type numbers of chromatophore precursors are generated in the first day of development and migrate normally in enz mutants, the numbers of all three chromatophore cell types that ultimately develop are reduced. Further, differentiated melanophores and xanthophores subsequently lose dendricity, and iridiphores are reduced in size. We demonstrate that enz function is required cell autonomously by melanophores and that the enz locus is located on chromosome 7. In addition, zebrafish enz appears to selectively regulate chromatophore development within the neural crest lineage since all other major derivatives develop normally. Our results suggest that enz is required relatively late in the development of all three embryonic chromatophore types and is normally necessary for terminal differentiation and the maintenance of cell size and morphology. Thus, although developmental regulation of different chromatophore sublineages in zebrafish is in part genetically distinct, enz provides an example of a common regulator of neural crest-derived chromatophore differentiation and morphology

The Mnn2 Mannosyltransferase Family Modulates Mannoprotein Fibril Length, Immune Recognition and Virulence of Candida albicans

The fungal cell wall is the first point of interaction between an invading fungal pathogen and the host immune system. The outer layer of the cell wall is comprised of GPI anchored proteins, which are post-translationally modified by both N- and O-linked glycans. These glycans are important pathogen associated molecular patterns (PAMPs) recognised by the innate immune system. Glycan synthesis is mediated by a series of glycosyl transferases, located in the endoplasmic reticulum and Golgi apparatus. Mnn2 is responsible for the addition of the initial α1,2-mannose residue onto the α1,6-mannose backbone, forming the N-mannan outer chain branches. In Candida albicans, the MNN2 gene family is comprised of six members (MNN2, MNN21, MNN22, MNN23, MNN24 and MNN26). Using a series of single, double, triple, quintuple and sextuple mutants, we show, for the first time, that addition of α1,2-mannose is required for stabilisation of the α1,6-mannose backbone and hence regulates mannan fibril length. Sequential deletion of members of the MNN2 gene family resulted in the synthesis of lower molecular weight, less complex and more uniform N-glycans, with the sextuple mutant displaying only un-substituted α1,6-mannose. TEM images confirmed that the sextuple mutant was completely devoid of the outer mannan fibril layer, while deletion of two MNN2 orthologues resulted in short mannan fibrils. These changes in cell wall architecture correlated with decreased proinflammatory cytokine induction from monocytes and a decrease in fungal virulence in two animal models. Therefore, α1,2-mannose of N-mannan is important for both immune recognition and virulence of C. albicans

Acetazolamide fails to decrease pulmonary artery pressure at high altitude in partially acclimatized humans.

In this randomized, double-blind placebo controlled trial our objectives were to determine if acetazolamide is capable of preventing high altitude pulmonary edema (HAPE) in trekkers traveling between 4250 m (Pheriche)\4350 m (Dingboche) and 5000 m (Lobuje) in Nepal; to determine if acetazolamide decreases pulmonary artery systolic pressures (PASP) at high altitude; and to determine if there is an association with PASP and signs and symptoms of HAPE. Participants received either acetazolamide 250 mg PO BID or placebo at Pheriche\Dingboche and were reassessed in Lobuje. The Lake Louise Consensus Criteria were used for the diagnosis of HAPE, and cardiac ultrasonography was used to measure the velocity of tricuspid regurgitation and estimate PASP. Complete measurements were performed on 339 of the 364 subjects (164 in the placebo group, 175 in the acetazolamide group). No cases of HAPE were observed in either study group nor were differences in the signs and symptoms of HAPE found between the two groups. Mean PASP values did not differ significantly between the acetazolamide and placebo groups (31.3 and 32.6 mmHg, respectively). An increasing number of signs and symptoms of HAPE was associated with elevated PASP (p < 0.01). The efficacy of acetazolamide against acute mountain sickness, however, was significant with a 21.9% incidence in the placebo group compared to 10.2 % in the acetazolamide group (p < 0.01). Given the lack of cases of HAPE in either group, we can draw no conclusions about the efficacy of acetazolamide in preventing HAPE, but the absence of effect on PASP suggests that any effect may be minor possibly owing to partial acclimatization during the trek up to 4200 m