Gene expression of EXT1 and EXT2 during mouse brain development

Integration of selective sweeps across the sheep genome: understanding the relationship between production and adaptation traits

BACKGROUND

Livestock populations are under constant selective pressure for higher productivity levels for different selective purposes. This pressure results in the selection of animals with unique adaptive and production traits. The study of genomic regions associated with these unique characteristics has the potential to improve biological knowledge regarding the adaptive process and how it is connected to production levels and resilience, which is the ability of an animal to adapt to stress or an imbalance in homeostasis. Sheep is a species that has been subjected to several natural and artificial selective pressures during its history, resulting in a highly specialized species for production and adaptation to challenging environments. Here, the data from multiple studies that aim at mapping selective sweeps across the sheep genome associated with production and adaptation traits were integrated to identify confirmed selective sweeps (CSS).

RESULTS

In total, 37 studies were used to identify 518 CSS across the sheep genome, which were classified as production (147 prodCSS) and adaptation (219 adapCSS) CSS based on the frequency of each type of associated study. The genes within the CSS were associated with relevant biological processes for adaptation and production. For example, for adapCSS, the associated genes were related to the control of seasonality, circadian rhythm, and thermoregulation. On the other hand, genes associated with prodCSS were related to the control of feeding behaviour, reproduction, and cellular differentiation. In addition, genes harbouring both prodCSS and adapCSS showed an interesting association with lipid metabolism, suggesting a potential role of this process in the regulation of pleiotropic effects between these classes of traits.

CONCLUSIONS

The findings of this study contribute to a deeper understanding of the genetic link between productivity and adaptability in sheep breeds. This information may provide insights into the genetic mechanisms that underlie undesirable genetic correlations between these two groups of traits and pave the way for a better understanding of resilience as a positive ability to respond to environmental stressors, where the negative effects on production level are minimized.

Transcription factors in neurodevelopmental and associated psychiatric disorders: A potential convergence for genetic and environmental risk factors

Neurodevelopmental disorders (NDDs) are a heterogeneous and highly prevalent group of psychiatric conditions marked by impairments in the nervous system. Their onset occurs during gestation, and the alterations are observed throughout the postnatal life. Although many genetic and environmental risk factors have been described in this context, the interactions between them challenge the understanding of the pathways associated with NDDs. Transcription factors (TFs)-a group of over 1,600 proteins that can interact with DNA, regulating gene expression through modulation of RNA synthesis-represent a point of convergence for different risk factors. In addition, TFs organize critical processes like angiogenesis, blood-brain barrier formation, myelination, neuronal migration, immune activation, and many others in a time and location-dependent way. In this review, we summarize important TF alterations in NDD and associated disorders, along with specific impairments observed in animal models, and, finally, establish hypotheses to explain how these proteins may be critical mediators in the context of genome-environment interactions.

Trimester-Specific Associations of Prenatal Lead Exposure With Infant Cord Blood DNA Methylation at Birth

Gestational exposure to lead (Pb) adversely impacts offspring health through multiple mechanisms, one of which is the alteration of the epigenome including DNA methylation. This study aims to identify differentially methylated CpG sites associated with trimester-specific maternal Pb exposure in umbilical cord blood (UCB) leukocytes. Eighty-nine mother-child dyads from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) longitudinal birth cohorts with available UCB samples were selected for DNA methylation analysis via the Infinium Methylation EPIC BeadChip, which quantifies methylation at >850 000 CpG sites. Maternal blood lead levels (BLLs) during each trimester (T1: 6.56 ± 5.35 µg/dL; T2: 5.93 ± 5.00 µg/dL; T3: 6.09 ± 4.51 µg/dL), bone Pb (patella: 11.8 ± 9.25 µg/g; tibia: 11.8 ± 6.73 µg/g), a measure of cumulative Pb exposure, and UCB Pb (4.86 ± 3.74 µg/dL) were measured. After quality control screening, data from 786 024 CpG sites were used to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs) by Pb biomarkers using separate linear regression models, controlling for sex and estimated UCB cell-type proportions. We identified 3 DMPs associated with maternal T1 BLL, 2 with T3 BLL, and 2 with tibia bone Pb. We identified one DMR within PDGFRL associated with T1 BLL, one located at chr6:30095136-30095295 with T3 BLL, and one within TRHR with tibia bone Pb (adjusted P-value < .05). Pathway analysis identified 15 overrepresented gene pathways for differential methylation that overlapped among all 3 trimesters with the largest overlap between T1 and T2 (adjusted P-value < .05). Pathways of interest include nodal signaling pathway and neurological system processes. These data provide evidence for differential methylation by prenatal Pb exposure that may be trimester-specific.

An investigation of genetic polymorphisms in heparan sulfate proteoglycan core proteins and key modification enzymes in an Australian Caucasian multiple sclerosis population

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease affecting the central nervous system in young adults. Heparan sulfate proteoglycans (HSPGs) are ubiquitous to the cell surface and the extracellular matrix. HSPG biosynthesis is a complex process involving enzymatic attachment of heparan sulfate (HS) chains to a core protein. HS side chains mediate specific ligand and growth factor interactions directing cellular processes including cell adhesion, migration and differentiation. Two main families of HSPGs exist, the syndecans (SDC1-4) and glypicans (GPC1-6). The SDCs are transmembrane proteins, while the GPC family are GPI linked to the cell surface. SDC1 has well-documented interactions with numerous signalling pathways. Genome-wide association studies (GWAS) have identified regions of the genome associated with MS including a region on chromosome 13 containing GPC5 and GPC6. International studies have revealed significant associations between this region and disease development. The exostosin-1 (EXT1) and sulfatase-1 (SULF1) are key enzymes contributing to the generation of HS chains. EXT1, with documented tumour suppressor properties, is involved in the initiation and polymerisation of the growing HS chain. SULF1 removes 6-O-sulfate groups from HS chains, affecting protein-ligand interactions and subsequent downstream signalling with HS modification potentially having significant effects on MS progression. In this study, we identified significant associations between single nucleotide polymorphisms in SDC1, GPC5 and GPC6 and MS in an Australian Caucasian case-control population. Further significant associations in these genes were identified when the population was stratified by sex and disease subtype. No association was found for EXT1 or SULF1.

Internalization mechanisms of brain-derived tau oligomers from patients with Alzheimer's disease, progressive supranuclear palsy and dementia with Lewy bodies

Tau aggregates propagate in brain cells and transmit to neighboring cells as well as anatomically connected brain regions by prion-like mechanisms. Soluble tau aggregates (tau oligomers) are the most toxic species that initiate neurodegeneration in tauopathies, such as Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and dementia with Lewy bodies (DLB). Exogenous tau aggregates have been shown to be internalized by brain cells; however, the precise cellular and molecular mechanisms that underlie the internalization of tau oligomers (TauO) remain elusive. Using brain-derived tau oligomers (BDTOs) from AD, PSP, and DLB patients, we investigated neuronal internalization mechanisms of BDTOs, including the heparan sulfate proteoglycan (HSPG)-mediated pathway, clathrin-mediated pathway, and caveolae-mediated pathway. Here, we demonstrated that the HSPG-mediated pathway regulates internalization of BDTOs from AD and DLB, while HSPG-mediated and other alternative pathways are involved in the internalization of PSP-derived tau oligomers. HSPG antagonism significantly reduced the internalization of TauO, prevented tau translocation to the endosomal-lysosomal system, and decreased levels of hyperphosphorylated tau in neurons, the well-known contributor for neurofibrillary tangles (NFT) accumulation, degeneration of neurons, and cognitive decline. Furthermore, siRNA-mediated silencing of heparan sulfate (HS)-synthesizing enzyme, exostosin-2, leads to decreased internalization of BDTOs, prevented tau-induced autophagy-lysosomal pathway impairment, and decreased hyperphosphorylated tau levels. Collectively, these findings suggest that HSPG-mediated endocytosis and exostsin-2 are involved in neuronal internalization of TauO and subsequent tau-dependent neuropathology in AD and DLB.

Guidance of retinal axons in mammals

In order to navigate through the surrounding environment many mammals, including humans, primarily rely on vision. The eye, composed of the choroid, sclera, retinal pigmented epithelium, cornea, lens, iris and retina, is the structure that receives the light and converts it into electrical impulses. The retina contains six major types of neurons involving in receiving and modifying visual information and passing it onto higher visual processing centres in the brain. Visual information is relayed to the brain via the axons of retinal ganglion cells (RGCs), a projection known as the optic pathway. The proper formation of this pathway during development is essential for normal vision in the adult individual. Along this pathway there are several points where visual axons face 'choices' in their direction of growth. Understanding how these choices are made has advanced significantly our knowledge of axon guidance mechanisms. Thus, the development of the visual pathway has served as an extremely useful model to reveal general principles of axon pathfinding throughout the nervous system. However, due to its particularities, some cellular and molecular mechanisms are specific for the visual circuit. Here we review both general and specific mechanisms involved in the guidance of mammalian RGC axons when they are traveling from the retina to the brain to establish precise and stereotyped connections that will sustain vision.

The role of heparan sulphate in development: the ectodermal story

Heparan sulphate (HS) is ubiquitously expressed and is formed of repeating glucosamine and glucuronic/iduronic acid units which are generally highly sulphated. HS is found in tissues bound to proteins forming HS proteoglycans (HSPGs) which are present on the cell membrane or in the extracellular matrix. HSPGs influence a variety of biological processes by interacting with physiologically important proteins, such as morphogens, creating storage pools, generating morphogen gradients and directly mediating signalling pathways, thereby playing vital roles during development. This review discusses the vital role HS plays in the development of tissues from the ectodermal lineage. The ectodermal layer differentiates to form the nervous system (including the spine, peripheral nerves and brain), eye, epidermis, skin appendages and tooth enamel.

MS2 phage ribonucleoproteins as exogenous internal control for RT-qPCR data normalization in gene expression study of developing rat brain

The most popular strategy for normalization of RT-qPCR data involves presenting them in comparison with expression of "housekeeping" genes. However, the required stable expression of the control genes is not always achievable. As an alternative, we used ribonucleoprotein phage particles as an exogenous internal control and demonstrated that this type of normalization provides a simple and reliable method for quantification in RT-qPCR experiments. Using phage-based normalization, we analyzed mRNA levels of three popular housekeeping genes coding β-actin, glyceraldehyde-3-phosphate dehydrogenase, and ribosomal protein L30 and showed high variability in their expression patterns during rat brain development, indicating that they should not be used as controls in gene expression studies of the developing brain either individually or in combination. Using phage-based controls, we showed interstrain differences and age-related changes in the expression of genes involved in proteoglycan biosynthesis and degradation in developing brain of senescence-accelerated OXYS rats and control Wistar rats.

Chondroitin sulphate N-acetylgalactosaminyl-transferase-1 inhibits recovery from neural injury

Extracellular factors that inhibit axon growth and intrinsic factors that promote it affect neural regeneration. Therapies targeting any single gene have not yet simultaneously optimized both types of factors. Chondroitin sulphate (CS), a glycosaminoglycan, is the most abundant extracellular inhibitor of axon growth. Here we show that mice carrying a gene knockout for CS N-acetylgalactosaminyltransferase-1 (T1), a key enzyme in CS biosynthesis, recover more completely from spinal cord injury than wild-type mice and even chondroitinase ABC-treated mice. Notably, synthesis of heparan sulphate (HS), a glycosaminoglycan promoting axonal growth, is also upregulated in TI knockout mice because HS-synthesis enzymes are induced in the mutant neurons. Moreover, chondroitinase ABC treatment never induces HS upregulation. Taken together, our results indicate that regulation of a single gene, T1, mediates excellent recovery from spinal cord injury by optimizing counteracting effectors of axon regeneration—an extracellular inhibitor of CS and intrinsic promoters, namely, HS-synthesis enzymes.

The glycosaminoglycan chondroitin sulphate inhibits axon growth. Here the authors show that mice deficient in chondroitin sulphate biosynthesis have increased levels of heparan sulphate, which is more efficient than chondroitinase in supporting recovery from spinal cord injury.

Transendothelial migration of effector T cells across inflamed endothelial barriers does not require heparan sulfate proteoglycans

Leukocyte diapedesis is a chemotactic multistep process that requires optimal chemoattractant presentation by the endothelial barrier. Recent studies have described a critical role for heparan sulfate glycosaminoglycans (HSGAGs) in the presentation and functions of chemokines essential for lymphocyte interactions with the lymph node vasculature. We wished to test whether HS expression by a prototypic endothelial cell type, i.e. human umbilical vein endothelial cells (HUVECs), is critical for their ability to support neutrophil and lymphocyte adhesion and transendothelial migration (TEM) under shear flow. We found that HUVECs deposit HS GAGs mainly at their basolateral compartments in both their resting and inflamed states. We next inactivated the key enzyme involved in HS biosynthesis, exostosin-1 (Ext1). Silencing Ext1 resulted in a complete loss of HS biosynthesis; nonetheless, TNF-α and IL-1β stimulation of key adhesion molecules and inflammatory chemokines necessary for neutrophil or lymphocyte adhesion and TEM remained intact. Ext1 silencing reduced neutrophil arrest and markedly impaired TEM, consistent with a role of basolateral HS GAGs in directing neutrophil crossing of inflamed endothelial barriers. Strikingly, however, the TEM of effector T cells across identically Ext1-silenced HUVECs remained normal. Importantly, the biosynthesis of the main promigratory chemokines for effector T cells and neutrophils, respectively, CCL2 and CXCL1, and their vesicle distributions were also Ext1 independent. These results suggest that transmigrating neutrophils must respond to chemokines transiently presented by apical and basolateral endothelial HS GAGs. In contrast, effector T cells can integrate chemotactic TEM signals directly from intra-endothelial chemokine stores rather than from externally deposited chemokines.

Diabetes genes identified by genome-wide association studies are regulated in mice by nutritional factors in metabolically relevant tissues and by glucose concentrations in islets

Background

Genome-wide association studies (GWAS) have recently identified many new genetic variants associated with the development of type 2 diabetes. Many of these variants are in introns of known genes or between known genes, suggesting they affect the expression of these genes. The regulation of gene expression is often tissue and context dependent, for example occurring in response to dietary changes, hormone levels, or many other factors. Thus, to understand how these new genetic variants associated with diabetes risk may act, it is necessary to understand the regulation of their cognate genes.

Results

We identified fourteen type 2 diabetes-associated genes discovered by the first waves of GWAS for which there was little prior evidence of their potential role in diabetes (Adam30, Adamts9, Camk1d, Cdc123, Cdkal1, Cdkn2a, Cdkn2b, Ext2, Hhex, Ide, Jazf1, Lgr5, Thada and Tspan8). We examined their expression in metabolically relevant tissues including liver, adipose tissue, brain, and hypothalamus obtained from mice under fasted, non-fasted and high fat diet-fed conditions. In addition, we examined their expression in pancreatic islets from these mice cultured in low and high glucose. We found that the expression of Jazf1 was reduced by high fat feeding in liver, with similar tendencies in adipose tissue and the hypothalamus. Adamts9 expression was decreased in the hypothalamus of high fat fed mice. In contrast, the expression of Camk1d, Ext2, Jazf1 and Lgr5 were increased in the brain of non-fasted animals compared to fasted mice. Most notably, the expression levels of most of the genes were decreased in islets cultured in high glucose.

Conclusions

These data provide insight into the metabolic regulation of these new type 2 diabetes genes that will be important for determining how the GWAS variants affect gene expression and ultimately the development of type 2 diabetes.

Netrin-1 attracts axons through FAK-dependent mechanotransduction

The mechanism by which extracellular cues influence intracellular biochemical cascades that guide axons is important, yet poorly understood. Because of the mechanical nature of axon extension, we explored whether the physical interactions of growth cones with their guidance cues might be involved. In the context of mouse spinal commissural neuron axon attraction to netrin-1, we found that mechanical attachment of netrin-1 to the substrate was required for axon outgrowth, growth cone expansion, axon attraction and phosphorylation of focal adhesion kinase (FAK) and Crk-associated substrate (CAS). Myosin II activity was necessary for traction forces >30 pN on netrin-1. Interestingly, while these myosin II-dependent forces on netrin-1 substrates or beads were needed to increase the kinase activity and phosphorylation of FAK, they were not necessary for netrin-1 to increase CAS phosphorylation. When FAK kinase activity was inhibited, the growth cone's ability to recruit additional adhesions and to generate forces >60 pN on netrin-1 was disrupted. Together, these findings demonstrate an important role for mechanotransduction during chemoattraction to netrin-1 and that mechanical activation of FAK reinforces interactions with netrin-1 allowing greater forces to be exerted.

Using a seed-network to query multiple large-scale gene expression datasets from the developing retina in order to identify and prioritize experimental targets

Understanding the gene networks that orchestrate the differentiation of retinal progenitors into photoreceptors in the developing retina is important not only due to its therapeutic applications in treating retinal degeneration but also because the developing retina provides an excellent model for studying CNS development. Although several studies have profiled changes in gene expression during normal retinal development, these studies offer at best only a starting point for functional studies focused on a smaller subset of genes. The large number of genes profiled at comparatively few time points makes it extremely difficult to reliably infer gene networks from a gene expression dataset. We describe a novel approach to identify and prioritize from multiple gene expression datasets, a small subset of the genes that are likely to be good candidates for further experimental investigation. We report progress on addressing this problem using a novel approach to querying multiple large-scale expression datasets using a 'seed network' consisting of a small set of genes that are implicated by published studies in rod photoreceptor differentiation. We use the seed network to identify and sort a list of genes whose expression levels are highly correlated with those of multiple seed network genes in at least two of the five gene expression datasets. The fact that several of the genes in this list have been demonstrated, through experimental studies reported in the literature, to be important in rod photoreceptor function provides support for the utility of this approach in prioritizing experimental targets for further experimental investigation. Based on Gene Ontology and KEGG pathway annotations for the list of genes obtained in the context of other information available in the literature, we identified seven genes or groups of genes for possible inclusion in the gene network involved in differentiation of retinal progenitor cells into rod photoreceptors. Our approach to querying multiple gene expression datasets using a seed network constructed from known interactions between specific genes of interest provides a promising strategy for focusing hypothesis-driven experiments using large-scale 'omics' data.

Brain heparanase expression is up-regulated during postnatal development and hypoxia-induced neovascularization in adult rats

Heparanase is an endo-beta-d-glucuronidase which specifically cleaves extracellular and cell surface heparan sulphates at intra-chain sites. Its enzymatic activity is strongly implicated in cell dissemination associated with tumor metastasis and inflammation. Indeed, heparanase gene is expressed in various tumors and its over-expression is correlated with increased tumor vascularity and metastatic potential of tumor cells. However, heparanase expression in non-invasive and non-immune tissue, including brain, has received less attention. Using RT-qPCR, western blot and histological analysis, we demonstrate in the adult rat that heparanase transcript is differentially expressed according to brain area, and that heparanase protein is mainly detected in neurons. Furthermore, we provide evidence that heparanase transcript and protein reach their greatest levels at early postnatal stages, in particular within the neocortex characterized by intensive structural plasticity. Using the in vitro model of PC12-induced neuronal differentiation, we suggest that developmental regulation of heparanase may coincide with axonal and dendritic pathfinding. At adulthood, we demonstrate that the increased heparanase transcript level correlates in the hippocampus with enhanced angiogenesis following repeated hypoxia exposures. Taken together, our results emphasize the potential importance of heparanase in brain homeostasis, both during development and adaptative responses to severe environmental challenges.

Spatiotemporal distribution of heparan sulfate epitopes during murine cartilage growth plate development

Heparan sulfate proteoglycans (HSPGs) are abundant in the pericellular matrix of both developing and mature cartilage. Increasing evidence suggests the action of numerous chondroregulatory molecules depends on HSPGs. In addition to specific functions attributed to their core protein, the complexity of heparan sulfate (HS) synthesis provides extraordinary structural and functional heterogeneity. Understanding the interactions of chondroregulatory molecules with HSPGs and their subsequent outcomes has been limited by the absence of a detailed analysis of HS species in cartilage. In this study, we characterize the distribution and variety of HS species in developing cartilage of normal mice. Cryo-sections of femur and tibia from normal mouse embryos were evaluated using immunostaining techniques. A panel of unique phage display antibodies specific to particular HS species were employed and visualized with secondary antibodies conjugated to Alexa-fluor dyes. Confocal microscopy demonstrates that HS species are dynamic structures within developing growth plate cartilage and the perichondrium. GlcNS6S-IdoUA2S-GlcNS6S species are down regulated and localization of GlcNS6S-IdoUA-GlcNS6S species within the hypertrophic zone of the growth plate is lost during normal development. Regional differences in HS structures are present within developing growth plates, implying that interactions with and responses to HS-binding proteins also may display regional specialization.

The stop signal revised: immature cerebellar granule neurons in the external germinal layer arrest pontine mossy fiber growth

During the formation of neuronal circuits, afferent axons often enter target regions before their target cells are mature and then make temporary contacts with nonspecific targets before forming synapses on specific target cells. The regulation of these different steps of afferent-target interactions is poorly understood. The cerebellum is a good model for addressing these aspects, because cerebellar development is well defined and identified neurons in the circuitry can be purified and combined in vitro. Previous reports from our laboratory showed that cultured granule neurons specifically arrest the extension of their pontine mossy fiber afferents, leading us to propose that granule cells arrested growth of their afferents as a prelude to synaptogenesis. However, we knew little about the differentiation state of the cultured granule cells that mediate afferent arrest. In this study, we better define the purified granule cell fraction by marker expression and morphology, and demonstrate that only freshly plated granule cells in the precursor and premigratory state arrest mossy fiber outgrowth. Mature granule cells, in contrast, support extension, defasciculation, and synapse formation, as in vivo. In addition, axonal tracing in vivo during the first postnatal week indicates that immature mossy fibers extend into the Purkinje cell layer but never into the external germinal layer (EGL), where precursors of granule cell targets reside. We found that the stop-growing signals are dependent on heparin-binding factors, and we propose that such signals in the EGL restrict the extension of mossy fiber afferents and prevent invasion of proliferative regions.

Nerve injury induces the expression of EXT2, a glycosyltransferase required for heparan sulfate synthesis

Heparan sulfate proteoglycans, which bear long chains of heparan sulfate glycosaminoglycan, play significant roles during embryogenesis, including the formation of the CNS. However, their involvement in nerve regeneration has not yet been clarified. Here, we found that the mRNA expression of EXT2, one of the crucial enzymes for heparan sulfate-glycosaminoglycan synthesis, was markedly up-regulated in injured hypoglossal motor neurons after axotomy. In addition, immunohistochemical staining with an antibody specific for heparan sulfate-glycosaminoglycan chains demonstrated increased expression of heparan sulfate-glycosaminoglycan chains in the injured nucleus. Furthermore, the mRNA expressions of glypican-1 and syndecan-1, which are both well-known heparan sulfate proteoglycans, were prominently up-regulated in injured motor neurons. These results suggest that the biosynthesis of heparan sulfate chains promoted by EXT2 is activated in injured motor neurons, and that glypican-1 and syndecan-1 are potent candidates for heparan sulfate proteoglycans involved in peripheral nerve regeneration.

Distinct tissue-specificity of three zebrafish ext1 genes encoding proteoglycan modifying enzymes and their relationship to somitic Sonic hedgehog signaling

Proteins of the EXT (Exostosin) 1 family are known for their role in human disease. Mutations in EXT1 cause hereditary multiple exostoses (HME), benign outgrowths of the bones, and therefore were classed as tumor suppressors. More recently, their role during embryonic development of Drosophila and mouse was addressed, revealing important functions of EXT1 genes in major signaling pathways. Here, we report the isolation of three zebrafish members of the EXT1 family, which we named ext1a, ext1b, and ext1c, respectively. They are expressed in restricted temporal and spatial domains during development. Both ext1a and ext1b are provided maternally and expressed during gastrulation: ext1a in the neurectoderm and ext1b in the embryonic midline and in the involuting mesendoderm of the germ ring. During somitogenesis stages, transcripts of all three ext genes can be found in the somitic mesoderm. Furthermore, ext1a is expressed in the dorsal neural tube. These expression domains become more pronounced at 24 hr postfertilization (hpf). At 48 hpf, ext1 genes are present in the brain, while somitic expression ceases. Zebrafish have three members of the EXT1 family, in contrast to only one EXT1 gene in mammals or Xenopus, consistent with the occurrence of partial genome duplications in the teleost lineage. Our expression analysis reveals that the three ext genes have distinct expression patterns, reflecting functional divergence after duplication. In addition, expression of ext1a and ext1c responds to elevated and reduced levels of Sonic hedgehog (shh) signaling in the somites, whereas expression of ext1b does not. This suggests a differential relationship between the shh pathway and individual ext gene function in zebrafish.

Molecular networks perturbed in a developmental animal model of brain injury

Methylazoxymethanol (MAM) is widely used as a developmental neurotoxin and exposure to its glucoside (i.e., cycasin) is associated with the prototypical neurological disorder western Pacific ALS/PDC. However, the specific molecular targets that play a key role in MAM-induced brain injury remain unclear. To reveal potential molecular networks targeted by MAM in the developing nervous system, we examined characteristic phenotypic changes (DNA damage, cytoarchitecture) induced by MAM and their correlation with gene expression differences using microarray assays (27,648 genes). Three day-old postnatal C57BL/6 mice (PND3) received a single injection of MAM and the cerebellum and cerebral cortex of PND4, 8, 15, and 22 mice were analyzed. DNA damage was detected in both the cerebellum (N7-mGua, TUNEL labeling) and cerebral cortex (N7-mGua) of PND4 mice, but progressive disruption of the cytoarchitecture was restricted to the cerebellum. A majority (>75%) of the genes affected (cerebellum 636 genes, cortex 1080 genes) by MAM were developmentally regulated, with a predominant response early (PND4) in the cerebellum and delayed (PND8 and 15) in the cerebral cortex. The genes and pathways (e.g., proteasome) affected by MAM in the cerebellum are distinct from cortex. The genes perturbed in the cerebellum reflect critical cellular processes such as development (17%), cell cycle (7%), protein metabolism (12%), and transcriptional regulation (9%) that could contribute to the observed cytoarchitectural disruption of the cerebellum. This study demonstrates for the first time that specific genes and molecular networks are affected by MAM during CNS development. Further investigation of these targets will help to understand how disruption of these developmental programs could contribute to chronic brain injury or neurodegenerative disease.

Inhibition of amyloid A amyloidogenesis in vivo and in tissue culture by 4-deoxy analogues of peracetylated 2-acetamido-2-deoxy-alpha- and beta-d-glucose: implications for the treatment of various amyloidoses

Two novel sugars, 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-alpha- and beta-D-xylo-hexopyranoses, have been synthesized and their effects on heparan sulfate biosynthesis using primary mouse hepatocytes in tissue culture have been assessed. At concentrations of 0.1 and 1.0 mmol/L a mixture of both anomers significantly inhibited the biosynthesis of heparan sulfate by 60% and 99%, respectively. At 1.0 mmol/L the average molecular weight of the heparan sulfate synthesized is reduced from 77 kd to 40 kd. The biosynthetic inhibition is apparent within 1 hour (the earliest time point examined) of exposure of the hepatocytes to the analogues and appears virtually complete throughout a 24-hour incubation period. Using a radiolabeled version of the beta-anomer we demonstrate that the analogue is incorporated into growing heparan sulfate chains. The nature of the analogue, the quantity of analogue isotope incorporated, and the reduction in the size of the heparan sulfate polysaccharide are consistent with UDP activation and incorporation of the analogue and truncation of the growing heparan sulfate chain. At 0.1 mmol/L, and in the presence of a constant concentration of serum amyloid A (the precursor to AA amyloid), each analogue inhibited amyloid deposition (by 95 to 99%) in a tissue culture model of AA amyloidogenesis. At 6 mg/dose twice daily each analogue inhibited in vivo splenic AA amyloid deposition by 65 to 70% when using a rapid induction model of mouse AA amyloidogenesis. These data indicate that polysaccharides, such as heparan sulfate, play an integral part in the pathogenesis of AA amyloid deposition, and potentially other forms of amyloid. These data support our previous work that demonstrated that agents that mimic aspects of heparan sulfate structure and that interfere with heparan sulfate:amyloid protein binding inhibit AA amyloid deposition. They emphasize that heparan sulfate likely plays a critical role in amyloidogenesis, and compounds that interfere with heparan sulfate biosynthesis may provide leads for the development of anti-amyloid therapeutic agents.

A general model for genetic regulation of turnover of glycosaminoglycans suggests a possible procedure for prediction of severity and clinical progress of mucopolysaccharidoses

Mucopolysaccharidoses are rare genetic diseases from the group of lysosomal storage disorders caused by deficiency of enzymes involved in degradation of mucopolysaccharides (glycosaminoglycans, GAGs). Within each mucopolysaccharidosis, there is a continuous spectrum of clinical features from the very severe to the more mildly affected individuals. Surprisingly, in most cases, it is not possible to predict severity and clinical progress (i.e., the natural history) of the disease on the basis of detection of particular mutations or residual activity of the deficient enzyme. In this article, the reasons for such an unexpected difficulty are discussed. A model for the correlation between residual activity of a lysosomal enzyme and the turnover rate of its substrate(s) has been proposed previously by others, however, in that model it was assumed that substrate concentration in the lysosome is not regulated, thus the residual activity of a hydrolase would be the only determinant of the rate of substrate accumulation. On the other hand, both a general model for genetic regulation of turnover of GAGs and results of very recent studies strongly suggest that expression of genes coding for enzymes involved in GAG synthesis is precisely regulated and may vary between individuals. Therefore, we propose that apart from measurement of residual activity of the enzyme involved in degradation of GAGs, the efficiency of synthesis of these compounds should also be estimated. If the hypothesis presented in this article is true, the ratio of the synthesis of glycosaminoglycans to the residual activity of the deficient enzyme should be of considerable prognostic value.

Heparan sulfate proteoglycans: Coordinators of multiple signaling pathways during chondrogenesis

Heparan sulfate proteoglycans are abundantly expressed in the pericellular matrix of both developing and mature cartilage. Increasing evidence indicates that the action of numerous chondroregulatory molecules depends on these proteoglycans. This review summarizes the current understanding of the interactions of heparan sulfate chains of cartilage proteoglycans with both soluble and nonsoluble ligands during the process of chondrogenesis. In addition, the consequences of mutating genes encoding heparan sulfate biosynthetic enzymes or heparan sulfate proteoglycan core proteins on cartilage development are discussed.