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Toll‐like receptor 2 (TLR2) belongs to the TLR protein family that plays an important role in the immune and inflammation response system. While TLR2 is predominantly expressed in immune cells, its expression has also been detected in the brain, specifically in microglia and astrocytes. Recent studies indicate that genomic deletion of TLR2 can result in impaired neurobehavioural function. It is currently not clear if the genomic deletion of TLR2 leads to any alterations in the microstructural features of the brain. In the current study, we noninvasively assess microstructural changes in the brain of TLR2‐deficient (tlr2−/−) zebrafish using state‐of‐the art magnetic resonance imaging (MRI) methods at ultrahigh magnetic field strength (17.6 T). A significant increase in cortical thickness and an overall trend towards increased brain volumes were observed in young tlr2−/− zebrafish. An elevated T2 relaxation time and significantly reduced apparent diffusion coefficient (ADC) unveil brain‐wide microstructural alterations, potentially indicative of cytotoxic oedema and astrogliosis in the tlr2−/− zebrafish. Multicomponent analysis of the ADC diffusivity signal by the phasor approach shows an increase in the slow ADC component associated with restricted diffusion. Diffusion tensor imaging and diffusion kurtosis imaging analysis revealed diminished diffusivity and enhanced kurtosis in various white matter tracks in tlr2−/− compared with control zebrafish, identifying the microstructural underpinnings associated with compromised white matter integrity and axonal degeneration. Taken together, our findings demonstrate that the genomic deletion of TLR2 results in severe alterations to the microstructural features of the zebrafish brain. This study also highlights the potential of ultrahigh field diffusion MRI techniques in discerning exceptionally fine microstructural details within the small zebrafish brain, offering potential for investigating microstructural changes in zebrafish models of various brain diseases. [ABSTRACT FROM AUTHOR]

Zebrafish (Danio rerio) is an important animal model for a wide range of neurodegenerative diseases. However, obtaining the cellular resolution that is essential for studying the zebrafish brain remains challenging as it requires high spatial resolution and signal-to-noise ratios (SNR). In the current study, we present the first MRI results of the zebrafish brain at the state-of-the-art magnetic field strength of 28.2 T. The performance of MRI at 28.2 T was compared to 17.6 T. A 20% improvement in SNR was observed at 28.2 T as compared to 17.6 T. Excellent contrast, resolution, and SNR allowed the identification of several brain structures. The normative T1 and T2 relaxation values were established over different zebrafish brain structures at 28.2 T. To zoom into the white matter structures, we applied diffusion tensor imaging (DTI) and obtained axial, radial, and mean diffusivity, as well as fractional anisotropy, at a very high spatial resolution. Visualisation of white matter structures was achieved by short-track track-density imaging by applying the constrained spherical deconvolution method (stTDI CSD). For the first time, an algorithm for stTDI with multi-shell multi-tissue (msmt) CSD was tested on zebrafish brain data. A significant reduction in false-positive tracks from grey matter signals was observed compared to stTDI with single-shell single-tissue (ssst) CSD. This allowed the non-invasive identification of white matter structures at high resolution and contrast. Our results show that ultra-high field DTI and tractography provide reproducible and quantitative maps of fibre organisation from tiny zebrafish brains, which can be implemented in the future for a mechanistic understanding of disease-related microstructural changes in zebrafish models of various brain diseases. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigates zebrafish larvae as a model for Mycobacterium tuberculosis infection, a major cause of tuberculosis in humans. Despite not being natural hosts, zebrafish larvae are successfully infected with M. tuberculosis, showing propagation for up to 9 days post-injection using a robotic system for efficiency. Fluorescence microscopy confirms microbial aggregates carrying labeled M. tuberculosis, mirroring the infection by M. marinum, a related surrogate model. Transcriptome analyses shows that M. tuberculosis triggers a specific transcriptional immune response in infected larvae, resembling the response to M. marinum. The study demonstrates the persistence of M. tuberculosis in zebrafish larvae for at least a week post-infection. It supports the use of the M. marinum infection model as a surrogate for tuberculosis for comparing key immune response genes induced by M. tuberculosis. Additionally, the research compares the zebrafish model's response to M. tuberculosis with human macrophage responses, revealing shared and unique gene expression patterns. This work contributes to efficient preclinical tools for tuberculosis research, underscoring the potential of zebrafish as a model host for discovering diagnostic markers of M. tuberculosis infections and for confirming the effects of potential drugs identified using the M. marinum infection model. Zebrafish is a natural host of various Mycobacterium species and a surrogate model organism for tuberculosis research. Mycobacterium marinum is evolutionarily one of the closest non-tuberculous species related to M. tuberculosis and shares the majority of virulence genes. Although zebrafish is not a natural host of the human pathogen, we have previously demonstrated successful robotic infection of zebrafish embryos with M. tuberculosis and performed drug treatment of the infected larvae. In the present study, we examined for how long M. tuberculosis can be propagated in zebrafish larvae and tested a time series of infected larvae to study the transcriptional response via Illumina RNA deep sequencing (RNAseq). Bacterial aggregates carrying fluorescently labeled M. tuberculosis could be detected up to 9 days post-infection. The infected larvae showed a clear and specific transcriptional immune response with a high similarity to the inflammatory response of zebrafish larvae infected with the surrogate species M. marinum. We conclude that M. tuberculosis can be propagated in zebrafish larvae for at least one week after infection and provide further evidence that M. marinum is a good surrogate model for M. tuberculosis. The generated extensive transcriptome data sets will be of great use to add translational value to zebrafish as a model for infection of tuberculosis using the M. marinum infection system. In addition, we identify new marker genes such as dusp8 and CD180 that are induced by M. tuberculosis infection in zebrafish and in human macrophages at later stages of infection that can be further investigated. [ABSTRACT FROM AUTHOR]

Snakes are limbless predators, and many species use venom to help overpower relatively large, agile prey. Snake venoms are complex protein mixtures encoded by several multilocus gene families that function synergistically to cause incapacitation. To examine venom evolution, we sequenced and interrogated the genome of a venomous snake, the king cobra (Ophiophagus hannah), and compared it, together with our unique transcriptome, microRNA, and proteome datasets from this species, with data from other vertebrates. In contrast to the platypus, the only other venomous vertebrate with a sequenced genome, we find that snake toxin genes evolve through several distinct co-option mechanisms and exhibit surprisingly variable levels of gene duplication and directional selection that correlate with their functional importance in prey capture. The enigmatic accessory venom gland shows a very different pattern of toxin gene expression from the main venom gland and seems to have recruited toxin-like lectin genes repeatedly for new nontoxic functions. In addition, tissue-specific microRNA analyses suggested the co-option of core genetic regulatory components of the venom secretory system from a pancreatic origin. Although the king cobra is limbless, we recovered coding sequences for all Hox genes involved in amniote limb development, with the exception of Hoxd12. Our results provide a unique view of the origin and evolution of snake venom and reveal multiple genome-level adaptive responses to natural selection in this complex biological weapon system. More generally, they provide insight into mechanisms of protein evolution under strong selection.

rRNAs are non-coding RNAs present in all prokaryotes and eukaryotes. In eukaryotes there are four rRNAs: 18S, 5.8S, 28S, originating from a common precursor (45S), and 5S. We have recently discovered the existence of two distinct developmental types of rRNA: a maternal-type, present in eggs and a somatic-type, expressed in adult tissues. Lately, next-generation sequencing has allowed the discovery of new small-RNAs deriving from longer non-coding RNAs, including small-RNAs from rRNAs (srRNAs). Here, we systemically investigated srRNAs of maternal- or somatic-type 18S, 5.8S, 28S, with small-RNAseq from many zebrafish developmental stages. We identified new srRNAs for each rRNA. For 5.8S, we found srRNA consisting of the 5' or 3' halves, with only the latter having different sequence for the maternal- and somatic-types. For 18S, we discovered 21 nt srRNA from the 5' end of the 18S rRNA with a striking resemblance to microRNAs; as it is likely processed from a stem-loop precursor and present in human and mouse Argonaute-complexed small-RNA. For 28S, an abundant 80 nt srRNA from the 3' end of the 28S rRNA was found. The expression levels during embryogenesis of these srRNA indicate they are not generated from rRNA degradation and might have a role in the zebrafish development. Key words: ribosomal RNA, small-rRNA derived, embryogenesis, zebrafish, development. Les ARNr sont des ARN non-codants qui sont présents chez tous les procaryotes et eucaryotes. Chez les eucaryotes, il y a quatre ARNr : 18S, 5,8S, 28S (lesquels sont dérivés d'un même ARN précurseur 45S) et 5S. Les auteurs ont récemment découvert l'existence de deux types distincts d'ARNr : un type maternel présent chez les oeufs et un type somatique présent chez les tissus adultes. Récemment, le séquençage de nouvelle génération a permis de découvrir de nouveaux petits ARN dérivés d'ARN plus longs, incluant des petits ARN dérivés d'ARNr (srRNA). Dans ce travail, les auteurs ont investigué de manière systématique les srRNA dérivés d'ARN 18S, 5,8S, 28S de type maternel ou somatique au moyen d'une approche RNA-Seq pour petits ARN chez plusieurs stades développementaux chez le poisson-zèbre. Les auteurs ont identifié de nouveaux srRNA pour chaque ARNr. Pour le 5,8S, des srRNA composés uniquement de la moitié 5' ou 3' ont été trouvés, et seul ces derniers présentaient une séquence différente chez les types maternels et somatiques. Pour les 18S, des srRNA de 21 nt issus de l'extrémité 5' ont été trouvés et ils ressemblent beaucoup à des microARN. Un tel produit est vraisemblablement dérivé d'un précurseur ayant une structure en épingle et il est aussi présent parmi les petits ARN en complexe avec la protéine Argonaute chez l'humain et la souris. Pour les 28S, un srRNA de 80 nt abondant et issu de l'extrémité 3= du l'ARNr 28S a été observé. Les niveaux d'expression de ces srRNA au cours de l'embryogenèse indiquent qu'ils ne sont pas générés par une dégradation des ARNr et qu'ils pourraient jouer un rôle dans le développement du poisson-zèbre. [Traduit par la Rédaction] Mots-clés : ARN ribosomique, dérivés de petits ARNr, embryogenèse, poisson-zèbre, développement., Introduction Several new classes of small non-coding RNAs have been discovered in the wake of the next-generation sequencing (NGS) revolution (Wittmann and Jack 2010). This has fueled interest in small-RNAs [...]