Developmental regulation and spatiotemporal redistribution of the sumoylation machinery in the rat central nervous system

Background

Small Ubiquitin-like MOdifier protein (SUMO) is a key regulator of nuclear functions but little is known regarding the role of the post-translational modification sumoylation outside of the nucleus, particularly in the Central Nervous System (CNS).

Methodology/Principal Findings

Here, we report that the expression levels of SUMO-modified substrates as well as the components of the sumoylation machinery are temporally and spatially regulated in the developing rat brain. Interestingly, while the overall sumoylation is decreasing during brain development, there are progressively more SUMO substrates localized at synapses. This increase is correlated with a differential redistribution of the sumoylation machinery into dendritic spines during neuronal maturation.

Conclusions/Significance

Overall, our data clearly demonstrate that the sumoylation process is developmentally regulated in the brain with high levels of nuclear sumoylation early in the development suggesting a role for this post-translational modification during the synaptogenesis period and a redistribution of the SUMO system towards dendritic spines at a later developmental stage to modulate synaptic protein function.

Expression patterns of ubiquitin conjugating enzyme UbcM2 during mouse embryonic development

Ubiquitin conjugating enzyme UbcM2 (Ubiquitin-conjugating enzymes from Mice, the number reveals the identification order) has been implicated in many critical processes, such like growth-inhibiting, mediating cell proliferation and regulation of some transcription factor, but the expression profile during mouse embryo development remains unclear. Hereby, during mid-later embryonic stage, the expression patterns of UbcM2 were examined using in situ hybridization and quantitative real-time PCR (qRT-PCR). The signals were significantly intense in central nervous system and skeletal system, weak in tongue, heart, lung, liver, and kidney. In the central nervous system, UbcM2 was principally expressed in thalamus, external germinal layer of cerebellum (EGL), mitral cell layer of olfactory bulb, hippocampus, marginal zone and ventricular zone of cerebral cortex, and spinal cord. In the skeletal system, UbcM2 was primarily expressed in proliferating cartilage. Furthermore, qRT-PCR analysis displayed that the expression of UbcM2 was ubiquitous at E15.5, most prominent in brain, weaker in lung liver and kidney, accompanied by the lowest level in tongue and heart. During brain development, the expression level of UbcM2 first ascended and then decreased from E12.5 to E18.5, the peak of which sustained starting at E14.5 until E16.5. Together, these results suggest that UbcM2 may play potential roles in the development of mouse diverse tissues and organs, particularly in the development of brain and skeleton.

Disabled-1 alternative splicing in human fetal retina and neural tumors

Background

The Reelin-Dab1 signaling pathway plays a critical role in the positioning of migrating neurons, dendrite formation and lamination in the developing central nervous system. We have previously identified two alternatively spliced forms of Dab1 in the developing chick retina: an early form, Dab1-E, expressed in retinal progenitor cells, and a late form, Dab1 or Dab1-L, expressed in amacrine and ganglion cells. Compared to Dab1-L, Dab1-E lacks two exons that encode two Src family kinase (SFK) phosphorylation sites.

Principal Findings

Both Dab1-L and Dab1-E-like transcripts were identified in human fetal retina. Expression of human Dab1-L in primary chick retinal cultures resulted in Reelin-mediated induction of SFK phosphorylation and formation of neurite-like processes. In contrast, human Dab1-E-expressing cells retained an undifferentiated morphology. The human Dab1 gene is located within a common fragile site, and it has been postulated that it may function as a tumor suppressor. Analysis of Dab1 splice forms in retinoblastoma and neuroblastoma tumor cells revealed relative enrichment of Dab1-L-like (includes exons 7 and 8) and Dab1-E-like (excludes exons 7 and 8) transcripts in retinoblastoma and neuroblastoma, respectively. Treatment of retinoblastoma cell line RB522A with Reelin resulted in increased tyrosine phosphorylation of Dab1. As Nova2 has previously been implicated in the exclusion of exons 9B and 9C in Dab1, we examined the expression of this splicing factor in neuroblastoma and retinoblastoma cell lines. Nova2 was only detected in neuroblastoma cells, suggesting a correlation between Nova2 expression and increased levels of Dab1-E-like splice forms in neuroblastoma.

Conclusions

These results indicate that alternative splicing of Dab1 is conserved in avian and mammalian species, with Dab1-L driving SFK phosphorylation in both species. Dab1-E- and Dab-L-like isoforms are also expressed in childhood neural tumors, with preferential enrichment of Dab1-L-like and Dab1-E-like isoforms in retinoblastoma and neuroblastoma, respectively.

[Ultrasound imaging of normal fetal central nervous system at 8 to 12 weeks of gestation]

With ongoing evolution of advanced ultrasound diagnostic in prenatal care the trend is to detect potential fetal anomalies in the first trimester if possible. Complex knowledge of normal fetal anatomy, embryology and ultrasound anatomy is important to be able to identify subtle abnormalities. In this review we demonstrate the possibilities of ultrasound imaging of fetal brain at late first trimester and describe normal central nervous system development week by week. Original images are presented.

A genome-wide analysis reveals that the Drosophila transcription factor Lola promotes axon growth in part by suppressing expression of the actin nucleation factor Spire

BACKGROUND

The phylogenetically conserved transcription factor Lola is essential for many aspects of axon growth and guidance, synapse formation and neural circuit development in Drosophila. To date it has been difficult, however, to obtain an overall view of Lola functions and mechanisms.

RESULTS

We use expression microarrays to identify the lola-dependent transcriptome in the Drosophila embryo. We find that lola regulates the expression of a large selection of genes that are known to affect each of several lola-dependent developmental processes. Among other loci, we find lola to be a negative regulator of spire, an actin nucleation factor that has been studied for its essential role in oogenesis. We show that spire is expressed in the nervous system and is required for a known lola-dependent axon guidance decision, growth of ISNb motor axons. We further show that reducing spire gene dosage suppresses this aspect of the lola phenotype, verifying that derepression of spire is an important contributor to the axon stalling phenotype of embryonic motor axons in lola mutants.

CONCLUSIONS

These data shed new light on the molecular mechanisms of many lola-dependent processes, and also identify several developmental processes not previously linked to lola that are apt to be regulated by this transcription factor. These data further demonstrate that excessive expression of the actin nucleation factor Spire is as deleterious for axon growth in vivo as is the loss of Spire, thus highlighting the need for a balance in the elementary steps of actin dynamics to achieve effective neuronal morphogenesis.

The Drosophila CPEB protein Orb2 has a novel expression pattern and is important for asymmetric cell division and nervous system function

Cytoplasmic polyadenylation element binding (CPEB) proteins bind mRNAs to regulate their localization and translation. While the first CPEBs discovered were germline specific, subsequent studies indicate that CPEBs also function in many somatic tissues including the nervous system. Drosophila has two CPEB family members. One of these, orb, plays a key role in the establishment of polarity axes in the developing egg and early embryo, but has no known somatic functions or expression outside of the germline. Here we characterize the other Drosophila CPEB, orb2. Unlike orb, orb2 mRNA and protein are found throughout development in many different somatic tissues. While orb2 mRNA and protein of maternal origin are distributed uniformly in early embryos, this pattern changes as development proceeds and by midembryogenesis the highest levels are found in the CNS and PNS. In the embryonic CNS, Orb2 appears to be concentrated in cell bodies and mostly absent from the longitudinal and commissural axon tracts. In contrast, in the adult brain, the protein is seen in axonal and dendritic terminals. Lethal effects are observed for both RNAi knockdowns and orb2 mutant alleles while surviving adults display locomotion and behavioral defects. We also show that orb2 funtions in asymmetric division of stem cells and precursor cells during the development of the embryonic nervous system and mesoderm.

Robo1 and Robo2 have distinct roles in pioneer longitudinal axon guidance

Pioneer longitudinal axons grow long distances parallel to the floor plate and precisely maintain their positions using guidance molecules released from the floor plate. Two receptors, Robo1 and Robo2, are critical for longitudinal axon guidance by the Slit family of chemorepellents. Previous studies showed that Robo1(-/-);2(-/-) double mutant mouse embryos have disruptions in both ventral and dorsal longitudinal tracts. However, the role of each Robo isoform remained unclear, because Robo1 or 2 single mutants have mild or no errors. Here we utilized a more sensitive genetic strategy to reduce Robo levels for determining any separate functions of the Robo1 and 2 isoforms. We found that Robo1 is the predominant receptor for guiding axons in ventral tracts and prevents midline crossing. In contrast, Robo2 is the main receptor for directing axons within dorsal tracts. Robo2 also has a distinct function in repelling neuron cell bodies from the floor plate. Therefore, while Robo1 and 2 have some genetic overlap to cooperate in guiding longitudinal axons, each isoform has distinct functions in specific longitudinal axon populations.

Insights into Hox protein function from a large scale combinatorial analysis of protein domains

Protein function is encoded within protein sequence and protein domains. However, how protein domains cooperate within a protein to modulate overall activity and how this impacts functional diversification at the molecular and organism levels remains largely unaddressed. Focusing on three domains of the central class Drosophila Hox transcription factor AbdominalA (AbdA), we used combinatorial domain mutations and most known AbdA developmental functions as biological readouts to investigate how protein domains collectively shape protein activity. The results uncover redundancy, interactivity, and multifunctionality of protein domains as salient features underlying overall AbdA protein activity, providing means to apprehend functional diversity and accounting for the robustness of Hox-controlled developmental programs. Importantly, the results highlight context-dependency in protein domain usage and interaction, allowing major modifications in domains to be tolerated without general functional loss. The non-pleoitropic effect of domain mutation suggests that protein modification may contribute more broadly to molecular changes underlying morphological diversification during evolution, so far thought to rely largely on modification in gene cis-regulatory sequences.

Neural stem cells in neurospheres, embryoid bodies, and central nervous system of human embryos

The process of neurogenesis and formation of neural stem cells is reported in human neurospheres (NS) and embryoid bodies (EB) derived from human embryonic stem cells, in vitro, and compared with neural tissue formed in human ectopic embryos in week 4 (stage 9), developed in vivo. This morphological study was done using digital imaging by light microscopy and routine transmission electron microscopy. Both NS and EB form neural rosettes from the surface epithelium much like the process of neural tube formation from ectoderm in the embryo. The rosette is the developmental signature of neuroprogenitors in cultures of differentiating embryonic stem cells and is a radial arrangement of columnar cells that express many of the proteins expressed in neuroepithelial cells in the neural tube. The NS produce all of the major classes of progeny of the neural tube, some of which have been documented here. Specific neural markers expressed in the NS and the clinical implications of this study in cell therapy are also discussed.

Heparan sulfate proteoglycan specificity during axon pathway formation in the Drosophila embryo

Axon guidance is influenced by the presence of heparan sulfate (HS) proteoglycans (HSPGs) on the surface of axons and growth cones (Hu, [2001]: Nat Neurosci 4:695-701; Irie et al. [2002]: Development 129:61-70; Inatani et al. [2003]: Science 302:1044-1046; Johnson et al. [2004]: Curr Biol 14:499-504; Steigemann et al. [2004]: Curr Biol 14:225-230). Multiple HSPGs, including Syndecans, Glypicans and Perlecans, carry the same carbohydrate polymer backbones, raising the question of how these molecules display functional specificity during nervous system development. Here we use the Drosophila central nervous system (CNS) as a model to compare the impact of eliminating Syndecan (Sdc) and/or the Glypican Dally-like (Dlp). We show that Dlp and Sdc share a role in promoting accurate patterns of axon fasciculation in the lateral longitudinal neuropil; however, unlike mutations in sdc, which disrupt the ability of the secreted repellent Slit to prevent inappropriate passage of axons across the midline, mutations in dlp show neither midline defects nor genetic interactions with Slit and its Roundabout (Robo) receptors at the midline. Dlp mutants do show genetic interactions with Slit and Robo in lateral fascicle formation. In addition, simultaneous loss of Dlp and Sdc demonstrates an important role for Dlp in midline repulsion, reminiscent of the functional overlap between Robo receptors. A comparison of HSPG distribution reveals a pattern that leaves midline proximal axons with relatively little Dlp. Finally, the loss of Dlp alters Slit distribution distal but not proximal to the midline, suggesting that distinct yet overlapping pattern of HSPG expression provides a spatial system that regulates axon guidance decisions.

Neural stem cell niches: roles for the hyaluronan-based extracellular matrix

Neural stem/progenitor cells capable of differentiating into the neurons and glial cells that populate the mammalian central nervous system (CNS) persist in specific neural stem cell niches that regulate stem cell proliferation, survival and differentiation. There is growing evidence that the extracellular matrix within neural stem cell niches is required for neural stem cell maintenance. Here, we review findings supporting a pivotal role for the glycosaminoglycan hyaluronan (HA) and its transmembrane receptors in neural stem/progenitor cell proliferation, differentiation and maturation. We also outline findings supporting changing roles for HA as cells become committed to distinct lineages in the brain and spinal cord.

Sox31 is involved in central nervous system anteroposterior regionalization through regulating the organizer activity in zebrafish

Sox superfamily proteins are DNA-binding transcriptional factors that contain highly conserved high-mobility group (HMG) box and take part in various development process. Sox31 is a maternal factor supplied in the oocyte and starts its zygotic expression during mid-blastula transition (MBT). From gastrulation stage, it mainly resides in neural tissue. Ectopically expression of Sox31 mRNA leads to cyclopia, fusion eyes, or totally loss of anterior head structure, in accompany with severe notochord defects. Molecular markers indicate that forebrain tissue reduces sharply while the posterior neural tissue expands anteriorly. In addition, organizer specification is also suppressed. Oppositely, an antisense morpholino designed functionally knockdown Sox31 causes typically dorsalized phenotype and reversed central nervous system (CNS) anteroposterior (AP) patterning. Gain of function with chimeric construct, where Sox31 HMG DNA binding domain is fused to a transcription activation domain (VP16) or transcription suppression domain (EnR), suggests that Sox31 acts as a transcriptional suppressor in vivo. The expression of Bozozok (Dharma), a direct target gene of pre-MBT Wnt/β-catenin signal, is suppressed by Sox31. Thus, to unveil the relationship between Sox31 and β-catenin-related transcriptional activity, we designed Top/Fop luciferase assay in HEK293T cells, and found that Sox31 could indeed suppress Tcf/Lef-dependent transcriptional activity without influencing the stability of β-catenin. Moreover, post-MBT Wnt signal was reduced in Sox31 morphants corresponding to the suppressed hindbrain structure, while phenotypic defects caused by excessive Sox31 could be rescued by Wnt antagonist dkk1. Taken together, Sox31 functions as an essential CNS AP patterning determinant and coordinates the CNS AP patterning process with organizer specification.

Croix B. GPR124, an orphan G protein-coupled receptor, is required for CNS-specific vascularization and establishment of the blood-brain barrier

Every organ in the body requires blood vessels for efficient delivery of oxygen and nutrients, but independent vascular beds are highly specialized to meet the individual needs of specific organs. The vasculature of the brain is tightly sealed, with blood-brain barrier (BBB) properties developing coincident with neural vascularization. G protein-coupled receptor 124 (GPR124) (tumor endothelial marker 5, TEM5), an orphan member of the adhesion family of G protein-coupled receptors, was previously identified on the basis of its overexpression in tumor vasculature. Here, we show that global deletion or endothelial-specific deletion of GPR124 in mice results in embryonic lethality associated with abnormal angiogenesis of the forebrain and spinal cord. Expression of GPR124 was found to be required for invasion and migration of blood vessels into neuroepithelium, establishment of BBB properties, and expansion of the cerebral cortex. Thus, GPR124 is an important regulator of neurovasculature development and a potential drug target for cerebrovascular diseases.

Functional analysis of conserved sequences within a temporally restricted neural precursor cell enhancer

Many of the key regulators of Drosophila CNS neural identity are expressed in defined temporal orders during neuroblast (NB) lineage development. To begin to understand the structural and functional complexity of enhancers that regulate ordered NB gene expression programs, we have undertaken the mutational analysis of the temporally restricted nerfin-1 NB enhancer. Our previous studies have localized the enhancer to a region just proximal to the nerfin-1 transcription start site. Analysis of this enhancer, using the phylogenetic footprint program EvoPrinter, reveals the presence of multiple sequence blocks that are conserved among drosophilids. cis-Decoder alignments of these conserved sequence blocks (CSBs) has identified shorter elements that are conserved in other Drosophila NB enhancers. Mutagenesis of the enhancer reveals that although each CSB is required for wild-type expression, neither position nor orientation of the CSBs within the enhancer is crucial for enhancer function; removal of less-conserved or non-conserved sequences flanking CSB clusters also does not significantly alter enhancer activity. While all three conserved E-box transcription factor (TF) binding sites (CAGCTG) are required for full function, adding an additional site at different locations within non-conserved sequences interferes with enhancer activity. Of particular note, none of the mutations resulted in ectopic reporter expression outside of the early NB expression window, suggesting that the temporally restricted pattern is defined by transcriptional activators and not by direct DNA binding repressors. Our work also points to an unexpectedly large number of TFs required for optimal enhancer function - mutant TF analysis has identified at least four that are required for full enhancer regulation.

Distinct physiological and behavioural functions for parental alleles of imprinted Grb10

Imprinted genes, defined by their preferential expression of a single parental allele, represent a subset of the mammalian genome and often have key roles in embryonic development, but also postnatal functions including energy homeostasis and behaviour. When the two parental alleles are unequally represented within a social group (when there is sex bias in dispersal and/or variance in reproductive success), imprinted genes may evolve to modulate social behaviour, although so far no such instance is known. Predominantly expressed from the maternal allele during embryogenesis, Grb10 encodes an intracellular adaptor protein that can interact with several receptor tyrosine kinases and downstream signalling molecules. Here we demonstrate that within the brain Grb10 is expressed from the paternal allele from fetal life into adulthood and that ablation of this expression engenders increased social dominance specifically among other aspects of social behaviour, a finding supported by the observed increase in allogrooming by paternal Grb10-deficient animals. Grb10 is, therefore, the first example of an imprinted gene that regulates social behaviour. It is also currently alone in exhibiting imprinted expression from each of the parental alleles in a tissue-specific manner, as loss of the peripherally expressed maternal allele leads to significant fetal and placental overgrowth. Thus Grb10 is, so far, a unique imprinted gene, able to influence distinct physiological processes, fetal growth and adult behaviour, owing to actions of the two parental alleles in different tissues.

The DOCK protein sponge binds to ELMO and functions in Drosophila embryonic CNS development

Cell morphogenesis, which requires rearrangement of the actin cytoskeleton, is essential to coordinate the development of tissues such as the musculature and nervous system during normal embryonic development. One class of signaling proteins that regulate actin cytoskeletal rearrangement is the evolutionarily conserved CDM (C. elegansCed-5, human DOCK180, DrosophilaMyoblast city, or Mbc) family of proteins, which function as unconventional guanine nucleotide exchange factors for the small GTPase Rac. This CDM-Rac protein complex is sufficient for Rac activation, but is enhanced upon the association of CDM proteins with the ELMO/Ced-12 family of proteins. We identified and characterized the role of Drosophila Sponge (Spg), the vertebrate DOCK3/DOCK4 counterpart as an ELMO-interacting protein. Our analysis shows Spg mRNA and protein is expressed in the visceral musculature and developing nervous system, suggesting a role for Spg in later embryogenesis. As maternal null mutants of spg die early in development, we utilized genetic interaction analysis to uncover the role of Spg in central nervous system (CNS) development. Consistent with its role in ELMO-dependent pathways, we found genetic interactions with spg and elmo mutants exhibited aberrant axonal defects. In addition, our data suggests Ncad may be responsible for recruiting Spg to the membrane, possibly in CNS development. Our findings not only characterize the role of a new DOCK family member, but help to further understand the role of signaling downstream of N-cadherin in neuronal development.

Prenatal micronutrient supplementation and intellectual and motor function in early school-aged children in Nepal

CONTEXT

Iron and zinc are important for the development of both intellectual and motor skills. Few studies have examined whether iron and zinc supplementation during gestation, a critical period of central nervous system development, affects children's later functioning.

OBJECTIVE

To examine intellectual and motor functioning of children whose mothers received micronutrient supplementation during pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

Cohort follow-up of 676 children aged 7 to 9 years in June 2007-April 2009 who had been born to women in 4 of 5 groups of a community-based, double-blind, randomized controlled trial of prenatal micronutrient supplementation between 1999 and 2001 in rural Nepal. Study children were also in the placebo group of a subsequent preschool iron and zinc supplementation trial.

INTERVENTIONS

Women whose children were followed up had been randomly assigned to receive daily iron/folic acid, iron/folic acid/zinc, or multiple micronutrients containing these plus 11 other micronutrients, all with vitamin A, vs a control group of vitamin A alone from early pregnancy through 3 months postpartum. These children did not receive additional micronutrient supplementation other than biannual vitamin A supplementation.

MAIN OUTCOME MEASURES

Children's intellectual functioning, assessed using the Universal Nonverbal Intelligence Test (UNIT); tests of executive function, including go/no-go, the Stroop test, and backward digit span; and motor function, assessed using the Movement Assessment Battery for Children (MABC) and finger-tapping test.

RESULTS

The difference across outcomes was significant (Bonferroni-adjusted P < .001) for iron/folic acid vs control but not for other supplement groups. The mean UNIT T score in the iron/folic acid group was 51.7 (SD, 8.5) and in the control group was 48.2 (SD, 10.2), with an adjusted mean difference of 2.38 (95% confidence interval [CI], 0.06-4.70; P = .04). Differences were not significant between the control group and either the iron/folic acid/zinc (0.73; 95% CI, -0.95 to 2.42) or multiple micronutrient (1.00; 95% CI, -0.55 to 2.56) groups. In tests of executive function, scores were better in the iron/folic acid group relative to the control group for the Stroop test (adjusted mean difference in proportion who failed, -0.14; 95% CI, -0.23 to -0.04) and backward digit span (adjusted mean difference, 0.36; 95% CI, 0.01-0.71) but not for the go/no-go test. The MABC score was lower (better) in the iron/folic acid group compared with the control group but not after adjustment for confounders (mean difference, -1.47; 95% CI, -3.06 to 0.12; P = .07). Finger-tapping test scores were higher (mean difference, 2.05; 95% CI, 0.87-3.24; P = .001) in the iron/folic acid group.

CONCLUSION

Aspects of intellectual functioning including working memory, inhibitory control, and fine motor functioning among offspring were positively associated with prenatal iron/folic acid supplementation in an area where iron deficiency is prevalent.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00115271.

The Batten disease Palmitoyl Protein Thioesterase 1 gene regulates neural specification and axon connectivity during Drosophila embryonic development

Palmitoyl Protein Thioesterase 1 (PPT1) is an essential lysosomal protein in the mammalian nervous system whereby defects result in a fatal pediatric disease called Infantile Neuronal Ceroids Lipofuscinosis (INCL). Flies bearing mutations in the Drosophila ortholog Ppt1 exhibit phenotypes similar to the human disease: accumulation of autofluorescence deposits and shortened adult lifespan. Since INCL patients die as young children, early developmental neural defects due to the loss of PPT1 are postulated but have yet to be elucidated. Here we show that Drosophila Ppt1 is required during embryonic neural development. Ppt1 embryos display numerous neural defects ranging from abnormal cell fate specification in a number of identified precursor lineages in the CNS, missing and disorganized neurons, faulty motoneuronal axon trajectory, and discontinuous, misaligned, and incorrect midline crossings of the longitudinal axon bundles of the ventral nerve cord. Defects in the PNS include a decreased number of sensory neurons, disorganized chordotonal neural clusters, and abnormally shaped neurons with aberrant dendritic projections. These results indicate that Ppt1 is essential for proper neuronal cell fates and organization; and to establish the local environment for proper axon guidance and fasciculation. Ppt1 function is well conserved from humans to flies; thus the INCL pathologies may be due, in part, to the accumulation of various embryonic neural defects similar to that of Drosophila. These findings may be relevant for understanding the developmental origin of neural deficiencies in INCL.

Guidance receptor degradation is required for neuronal connectivity in the Drosophila nervous system

Axon pathfinding and synapse formation rely on precise spatiotemporal localization of guidance receptors. However, little is known about the neuron-specific intracellular trafficking mechanisms that underlie the sorting and activity of these receptors. Here we show that loss of the neuron-specific v-ATPase subunit a1 leads to progressive endosomal guidance receptor accumulations after neuronal differentiation. In the embryo and in adult photoreceptors, these accumulations occur after axon pathfinding and synapse formation is complete. In contrast, receptor missorting occurs sufficiently early in neurons of the adult central nervous system to cause connectivity defects. An increase of guidance receptors, but not of membrane proteins without signaling function, causes specific gain-of-function phenotypes. A point mutant that promotes sorting but prevents degradation reveals spatiotemporally specific guidance receptor turnover and accelerates developmental defects in photoreceptors and embryonic motor neurons. Our findings indicate that a neuron-specific endolysosomal degradation mechanism is part of the cell biological machinery that regulates guidance receptor turnover and signaling.

[Pioneer neurons: a basis or bottleneck of diversity of nervous systems of Lophotrochozoa?]

In a case study on development of larvae of Trochozoa species of different systematic positions, it was shown that peripheral neurons differentiated firstly. According to the characters of early peripheral neurons, in particular their localization in parts that differed from known zones of appearance of central ganglia, the difficult periphery of processes used as a "frame" by differentiated neurons of definitive nervous system, and transient expression of specific markers, it is reputed that these cells are pioneer. On the one hand, pioneer neurons are the bottleneck of morphogenesis diversity in late stages of development which prepare, in early larvae, the framework of the further central nervous system. On the other hand, navigation and marking using pioneer neurons can be a mechanism of evolutionary lability of definitive neural structures. Functional adaptive significance of pioneer neurons of larvae of Trochozoa animals, probably, is in the maintenance of a fast change from larvae life-form to adult life-form in metamorphosis that decreases the time of animals at intermediate stages of morphogenesis, which are associated with a dramatic fall in adaptation.

Role of central nervous system insulin resistance in fetal alcohol spectrum disorders

Fetal alcohol spectrum disorder (FASD) is the most common preventable cause of mental retardation in the USA. Ethanol impairs neuronal survival and function by two major mechanisms: 1) it inhibits insulin signaling required for viability, metabolism, synapse formation, and acetylcholine production; and 2) it functions as a neurotoxicant, causing oxidative stress, DNA damage and mitochondrial dysfunction. Ethanol inhibition of insulin signaling is mediated at the insulin receptor (IR) level and caused by both impaired receptor binding and increased activation of phosphatases that reverse IR tyrosine kinase activity. As a result, insulin activation of PI3K-Akt, which mediates neuronal survival, motility, energy metabolism, and plasticity, is impaired. The neurotoxicant effects of ethanol promote DNA damage, which could contribute to mitochondrial dysfunction and oxidative stress. Therefore, chronic in utero ethanol exposure produces a dual state of CNS insulin resistance and oxidative stress, which we postulate plays a major role in ethanol neurobehavioral teratogenesis. We propose that many of the prominent adverse effects of chronic prenatal exposure to ethanol on CNS development and function may be prevented or reduced by treatment with peroxisome-proliferated activated receptor (PPAR) agonists which enhance insulin sensitivity by increasing expression and function of insulin-responsive genes, and reducing cellular oxidative stress.

Identification and developmental expression of Dec2 in zebrafish

The involvement of Dec2, a member of the basic helix-loop-helix (bHLH) family, in cellular differentiation, hypoxia response, and circadian regulation has been investigated. Here we report the previously unknown spatiotemporal expression of Dec2 in zebrafish embryogenesis. Dec2 is dynamically expressed in zebrafish pineal gland, tract of the postoptic commissure, brain, notochord, heart, common cardinal vein (CCV), axial vein, pronephric duct, swim bladder, and early somites during embryogenesis, which implies that Dec2 is involved in zebrafish central nervous system development, cardiogenesis, and internal organs and somites formation. The embryonic expression patterns of zebrafish Dec2 and its homolog Dec1 partially overlap, but are distinct from each other. The Dec2 expression level was lower than that of Dec1 during zebrafish embryogenesis. Although Dec1 also contributed to zebrafish somites formation, cardiogenesis, and internal organs and central nervous system development, the two Dec genes were not likely to be simply redundant during zebrafish embryogenesis. Our results imply that Dec2, like its homolog Dec1, is involved in zebrafish cardiogenesis, central nervous system development, and internal organs and somites formation with distinct developmental roles.

Defective adult oligodendrocyte and Schwann cell development, pigment pattern, and craniofacial morphology in puma mutant zebrafish having an alpha tubulin mutation

The processes of myelination remain incompletely understood but are of profound biomedical importance owing to the several dysmyelinating and demyelinating disorders known in humans. Here, we analyze the zebrafish puma mutant, isolated originally for pigment pattern defects limited to the adult stage. We show that puma mutants also have late-arising defects in Schwann cells of the peripheral nervous system, locomotor abnormalities, and sex-biased defects in adult craniofacial morphology. Using methods of positional cloning, we identify a critical genetic interval harboring two alpha tubulin loci, and we identify a chemically induced missense mutation in one of these, tubulin alpha 8-like 3a (tuba8l3a). We demonstrate tuba8l3a expression in the central nervous system (CNS), leading us to search for defects in the development of oligodendrocytes, the myelinating cells of the CNS. We find gross reductions in CNS myelin and oligodendrocyte numbers in adult puma mutants, and these deficits are apparent already during the larval-to-adult transformation. By contrast, analyses of embryos and early larvae reveal a normal complement of oligodendrocytes that nevertheless fail to localize normal amounts of myelin basic protein (mbp) mRNA in cellular processes, and fail to organize these processes as in the wild-type. This study identifies the puma mutant as a valuable model for studying microtubule-dependent events of myelination, as well as strategies for remyelination in the adult.

Proliferating neural progenitors in the developing CNS of zebrafish require Jagged2 and Jagged1b

In the central nervous system (CNS), giving rise to the diversity and the complexity of neurons is the spatial and temporal differentiation of neural stem cells and/or neural precursors. Here, we investigated the role of Jagged-mediated Notch signaling in the maintenance and differentiation of progenitor cells during late neurogenesis by analyzing the expression patterns of zebrafish jagged homologues, and by injecting their morpholinos. Expression of both jagged2 and jagged1b mRNA in the CNS suggested that they might be involved in control of differentiating neural progenitors in which they are involved later in development. In Jagged2 and Jagged1b knock-down embryos, the overall rate of cell division dramatically decreased, and the ectopic VeMe neurons were generated. The results suggest that Jagged-Notch signaling plays a critical role in the maintenance of proliferating neural precursors, and that the generation of late-born neurons, especially VeMe neurons, is regulated by the interplay between Jagged2 and Jagged1b.