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Wang C, Szaro BG. Post-transcriptional regulation mediated by specific neurofilament introns in vivo. J Cell Sci 2016; 129:1500-11. [PMID: 26906423 DOI: 10.1242/jcs.185199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 02/17/2016] [Indexed: 11/20/2022] Open
Abstract
Neurons regulate genes post-transcriptionally to coordinate the supply of cytoskeletal proteins, such as the medium neurofilament (NEFM), with demand for structural materials in response to extracellular cues encountered by developing axons. By using a method for evaluating functionality of cis-regulatory gene elements in vivo through plasmid injection into Xenopus embryos, we discovered that splicing of a specific nefm intron was required for robust transgene expression, regardless of promoter or cell type. Transgenes utilizing the nefm 3'-UTR but substituting other nefm introns expressed little or no protein owing to defects in handling of the messenger (m)RNA as opposed to transcription or splicing. Post-transcriptional events at multiple steps, but mainly during nucleocytoplasmic export, contributed to these varied levels of protein expression. An intron of the β-globin gene was also able to promote expression in a manner identical to that of the nefm intron, implying a more general preference for certain introns in controlling nefm expression. These results expand our knowledge of intron-mediated gene expression to encompass neurofilaments, indicating an additional layer of complexity in the control of a cytoskeletal gene needed for developing and maintaining healthy axons.
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Affiliation(s)
- Chen Wang
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA
| | - Ben G Szaro
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA
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Liu Y, Wang C, Destin G, Szaro BG. Microtubule-associated protein tau promotes neuronal class II β-tubulin microtubule formation and axon elongation in embryonic Xenopus laevis. Eur J Neurosci 2015; 41:1263-75. [PMID: 25656701 DOI: 10.1111/ejn.12848] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 12/13/2014] [Accepted: 01/07/2015] [Indexed: 01/06/2023]
Abstract
Compared with its roles in neurodegeneration, much less is known about microtubule-associated protein tau's normal functions in vivo, especially during development. The external development and ease of manipulating gene expression of Xenopus laevis embryos make them especially useful for studying gene function during early development. To study tau's functions in axon outgrowth, we characterized the most prominent tau isoforms of Xenopus embryos and manipulated their expression. None of these four isoforms were strictly analogous to those commonly studied in mammals, as all constitutively contained exon 10, which is preferentially removed from mammalian fetal tau isoforms, as well as exon 8, which in mammals is rare. Nonetheless, like mammalian tau, Xenopus tau exhibited alternative splicing of exon 4a, which in mammals distinguishes 'big' tau of peripheral neurons, and exon 6. Strongly suppressing tau expression with antisense morpholino oligonucleotides only modestly compromised peripheral nerve outgrowth of intact tadpoles, but severely disrupted neuronal microtubules containing class II β-tubulins while leaving other microtubules largely unperturbed. Thus, the relatively mild dependence of axon development on tau likely resulted from having only a single class of microtubules disrupted by its loss. Also, consistent with its greater expression in long peripheral axons, boosting expression of 'big' tau increased neurite outgrowth significantly and enhanced tubulin acetylation more so than did the smaller isoform. These data demonstrate the utility of Xenopus as a tool to gain new insights into tau's functions in vivo.
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Affiliation(s)
- Yuanyuan Liu
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Chen Wang
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Giovanny Destin
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Ben G Szaro
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY, 12222, USA
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Szaro BG, Strong MJ. Regulation of Cytoskeletal Composition in Neurons: Transcriptional and Post-transcriptional Control in Development, Regeneration, and Disease. ADVANCES IN NEUROBIOLOGY 2011. [DOI: 10.1007/978-1-4419-6787-9_24] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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Huang HS, Kubish GM, Redmond TM, Turner DL, Thompson RC, Murphy GG, Uhler MD. Direct transcriptional induction of Gadd45gamma by Ascl1 during neuronal differentiation. Mol Cell Neurosci 2010; 44:282-96. [PMID: 20382226 PMCID: PMC2905796 DOI: 10.1016/j.mcn.2010.03.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 03/23/2010] [Accepted: 03/24/2010] [Indexed: 10/19/2022] Open
Abstract
The basic helix-loop-helix transcription factor Ascl1 plays a critical role in the intrinsic genetic program responsible for neuronal differentiation. Here, we describe a novel model system of P19 embryonic carcinoma cells with doxycycline-inducible expression of Ascl1. Microarray hybridization and real-time PCR showed that these cells demonstrated increased expression of many neuronal proteins in a time- and concentration-dependent manner. Interestingly, the gene encoding the cell cycle regulator Gadd45gamma was increased earliest and to the greatest extent following Ascl1 induction. Here, we provide the first evidence identifying Gadd45gamma as a direct transcriptional target of Ascl1. Transactivation and chromatin immunoprecipitation assays identified two E-box consensus sites within the Gadd45gamma promoter necessary for Ascl1 regulation, and demonstrated that Ascl1 is bound to this region within the Gadd45gamma promoter. Furthermore, we found that overexpression of Gadd45gamma itself is sufficient to initiate some aspects of neuronal differentiation independent of Ascl1.
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Affiliation(s)
- Holly S. Huang
- Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI, 48105
| | - Ginger M. Kubish
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
| | - Tanya M. Redmond
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
| | - David L. Turner
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI, 48105
| | - Robert C. Thompson
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
- Department of Psychiatry, University of Michigan, Ann Arbor, MI, 48105
| | - Geoffrey G. Murphy
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
| | - Michael D. Uhler
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48105
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI, 48105
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Liu Y, Gervasi C, Szaro BG. A crucial role for hnRNP K in axon development in Xenopus laevis. Development 2008; 135:3125-35. [PMID: 18725517 DOI: 10.1242/dev.022236] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We report that hnRNP K, an RNA-binding protein implicated in multiple aspects of post-transcriptional gene control, is essential for axon outgrowth in Xenopus. Its intracellular localization was found to be consistent with one of its known roles as an mRNA shuttling protein. In early embryos, it was primarily nuclear, whereas later it occupied both the nucleus and cytoplasm to varying degrees in different neuronal subtypes. Antisense hnRNP K morpholino oligonucleotides (MOs) microinjected into blastomeres suppressed hnRNP K expression from neural plate stages through to at least stage 40. Differentiating neural cells in these embryos expressed several markers for terminally differentiated neurons but failed to make axons. Rescue experiments and the use of two separate hnRNP K MOs were carried out to confirm that these effects were specifically caused by knockdown of hnRNP K expression. For insights into the involvement of hnRNP K in neuronal post-transcriptional gene control at the molecular level, we compared effects on expression of the medium neurofilament protein (NF-M), the RNA for which binds hnRNP K, with that of peripherin, another intermediate filament protein, the RNA for which does not bind hnRNP K. hnRNP K knockdown compromised NF-M mRNA nucleocytoplasmic export and translation, but had no effect on peripherin. Because eliminating NF-M from Xenopus axons attenuates, but does not abolish, their outgrowth, hnRNP K must target additional RNAs needed for axon development. Our study supports the idea that translation of at least a subset of RNAs involved in axon development is controlled by post-transcriptional regulatory modules that have hnRNP K as an essential element.
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Affiliation(s)
- Yuanyuan Liu
- The Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, Albany, NY 12222, USA
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Ananthakrishnan L, Szaro BG. Transcriptional and translational dynamics of light neurofilament subunit RNAs during Xenopus laevis optic nerve regeneration. Brain Res 2008; 1250:27-40. [PMID: 19027722 DOI: 10.1016/j.brainres.2008.11.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2008] [Revised: 10/24/2008] [Accepted: 11/01/2008] [Indexed: 12/01/2022]
Abstract
Neurofilaments (NFs), which comprise one of three cytoskeletal polymers of vertebrate axons, are heteropolymers of multiple NF subunit proteins. During Xenopus laevis optic nerve regeneration, NF subunit composition undergoes progressive changes that correlate with regenerative success. Understanding the relative contributions of transcriptional and post-transcriptional gene regulatory mechanisms to these changes should therefore provide insights into the control of the axonal growth program. Previously, we examined this issue with respect to the medium neurofilament protein (NF-M). Because the integrity of NF heteropolymers depends upon maintaining properly balanced expression among multiple subunits, we have now extended this analysis to include the four light NF subunits - peripherin, the light NF triplet protein (NF-L), and two additional alpha-internexin-like proteins. Within 3 days after an optic nerve crush injury to one eye, primary transcript levels of NF subunits increased in both eyes. Levels of mRNA, however, increased in only the operated eye and did so later than did increases in primary transcript, indicating that mRNA levels are under significant post-transcriptional regulation. As measured by polysome profiling, the translational efficiencies of individual NF subunit mRNAs also shifted throughout regeneration, with operated eye mRNAs being generally more translationally active than those of unoperated eyes. Also, in operated eyes, the precise mix of efficiently and poorly translated messages throughout regeneration varied independently for each subunit, indicating that their translations are fine-tuned separately. These results suggest a model whereby traumatic disruption of visual circuitry leads to increased expression of NF primary transcripts in both eyes. These increases are subsequently modulated post-transcriptionally to accommodate shifting demands at each phase of regeneration for NF heteropolymers of differing composition in regrowing axons.
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Ananthakrishnan L, Gervasi C, Szaro B. Dynamic regulation of middle neurofilament RNA pools during optic nerve regeneration. Neuroscience 2008; 153:144-53. [DOI: 10.1016/j.neuroscience.2008.02.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Revised: 12/10/2007] [Accepted: 02/04/2008] [Indexed: 10/22/2022]
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Gervasi C, Szaro BG. Performing functional studies of Xenopus laevis intermediate filament proteins through injection of macromolecules into early embryos. Methods Cell Biol 2004; 78:673-701. [PMID: 15646635 DOI: 10.1016/s0091-679x(04)78023-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Christine Gervasi
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, Albany, New York 12222, USA
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Gervasi C, Thyagarajan A, Szaro BG. Increased expression of multiple neurofilament mRNAs during regeneration of vertebrate central nervous system axons. J Comp Neurol 2003; 461:262-75. [PMID: 12724842 DOI: 10.1002/cne.10695] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Characteristic changes in the expression of neuronal intermediate filaments (nIFs), an abundant cytoskeletal component of vertebrate axons, accompany successful axon regeneration. In mammalian regenerating PNS, expression of nIFs that are characteristic of mature neurons becomes suppressed throughout regeneration, whereas that of peripherin, which is abundant in developing axons, increases. Comparable changes are absent from mammalian injured CNS; but in goldfish and lamprey CNS, expression of several nIFs increases during axon regrowth. To obtain a broader view of the nIF response of successfully regenerating vertebrate CNS, in situ hybridization and video densitometry were used to track multiple nIF mRNAs during optic axon regeneration in Xenopus laevis. As in other successfully regenerating systems, peripherin expression increased rapidly after injury and expression of those nIFs characteristic of mature retinal ganglion cells decreased. Unlike the decrease in nIF mRNAs of regenerating PNS, that of Xenopus retinal ganglion cells was transient, with most nIF mRNAs increasing above normal during axon regrowth. At the peak of regeneration, increases in each nIF mRNA resulted in a doubling of the total amount of nIF mRNA, as well as a shift in the relative proportions contributed by each nIF. The relative proportions of peripherin and NF-M increased above normal, whereas proportions of xefiltin and NF-L decreased and that of XNIF remained the same. The increases in peripherin and NF-M mRNAs were accompanied by increases in protein. These results are consistent with the hypothesis that successful axon regeneration involves changes in nIF subunit composition conducive to growth and argue that a successful injury response differs between CNS and PNS.
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Affiliation(s)
- Christine Gervasi
- Department of Biological Sciences, State University of New York--University at Albany, Albany, New York 12222, USA
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10
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Abstract
The highly regulated expression of neurofilament (NF) proteins during axon outgrowth suggests that NFs are important for axon development, but their contribution to axon growth is unclear. Previous experiments in Xenopus laevis embryos demonstrated that antibody-induced disruption of NFs stunts axonal growth but left unresolved how the loss of NFs affects the dynamics of axon growth. In the current study, dissociated cultures were made from the spinal cords of embryos injected at the two-cell stage with an antibody to the middle molecular mass NF protein (NF-M), and time-lapse videomicroscopy was used to study early neurite outgrowth in descendants of both the injected and uninjected blastomeres. The injected antibody altered the growth dynamics primarily in long neurites (>85 microm). These neurites were initiated just as early and terminated growth no sooner than did normal ones. Rather, they spent relatively smaller fractions of time actively extending than normal. When growth occurred, it did so at the same velocity. In very young neurites, which have NFs made exclusively of peripherin, NFs were unaffected, but in the shaft of older neurites, which have NFs that contain NF-M, NFs were disrupted. Thus growth was affected only after NFs were disrupted. In contrast, the distributions of alpha-tubulin and mitochondria were unaffected; thus organelles were still transported into neurites. However, mitochondrial staining was brighter in descendants of injected blastomeres, suggesting a greater demand for energy. Together, these results suggest a model in which intra-axonal NFs facilitate elongation of long axons by making it more efficient.
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Undamatla J, Szaro BG. Differential expression and localization of neuronal intermediate filament proteins within newly developing neurites in dissociated cultures of Xenopus laevis embryonic spinal cord. CELL MOTILITY AND THE CYTOSKELETON 2001; 49:16-32. [PMID: 11309837 DOI: 10.1002/cm.1017] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The molecular subunit composition of neurofilaments (NFs) progressively changes during axon development. In developing Xenopus laevis spinal cord, peripherin emerges at the earliest stages of neurite outgrowth. NF-M and XNIF (an alpha-internexin-like protein) appear later, as axons continue to elongate, and NF-L is expressed after axons contact muscle. Because NFs are the most abundant component of the vertebrate axonal cytoskeleton, we must understand why these changes occur before we can fully comprehend how the cytoskeleton regulates axon growth and morphology. Knowing where these proteins are localized within developing neurites and how their expression changes with cell contact is essential for this understanding. Thus, we examined by immunofluorescence the expression and localization of these NF subunits within dissociated cultures of newly differentiating spinal cord neurons. In young neurites, peripherin was most abundant in distal neuritic segments, especially near branch points and extending into the central domain of the growth cone. In contrast, XNIF and NF-M were usually either absent from very young neurites or exhibited a proximal to distal gradient of decreasing intensity. In older neurites, XNIF and NF-M expression increased, whereas that of peripherin declined. All three of these proteins became more evenly distributed along the neurites, with some branches staining more intensely than others. At 24 h, NF-L appeared, and in 48-h cultures, its expression, along with that of NF-M, was greater in neurites contacting muscle cells, arguing that the upregulation of these two subunits is dependent on contact with target cells. Moreover, this contact had no effect on XNIF or peripherin expression. Our findings are consistent with a model in which peripherin plays an important structural role in growth cones, XNIF and NF-M help consolidate the intermediate filament cytoskeleton beginning in the proximal neurite, and increased levels of NF-L and NF-M help further solidify the cytoskeleton of axons that successfully reach their targets.
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Affiliation(s)
- J Undamatla
- Neurobiology Research Center and the Department of Biological Sciences, University at Albany, State University of New York, Albany 12222, USA
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Roosa JR, Gervasi C, Szaro BG. Structure, biological activity of the upstream regulatory sequence, and conserved domains of a middle molecular mass neurofilament gene of Xenopus laevis. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2000; 82:35-51. [PMID: 11042356 DOI: 10.1016/s0169-328x(00)00180-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
During development, the molecular compositions of neurofilaments (NFs) undergo progressive modifications that correlate with successive stages of axonal outgrowth. Because NFs are the most abundant component of the axonal cytoskeleton, understanding how these modifications are regulated is essential for knowing how axons control their structural properties during growth. In vertebrates ranging from lamprey to mammal, orthologs of the middle molecular mass NF protein (NF-M) share similar patterns of expression during axonal outgrowth, which suggests that these NF-M genes may share conserved regulatory elements. These elements might be identified by comparing the sequences and activities of regulatory domains among the vertebrate NF-M genes. The frog, Xenopus laevis, is a good choice for such studies, because its early neural development can be observed readily and because transgenic embryos can be made easily. To begin such studies, we isolated genomic clones of Xenopus NF-M(2), tested the activity of its upstream regulatory sequence (URS) in transgenic embryos, and then compared sequences of regulatory regions among vertebrate NF-M genes to search for conserved elements. Studies with reporter genes in transgenic embryos found that the 1. 5 kb URS lacked the elements sufficient for neuron-specific gene expression but identified conserved regions with basal regulatory activity. These studies further demonstrated that the NF-M 1.5 kb URS was highly susceptible to positional effects, a property that may be relevant to the highly variant, tissue-specific expression that is seen among members of the intermediate filament gene family. Non-coding regions of vertebrate NF-M genes contained several conserved elements. The region of highest conservation fell within the 3' untranslated region, a region that has been shown to regulate expression of another NF gene, NF-L. Transgenic Xenopus may thus prove useful for testing further the activity of conserved elements during axonal development and regeneration.
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Affiliation(s)
- J R Roosa
- Neurobiology Research Center and The Department of Biological Sciences, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA
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Gervasi C, Stewart CB, Szaro BG. Xenopus laevis peripherin (XIF3) is expressed in radial glia and proliferating neural epithelial cells as well as in neurons. J Comp Neurol 2000. [DOI: 10.1002/1096-9861(20000731)423:3<512::aid-cne13>3.0.co;2-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Zhao Y, Szaro BG. Xefiltin, aXenopus laevis neuronal intermediate filament protein, is expressed in actively growing optic axons during development and regeneration. ACTA ACUST UNITED AC 1997. [DOI: 10.1002/(sici)1097-4695(19971120)33:6<811::aid-neu8>3.0.co;2-c] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Gervasi C, Szaro BG. Sequence and expression patterns of two forms of the middle molecular weight neurofilament protein (NF-M) of Xenopus laevis. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1997; 48:229-42. [PMID: 9332720 DOI: 10.1016/s0169-328x(97)00096-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The middle molecular weight neurofilament protein (NF-M) is relevant to our understanding of vertebrate neurofilaments in growing axons, both because it exists in all vertebrates and because it undergoes characteristic changes in its phosphorylation state during axonal development. Indeed, all vertebrate neurofilament proteins are believed to have originated by gene duplication from an ancestral, NF-M-like protein. The role of NF-M in axonal development has been studied extensively in the frog, Xenopus laevis, through the use of monoclonal antibodies. To acquire a better understanding of the relationship of X. laevis NF-M to that of other vertebrates and to obtain additional reagents to study and perturb neurofilaments in developing axons, we isolated cDNA clones from the nervous system. These clones encoded two forms of NF-M, which exhibited 93% amino acid identity overall and 94%, 96% and 90% identity over their head, rod, and tail domains, respectively. Synonymous nucleotide substitution rates between the two forms tied their origin to an ancestral duplication of the Xenopus genome, which occurred approximately 30 million years ago. Non-synonymous substitution rates indicated that the tail domain is evolving more rapidly than the rod domain. Both forms shared structural features in common with other vertebrate NF-Ms but had only a single example of the KSP phosphorylation motif that is repeated multiple times in the NF-Ms of bird, goldfish and mammal. In post-metamorphic frogs, the NF-M(1) transcript was consistently expressed at higher levels than that of NF-M(2), although their anatomical patterns of expression were qualitatively similar. During development, however, only NF-M(2) was detectable in retinal ganglion cells through stage 42. We speculate that the differences observed between these two forms may represent early stages of protein diversification akin to what occurred after the gene duplications that gave rise to other vertebrate neurofilament proteins.
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Affiliation(s)
- C Gervasi
- Department of Biological Sciences, University at Albany, State University of New York 12222, USA
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Klymkowsky MW. Intermediate filament organization, reorganization, and function in the clawed frog Xenopus. Curr Top Dev Biol 1996; 31:455-86. [PMID: 8746673 DOI: 10.1016/s0070-2153(08)60236-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- M W Klymkowsky
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder 80309, USA
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Riederer BM, Marugg RA, Schönenberger N. A novel neuro-muscular marker for the heavy subunit of neurofilament proteins, NF-H, and striated muscle myosin of Xenopus laevis. Neurosci Lett 1995; 202:125-8. [PMID: 8787847 DOI: 10.1016/0304-3940(95)12224-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A novel monoclonal antibody, M7, is described, that reacts on Western blots with the large subunit of the neurofilament triplet proteins (NF-H) and with striated muscle myosin of Xenopus laevis. Enzymatically digested neurofilament and myosin proteins revealed different immunoreactive peptide fragments on Western blots. Therefore, the antibody must react with immunologically related epitopes common to both proteins. Immunohistochemistry showed staining of large and small axons in CNS and PNS, and nerves could be followed into endplate regions of skeletal muscles. These muscles were characterized by a striated immunostaining of the M-lines. Despite the crossreactivity of M7 with NF-H and muscle myosin, this antibody may be a tool to study innervation of muscle fibers, and to define changes in the neuromuscular organization during early development and metamorphosis of tadpoles.
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Gervasi C, Szaro BG. The Xenopus laevis homologue to the neuronal cyclin-dependent kinase (cdk5) is expressed in embryos by gastrulation. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1995; 33:192-200. [PMID: 8750877 DOI: 10.1016/0169-328x(95)00109-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Phosphorylation of the neuronal cytoskeletal proteins NF-H, NF-M and tau is important for normal axonal development, and is involved in axonal injury and neurodegenerative diseases. In mammalian neurons, one kinase that phosphorylates these axonal cytoskeletal proteins is cyclin-dependent kinase 5 (cdk5). Cdk5 is a member of the family of cyclin-dependent kinases (cdks), whose other family members regulate mitosis. Unlike the other cdks, cdk5 is abundant in differentiated neurons. Embryos of the clawed frog Xenopus laevis have proved useful for studying other cyclin-dependent kinases, neurofilament proteins and tau during development. As a first step in studying the role of cdk5 and its effects on neurofilaments during Xenopus neural development, four cDNA clones were isolated by screening a frog brain cDNA library at lowered stringency with a cDNA probe to rat cdk5. The frog cdk5 clones encoded a protein of 292 amino acids that was 97% identical to rat cdk5. In situ hybridization demonstrated that the Xenopus cdk5 transcript, like that of mammals, was expressed in differentiated post-mitotic neurons. The high degree of sequence homology and shared neuronal expression suggests that the role of cdk5 in neurons is highly conserved between mammals and amphibians. Northern blot analysis indicated that during Xenopus development, cdk5 mRNA was first expressed between the midblastula transition and gastrulation, which both occur long before neuronal differentiation. These stages mark the transition from synchronous to asynchronous cell division and are the earliest stages of zygotic gene expression. This early expression of Xenopus cdk5 mRNA implies a role for cdk5 during embryogenesis that is separate from its role as an axonal cytoskeletal protein kinase. These observations provide the foundation for exploiting X. laevis embryos to study the role of cdk5 both in the early stages of axonal differentiation and also in early embryogenesis.
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Affiliation(s)
- C Gervasi
- Department of Biological Sciences, State University of New York, Albany 12222, USA
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Lee JE, Hollenberg SM, Snider L, Turner DL, Lipnick N, Weintraub H. Conversion of Xenopus ectoderm into neurons by NeuroD, a basic helix-loop-helix protein. Science 1995; 268:836-44. [PMID: 7754368 DOI: 10.1126/science.7754368] [Citation(s) in RCA: 832] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Basic helix-loop-helix (bHLH) proteins are instrumental in determining cell type during development. A bHLH protein, termed NeuroD, for neurogenic differentiation, has now been identified as a differentiation factor for neurogenesis because (i) it is expressed transiently in a subset of neurons in the central and peripheral nervous systems at the time of their terminal differentiation into mature neurons and (ii) ectopic expression of neuroD in Xenopus embryos causes premature differentiation of neuronal precursors. Furthermore, neuroD can convert presumptive epidermal cells into neurons and also act as a neuronal determination gene. However, unlike another previously identified proneural gene (XASH-3), neuroD seems competent to bypass the normal inhibitory influences that usually prevent neurogenesis in ventral and lateral ectoderm and is capable of converting most of the embryonic ectoderm into neurons. The data suggest that neuroD may participate in the terminal differentiation step during vertebrate neuronal development.
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Affiliation(s)
- J E Lee
- Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA
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Takeda S, Okabe S, Funakoshi T, Hirokawa N. Differential dynamics of neurofilament-H protein and neurofilament-L protein in neurons. J Biophys Biochem Cytol 1994; 127:173-85. [PMID: 7929561 PMCID: PMC2120184 DOI: 10.1083/jcb.127.1.173] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Neurofilaments (NFs) are composed of triplet proteins, NF-H, NF-M, and NF-L. To understand the dynamics of NFs in vivo, we studied the dynamics of NF-H and compared them to those of NF-L, using the combination of microinjection technique and fluorescence recovery after photobleaching. In the case of NF-L protein, the bleached zone gradually restored its fluorescence intensity with a recovery half time of approximately 35 min. On the other hand, recovery of the bleached zone of NF-H was considerably faster, taking place in approximately 19 min. However, in both cases the bleached zone was stationary. Thus, it was suggested that NF-H is the dynamic component of the NF array and is interchangeable, but that it assembles with the other neurofilament triplet proteins in a more exchangeable way, implying that the location of NF-H is in the periphery of the core NF array mainly composed of NF-L subunits. Immunoelectron microscopy investigations of the incorporation sites of NF-H labeled with biotin compounds also revealed the lateral insertion of NF-H subunits into the preexisting NF array, taking after the pattern seen in the case of NF-L. In summary, our results demonstrate that the dynamics of the L and H subunit proteins in situ are quite different from each other, suggesting different and separated mechanisms or structural specialization underlying the behavior of the two proteins.
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Affiliation(s)
- S Takeda
- Department of Anatomy and Cell Biology, Faculty of Medicine, University of Tokyo, Japan
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21
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Lin W, Szaro BG. Maturation of neurites in mixed cultures of spinal cord neurons and muscle cells from Xenopus laevis embryos followed with antibodies to neurofilament proteins. JOURNAL OF NEUROBIOLOGY 1994; 25:1235-48. [PMID: 7815056 DOI: 10.1002/neu.480251006] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Dissociated cell cultures of Xenopus laevis embryonic spinal cord have proved useful for studying the differentiation of neuronal ionic channels and membrane properties and for examining the dynamics of microtubules in developing neurons. To examine their usefulness for studying neurofilaments in developing neurites, we prepared similar cultures from stage 22 embryos. Between 3 and 55 h after plating, these cultures were fixed and immunostained with antibodies directed against various epitopes of neurofilament proteins from X. laevis. These antibodies were specific for nonphosphorylated epitopes of the two low molecular weight Xenopus neurofilament proteins (Xenopus NF-L and the Xenopus neuronal intermediate filament protein, XNIF), both phosphorylated and nonphosphorylated epitopes of the Xenopus middle molecular weight neurofilament protein (NF-M), and a nonphosphorylated epitope of the Xenopus high molecular weight neurofilament protein (NF-H). The emergence of these neurofilament proteins in culture was compared to the time course previously reported for them in Xenopus spinal cord neurons in situ. To facilitate the comparison of times in culture to developmental stages, the age of cultured neurons was converted to an equivalent Nieuwkoop and Faber normal stage using data presented here on the effect of changing temperature on developmental rates of X. laevis. With the exception of the nonphosphorylated epitope of NF-H, which is indicative of the most mature axons found in situ, the emergence of the other neurofilament protein antibody epitopes closely paralleled that previously reported for these antibodies in situ. Thus, with respect to XNIF, NF-M, and NF-L, the neurites of cultured neurons were typical of young, embryonic Xenopus laevis spinal cord axons. This system should prove useful for studying both the function of these neurofilament proteins during the early stages of axonal development and the dynamics of their transport.
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Affiliation(s)
- W Lin
- Department of Biological Sciences, State University of New York, Albany 12222
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22
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Turner DL, Weintraub H. Expression of achaete-scute homolog 3 in Xenopus embryos converts ectodermal cells to a neural fate. Genes Dev 1994; 8:1434-47. [PMID: 7926743 DOI: 10.1101/gad.8.12.1434] [Citation(s) in RCA: 897] [Impact Index Per Article: 28.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In Drosophila, the proneural genes of the achaete-scute complex encode transcriptional activators that can commit cells to a neural fate. We have isolated cDNAs for two Xenopus achaete-scute homologs, ASH3a and ASH3b, which are expressed in a subset of central nervous system (CNS) neuroblasts during early neurogenesis. After expressing either ASH3 protein in developing Xenopus embryos, we find enlargement of the CNS at the expense of adjacent non-neural ectoderm. Analysis of molecular markers for neural, epidermal, and neural crest cells indicates that CNS expansion occurs as early as neural plate formation. ASH3-dependent CNS enlargement appears to require neural induction, as it does not occur in animal cap explants. Inhibition of DNA synthesis shows that additional CNS tissue does not depend on cell division--rather it reflects conversion of prospective neural crest and epidermal cells to a neural fate. The differentiation of the early forming primary neurons also seems to be prevented by ASH3 expression. This may be secondary to the observed activation of Xotch transcription by ASH3.
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Affiliation(s)
- D L Turner
- Department of Genetics, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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23
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Zhao Y, Szaro BG. The return of phosphorylated and nonphosphorylated epitopes of neurofilament proteins to the regenerating optic nerve of Xenopus laevis. J Comp Neurol 1994; 343:158-72. [PMID: 7517961 DOI: 10.1002/cne.903430112] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Neurofilament proteins of mammalian axotomized peripheral axons, which regenerate effectively, resemble those of embryonic axons. However, injured centrally projecting mammalian axons, which fail to regenerate, have very different neurofilament compositions than during development. If changes in neurofilament composition after injury reflect the ability of axotomized neurons to regenerate effectively, then the neurofilaments of centrally projecting axons that can regenerate should more closely resemble those of developing axons. In this study, the neurofilament compositions of injured optic axons of the frog, Xenopus laevis, were examined, since these axons can regenerate a fully functional projection. Antibodies to phosphorylated and nonphosphorylated forms of neurofilament proteins that had been used previously to study the neurofilament composition of newly developing X. laevis optic axons were used in immunocytochemical studies to examine the return of neurofilaments to the optic nerve after an intraorbital nerve crush. Intraocularly injected wheat germ agglutinin conjugated to horseradish peroxidase was used to label the regenerating axons independently of their neurofilaments. Neurofilament immunoreactivities disappeared rapidly from crushed axons during the first week after surgery. By nine days after surgery, antibodies to nonphosphorylated forms of middle (NF-M) and low molecular weight (NF-L) neurofilament proteins and the Xenopus neuronal intermediate filament protein (XNIF) began to stain the nerve just beyond the lesion. By this time, however, growing axonal terminals had reached the optic chiasm. Antibodies to phosphorylated epitopes of NF-M began to stain axons at 15 days, just as growing axons began to arrive at the optic tectum. Nonphosphorylated high molecular weight neurofilament protein (NF-H) began to appear in axons between 18 and 21 days after surgery. Thus, the reappearance of neurofilaments during optic axon regeneration resembled the general pattern seen during development. The chief difference between development and regeneration was that neurofilament epitopes took longer to emerge during regeneration. One possibility is that cues encountered along the optic pathway influence the neurofilament composition of retinal ganglion cell axons. Then, the greater distances travelled by regenerating axons could account for the longer time taken for their neurofilament compositions to mature.
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Affiliation(s)
- Y Zhao
- Department of Biological Sciences, State University of New York, Albany 12222
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24
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Burton PR, Wentz MA. Neurofilaments are prominent in bullfrog olfactory axons but are rarely seen in those of the tiger salamander, Ambystoma tigrinum. J Comp Neurol 1992; 317:396-406. [PMID: 1578003 DOI: 10.1002/cne.903170406] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Bullfrog olfactory axons show variable numbers (0-29) of structurally typical neurofilaments (NFs) about 10 nm in diameter. In studies tracking these NFs through serial sections of axons in cross section, they were found to be discontinuous, with a calculated average length of about 118 microns. In contrast to olfactory axons in bullfrogs, those of the tiger salamander Ambystoma trigrinum rarely show NFs. To be certain that the absence of NFs is a specific characteristic of olfactory axons, pieces of salamander spinal cord, optic nerve, and sciatic nerve were examined and found to contain typical NFs. To minimize the possibility that NFs in salamander olfactory axons were degraded or poorly fixed during preparation for electron microscopy, samples were fixed by using a variety of fixative and buffer combinations. To exclude the possibility that proteases degraded NFs during processing, prior to fixation some pieces of olfactory nerve were incubated in physiological saline containing protease inhibitors. Regardless of the preparation method, NFs were generally not seen in salamander olfactory axons. Extracts of salamander olfactory nerve were subjected to SDS-polyacrylamide gel electrophoresis (PAGE) and immunoblotting studies with monoclonal antibodies to the three NF subunit proteins. The immunoblots showed negligible or trace amounts of NF-L (light) and NF-H (heavy), while an NF-M (medium) protein having a molecular mass (Mr) of 160 kD was present in abundance. Extracts of salamander spinal cord, on the other hand, showed all three subunit proteins (with Mrs of 230, 160, and 77 kD). If one assumes that cells assemble structural elements to provide for a given function, the findings suggest that NFs in olfactory neurons of bullfrogs provide a function that may be missing in olfactory neurons of the salamander; the evidence also suggests that the absence of NFs in the salamander may be due to a deficiency in two of the three NF subunit proteins.
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Affiliation(s)
- P R Burton
- Department of Physiology and Cell Biology, University of Kansas, Lawrence 66045
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25
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Szaro B, Pant H, Way J, Battey J. Squid low molecular weight neurofilament proteins are a novel class of neurofilament protein. A nuclear lamin-like core and multiple distinct proteins formed by alternative RNA processing. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98582-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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26
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Szaro BG, Grant P, Lee VM, Gainer H. Inhibition of axonal development after injection of neurofilament antibodies into a Xenopus laevis embryo. J Comp Neurol 1991; 308:576-85. [PMID: 1865017 DOI: 10.1002/cne.903080406] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The ability to target specific cytoskeletal components in axons for disruption within intact developing embryos would provide a valuable tool for studying neuronal development. Neurofilaments are an attractive target for such an approach, because they are neuron specific and are expressed late in embryogenesis principally beginning during axon outgrowth. No pharmacological agents are currently available that disrupt neurofilaments without also affecting general development. One approach that has been used successfully to affect proteins in vivo is to inject specific antibodies into living cells. We employed this approach in Xenopus laevis embryos by injecting two antibodies directed against the middle molecular weight neurofilament protein (NF-M) into a single blastomere of a two-cell stage embryo. Injected antibodies could be detected for as long as 3.5 days in cells descended from the injected blastomere. Only cell bodies of neurons descended from anti-NF-M-injected blastomeres contained abnormal accumulations of intermediate filament proteins, and peripheral nerve development was unilaterally retarded in these neurofilament antibody-injected tadpoles. Such accumulations and peripheral nerve defects were not seen in neurons derived from uninjected blastomeres or from blastomeres injected with control antibodies. These data demonstrate the usefulness of specific antibodies to perturb neuronal development in intact frog embryos and, in addition, suggest a role for neurofilaments in axon elongation.
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Affiliation(s)
- B G Szaro
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
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27
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Szaro BG, Whitnall MH, Gainer H. Phosphorylation-dependent epitopes on neurofilament proteins and neurofilament densities differ in axons in the corticospinal and primary sensory dorsal column tracts in the rat spinal cord. J Comp Neurol 1990; 302:220-35. [PMID: 1705265 DOI: 10.1002/cne.903020204] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The highest molecular weight neurofilament protein (NF-H) is multiply phosphorylated at epitopes which can be distinguished by specific monoclonal antibodies on Western blots. Eight characterized antibodies were used in immunocytochemistry to examine the tissue distributions of phosphorylated variants of NF-H in axons of the adult rat spinal cord. The most striking difference in staining was found between axons in the cuneate tract and those in the neighboring dorsal corticospinal tract. Axons in the cuneate tract reacted intensely with antibodies to phosphorylated epitopes of NF-H and poorly with antibodies to dephosphorylated epitopes of NF-H, whereas the reverse was the case for the axons of the dorsal corticospinal tract. These differences showed that systematic variations in the phosphorylation of NF-H in long-tract axons in the central nervous system occur as a function of cell type. When the cytoskeletons of these axons were compared by electron microscopy, the neurofilaments of the cuneate fibers were seen to be more abundant and formed a latticework, more compactly organized than the neurofilaments of the dorsal corticospinal axons. By comparison, the dorsal corticospinal axons were relatively richer in microtubules than the cuneate axons. Although the cuneate fiber tract contained many more large (greater than 2.0 microns 2 in cross section) axons than did the dorsal corticospinal tract, these differences in cytoskeletal organization were apparent even when myelinated axons of similar sizes (0.4 micron 2 to 2.0 microns 2) were compared. In addition, the number of neurofilaments in cuneate axons in the 0.4 to 2.0 microns 2 size range was significantly better correlated with axon size than was the case for this size range of dorsal corticospinal axons. Thus, the differences seen in the organization of the neurofilament latticework and the phosphorylation of NF-H between axons found in these two tracts both appeared to be correlated with cell type, and were independent of length or caliber of the axons.
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Affiliation(s)
- B G Szaro
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
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28
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Tingstedt JE, Nielsen JB, Larsson LI. Characterization of MSH/ACTH-like immunoreactivity in sciatic nerves of Xenopus laevis by immunocytochemistry, western blotting and radioimmunoassay. HISTOCHEMISTRY 1990; 95:137-41. [PMID: 1964445 DOI: 10.1007/bf00266585] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Previous studies have indicated that rat neurofilament protein may contain an endogenous MSH-like epitope with neuroregenerative properties. The presence of such an epitope has now been studied in nerve tissue from Xenopus laevis. Western blot analyses of sciatic nerve tissue using an assortment of sequence-specific MSH/ACTH antisera revealed the presence of two major immunoreactive protein bands of 52 and 50 kDa, which contained a mid-region MSH-like epitope. Weaker staining occurred in another protein band at 135 kDa. Immunocytochemistry revealed the immunoreactivity to reside in the axis cylinders of the nerve fibers. Other antisera, recognizing other regions of MSH/ACTH produced strong staining of Xenopus intermediate lobes, but failed to stain sciatic nerves. Thus, the proteins detected have no clear relation to either Xenopus neurofilament proteins or proopiomelanocortin.
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Affiliation(s)
- J E Tingstedt
- Department of Molecular Cell Biology, State Serum Institute, Copenhagen, Denmark
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29
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Chu DT, Klymkowsky MW. The appearance of acetylated alpha-tubulin during early development and cellular differentiation in Xenopus. Dev Biol 1989; 136:104-17. [PMID: 2680681 DOI: 10.1016/0012-1606(89)90134-6] [Citation(s) in RCA: 124] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Early development in Xenopus is characterized by dramatic changes in the organization of the microtubule cytoskeleton. We have used whole-mount immunocytochemistry to follow the expression of the acetylated form of alpha-tubulin during early Xenopus development. In the egg and early embryo, the monoclonal anti-acetylated tubulin antibody 6-11B-1 stained meiotic and mitotic spindles, midbody microtubules, and what appears to be the central region of the sperm aster; the antibody did not stain the sperm aster itself or the cortical microtubule system associated with the rotation of the fertilized egg. Following gastrulation, acetylated tubulin disappeared from all but mitotic midbody microtubules. During the course of neurulation high levels of acetylated tubulin reappeared in the precursors of the ciliated epidermal cells (stage 15), transiently in neural folds (stage 16/17), in neuronal processes (stage 18/19), and in somas (stage 21). The changing pattern of anti-acetylated tubulin staining during Xenopus development raises intriguing questions as to the physiological significance of tubulin acetylation.
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Affiliation(s)
- D T Chu
- Molecular, Cellular, & Developmental Biology, University of Colorado, Boulder 80309-0347
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30
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Szaro BG, Lee VM, Gainer H. Spatial and temporal expression of phosphorylated and non-phosphorylated forms of neurofilament proteins in the developing nervous system of Xenopus laevis. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1989; 48:87-103. [PMID: 2502330 DOI: 10.1016/0165-3806(89)90095-3] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Immunocytochemical studies of developing Xenopus laevis embryos and tadpoles (stages 12 1/2 to 46) were performed using a panel of 11 monoclonal antibodies to phosphorylated and non-phosphorylated forms of the neurofilament proteins. These included nine antibodies to the middle molecular weight neurofilament protein (XNF-M, 175 kDa), and two additional antibodies to non-phosphorylated forms of the other two neurofilament proteins (XNF-L, 73 kDa; XNF-H, 205 kDa). The developmental expression of XNF-M, XNF-L and XNF-H, and the progressive phosphorylation of XNF-M in the rhombencephalon, spinal cord, and optic nerve were studied using these antibodies. In the spinal cord and rhombencephalon, non-phosphorylated forms of XNF-M were initially detected during neural tube stages (stages 22-26), one day before XNF-L and XNF-H at early tadpole stages (stage 35/36). In the eye, XNF-M was observed initially during tailbud stages (stage 29/30), but neither XNF-L nor XNF-H was seen even by stage 46 (swimming tadpole). The phosphorylation of XNF-M occurred over a protracted period of several days, both in the neural tube and visual system, and could be divided into four phases. (1) When initially expressed, XNF-M was hypophosphorylated. This was indicated by the early immunostaining of axons and cell bodies with antibodies to dephosphorylated epitopes on XNF-M and by the absence of staining with antibodies to phosphorylated epitopes. (2) After a short timelag (3-9 h) axons were stained by some, but not all antibodies to phosphorylated epitopes. (3) Approximately one day later, all antibodies to phosphorylated epitopes stained the relevant axons. However, XNF-M was not yet fully phosphorylated, as indicated by the continued staining of these axons with antibodies to dephosphorylated epitopes of XNF-M. (4) Two to 3 days after the initial expression of XNF-M, dephosphorylated epitopes disappeared from the axons, establishing the adult pattern. During development, the most heavily phosphorylated neurofilament proteins present at a given stage were found first in distal regions of the axons and progressed gradually toward the neuronal perikarya as development proceeded. This gradient of phosphorylation, established early within the axon, suggests that neurofilaments in the axons mature from their distal ends toward the cell body, a process which may be regulated by local factors within the axons themselves. The similarity of the basic features of NF-M phosphorylation in mammalian, avian, and amphibian axons underscores the importance of this phenomenon for the development of a mature axon.
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Affiliation(s)
- B G Szaro
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892
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31
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Oren N, Micevych PE, Letinsky MS. Presence of alpha-melanocyte-stimulating hormone-like immunoreactivity in the innervation of amphibian skeletal muscle. J Neurosci Res 1989; 23:225-33. [PMID: 2547085 DOI: 10.1002/jnr.490230213] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Amphibian motor nerve terminals are sensitive to a wide variety of peptides, including alpha-melanocyte-stimulating hormone (alpha-MSH). We determined the presence and distribution of alpha-MSH-like immunoreactivity (alpha-MSHLI) in the innervation of the cutaneous pectoris muscle from bullfrog (Rana catesbeiana) tadpoles and postmetamorphic froglets, and adult frogs (R. catesbeiana and R. pipiens). alpha-MSHLI was found in unmyelinated, noncholinergic axons, in motor axons, and in motor nerve terminals. In motor axons, alpha-MSHLI was predominantly associated with neurofilaments. The distribution of this form of alpha-MSHLI changed during development and seasonally in adult frogs. The possible functional roles of this alpha-MSHLI are discussed.
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Affiliation(s)
- N Oren
- Department of Physiology, University of California, Los Angeles 90024-1751
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