Stem cell potential remains unchanged.
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Cloning, Organism↗
Biomedical subjects
John A Kessler
Publications and source records attributed to John A Kessler.
Neural tube defects and folate pathway genes: family-based association tests of gene-gene and gene-environment interactions.
BACKGROUND: Folate metabolism pathway genes have been examined for association with neural tube defects (NTDs) because folic acid supplementation reduces the risk of this debilitating birth defect. Most studies addressed these genes individually, often with different populations providing conflicting results. OBJECTIVES: Our study evaluates several folate pathway genes for association with human NTDs, incorporating an environmental cofactor: maternal folate supplementation. METHODS: In 304 Caucasian American NTD families with myelomeningocele or anencephaly, we examined 28 polymorphisms in 11 genes: folate receptor 1, folate receptor 2, solute carrier family 19 member 1, transcobalamin II, methylenetetrahydrofolate dehydrogenase 1, serine hydroxymethyl-transferase 1, 5,10-methylenetetrahydrofolate reductase (MTHFR), 5-methyltetrahydrofolate-homo-cysteine methyltransferase, 5-methyltetrahydrofolate-homocysteine methyltransferase reductase, betaine-homocysteine methyltransferase (BHMT), and cystathionine-beta-synthase. RESULTS: Only single nucleotide polymorphisms (SNPs) in BHMT were significantly associated in the overall data set; this significance was strongest when mothers took folate-containing nutritional supplements before conception. The BHMT SNP rs3733890 was more significant when the data were stratified by preferential transmission of the MTHFR rs1801133 thermolabile T allele from parent to offspring. Other SNPs in folate pathway genes were marginally significant in some analyses when stratified by maternal supplementation, MTHFR, or BHMT allele transmission. CONCLUSIONS: BHMT rs3733890 is significantly associated in our data set, whereas MTHFR rs1801133 is not a major risk factor. Further investigation of folate and methionine cycle genes will require extensive SNP genotyping and/or resequencing to identify novel variants, inclusion of environmental factors, and investigation of gene-gene interactions in large data sets.
Alleles↗
SNPs in the neural cell adhesion molecule 1 gene (NCAM1) may be associated with human neural tube defects.
Neural tube defects (NTDs) are common birth defects, occurring in approximately 1/1,000 births; both genetic and environmental factors are implicated. To date, no major genetic risk factors have been identified. Throughout development, cell adhesion molecules are strongly implicated in cell-cell interactions, and may play a role in the formation and closure of the neural tube. To evaluate the role of neural cell adhesion molecule 1 (NCAM1) in risk of human NTDs, we screened for novel single-nucleotide polymorphisms (SNPs) within the gene. Eleven SNPs across NCAM1 were genotyped using TaqMan. We utilized a family-based approach to evaluate evidence for association and/or linkage disequilibrium. We evaluated American Caucasian simplex lumbosacral myelomeningocele families (n=132 families) using the family based association test (FBAT) and the pedigree disequilibrium test (PDT). Association analysis revealed a significant association between risk for NTDs and intronic SNP rs2298526 using both the FBAT test (P=0.0018) and the PDT (P=0.0025). Using the HBAT version of the FBAT to look for haplotype association, all pairwise comparisons with SNP rs2298526 were also significant. A replication study set, consisting of 72 additional families showed no significant association; however, the overall trend for overtransmission of the less common allele of SNP rs2298526 remained significant in the combined sample set. In addition, we analyzed the expression pattern of the NCAM1 protein in human embryos, and while NCAM1 is not expressed within the neural tube at the time of closure, it is expressed in the surrounding and later in differentiated neurons of the CNS. These results suggest variations in NCAM1 may influence risk for human NTDs.
Gene Expression Regulation, Developmental↗
The genetics of tethered cord syndrome.
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Chromosome Aberrations↗
Analysis of ALDH1A2, CYP26A1, CYP26B1, CRABP1, and CRABP2 in human neural tube defects suggests a possible association with alleles in ALDH1A2.
BACKGROUND: Vitamin A (retinol), in the form of retinoic acid (RA), is essential for normal development of the human embryo. Studies in the mouse and zebrafish have shown that retinol is metabolized in the developing spinal cord and must be maintained in a precise balance along the anteroposterior axis. Both excess and deficiency of RA can affect morphogenesis, including failures of neural tube closure. METHODS: We chose to investigate 5 genes involved in the metabolism or synthesis of RA, ALDH1A2, CYP26A1, CYP26B1, CRABP1, and CRABP2, for their role in the development of human neural tube defects, such as spina bifida. RESULTS: An association analysis using both allelic and genotypic single-locus tests revealed a significant association between the risk for spina bifida and 3 polymorphisms in the gene ALDH1A2; however, we found no evidence of a significant multilocus association. CONCLUSIONS: These results may suggest that polymorphisms in ALDH1A2 may influence the risk for lumbosacral myelomeningocele in humans.
Alleles↗
New tool for an old problem: can RNAi efficiently resolve the issue of genetic redundancy?
RNA interference (RNAi) has become a generally accepted tool for inhibiting gene expression in many laboratory organisms. Nagel et al.,(1) in a recent paper, give an example of how this tool can also be used to address the question of genetic redundancy. Their focus was on the redundancy in Drosophila melanogaster of the Enhancer of split gene complex [E(spl)-C] which comprises seven highly related genes. Their somewhat conflicting findings are probably the typical scenario for most RNAi experiments: some expected results and some surprises.
Animals↗
LIF and BMP signaling generate separate and discrete types of GFAP-expressing cells.
Bone morphogenetic protein (BMP) and leukemia inhibitory factor (LIF) signaling both promote the differentiation of neural stem/progenitor cells into glial fibrillary acidic protein (GFAP) immunoreactive cells. This study compares the cellular and molecular characteristics, and the potentiality, of GFAP(+) cells generated by these different signaling pathways. Treatment of cultured embryonic subventricular zone (SVZ) progenitor cells with LIF generates GFAP(+) cells that have a bipolar/tripolar morphology, remain in cell cycle, contain progenitor cell markers and demonstrate self-renewal with enhanced neurogenesis - characteristics that are typical of adult SVZ and subgranular zone (SGZ) stem cells/astrocytes. By contrast, BMP-induced GFAP(+) cells are stellate, exit the cell cycle, and lack progenitor traits and self-renewal--characteristics that are typical of astrocytes in the non-neurogenic adult cortex. In vivo, transgenic overexpression of BMP4 increases the number of GFAP(+) astrocytes but depletes the GFAP(+) progenitor cell pool, whereas transgenic inhibition of BMP signaling increases the size of the GFAP(+) progenitor cell pool but reduces the overall numbers of astrocytes. We conclude that LIF and BMP signaling generate different astrocytic cell types, and propose that these cells are, respectively, adult progenitor cells and mature astrocytes.
Animals↗
Interactions between ID and OLIG proteins mediate the inhibitory effects of BMP4 on oligodendroglial differentiation.
Bone morphogenetic protein (BMP) signaling inhibits the generation of oligodendroglia and enhances generation of astrocytes by neural progenitor cells both in vitro and in vivo. This study examined the mechanisms underlying the effects of BMP signaling on glial lineage commitment. Treatment of cultured neural progenitor cells with BMP4 induced expression of all four members of the inhibitor of differentiation (ID) family of helix-loop-helix transcriptional inhibitors and blocked oligodendrocyte (OL) lineage commitment. Overexpression of Id4 or Id2 but not Id1 or Id3 in cultured progenitor cells reproduced both the inhibitory effects of BMP4 treatment on OL lineage commitment and the stimulatory effects on astrogliogenesis. Conversely, decreasing the levels of Id4 mRNA by RNA interference enhanced OL differentiation and inhibited the effects of BMP4 on glial lineage commitment. This suggests that induction of Id4 expression mediates effects of BMP signaling. Bacterial two-hybrid and co-immunoprecipitation studies demonstrated that ID4, and to a lesser extent ID2, complexed with the basic-helix-loop-helix transcription (bHLH) factors OLIG1 and OLIG2, which are required for the generation of OLs. By contrast, ID1 and ID3 did not complex with the OLIG proteins. In addition, the OLIG and ID proteins both interacted with the E2A proteins E12 and E47. Further, exposure of cultured progenitor cells to BMP4 changed the intracellular localization of OLIG1 and OLIG2 from a predominantly nuclear to a predominantly cytoplasmic localization. These observations suggest that the induction of ID4 and ID2, and their sequestration of both OLIG proteins and E2A proteins mediate the inhibitory effects of BMP signaling on OL lineage commitment and contribute to the generation of astrocytes.
Animals↗
Autosomal dominant occipital cephalocele.
The authors report the clinical and radiographic characteristics of a non-consanguineous Vietnamese kindred with an autosomal dominant form of occipital cephalocele. Affected family members all presented with occipital subscalp bulges at birth. Except for the proband, all individuals were developmentally normal with otherwise normal neurologic examinations. Unaffected family members, including obligate carriers, share no clinical characteristics, demonstrating incomplete penetrance.
Abnormalities, Multiple↗
Sox1 acts through multiple independent pathways to promote neurogenesis.
Although Sox1, Sox2, and Sox3 are all part of the Sox-B1 group of transcriptional regulators, only Sox1 appears to play a direct role in neural cell fate determination and differentiation. We find that overexpression of Sox1 but not Sox2 or Sox3 in cultured neural progenitor cells is sufficient to induce neuronal lineage commitment. Sox1 binds directly to the Hes1 promoter and suppresses Hes1 transcription, thus attenuating Notch signaling. Sox1 also binds to beta-catenin and suppresses beta-catenin-mediated TCF/LEF signaling, thus potentially attenuating the wnt signaling pathway. The C-terminus of Sox1 is required for both of these interactions. Sox1 also promotes exit of cells from cell cycle and up-regulates transcription of the proneural bHLH transcription factor neurogenin 1 (ngn1). These observations suggest that Sox1 works through multiple independent pathways to promote neuronal cell fate determination and differentiation.
Basic Helix-Loop-Helix Proteins↗
Bone morphogenetic protein-2 and -4 limit the number of enteric neurons but promote development of a TrkC-expressing neurotrophin-3-dependent subset.
The hypothesis that BMPs (bone morphogenetic proteins), which act early in gut morphogenesis, also regulate specification and differentiation in the developing enteric nervous system (ENS) was tested. Expression of BMP-2 and BMP-4, BMPR-IA (BMP receptor subunit), BMPR-IB, and BMPR-II, and the BMP antagonists, noggin, gremlin, chordin, and follistatin was found when neurons first appear in the primordial bowel at embryonic day 12 (E12). Agonists, receptors, and antagonists were detected in separated populations of neural crest- and noncrest-derived cells. When applied to immunopurified E12 ENS precursors, BMP-2 and BMP-4 induced nuclear translocation of phosphorylated Smad-1 (Sma and Mad-related protein). The number of neurons developing from these cells was increased by low concentrations and decreased by high concentrations of BMP-2 or BMP-4. BMPs induced the precocious appearance of TrkC-expressing neurons and their dependence on neurotrophin-3 for survival. BMP-4 interacted with glial cell line-derived neurotrophic factor (GDNF) to enhance neuronal development but limited GDNF-driven expansion of the precursor pool. BMPs also promoted development of smooth muscle from mesenchymal cells immunopurified at E12. To determine the physiological significance of these observations, the BMP antagonist noggin was overexpressed in the developing ENS of transgenic mice under the control of the neuron-specific enolase promoter. Neuronal numbers in both enteric plexuses and smooth muscle were increased throughout the postnatal small intestine. These increases were already apparent by E18. In contrast, TrkC-expressing neurons decreased in both plexuses of postnatal noggin-overexpressing animals, again an effect detectable at E18. BMP-2 and/or BMP-4 thus limit the size of the ENS but promote the development of specific subsets of enteric neurons, including those that express TrkC.
Active Transport, Cell Nucleus↗
The presence of FGF2 signaling determines whether beta-catenin exerts effects on proliferation or neuronal differentiation of neural stem cells.
Neural stem cells proliferate and maintain multipotency when cultured in the presence of FGF2, but subsequent lineage commitment by the cells is nevertheless influenced by the exposure to FGF2. Here we show that FGF2 effects on neural stem cells are mediated, in part, by beta-catenin. Conversely, the effects of beta-catenin in neural stem cells depend in part upon whether there is concurrent fibroblast growth factor (FGF) signaling. FGF2 increases beta-catenin signaling through several different mechanisms including increased expression of beta-catenin mRNA, increased nuclear translocation of beta-catenin, increased phosphorylation of GSK-3beta, and tyrosine phosphorylation of beta-catenin. Overexpression of beta-catenin in the presence of FGF2 helps to maintain neural progenitor cells in a proliferative state. However, overexpression of beta-catenin in the absence of FGF2 enhances neuronal differentiation. Further, chromatin immunoprecipitation (ChIP) assays demonstrate that both beta-catenin and Lef1 bind directly to the neurogenin promoter, and luciferase reporter assays demonstrate that beta-catenin is directly involved in the regulation of neurogenin 1 and possibly other proneural genes when neural stem cells are cultured in the presence of FGF2. We suggest that the balance between the mitogenic effects and the proneural effects of beta-catenin is determined by the presence of FGF signaling.
Animals↗
Selective differentiation of neural progenitor cells by high-epitope density nanofibers.
Neural progenitor cells were encapsulated in vitro within a three-dimensional network of nanofibers formed by self-assembly of peptide amphiphile molecules. The self-assembly is triggered by mixing cell suspensions in media with dilute aqueous solutions of the molecules, and cells survive the growth of the nanofibers around them. These nanofibers were designed to present to cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density. Relative to laminin or soluble peptide, the artificial nanofiber scaffold induced very rapid differentiation of cells into neurons, while discouraging the development of astrocytes. This rapid selective differentiation is linked to the amplification of bioactive epitope presentation to cells by the nanofibers.
Animals↗
TERC is not a major gene in human neural tube defects.
BACKGROUND: Neural tube defects (NTDs) are the second most common birth defects, after congenital heart defects. Telomerase, the reverse transcriptase that maintains telomere DNA, has been shown to be important for neural tube development and bilateral symmetry in the brain. In knockout mice null for the telomerase RNA component (TERC), telomere loss results in the failure of neural tube closure, primarily at the forebrain and midbrain. METHODS: We investigated TERC for variants that may predispose to human NTDs in 477 NTD cases with a variety of phenotypic presentations. RESULTS: Two novel single nucleotide polymorphisms were identified in the human TERC sequence but showed no association with the NTD phenotype. CONCLUSIONS: Variants in TERC are unlikely to be a major risk factor for the most common form of human NTDs, lumbosacral myelomeningocele.
Animals↗
Bone morphogenetic protein signaling regulates postnatal hair follicle differentiation and cycling.
Hair follicle morphogenesis and cycling were examined in transgenic mice that overexpress the bone morphogenetic protein (BMP) inhibitor Noggin under the control of the neuron-specific enolase promoter. The Noggin transgene was misexpressed in the proximal portion of the hair follicle, primarily the matrix cells, apart from the usual expression in neurons. Transgene expression appeared only after induction of both the primary (tylotrich) and secondary (nontylotrich) pelage hair follicles had already occurred, thus allowing examination of the role of BMP signaling in follicles that had been induced normally in the presence of BMPs. The overexpression of Noggin in these animals resulted in a dramatic loss of hair postnatally. There was an apparently normal, but shortened period of postnatal hair follicle morphogenesis, followed by premature initiation of hair follicle cycling via entry into the first catagen transformation. This resulted in a complete loss of hair shafts from the nontylotrich hair follicles in these mice while the tylotrich hair follicles were normal. The onset of anagen of the first postnatal hair follicle cycle was also accelerated in the transgenic mice. Our results show that BMP signaling is specifically required for proper proliferation and differentiation during late morphogenesis of nontylotrich hair follicles and that inhibition of this signaling pathway may be one of the triggers for the onset of catagen when the follicles are in anagen and the onset of anagen when the follicles are in telogen. Ectopic sebocyte differentiation was another hallmark of the phenotype of these transgenic mice suggesting that BMP signaling may be an important determinant of lineage selection by common progenitor cells in the skin. BMPs likely promote a hair follicle-type differentiation pathway of keratinocytes while suppressing the sebaceous differentiation pathway of skin epithelium.
Animals↗
Transgenic mice overexpressing BMP4 develop a fibrodysplasia ossificans progressiva (FOP)-like phenotype.
Fibrodysplasia ossificans progressiva (FOP) is a rare hereditary connective tissue disease characterized by progressive postnatal heterotopic bone formation. Although the genetic defects of FOP are not known, several lines of evidence have suggested that bone morphogenetic protein-4 (BMP4) may be involved in the pathophysiology. Nevertheless BMP4-transgenic mice have previously failed to develop the disorder and there has been no good animal model of the disease. Here, we report that a unique transgenic mouse line that overexpresses BMP4 under control of the neuron-specific enolase (NSE) promoter develops a FOP-like phenotype. Mating of these animals with transgenic animals that overexpress the BMP inhibitor noggin prevents the disorder, confirming the role of BMP4 in the pathogenesis of the disease. Heterotopic bone formation in these animals appears to follow the classic endochondral ossification pathway. Sex-mismatched cell transplantation experiments indicate that multiple cell sources contribute to the heterotopic ossification. This remarkable animal model provides a unique opportunity to further study the role of the BMP signaling pathway in heterotopic ossification and to improve our understanding of the clinical aspects of FOP.
Animals↗
Target-derived BMP signaling limits sensory neuron number and the extent of peripheral innervation in vivo.
The role of target-derived BMP signaling in development of sensory ganglia and the sensory innervation of the skin was examined in transgenic animals that overexpress either the BMP inhibitor noggin or BMP4 under the control of a keratin 14 (K14) promoter. Overexpression of noggin resulted in a significant increase in the number of neurons in the trigeminal and dorsal root ganglia. Conversely, overexpression of BMP4 resulted in a significant decrease in the number of dorsal root ganglion neurons. There was no significant change in proliferation of trigeminal ganglion neurons in the noggin transgenic animals, and neuron numbers did not undergo the normal developmental decrease between E12.5 and the adult, suggesting that programmed cell death was decreased in these animals. The increase in neuron numbers in the K14-noggin animals was followed by an extraordinary increase in the density of innervation in the skin and a marked change in the pattern of innervation by different types of fibers. Conversely, the density of innervation of the skin was decreased in the BMP4 overexpressing animals. Further Merkel cells and their innervation were increased in the K14-noggin mice and decreased in the K14-BMP4 mice. The changes in neuron numbers and the density of innervation were not accompanied by a change in the levels of neurotrophins in the skin. These findings indicate that the normal developmental decrease in neuron numbers in sensory ganglia depends upon BMP signaling, and that BMPs may limit both the final neuron number in sensory ganglia as well as the extent of innervation of targets. Coupled with prior observations, this suggests that BMP signaling may regulate the acquisition of dependence of neurons on neurotrophins for survival, as well as their dependence on target-derived neurotrophins for determining the density of innervation of the target.
Animals↗
Beta-catenin signaling is required for neural differentiation of embryonic stem cells.
Culture of embryonic stem (ES) cells at high density inhibits both beta-catenin signaling and neural differentiation. ES cell density does not influence beta-catenin expression, but a greater proportion of beta-catenin is targeted for degradation in high-density cultures. Moreover, in high-density cultures, beta-catenin is preferentially localized to the membrane further reducing beta-catenin signaling. Increasing beta-catenin signaling by treatment with Wnt3a-conditioned medium, by overexpression of beta-catenin, or by overexpression of a dominant-negative form of E-cadherin promotes neurogenesis. Furthermore, beta-catenin signaling is sufficient to induce neurogenesis in high-density cultures even in the absence of retinoic acid (RA), although RA potentiates the effects of beta-catenin. By contrast, RA does not induce neurogenesis in high-density cultures in the absence of beta-catenin signaling. Truncation of the armadillo domain of beta-catenin, but not the C terminus or the N terminus, eliminates its proneural effects. The proneural effects of beta-catenin reflect enhanced lineage commitment rather than proliferation of neural progenitor cells. Neurons induced by beta-catenin overexpression either alone or in association with RA express the caudal neuronal marker Hoxc4. However, RA treatment inhibits the beta-catenin-mediated generation of tyrosine hydroxylase-positive neurons, suggesting that not all of the effects of RA are dependent upon beta-catenin signaling. These observations suggest that beta-catenin signaling promotes neural lineage commitment by ES cells, and that beta-catenin signaling may be a necessary co-factor for RA-mediated neuronal differentiation. Further, enhancement of beta-catenin signaling with RA treatment significantly increases the numbers of neurons generated from ES cells, thus suggesting a method for obtaining large numbers of neural species for possible use in for ES cell transplantation.
Animals↗