Neuroepithelial cells require fucosylated glycans to guide the migration of vagus motor neuron progenitors in the developing zebrafish hindbrain

The Ptk2-Pma1 pathway enhances tolerance to terbinafine in Trichophyton rubrum

The increasing prevalence of dermatophyte resistance to terbinafine, a key drug in the treatment of dermatophytosis, represents a significant obstacle to treatment. Trichophyton rubrum is the most commonly isolated fungus in dermatophytosis. In T. rubrum, we identified TERG_07844, a gene encoding a previously uncharacterized putative protein kinase, as an ortholog of budding yeast Saccharomyces cerevisiae polyamine transport kinase 2 (Ptk2), and found that T. rubrum Ptk2 (TrPtk2) is involved in terbinafine tolerance. In both T. rubrum and S. cerevisiae, Ptk2 knockout strains were more sensitive to terbinafine compared with the wild types, suggesting that promotion of terbinafine tolerance is a conserved function of fungal Ptk2. Pma1 is activated through phosphorylation by Ptk2 in S. cerevisiae. Overexpression of T. rubrum Pma1 (TrPma1) in T. rubrum Ptk2 knockout strain (ΔTrPtk2) suppressed terbinafine sensitivity, suggesting that the induction of terbinafine tolerance by TrPtk2 is mediated by TrPma1. Furthermore, omeprazole, an inhibitor of plasma membrane proton pump Pma1, increased the terbinafine sensitivity of clinically isolated terbinafine-resistant strains. These findings suggest that, in dermatophytes, the TrPtk2-TrPma1 pathway plays a key role in promoting intrinsic terbinafine tolerance and may serve as a potential target for combinational antifungal therapy against terbinafine-resistant dermatophytes.

Novel insight into FCSK-congenital disorder of glycosylation through a CRISPR-generated cell model

BACKGROUND

FCSK-congenital disorder of glycosylation (FCSK-CDG) is a recently discovered rare autosomal recessive genetic disorder with defective fucosylation due to mutations in the fucokinase encoding gene, FCSK. Despite the essential role of fucokinase in the fucose salvage pathway and severe multisystem manifestations of FCSK-CDG patients, it is not elucidated which cells or which types of fucosylation are affected by its deficiency.

METHODS

In this study, CRISPR/Cas9 was employed to construct an FCSK-CDG cell model and explore the molecular mechanisms of the disease by lectin flow cytometry and real-time PCR analyses.

RESULTS

Comparison of cellular fucosylation by lectin flow cytometry in the created CRISPR/Cas9 FCSK knockout and the same unedited cell lines showed no significant change in the amount of cell surface fucosylated glycans, which is consistent with the only documented previous study on different cell types. It suggests a probable effect of this disease on secretory glycoproteins. Investigating O-fucosylation by analysis of the NOTCH3 gene expression as a potential target revealed a significant decrease in the FCSK knockout cells compared with the same unedited ones, proving the effect of fucokinase deficiency on EGF-like repeats O-fucosylation.

CONCLUSION

This study expands insight into the FCSK-CDG molecular mechanism; to the best of our knowledge, it is the first research conducted to reveal a gene whose expression level alters due to this disease.

Development and regeneration of the vagus nerve

The vagus nerve, with its myriad constituent axon branches and innervation targets, has long been a model of anatomical complexity in the nervous system. The branched architecture of the vagus nerve is now appreciated to be highly organized around the topographic and/or molecular identities of the neurons that innervate each target tissue. However, we are only just beginning to understand the developmental mechanisms by which heterogeneous vagus neuron identity is specified, patterned, and used to guide the axons of particular neurons to particular targets. Here, we summarize our current understanding of the complex topographic and molecular organization of the vagus nerve, the developmental basis of neuron specification and patterned axon guidance that supports this organization, and the regenerative mechanisms that promote, or inhibit, the restoration of vagus nerve organization after nerve damage. Finally, we highlight key unanswered questions in these areas and discuss potential strategies to address these questions.

Comparative analysis of the cardiac structure and transcriptome of scallop and snail, perspectives on heart chamber evolution

The evolution of a two-chambered heart, with an atrium and a ventricle, has improved heart function in both deuterostomes (vertebrates) and some protostomes (invertebrates). Although studies have examined the unique structure and function of these two chambers, molecular comparisons are few and limited to vertebrates. Here, we focus on the two-chambered protostome heart of the mollusks, offering data that may provide a better understanding of heart evolution. Specifically, we asked if the atrium and ventricle differ at the molecular level in the mollusk heart. To do so, we examined two very different species, the giant African land snail (Lissachatina fulica) and the relatively small, aquatic yesso scallop (Mizuhopecten yessoensis), with the assumption that if they exhibited commonality these similarities would likely reflect those across the phylum. We found that, although the hearts of these two species differed histologically, their cardiac gene function enrichments were similar, as revealed by transcriptomic analysis. Furthermore, the atrium and ventricle in each species had distinct gene function clusters, suggesting an evolutionary differentiation of cardiac chambers in mollusks. Finally, to explore the relationship between vertebrate and invertebrate two-chambered hearts, we compared our transcriptomic data with published data from the zebrafish, a well-studied vertebrate model with a two-chambered heart. Our analysis indicated a functional similarity of ventricular genes between the mollusks and the zebrafish, suggesting that the ventricle was differentiated to achieve the same functions in invertebrates and vertebrates. As the first such study on protostomes, our findings offered initial insights into how the two-chambered heart arose, including a possible understanding of its occurrence in both protostomes and deuterostomes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00202-0.

L-Fucose promotes enteric nervous system regeneration in type 1 diabetic mice by inhibiting SMAD2 signaling pathway in enteric neural precursor cells

BACKGROUND

Diabetes can lead to extensive damage to the enteric nervous system (ENS), causing gastrointestinal motility disorders. However, there is currently a lack of effective treatments for diabetes-induced ENS damage. Enteric neural precursor cells (ENPCs) closely regulate the structural and functional integrity of the ENS. L-Fucose, is a dietary sugar that has been showed to effectively ameliorate central nervous system injuries, but its potential for ameliorating ENS damage and the involvement of ENPCs in this process remains uncertain.

METHODS

Genetically engineered mice were generated for lineage tracing of ENPCs in vivo. Using diabetic mice in vivo and high glucose-treated primary ENPCs in vitro, the effects of L-Fucose on the injured ENS and ENPCs was evaluated by assessing gastrointestinal motility, ENS structure, and the differentiation of ENPCs. The key signaling pathways in regulating neurogenesis and neural precursor cells properties, transforming growth factor-β (TGF-β) and its downstream signaling pathways were further examined to clarify the potential mechanism of L-Fucose on the injured ENS and ENPCs.

RESULTS

L-Fucose improved gastrointestinal motility in diabetic mice, including increased defecation frequency (p < 0.05), reduced total gastrointestinal transmission time (p < 0.001) and bead expulsion time (p < 0.05), as well as enhanced spontaneous contractility and electric field stimulation-induced contraction response in isolated colonic muscle strips (p < 0.001). The decrease in the number of neurons and glial cells in the ENS of diabetic mice were reversed by L-Fucose treatment. More importantly, L-Fucose treatment significantly promoted the proportion of ENPCs differentiated into neurons and glial cells both in vitro and in vivo, accompanied by inhibiting SMAD2 phosphorylation.

CONCLUSIONS

L-Fucose could promote neurogenesis and gliogenesis derived from ENPCs by inhibiting the SMAD2 signaling, thus facilitating ENS regeneration and gastrointestinal motility recovery in type 1 diabetic mice. Video Abstract.

Protein fucosylation is required for Notch dependent vascular integrity in zebrafish

The onset of circulation in a developing embryo requires intact blood vessels to prevent hemorrhage. The development of endothelial cells, and their subsequent recruitment of perivascular mural cells are important processes to establish and maintain vascular integrity. These processes are genetically controlled during development, and mutations that affect endothelial cell specification, pattern formation, or maturation through the addition of mural cells can result in early developmental hemorrhage. We created a strong loss of function allele of the zebrafish GDP-mannose 4,6 dehydratase (gmds) gene that is required for the de novo synthesis of GDP-fucose, and homozygous embryos display cerebral hemorrhages. Our data demonstrate that gmds mutants have early defects in vascular patterning with ectopic branches observed at time of hemorrhage. Subsequently, defects in the number of mural cells that line the vasculature are observed. Moreover, activation of Notch signaling rescued hemorrhage phenotypes in gmds mutants, highlighting a potential downstream pathway that requires protein fucosylation for vascular integrity. Finally, supplementation with fucose can rescue hemorrhage frequency in gmds mutants, demonstrating that synthesis of GDP-fucose via an alternative (salvage) pathway may provide an avenue toward therapeutic correction of phenotypes observed due to defects in de novo GDP-fucose synthesis. Together, these data are consistent with a novel role for the de novo and salvage protein fucosylation pathways in regulating vascular integrity through a Notch dependent mechanism.

Brain-Body Control of Glucose Homeostasis-Insights From Model Organisms

Tight regulation of blood glucose is essential for long term health. Blood glucose levels are defended by the correct function of, and communication between, internal organs including the gastrointestinal tract, pancreas, liver, and brain. Critically, the brain is sensitive to acute changes in blood glucose level and can modulate peripheral processes to defend against these deviations. In this mini-review we highlight select key findings showcasing the utility, strengths, and limitations of model organisms to study brain-body interactions that sense and control blood glucose levels. First, we discuss the large platform of genetic tools available to investigators studying mice and how this field may yet reveal new modes of communication between peripheral organs and the brain. Second, we discuss how rats, by virtue of their size, have unique advantages for the study of CNS control of glucose homeostasis and note that they may more closely model some aspects of human (patho)physiology. Third, we discuss the nascent field of studying the CNS control of blood glucose in the zebrafish which permits ease of genetic modification, large-scale measurements of neural activity and live imaging in addition to high-throughput screening. Finally, we briefly discuss glucose homeostasis in drosophila, which have a distinct physiology and glucoregulatory systems to vertebrates.

Ascites from Ovarian Cancer Induces Novel Fucosylated Proteins

Ovarian cancer is considered to be the most lethal type of gynecological cancer. During the advanced stages of ovarian cancer, an accumulation of ascites is observed. Fucosylation has been classified as an abnormal post-translational modification that is present in many diseases, including ovarian cancer. Ovarian cancer cells that are cultured with ascites stimulation change their morphology; concomitantly, the fucosylation process is altered. However, it is not known which fucosylated proteins are modified. The goal of this work was to identify the differentially fucosylated proteins that are expressed by ovarian cancer cell lines that are cultured with ovarian cancer patients' ascites. Aleuria aurantia lectin was used to detect fucosylation, and some changes were observed, especially in the cell membrane. Affinity chromatography and mass spectrometry (MALDI-TOF) were used to identify 6 fucosylated proteins. Four proteins (Intermediate filament family orphan 1 [IFFO1], PHD finger protein 20-like protein 1 [PHF20L1], immunoglobulin gamma 1 heavy chain variable region partial [IGHV1-2], and Zinc finger protein 224 [ZNF224]) were obtained from cell cultures stimulated with ascites, and the other two proteins (Peregrin [BRPF1] and Dystrobrevin alpha [DTNA]) were obtained under normal culture conditions. The fucosylated state of some of these proteins was further analyzed. The experimental results show that the ascites of ovarian cancer patients modulated the fucosylation process. The PHD finger protein 20-like protein 1, Zinc finger protein 224 and Peregrin proteins colocalize with fucosylation at different levels.

poFUT1 promotes endometrial decidualization by enhancing the O-fucosylation of Notch1

BACKGROUND

Endometrial stromal cell decidualization is critical for embryo implantation. Dysfunctional decidualization leads to implantation failure, miscarriage and even pregnancy associated disorders in subsequent pregnancy trimesters. Protein glycosylation is involved in many physiological and pathological processes. Protein O-fucosyltransferase 1 (poFUT1) is the key enzyme for the O-fucosylation of proteins. However, the role and mechanism of poFUT1 in human endometrial stromal cell decidualization remain elusive.

METHODS

We employed immunohistochemistry to detect the level of poFUT1 in the uterine endometrium from those of the proliferative phase, secretory phase, early pregnancy women and miscarriage patients. Using human endometrial stromal cells (hESCs) and a mouse model, the underlying mechanisms of poFUT1 in decidualization was investigated.

FINDINGS

The level of poFUT1 was increased in the stromal cells of the secretory phase relative to those in the proliferative phase of the menstrual cycle, and decreased in the stromal cells of miscarriage patients compared to women with healthy early pregnancies. Furthermore, we found that poFUT1 promoted hESCs decidualization. The results also demonstrated that poFUT1 increased O-fucosylation on Notch1 in hESCs, which activated Notch1 signaling pathway. Activated Notch1 (NICD), as a specific trans-factor of PRL and IGFBP1 promoters, enhanced PRL and IGFBP1 transcriptional activity, thus inducing hESCs decidualization.

INTERPRETATION

Level of poFUT1 is lower in the uterine endometrium from miscarriage patients than early pregnancy women. poFUT1 is critical in endometrial decidualization by controlling the O-fucosylation on Notch1. Our findings provide a new mechanism perspective on poFUT1 in uterine decidualization that may be a useful diagnostic and therapeutic target for miscarriage. FUND: National Natural Science Foundation of China (31770857, 31670810 and 31870794). Liaoning Provincial Program for Top Discipline of Basic Medical Sciences.

Survey of Human Chromosome 21 Gene Expression Effects on Early Development in Danio rerio

Trisomy for human chromosome 21 (Hsa21) results in Down syndrome (DS), one of the most genetically complex conditions compatible with human survival. Assessment of the physiological consequences of dosage-driven overexpression of individual Hsa21 genes during early embryogenesis and the resulting contributions to DS pathology in mammals are not tractable in a systematic way. A recent study looked at loss-of-function of a subset of Caenorhabditis elegans orthologs of Hsa21 genes and identified ten candidates with behavioral phenotypes, but the equivalent over-expression experiment has not been done. We turned to zebrafish as a developmental model and, using a number of surrogate phenotypes, we screened Hsa21 genes for effects on early embyrogenesis. We prepared a library of 164 cDNAs of conserved protein coding genes, injected mRNA into early embryos and evaluated up to 5 days post-fertilization (dpf). Twenty-four genes produced a gross morphological phenotype, 11 of which could be reproduced reliably. Seven of these gave a phenotype consistent with down regulation of the sonic hedgehog (Shh) pathway; two showed defects indicative of defective neural crest migration; one resulted consistently in pericardial edema; and one was embryonic lethal. Combinatorial injections of multiple Hsa21 genes revealed both additive and compensatory effects, supporting the notion that complex genetic relationships underlie end phenotypes of trisomy that produce DS. Together, our data suggest that this system is useful in the genetic dissection of dosage-sensitive gene effects on early development and can inform the contribution of both individual loci and their combinatorial effects to phenotypes relevant to the etiopathology of DS.

Small GTPase R-Ras participates in neural tube formation in zebrafish embryonic spinal cord

Ras related (R-Ras), a small GTPase, is involved in the maintenance of apico-basal polarity in neuroepithelial cells of the zebrafish hindbrain, axonal collapse in cultured murine hippocampal neurons, and maturation of blood vessels in adult mice. However, the role of R-Ras in neural tube formation remains unknown. Using antisense morpholino oligonucleotides (AMOs), we found that in the spinal cord of zebrafish embryos, the lumen was formed bilaterally in rras morphants, whereas it was formed at the midline in control embryos. As AMO can cause off-target effects, we generated rras mutant zebrafish lines using CRISPR/Cas9 technology. Although these rras mutant embryos did not have a bilateral lumen in the spinal cord, the following findings suggest that the phenotype is unlikely due to an off-target effect of rras AMO: 1) The rras morphant phenotype was rescued by an injection of AMO-resistant rras mRNA, and 2) a bilaterally segregated spinal cord was not observed in rras mutant embryos injected with rras AMO. The results suggest that the function of other ras family genes may be redundant in rras mutants. Previous research reported a bilaterally formed lumen in the spinal cord of zebrafish embryos with a mutation in a planar cell polarity (PCP) gene, van gogh-like 2 (vangl2). In the present study, in cultured cells, R-Ras was co-immunoprecipitated with Vangl2 but not with another PCP regulator, Pricke1. Interestingly, the interaction between R-Ras and Vangl2 was stronger in guanine-nucleotide free point mutants of R-Ras than in wild-type or constitutively active (GTP-bound) forms of R-Ras. R-Ras may regulate neural tube formation in cooperation with Vangl2 in the developing zebrafish spinal cord.

Biological functions of fucose in mammals

Fucose is a 6-deoxy hexose in the l-configuration found in a large variety of different organisms. In mammals, fucose is incorporated into N-glycans, O-glycans and glycolipids by 13 fucosyltransferases, all of which utilize the nucleotide-charged form, GDP-fucose, to modify targets. Three of the fucosyltransferases, FUT8, FUT12/POFUT1 and FUT13/POFUT2, are essential for proper development in mice. Fucose modifications have also been implicated in many other biological functions including immunity and cancer. Congenital mutations of a Golgi apparatus localized GDP-fucose transporter causes leukocyte adhesion deficiency type II, which results in severe developmental and immune deficiencies, highlighting the important role fucose plays in these processes. Additionally, changes in levels of fucosylated proteins have proven as useful tools for determining cancer diagnosis and prognosis. Chemically modified fucose analogs can be used to alter many of these fucose dependent processes or as tools to better understand them. In this review, we summarize the known roles of fucose in mammalian physiology and pathophysiology. Additionally, we discuss recent therapeutic advances for cancer and other diseases that are a direct result of our improved understanding of the role that fucose plays in these systems.

Inhibition of Delta-induced Notch signaling using fucose analogs

Notch is a cell-surface receptor that controls cell-fate decisions and is regulated by O-glycans attached to epidermal growth factor-like (EGF) repeats in its extracellular domain. Protein O-fucosyltransferase 1 (Pofut1) modifies EGF repeats with O-fucose and is essential for Notch signaling. Constitutive activation of Notch signaling has been associated with a variety of human malignancies. Therefore, tools that inhibit Notch activity are being developed as cancer therapeutics. To this end, we screened L-fucose analogs for their effects on Notch signaling. Two analogs, 6-alkynyl and 6-alkenyl fucose, were substrates of Pofut1 and were incorporated directly into Notch EGF repeats in cells. Both analogs were potent inhibitors of binding to and activation of Notch1 by Notch ligands Dll1 and Dll4, but not by Jag1. Mutagenesis and modeling studies suggest that incorporation of the analogs into EGF8 of Notch1 markedly reduces the ability of Delta ligands to bind and activate Notch1.

Vagus Motor Neuron Topographic Map Determined by Parallel Mechanisms of hox5 Expression and Time of Axon Initiation

Many networks throughout the nervous system are organized into topographic maps, where the positions of neuron cell bodies in the projecting field correspond with the positions of their axons in the target field. Previous studies of topographic map development show evidence for spatial patterning mechanisms, in which molecular determinants expressed across the projecting and target fields are matched directly in a point-to-point mapping process. Here, we describe a novel temporal mechanism of topographic map formation that depends on spatially regulated differences in the timing of axon outgrowth and functions in parallel with spatial point-to-point mapping mechanisms. We focus on the vagus motor neurons, which are topographically arranged in both mammals and fish. We show that cell position along the anterior-posterior axis of hindbrain rhombomere 8 determines expression of hox5 genes, which are expressed in posterior, but not anterior, vagus motor neurons. Using live imaging and transplantation in zebrafish embryos, we additionally reveal that axon initiation is delayed in posterior vagus motor neurons independent of neuron birth time. We show that hox5 expression directs topographic mapping without affecting time of axon outgrowth and that time of axon outgrowth directs topographic mapping without affecting hox5 expression. The vagus motor neuron topographic map is therefore determined by two mechanisms that act in parallel: a hox5-dependent spatial mechanism akin to classic mechanisms of topographic map formation and a novel axon outgrowth-dependent temporal mechanism in which time of axon formation is spatially regulated to direct axon targeting.

Transcriptome analysis of different developmental stages of amphioxus reveals dynamic changes of distinct classes of genes during development

Vertebrates diverged from other chordates approximately 500 million years ago and have adopted several modifications of developmental processes. Amphioxus is widely used in evolutionary developmental biology research, such as on the basic patterning mechanisms involved in the chordate body plan and the origin of vertebrates. The fast development of next-generation sequencing has advanced knowledge of the genomic organization of amphioxus; however, many aspects of gene regulation during amphioxus development have not been fully characterized. In this study, we applied high-throughput sequencing on the transcriptomes of 13 developmental stages of Chinese amphioxus to gain a comprehensive understanding of transcriptional processes occurring from the fertilized egg to the adult stage. The expression levels of 3,423 genes were significantly changed (FDR ≤ 0.01). All of these genes were included in a clustering analysis, and enrichment of biological functions associated with these clusters was determined. Significant changes were observed in several important processes, including the down-regulation of the cell cycle and the up-regulation of translation. These results should build a foundation for identifying developmentally important genes, especially those regulatory factors involved in amphioxus development, and advance understanding of the developmental dynamics in vertebrates.

Mechanosensory Genes Pkd1 and Pkd2 Contribute to the Planar Polarization of Brain Ventricular Epithelium

Directional beating of ependymal (E) cells' cilia in the walls of the ventricles in the brain is essential for proper CSF flow. E cells display two forms of planar cell polarity (PCP): rotational polarity of individual cilium and translational polarity (asymmetric positioning of cilia in the apical area). The orientation of individual E cells varies according to their location in the ventricular wall (location-specific PCP). It has been hypothesized that hydrodynamic forces on the apical surface of radial glia cells (RGCs), the embryonic precursors of E cells, could guide location-specific PCP in the ventricular epithelium. However, the detection mechanisms for these hydrodynamic forces have not been identified. Here, we show that the mechanosensory proteins polycystic kidney disease 1 (Pkd1) and Pkd2 are present in primary cilia of RGCs. Ablation of Pkd1 or Pkd2 in Nestin-Cre;Pkd1(flox/flox) or Nestin-Cre;Pkd2(flox/flox) mice, affected PCP development in RGCs and E cells. Early shear forces on the ventricular epithelium may activate Pkd1 and Pkd2 in primary cilia of RGCs to properly polarize RGCs and E cells. Consistently, Pkd1, Pkd2, or primary cilia on RGCs were required for the proper asymmetric localization of the PCP protein Vangl2 in E cells' apical area. Analyses of single- and double-heterozygous mutants for Pkd1 and/or Vangl2 suggest that these genes function in the same pathway to establish E cells' PCP. We conclude that Pkd1 and Pkd2 mechanosensory proteins contribute to the development of brain PCP and prevention of hydrocephalus.

SIGNIFICANCE STATEMENT

This study identifies key molecules in the development of planar cell polarity (PCP) in the brain and prevention of hydrocephalus. Multiciliated ependymal (E) cells within the brain ventricular epithelium generate CSF flow through ciliary beating. E cells display location-specific PCP in the orientation and asymmetric positioning of their cilia. Defects in this PCP can result in hydrocephalus. Hydrodynamic forces on radial glial cells (RGCs), the embryonic progenitors of E cells, have been suggested to guide PCP. We show that the mechanosensory proteins Pkd1 and Pkd2 localize to primary cilia in RGCs, and their ablation disrupts the development of PCP in E cells. Early shear forces on RGCs may activate Pkd1 and Pkd2 in RGCs' primary cilia to properly orient E cells. This study identifies key molecules in the development of brain PCP and prevention of hydrocephalus.

Disruptions in a cluster of computationally identified enhancers near FOXC1 and GMDS may influence brain development

Regulatory elements are more evolutionarily conserved and provide a larger mutational target than coding regions of the human genome, suggesting that mutations in non-coding regions contribute significantly to development and disease. Using a computational approach to predict gene regulatory enhancers, we found that many known and predicted embryonic enhancers cluster in genomic loci harboring development-associated genes. One of the densest clusters of predicted enhancers in the human genome is near the genes GMDS and FOXC1. GMDS encodes a short-chain mannose dehydrogenase enzyme involved in the regulation of hindbrain neural migration, and FOXC1 encodes a developmental transcription factor required for brain, heart, and eye development. We experimentally validate four novel enhancers in this locus and demonstrate that these enhancers show consistent activity during embryonic development in domains that overlap with the expression of FOXC1 and GMDS. These four enhancers contain binding motifs for several transcription factors, including the ZIC family of transcription factors. Removal of the ZIC binding sites significantly alters enhancer activity in three of these enhancers, reducing expression in the eye, hindbrain, and limb, suggesting a mechanism whereby ZIC family members may transcriptionally regulate FOXC1 and/or GMDS expression. Our findings uncover novel enhancer regions that may control transcription in a topological domain important for embryonic development.

Comparative distribution and in vitro activities of the urotensin II-related peptides URP1 and URP2 in zebrafish: evidence for their colocalization in spinal cerebrospinal fluid-contacting neurons

Urotensin II (UII) is an evolutionarily conserved neuropeptide initially isolated from teleost fish on the basis of its smooth muscle-contracting activity. Subsequent studies have demonstrated the occurrence of several UII-related peptides (URPs), such that the UII family is now known to include four paralogue genes called UII, URP, URP1 and URP2. These genes probably arose through the two rounds of whole genome duplication that occurred during early vertebrate evolution. URP has been identified both in tetrapods and teleosts. In contrast, URP1 and URP2 have only been observed in ray-finned and cartilaginous fishes, suggesting that both genes were lost in the tetrapod lineage. In the present study, the distribution of urp1 mRNA compared to urp2 mRNA is reported in the central nervous system of zebrafish. In the spinal cord, urp1 and urp2 mRNAs were mainly colocalized in the same cells. These cells were also shown to be GABAergic and express the gene encoding the polycystic kidney disease 2-like 1 (pkd2l1) channel, indicating that they likely correspond to cerebrospinal fluid-contacting neurons. In the hindbrain, urp1-expressing cells were found in the intermediate reticular formation and the glossopharyngeal-vagal motor nerve nuclei. We also showed that synthetic URP1 and URP2 were able to induce intracellular calcium mobilization in human UII receptor (hUT)-transfected CHO cells with similar potencies (pEC50=7.99 and 7.52, respectively) albeit at slightly lower potencies than human UII and mammalian URP (pEC50=9.44 and 8.61, respectively). The functional redundancy of URP1 and URP2 as well as the colocalization of their mRNAs in the spinal cord suggest the robustness of this peptidic system and its physiological importance in zebrafish.

Proper migration and axon outgrowth of zebrafish cranial motoneuron subpopulations require the cell adhesion molecule MDGA2A

The formation of functional neuronal circuits relies on accurate migration and proper axonal outgrowth of neuronal precursors. On the route to their targets migrating cells and growing axons depend on both, directional information from neurotropic cues and adhesive interactions mediated via extracellular matrix molecules or neighbouring cells. The inactivation of guidance cues or the interference with cell adhesion can cause severe defects in neuronal migration and axon guidance. In this study we have analyzed the function of the MAM domain containing glycosylphosphatidylinositol anchor 2A (MDGA2A) protein in zebrafish cranial motoneuron development. MDGA2A is prominently expressed in distinct clusters of cranial motoneurons, especially in the ones of the trigeminal and facial nerves. Analyses of MDGA2A knockdown embryos by light sheet and confocal microscopy revealed impaired migration and aberrant axonal outgrowth of these neurons; suggesting that adhesive interactions mediated by MDGA2A are required for the proper arrangement and outgrowth of cranial motoneuron subtypes.

A novel mutation in leukocyte adhesion deficiency type II/CDGIIc

Leukocyte adhesion deficiencies (LAD) are autosomal recessive immunodeficiency syndromes characterized by severe and recurrent bacterial infections, impaired wound healing and leukocytosis. Block in different steps in the leukocyte adhesion cascade causes different types of leukocyte adhesion deficiencies, LAD type I, II and III. In LAD type II, the rolling phase of the leukocyte adhesion cascade is affected due to mutations in the specific fucose transporter GFTP (GDP fucose transporter), causing defect in the biosynthesis of selectin ligands on leukocytes. Thus this syndrome is also called congenital disorder of glycosylation IIc (CGDIIc). LAD II/CGDIIc is very rare and has been diagnosed in nine children to date. Fever, leukocytosis, typical dysmorphic features, growth, psychomotor retardation and the Bombay blood group, are characteristic findings in patients. Here, we describe two Turkish siblings with a novel mutation in GFTP. They both have the characteristic features of the syndrome. The older sibling died of severe bacterial pneumonia at the age of 3 years. The younger sibling, diagnosed at the age of 3 months, responded to high dose oral fucose supplementation. Secundum atrial septal defect which was not described in previously reported patients, but present in both of our patients, may primarily related to the defect in fucosylation.

Negative feedback regulation of Wnt signaling via N-linked fucosylation in zebrafish

L-fucose, a monosaccharide widely distributed in eukaryotes and certain bacteria, is a determinant of many functional glycans that play central roles in numerous biological processes. The molecular mechanism, however, by which fucosylation mediates these processes remains largely elusive. To study how changes in fucosylation impact embryonic development, we up-regulated N-linked fucosylation via over-expression of a key GDP-Fucose transporter, Slc35c1, in zebrafish. We show that Slc35c1 overexpression causes elevated N-linked fucosylation and disrupts embryonic patterning in a transporter activity dependent manner. We demonstrate that patterning defects associated with enhanced N-linked fucosylation are due to diminished canonical Wnt signaling. Chimeric analyses demonstrate that elevated Slc35c1 expression in receiving cells decreases the signaling range of Wnt8a during zebrafish embryogenesis. Moreover, we provide biochemical evidence that this decrease is associated with reduced Wnt8 ligand and elevated Lrp6 coreceptor, which we show are both substrates for N-linked fucosylation in zebrafish embryos. Strikingly, slc35c1 expression is regulated by canonical Wnt signaling. These results suggest that Wnt limits its own signaling activity in part via up-regulation of a transporter, slc35c1 that promotes terminal fucosylation and thereby limits Wnt activity.

In silico analysis of the fucosylation-associated genome of the human blood fluke Schistosoma mansoni: cloning and characterization of the enzymes involved in GDP-L-fucose synthesis and Golgi import

BACKGROUND

Carbohydrate structures of surface-expressed and secreted/excreted glycoconjugates of the human blood fluke Schistosoma mansoni are key determinants that mediate host-parasite interactions in both snail and mammalian hosts. Fucose is a major constituent of these immunologically important glycans, and recent studies have sought to characterize fucosylation-associated enzymes, including the Golgi-localized fucosyltransferases that catalyze the transfer of L-fucose from a GDP-L-fucose donor to an oligosaccharide acceptor. Importantly, GDP-L-fucose is the only nucleotide-sugar donor used by fucosyltransferases and its availability represents a bottleneck in fucosyl-glycotope expression.

METHODS

A homology-based genome-wide bioinformatics approach was used to identify and molecularly characterize the enzymes that contribute to GDP-L-fucose synthesis and Golgi import in S. mansoni. Putative functions were further investigated through molecular phylogenetic and immunocytochemical analyses.

RESULTS

We identified homologs of GDP-D-mannose-4,6-dehydratase (GMD) and GDP-4-keto-6-deoxy-D-mannose-3,5-epimerase-4-reductase (GMER), which constitute a de novo pathway for GDP-L-fucose synthesis, in addition to a GDP-L-fucose transporter (GFT) that putatively imports cytosolic GDP-L-fucose into the Golgi. In silico primary sequence analyses identified characteristic Rossman loop and short-chain dehydrogenase/reductase motifs in GMD and GMER as well as 10 transmembrane domains in GFT. All genes are alternatively spliced, generating variants of unknown function. Observed quantitative differences in steady-state transcript levels between miracidia and primary sporocysts may contribute to differential glycotope expression in early larval development. Additionally, analyses of protein expression suggest the occurrence of cytosolic GMD and GMER in the ciliated epidermal plates and tegument of miracidia and primary sporocysts, respectively, which is consistent with previous localization of highly fucosylated glycotopes.

CONCLUSIONS

This study is the first to identify and characterize three key genes that are putatively involved in the synthesis and Golgi import of GDP-L-fucose in S. mansoni and provides fundamental information regarding their genomic organization, genetic variation, molecular phylogenetics, and developmental expression in intramolluscan larval stages.

Phox2b expression in the taste centers of fish

The homeodomain transcription factor Phox2b controls the formation of the sensory-motor reflex circuits of the viscera in vertebrates. Among Phox2b-dependent structures characterized in rodents is the nucleus of the solitary tract, the first relay for visceral sensory input, including taste. Here we show that Phox2b is expressed throughout the primary taste centers of two cyprinid fish, Danio rerio and Carassius auratus, i.e., in their vagal, glossopharyngeal, and facial lobes, providing the first molecular evidence for their homology with the nucleus of the solitary tract of mammals and suggesting that a single ancestral Phox2b-positive neuronal type evolved to give rise to both fish and mammalian structures. In zebrafish larvae, the distribution of Phox2b²⁺ neurons, combined with the expression pattern of Olig4 (a homologue of Olig3, determinant of the nucleus of the solitary tract in mice), reveals that the superficial position and sheet-like architecture of the viscerosensory column in cyprinid fish, ideally suited for the somatotopic representation of oropharyngeal and bodily surfaces, arise by radial migration from a dorsal progenitor domain, in contrast to the tangential migration observed in amniotes.

Dynamics of the leading process, nucleus, and Golgi apparatus of migrating cortical interneurons in living mouse embryos

Precisely arranged cytoarchitectures such as layers and nuclei depend on neuronal migration, of which many in vitro studies have revealed the mode and underlying mechanisms. However, how neuronal migration is achieved in vivo remains unknown. Here we established an imaging system that allows direct visualization of cortical interneuron migration in living mouse embryos. We found that during nucleokinesis, translocation of the Golgi apparatus either precedes or occurs in parallel to that of the nucleus, suggesting the existence of both a Golgi/centrosome-dependent and -independent mechanism of nucleokinesis. Changes in migratory direction occur when the nucleus enters one of the leading process branches, which is accompanied by the retraction of other branches. The nucleus occasionally swings between two branches before translocating into one of them, the occurrence of which is most often preceded by Golgi apparatus translocation into that branch. These in vivo observations provide important insight into the mechanisms of neuronal migration and demonstrate the usefulness of our system for studying dynamic events in living animals.

A zebrafish model of PMM2-CDG reveals altered neurogenesis and a substrate-accumulation mechanism for N-linked glycosylation deficiency

PMM2-CDG patients have phosphomannomutase (Pmm2) deficiency, with developmental and N-linked glycosylation defects attributed to depletion of mannose-1-phosphate and downstream lipid-linked oligosaccharides (LLOs). This, the first PMM2-CDG zebrafish model, shows, unexpectedly, that accumulation of the Pmm2 substrate mannose-6-phosphate explains LLO deficiency.

Congenital disorder of glycosylation (PMM2-CDG) results from mutations in pmm2, which encodes the phosphomannomutase (Pmm) that converts mannose-6-phosphate (M6P) to mannose-1-phosphate (M1P). Patients have wide-spectrum clinical abnormalities associated with impaired protein N-glycosylation. Although it has been widely proposed that Pmm2 deficiency depletes M1P, a precursor of GDP-mannose, and consequently suppresses lipid-linked oligosaccharide (LLO) levels needed for N-glycosylation, these deficiencies have not been demonstrated in patients or any animal model. Here we report a morpholino-based PMM2-CDG model in zebrafish. Morphant embryos had developmental abnormalities consistent with PMM2-CDG patients, including craniofacial defects and impaired motility associated with altered motor neurogenesis within the spinal cord. Significantly, global N-linked glycosylation and LLO levels were reduced in pmm2 morphants. Although M1P and GDP-mannose were below reliable detection/quantification limits, Pmm2 depletion unexpectedly caused accumulation of M6P, shown earlier to promote LLO cleavage in vitro. In pmm2 morphants, the free glycan by-products of LLO cleavage increased nearly twofold. Suppression of the M6P-synthesizing enzyme mannose phosphate isomerase within the pmm2 background normalized M6P levels and certain aspects of the craniofacial phenotype and abrogated pmm2-dependent LLO cleavage. In summary, we report the first zebrafish model of PMM2-CDG and uncover novel cellular insights not possible with other systems, including an M6P accumulation mechanism for underglycosylation.

"Casting" light on the role of glycosylation during embryonic development: insights from zebrafish

Zebrafish (Danio rerio) remains a versatile model organism for the investigation of early development and organogenesis, and has emerged as a valuable platform for drug discovery and toxicity evaluation [1-6]. Harnessing the genetic power and experimental accessibility of this system, three decades of research have identified key genes and pathways that control the development of multiple organ systems and tissues, including the heart, kidney, and craniofacial cartilage, as well as the hematopoietic, vascular, and central and peripheral nervous systems [7-31]. In addition to their application in large mutagenic screens, zebrafish has been used to model a variety of diseases such as diabetes, polycystic kidney disease, muscular dystrophy and cancer [32-36]. As this work continues to intersect with cellular pathways and processes such as lipid metabolism, glycosylation and vesicle trafficking, investigators are often faced with the challenge of determining the degree to which these pathways are functionally conserved in zebrafish. While they share a high degree of genetic homology with mouse and human, the manner in which cellular pathways are regulated in zebrafish during early development, and the differences in the organ physiology, warrant consideration before functional studies can be effectively interpreted and compared with other vertebrate systems. This point is particularly relevant for glycosylation since an understanding of the glycan diversity and the mechanisms that control glycan biosynthesis during zebrafish embryogenesis (as in many organisms) is still developing.Nonetheless, a growing number of studies in zebrafish have begun to cast light on the functional roles of specific classes of glycans during organ and tissue development. While many of the initial efforts involved characterizing identified mutants in a number of glycosylation pathways, the use of reverse genetic approaches to directly model glycosylation-related disorders is now increasingly popular. In this review, the glycomics of zebrafish and the developmental expression of their glycans will be briefly summarized along with recent chemical biology approaches to visualize certain classes of glycans within developing embryos. Work regarding the role of protein-bound glycans and glycosaminoglycans (GAG) in zebrafish development and organogenesis will also be highlighted. Lastly, future opportunities and challenges in the expanding field of zebrafish glycobiology are discussed.

Human deficiencies of fucosylation and sialylation affecting selectin ligands

Selectins are carbohydrate-binding adhesion molecules that are required for leukocyte trafficking to secondary lymphoid organs and to sites of infection. They interact with fucosylated and sialylated ligands bearing sialyl-Lewis X as a minimal carbohydrate structure. With this in mind, it should be expected that individuals with deficient fucosylation or sialylation show immunodeficiency. However, as this review shows, the picture appears to be more complex and more interesting. Although there are only few patients with such glycosylation defects, they have turned out to be very instructive for our understanding of the functions of fucosylation and sialylation in immunity, development and hemostasis.

Yoshiki Hotta and the dawn of zebrafish molecular neurogenetics in Japan

Abstract: After coming back to Japan to work in the Department of Physics at the University of Tokyo, Yoshiki Hotta spent a year or so on searching for behavioral mutants of goldfish. Although this endeavor did not succeed, he remained an adamant supporter of the development of zebrafish research in Japan. Here we review how his support helped zebrafish neurogenetics in Japan gain a unique position in the world research community.

Discovery and replication of dopamine-related gene effects on caudate volume in young and elderly populations (N=1198) using genome-wide search

The caudate is a subcortical brain structure implicated in many common neurological and psychiatric disorders. To identify specific genes associated with variations in caudate volume, structural magnetic resonance imaging and genome-wide genotypes were acquired from two large cohorts, the Alzheimer's Disease NeuroImaging Initiative (ADNI; N=734) and the Brisbane Adolescent/Young Adult Longitudinal Twin Study (BLTS; N=464). In a preliminary analysis of heritability, around 90% of the variation in caudate volume was due to genetic factors. We then conducted genome-wide association to find common variants that contribute to this relatively high heritability. Replicated genetic association was found for the right caudate volume at single-nucleotide polymorphism rs163030 in the ADNI discovery sample (P=2.36 × 10⁻⁶) and in the BLTS replication sample (P=0.012). This genetic variation accounted for 2.79 and 1.61% of the trait variance, respectively. The peak of association was found in and around two genes, WDR41 and PDE8B, involved in dopamine signaling and development. In addition, a previously identified mutation in PDE8B causes a rare autosomal-dominant type of striatal degeneration. Searching across both samples offers a rigorous way to screen for genes consistently influencing brain structure at different stages of life. Variants identified here may be relevant to common disorders affecting the caudate.

Metabolic labeling of fucosylated glycans in developing zebrafish

Many developmental processes depend on proper fucosylation, but this post-translational modification is difficult to monitor in vivo. Here we applied a chemical reporter strategy to visualize fucosylated glycans in developing zebrafish. Using azide-derivatized analogues of fucose, we metabolically labeled cell-surface glycans and then detected the incorporated azides via copper-free click chemistry with a difluorinated cyclooctyne probe. We found that the fucose salvage pathway enzymes are expressed during zebrafish embryogenesis but that they process the azide-modified substrates inefficiently. We were able to bypass the salvage pathway by using an azide-functionalized analogue of GDP-fucose. This nucleotide sugar was readily accepted by fucosyltransferases and provided robust cell-surface labeling of fucosylated glycans, as determined by flow cytometry and confocal microscopy analysis. We used this technique to image fucosylated glycans in the enveloping layer of zebrafish embryos during the first 5 days of development. This work provides a method to study the biosynthesis of fucosylated glycans in vivo.

Biocompatible copper(I) catalysts for in vivo imaging of glycans

The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is the standard method for bioorthogonal conjugation. However, current Cu(I) catalyst formulations are toxic, hindering their use in living systems. Here we report that BTTES, a tris(triazolylmethyl)amine-based ligand for Cu(I), promotes the cycloaddition reaction rapidly in living systems without apparent toxicity. This catalyst allows, for the first time, noninvasive imaging of fucosylated glycans during zebrafish early embryogenesis. We microinjected embryos with alkyne-bearing GDP-fucose at the one-cell stage and detected the metabolically incorporated unnatural sugars using the biocompatible click chemistry. Labeled glycans could be imaged in the enveloping layer of zebrafish embryos between blastula and early larval stages. This new method paves the way for rapid, noninvasive imaging of biomolecules in living organisms.

Neural and synaptic defects in slytherin, a zebrafish model for human congenital disorders of glycosylation

Congenital disorder of glycosylation type IIc (CDG IIc) is characterized by mental retardation, slowed growth and severe immunodeficiency, attributed to the lack of fucosylated glycoproteins. While impaired Notch signaling has been implicated in some aspects of CDG IIc pathogenesis, the molecular and cellular mechanisms remain poorly understood. We have identified a zebrafish mutant slytherin (srn), which harbors a missense point mutation in GDP-mannose 4,6 dehydratase (GMDS), the rate-limiting enzyme in protein fucosylation, including that of Notch. Here we report that some of the mechanisms underlying the neural phenotypes in srn and in CGD IIc are Notch-dependent, while others are Notch-independent. We show, for the first time in a vertebrate in vivo, that defects in protein fucosylation leads to defects in neuronal differentiation, maintenance, axon branching, and synapse formation. Srn is thus a useful and important vertebrate model for human CDG IIc that has provided new insights into the neural phenotypes that are hallmarks of the human disorder and has also highlighted the role of protein fucosylation in neural development.

Movement, technology and discovery in the zebrafish

Zebrafish provide unique opportunities for optogenetic studies of behavior. Here, we review the most recent work using optogenetic and imaging approaches to study the neuronal circuits controlling movements in the transparent zebrafish. Specifically, we focus on what we have learned from zebrafish about neuronal migration, network formation and behavioral control, and what the future may hold.