Development of the Swimbladder Surfactant System and Biogenesis of Lysosome-Related Organelles Is Regulated by BLOS1 in Zebrafish

Validation of GCN5L1/BLOC1S1/BLOS1 antibodies using knockout cells and tissue

GCN5L1, also known as BLOC1S1 and BLOS1, is a small intracellular protein involved in many key biological processes. Over the last decade, GCN5L1 has been implicated in the regulation of protein lysine acetylation, energy metabolism, endo-lysosomal function, and cellular immune pathways. An increasing number of published papers have used commercially-available reagents to interrogate GCN5L1 function. However, in many cases these reagents have not been rigorously validated, leading to potentially misleading results. In this report we tested several commercially-available antibodies for GCN5L1, and found that two-thirds of those available did not unambiguously detect the protein by western blot in cultured mouse cells or ex vivo liver tissue. These data suggest that previously published studies which used these unverified antibodies to measure GCN5L1 protein abundance, in the absence of other independent methods of corroboration, should be interpreted with appropriate caution.

Toxicogenomics of Five Cytostatics in Fathead Minnow (Pimephales promelas) Larvae

In this study, the toxicogenomic effects of five cytostatics (tamoxifen, methotrexate, capecitabine, cyclophosphamide, and ifosfamide) on fathead minnow (Pimephales promelas) larvae were evaluated. Post-fertilization eggs were exposed to increasing concentrations of the drugs for six days. The expression levels of two genetic biomarkers for toxicity and four thyroid hormone-related gene pathways were measured. Interestingly, the results showed that all concentrations of the five cytostatics affect the transcription levels of both toxicity biomarker genes. Additionally, the thyroid hormone-related genes had different expression levels than the control, with the most significant changes observed in those larvae exposed to cyclophosphamide and ifosfamide. While a previous study found no effects on fish morphology, this study suggests that the five cytostatics modify subtle molecular responses of P. promelas, highlighting the importance of assessing multibiological level endpoints throughout the lifecycle of animals to understand the full portrait of potential effects of cytostatics and other contaminants.

Bmpali, Bmb1 and Bmcap are necessary for uric acid granule formation in Bombyx mori

Uric acid is the end-product of nitrogen metabolism of the silkworm and other lepidopterans. The accumulation of uric acid particles in the epidermis causes the larval silkworm to appear white and opaque. However, the mechanism of uric acid granule formation is still unclear. Silkworm epidermis color is linked to the genes responsible for uric acid particle formation. We first identified two genes in the Bombyx mori genome that encode subunits of the Bloc-1 (Biogenesis of Lysosome-related Organelles Complex-1) by homology to these genes in other eukaryotes, Bmpali and Bmb1. Mutation in these genes caused a transparent phenotype in the silkworm larvae, and the loss of BmBloc-1 subunit gene Bmcap resulted in the same phenotype. These three genes are highly conserved between human and silkworm. We discovered that Bmpali, Bmcap, and Bmb1 localize in the cytoplasm of BmN cells. Yeast two-hybrid assays demonstrated that the Bmpali physically interacts with both Bmcap and Bmb1. Investigating the roles of Bmpali, Bmb1, and Bmcap is essential for uric acid granule formation understanding in Bombyx mori. These mutants present a valuable silkworm model for studying the biogenesis of lysosome-related organelles (LROs).

A surfactant lipid layer of endosomal membranes facilitates airway gas filling in Drosophila

The mechanisms underlying the construction of an air-liquid interface in respiratory organs remain elusive. Here, we use live imaging and genetic analysis to describe the morphogenetic events generating an extracellular lipid lining of the Drosophila airways required for their gas filing and animal survival. We show that sequential Rab39/Syx1A/Syt1-mediated secretion of lysosomal acid sphingomyelinase (Drosophila ASM [dASM]) and Rab11/35/Syx1A/Rop-dependent exosomal secretion provides distinct components for lipid film assembly. Tracheal inactivation of Rab11 or Rab35 or loss of Rop results in intracellular accumulation of exosomal, multi-vesicular body (MVB)-derived vesicles. On the other hand, loss of dASM or Rab39 causes luminal bubble-like accumulations of exosomal membranes and liquid retention in the airways. Inactivation of the exosomal secretion in dASM mutants counteracts this phenotype, arguing that the exosomal secretion provides the lipid vesicles and that secreted lysosomal dASM organizes them into a continuous film. Our results reveal the coordinated functions of extracellular vesicle and lysosomal secretions in generating a lipid layer crucial for airway gas filling and survival.

Two High-Quality Cygnus Genome Assemblies Reveal Genomic Variations Associated with Plumage Color

As an exemplary model for examining molecular mechanisms responsible for extreme phenotypic variations, plumage color has garnered significant interest. The Cygnus genus features two species, Cygnus olor and Cygnus atratus, that exhibit striking disparities in plumage color. However, the molecular foundation for this differentiation has remained elusive. Herein, we present two high-quality genomes for C. olor and C. atratus, procured using the Illumina and Nanopore technologies. The assembled genome of C. olor was 1.12 Gb in size with a contig N50 of 26.82 Mb, while its counterpart was 1.13 Gb in size with a contig N50 of 21.91 Mb. A comparative analysis unveiled three genes (TYR, SLC45A2, and SLC7A11) with structural variants in the melanogenic pathway. Notably, we also identified a novel gene, PWWP domain containing 2A (PWWP2A), that is related to plumage color, for the first time. Using targeted gene modification analysis, we demonstrated the potential genetic effect of the PWWP2A variant on pigment gene expression and melanin production. Finally, our findings offer insight into the intricate pattern of pigmentation and the role of polygenes in birds. Furthermore, these two high-quality genome references provide a comprehensive resource and perspective for comparative functional and genetic studies of evolution within the Cygnus genus.

GCN5L1 regulates pulmonary surfactant production by modulating lamellar body biogenesis and trafficking in mouse alveolar epithelial cells

BACKGROUND

The pulmonary surfactant that lines the air-liquid surface within alveoli is a protein-lipid mixture essential for gas exchange. Surfactant lipids and proteins are synthesized and stored in the lamellar body (LB) before being secreted from alveolar type II (AT2) cells. The molecular and cellular mechanisms that regulate these processes are incompletely understood. We previously identified an essential role of general control of amino acid synthesis 5 like 1 (GCN5L1) and the biogenesis of lysosome-related organelle complex 1 subunit 1 (BLOS1) in surfactant system development in zebrafish. Here, we explored the role of GCN5L1 in pulmonary surfactant regulation.

METHOD

GCN5L1 knockout cell lines were generated with the CRISPR/Cas9 system. Cell viability was analyzed by MTT assay. Released surfactant proteins were measured by ELISA. Released surfactant lipids were measured based on coupled enzymatic reactions. Gene overexpression was mediated through lentivirus. The RNA levels were detected through RNA-sequencing (RNA-seq) and quantitative reverse transcription (qRT)- polymerase chain reaction (PCR). The protein levels were detected through western blotting. The cellular localization was analyzed by immunofluorescence. Morphology of the lamellar body was analyzed through transmission electron microscopy (TEM), Lysotracker staining, and BODIPY phosphatidylcholine labeling.

RESULTS

Knocking out GCN5L1 in MLE-12 significantly decreased the release of surfactant proteins and lipids. We detected the downregulation of some surfactant-related genes and misregulation of the ROS-Erk-Foxo1-Cebpα axis in mutant cells. Modulating the activity of the axis or reconstructing the mitochondrial expression of GCN5L1 could partially restore the expression of these surfactant-related genes. We further showed that MLE-12 cells contained many LB-like organelles that were lipid enriched and positive for multiple LB markers. These organelles were smaller in size and accumulated in the absence of GCN5L1, indicating both biogenesis and trafficking defects. Accumulated endogenous surfactant protein (SP)-B or exogenously expressed SP-B/SP-C in adenosine triphosphate-binding cassette transporterA3 (ABCA3)-positive organelles was detected in mutant cells. GCN5L1 localized to the mitochondria and LBs. Reconstruction of mitochondrial GCN5L1 expression rescued the organelle morphology but failed to restore the trafficking defect and surfactant release, indicating specific roles associated with different subcellular localizations.

CONCLUSIONS

In summary, our study identified GCN5L1 as a new regulator of pulmonary surfactant that plays a role in the biogenesis and positioning/trafficking of surfactant-containing LBs.

The impaired swim bladder via ROS-mediated inhibition of the Wnt / Hedgehog pathway in zebrafish embryos exposed to eight toxic chemicals and binary chemical mixtures

To comprehensively explore the potential toxicity of aquatic organisms exposed to chlorinated or brominated flame retardants (BFRs) and metals mixtures, it is necessary to find a common pathway to relate local toxic targeted sites or organs. A key challenge in environmental risk assessment (ERA) is how to clarify the same or different sites or organs of toxic action in a species after exposure to individual chemicals or chemical mixtures. In this study, zebrafish embryo was used to evaluate the sub-lethal toxicity (swim bladder damage) of tris(2,3-dibromo propyl) isocyanurate (TBC), chlorinated paraffins (CPs), hexabromocyclododecane (HBCD), Cu, Cd, Pb, Ag, and Zn through optical microscopy methods, and corresponding sub-lethal molecular levels (inflammation-related enzymes [deiodinase (DIO) enzymes] and transcriptional levels of key genes) in fish through quantitative real-time PCR (qRT-PCR). The tested chemicals all caused failed inflation of the swim bladder, as indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Following embryonic exposure to respective TBC + Cu, HBCD + TBC, and Cd + Pb mixtures, as the concentration of the respective Cu, TBC, and Pb increased, the deformity of the swim bladder increased, as also indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Additionally, eight chemicals down-regulated Wnt (wnt3, wnt9b, fzd3b, wnt1, fzd5, and fdz1) signaling pathways, which were neurotoxic responses to individual chemical treatments and Hedgehog (ihh, shh, ptc1 and ptc2) signaling pathways. Moreover, excessive ROS induced by eight chemicals effectively induced defects in the swim bladder and Wnt/Hedgehog signaling, which also be proved in respective TBC + Cu, HBCD + TBC, and Cd + Pb mixture treatments. Our results first revealed that eight chemicals caused swim bladder developmental defects via ROS-mediated inhibition of the Wnt and Hedgehog pathways, which revealed the common targeted sites or organs (swim bladders) for further studying the toxic mechanisms underlying the chemical mixtures.

Lysosome-related organelles promote stress and immune responses in C. elegans

Lysosome-related organelles (LROs) play diverse roles and their dysfunction causes immunodeficiency. However, their primordial functions remain unclear. Here, we report that C. elegans LROs (gut granules) promote organismal defenses against various stresses. We find that toxic benzaldehyde exposure induces LRO autofluorescence, stimulates the expression of LRO-specific genes and enhances LRO transport capacity as well as increases tolerance to benzaldehyde, heat and oxidative stresses, while these responses are impaired in glo-1/Rab32 and pgp-2 ABC transporter LRO biogenesis mutants. Benzaldehyde upregulates glo-1- and pgp-2-dependent expression of heat shock, detoxification and antimicrobial effector genes, which requires daf-16/FOXO and/or pmk-1/p38MAPK. Finally, benzaldehyde preconditioning increases resistance against Pseudomonas aeruginosa PA14 in a glo-1- and pgp-2-dependent manner, and PA14 infection leads to the deposition of fluorescent metabolites in LROs and induction of LRO genes. Our study suggests that LROs may play a role in systemic responses to stresses and in pathogen resistance.

Validation of GCN5L1/BLOC1S1/BLOS1 Antibodies Using Knockout Cells and Tissue

GCN5L1, also known as BLOC1S1 and BLOS1, is a small intracellular protein involved in a number of key biological processes. Over the last decade, GCN5L1 has been implicated in the regulation of protein lysine acetylation, energy metabolism, endo-lysosomal function, and cellular immune pathways. An increasing number of published papers have used commercially-available reagents to interrogate GCN5L1 function. However, in many cases these reagents have not been rigorously validated, leading to potentially misleading results. In this report we tested several commercially-available antibodies for GCN5L1, and found that two-thirds of those available did not unambiguously detect the protein by western blot in cultured mouse cells or ex vivo liver tissue. These data suggest that previously published studies which used these unverified antibodies to measure GCN5L1 protein abundance, in the absence of other independent methods of corroboration, should be interpreted with appropriate caution.

Cadmium impairs zebrafish swim bladder development via ROS mediated inhibition of the Wnt / Hedgehog pathway

The posterior swim bladder is an important organ in teleost fishes, that primarily maintains buoyancy and motility for swimming and survival. In this study, we examined the molecular mechanisms of the toxicity of cadmium (Cd) on the early development of the swim bladder in zebrafish. Embryonic Cd exposure resulted in the non-inflation of the swim bladder when the ambient Cd concentration was greater than or equal to 0.25 mg/L. Cd disturbed surfactant lipid distribution and inhibited the formation of all three tissue layers in the swim bladder. Additionally, excessive Cd down-regulated Wnt (fzd3, nkd1, fzd7 and axin2) and Hedgehog (ihh, shh, ptc1 and ptc2) signaling pathways. Conversely, Wnt signaling activation partially neutralized Cd-induced swim bladder developmental defects. Moreover, ROS scavenger reduced Glutathione (GSH) effectively recovered Cd induced defects in swim bladder and Wnt/Hedgehog signaling. Taken together, our results first revealed that Cd caused swim bladder developmental defects via ROS-mediated inhibition of the Wnt and Hedgehog pathways. These results herein provide important data for future toxicological studies and risk assessments of Cd.

Zebrafish Syndromic Albinism Models as Tools for Understanding and Treating Pigment Cell Disease in Humans

Simple Summary

Zebrafish (Danio rerio) is an emerging model for studying many diseases, including disorders originating in black pigment cells, melanocytes. In this review of the melanocyte literature, we discuss the current knowledge of melanocyte biology relevant to understanding different forms of albinism and the potential of the zebrafish model system for finding novel mechanisms and treatments.

Abstract

Melanin is the pigment that protects DNA from ultraviolet (UV) damage by absorbing excess energy. Melanin is produced in a process called melanogenesis. When melanogenesis is altered, diseases such as albinism result. Albinism can result in an increased skin cancer risk. Conversely, black pigment cell (melanocyte) development pathways can be misregulated, causing excessive melanocyte growth that leads to melanoma (cancer of melanocytes). Zebrafish is an emerging model organism used to study pigment disorders due to their high fecundity, visible melanin development in melanophores (melanocytes in mammals) from 24 h post-fertilization, and conserved melanogenesis pathways. Here, we reviewed the conserved developmental pathways in zebrafish melanophores and mammalian melanocytes. Additionally, we summarized the progress made in understanding pigment cell disease and evidence supporting the strong potential for using zebrafish to find novel treatment options for albinism.

Bi-allelic variants in HOPS complex subunit VPS41 cause cerebellar ataxia and abnormal membrane trafficking

Membrane trafficking is a complex, essential process in eukaryotic cells responsible for protein transport and processing. Deficiencies in vacuolar protein sorting (VPS) proteins, key regulators of trafficking, cause abnormal intracellular segregation of macromolecules and organelles and are linked to human disease. VPS proteins function as part of complexes such as the homotypic fusion and vacuole protein sorting (HOPS) tethering complex, composed of VPS11, VPS16, VPS18, VPS33A, VPS39 and VPS41. The HOPS-specific subunit VPS41 has been reported to promote viability of dopaminergic neurons in Parkinson’s disease but to date has not been linked to human disease. Here, we describe five unrelated families with nine affected individuals, all carrying homozygous variants in VPS41 that we show impact protein function. All affected individuals presented with a progressive neurodevelopmental disorder consisting of cognitive impairment, cerebellar atrophy/hypoplasia, motor dysfunction with ataxia and dystonia, and nystagmus. Zebrafish disease modelling supports the involvement of VPS41 dysfunction in the disorder, indicating lysosomal dysregulation throughout the brain and providing support for cerebellar and microglial abnormalities when vps41 was mutated. This provides the first example of human disease linked to the HOPS-specific subunit VPS41 and suggests the importance of HOPS complex activity for cerebellar function.

Synaptic Vesicle Precursors and Lysosomes Are Transported by Different Mechanisms in the Axon of Mammalian Neurons

BORC is a multisubunit complex previously shown to promote coupling of mammalian lysosomes and C. elegans synaptic vesicle (SV) precursors (SVPs) to kinesins for anterograde transport of these organelles along microtubule tracks. We attempted to meld these observations into a unified model for axonal transport in mammalian neurons by testing two alternative hypotheses: (1) that SV and lysosomal proteins are co-transported within a single type of “lysosome-related vesicle” and (2) that SVPs and lysosomes are distinct organelles, but both depend on BORC for axonal transport. Analyses of various types of neurons from wild-type rats and mice, as well as from BORC-deficient mice, show that neither hypothesis is correct. We find that SVPs and lysosomes are transported separately, but only lysosomes depend on BORC for axonal transport in these neurons. These findings demonstrate that SVPs and lysosomes are distinct organelles that rely on different machineries for axonal transport in mammalian neurons.

De Pace et al. show that lysosomes and synaptic vesicle precursors (SVPs) are distinct organelles that move separately from the soma to the axon in rat and mouse neurons. Moreover, they demonstrate that the BLOC-1-related complex (BORC) is required for the transport of lysosomes but not SVPs in mouse neurons.

A novel BLOC1S5-related HPS-11 patient and zebrafish with bloc1s5 disruption

Hermansky-Pudlak Syndrome (HPS) cases present with a variable degree of OCA and bleeding tendency. HPS is categorized into eleven types based on eleven causative genes, and disease severity varies among different types. By whole-exome sequencing performed on a family trio and Sanger sequencing of candidate variants, we identified a novel homozygous variant (NM_201280.3: c.181delC, p.Val61*) in BLOC1S5 in the patient who presents OCA and mild bleeding diathesis, and his healthy parents are heterozygous carriers. The variant can be considered pathogenic based on the guideline American College of Medical Genetics and Genomics, and the patient is proposed to be affected with HPS-11. In this study, we also explored bloc1s5 in zebrafish. bloc1s5 mRNA can be detected during early development of zebrafish. bloc1s5 knockdown zebrafish present with retinal hypopigmentation, thrombocytes loss and pericardial edema, and dll4/notch1 signaling and vascular integrity signaling are down-regulated at mRNA level in bloc1s5 morphants. The data from the first HPS-11 patient in Chinese population expand phenotypic and genotypic spectrum of HPS-11. Disruption of bloc1s5 in zebrafish recapitulates HPS-11-like phenotypes, and the potential signaling pathways associated with bloc1s5 are proposed. Altogether, this study may facilitate genetic counseling of HPS and investigation about BLOC1S5.

Bi-allelic VPS16 variants limit HOPS/CORVET levels and cause a mucopolysaccharidosis-like disease

Lysosomal storage diseases, including mucopolysaccharidoses, result from genetic defects that impair lysosomal catabolism. Here, we describe two patients from two independent families presenting with progressive psychomotor regression, delayed myelination, brain atrophy, neutropenia, skeletal abnormalities, and mucopolysaccharidosis-like dysmorphic features. Both patients were homozygous for the same intronic variant in VPS16, a gene encoding a subunit of the HOPS and CORVET complexes. The variant impaired normal mRNA splicing and led to an ~85% reduction in VPS16 protein levels in patient-derived fibroblasts. Levels of other HOPS/CORVET subunits, including VPS33A, were similarly reduced, but restored upon re-expression of VPS16. Patient-derived fibroblasts showed defects in the uptake and endosomal trafficking of transferrin as well as accumulation of autophagosomes and lysosomal compartments. Re-expression of VPS16 rescued the cellular phenotypes. Zebrafish with disrupted vps16 expression showed impaired development, reduced myelination, and a similar accumulation of lysosomes and autophagosomes in the brain, particularly in glia cells. This disorder resembles previously reported patients with mutations in VPS33A, thus expanding the family of mucopolysaccharidosis-like diseases that result from mutations in HOPS/CORVET subunits.

Autophagy Is Required for Maturation of Surfactant-Containing Lamellar Bodies in the Lung and Swim Bladder

Autophagy is an intracellular degradation system, but its physiological functions in vertebrates are not yet fully understood. Here, we show that autophagy is required for inflation of air-filled organs: zebrafish swim bladder and mouse lung. In wild-type zebrafish swim bladder and mouse lung type II pulmonary epithelial cells, autophagosomes are formed and frequently fuse with lamellar bodies. The lamellar body is a lysosome-related organelle that stores a phospholipid-containing surfactant complex that lines the air-liquid interface and reduces surface tension. We find that autophagy is critical for maturation of the lamellar body. Accordingly, atg-deficient zebrafish fail to maintain their position in the water, and type-II-pneumocyte-specific Fip200-deficient mice show neonatal lethality with respiratory failure. Autophagy suppression does not affect synthesis of the surfactant phospholipid, suggesting that autophagy supplies lipids and membranes to lamellar bodies. These results demonstrate an evolutionarily conserved role of autophagy in lamellar body maturation.

The road to lysosome-related organelles: Insights from Hermansky-Pudlak syndrome and other rare diseases

Lysosome-related organelles (LROs) comprise a diverse group of cell type-specific, membrane-bound subcellular organelles that derive at least in part from the endolysosomal system but that have unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky-Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.

Recent advances in understanding the molecular basis of melanogenesis in melanocytes

Melanin pigments are responsible for human skin and hair color, and they protect the body from harmful ultraviolet light. The black and brown melanin pigments are synthesized in specialized lysosome-related organelles called melanosomes in melanocytes. Mature melanosomes are transported within melanocytes and transferred to adjacent keratinocytes, which constitute the principal part of human skin. The melanosomes are then deposited inside the keratinocytes and darken the skin (a process called tanning). Owing to their dark color, melanosomes can be seen easily with an ordinary light microscope, and melanosome research dates back approximately 150 years; since then, biochemical studies aimed at isolating and purifying melanosomes have been conducted. Moreover, in the last two decades, hundreds of molecules involved in regulating melanosomal functions have been identified by analyses of the genes of coat-color mutant animals and patients with genetic diseases characterized by pigment abnormalities, such as hypopigmentation. In recent years, dynamic analyses by more precise microscopic observations have revealed specific functions of a variety of molecules involved in melanogenesis. This review article focuses on the latest findings with regard to the steps (or mechanisms) involved in melanosome formation and transport of mature melanosomes within epidermal melanocytes. Finally, we will touch on current topics in melanosome research, particularly on the "melanosome transfer" and "post-transfer" steps, and discuss future directions in pigment research.

Modeling Lysosomal Storage Diseases in the Zebrafish

Lysosomal storage diseases (LSDs) are a family of 70 metabolic disorders characterized by mutations in lysosomal proteins that lead to storage material accumulation, multiple-organ pathologies that often involve neurodegeneration, and early mortality in a significant number of patients. Along with the necessity for more effective therapies, there exists an unmet need for further understanding of disease etiology, which could uncover novel pathways and drug targets. Over the past few decades, the growth in knowledge of disease-associated pathways has been facilitated by studies in model organisms, as advancements in mutagenesis techniques markedly improved the efficiency of model generation in mammalian and non-mammalian systems. In this review we highlight non-mammalian models of LSDs, focusing specifically on the zebrafish, a vertebrate model organism that shares remarkable genetic and metabolic similarities with mammals while also conferring unique advantages such as optical transparency and amenability toward high-throughput applications. We examine published zebrafish LSD models and their reported phenotypes, address organism-specific advantages and limitations, and discuss recent technological innovations that could provide potential solutions.

Dissecting the Vesicular Trafficking Function of IFT Subunits

Intraflagellar transport (IFT) was initially identified as a transport machine with multiple protein subunits, and it is essential for the assembly, disassembly, and maintenance of cilium/flagellum, which serves as the nexus of extracellular-to-intracellular signal integration. To date, in addition to its well-established and indispensable roles in ciliated cells, most IFT subunits have presented more general functions of vesicular trafficking in the non-ciliated cells. Thus, this review aims to summarize the recent progress on the vesicular trafficking functions of the IFT subunits and to highlight the issues that may arise in future research.

The synthetic pyrethroid deltamethrin impairs zebrafish (Danio rerio) swim bladder development

Deltamethrin (DM) is a widely used insecticide and reveals neural, cardiovascular and reproductive toxicity to various aquatic organisms. It has been known that DM negatively affects motion of zebrafish (Danio rerio). However, little is known in relation to the impacts of DM on development of swim bladder, which is a key organ for motion. In the present study, zebrafish embryos were exposed to 20 and 40 µg/L DM. The changes of swim bladder morphology were observed and transcription levels of key genes were compared between DM treatments and the control. The results showed that DM treatments significantly blocked the formation of progenitor and tissue layers in swim bladder of zebrafish embryos, leading to failed inflation of swim bladder. Compared with the control, the key genes (pbx1, foxA3, mnx1, has2, anxa5b, hprt1l and elovl1a) responsible for swim bladder development also showed decreased levels in response to DM treatments, suggesting that DM might specifically affect swim bladder development. Moreover, transcription levels of genes in the Wnt (wnt5b, tcf3a, wnt1, wnt9b, fzd1, fzd3 and fzd5) and Hedgehog (ihhb, ptc1 and ptc2) signaling pathways all decreased significantly in response to DM treatments, compared with the control. Considering the importance of Wnt and Hedgehog pathways in development of swim bladder, these results suggested that DM might affect swim bladder development through inhibiting the Wnt and Hedgehog pathways. Overall, the present study reported that swim bladder might be a potential target organ of DM toxicity in zebrafish, which contributed more information to the evaluation of DM's environmental risks.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.