Bodea, Gabriela O; McKelvey, Eleanor G Z; Faulkner, Geoffrey J
Retrotransposon-induced mosaicism in the neural genome (Journal Article)
In: Open Biology, 8 (7), pp. 180074, 2018, ISSN: 2046-2441.
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Over the past decade, major discoveries in retrotransposon biology have depicted the neural genome as a dynamic structure during life. In particular, the retrotransposon LINE-1 (L1) has been shown to be transcribed and mobilized in the brain. Retrotransposition in the developing brain, as well as during adult neurogenesis, provides a milieu in which neural diversity can arise. Dysregulation of retrotransposon activity may also contribute to neurological disease. Here, we review recent reports of retrotransposon activity in the brain, and discuss the temporal nature of retrotransposition and its regulation in neural cells in response to stimuli. We also put forward hypotheses regarding the significance of retrotransposons for brain development and neurological function, and consider the potential implications of this phenomenon for neuropsychiatric and neurodegenerative conditions.
Richardson, Sandra R; Gerdes, Patricia; Gerhardt, Daniel J; Sanchez-Luque, Francisco J; Bodea, Gabriela-Oana; noz-Lopez, Martin Mu; Jesuadian, Samuel J; Kempen, Marie-Jeanne H C; Carreira, Patricia E; Jeddeloh, Jeffrey A; Garcia-Perez, Jose L; Jr, Haig H Kazazian; Ewing, Adam D; Faulkner, Geoffrey J
In: Genome Res., 27 (8), pp. 1395–1405, 2017.
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LINE-1 (L1) retrotransposons are a noted source of genetic
diversity and disease in mammals. To expand its genomic
footprint, L1 must mobilize in cells that will contribute
their genetic material to subsequent generations. Heritable L1
insertions may therefore arise in germ cells and in
pluripotent embryonic cells, prior to germline specification,
yet the frequency and predominant developmental timing of such
events remain unclear. Here, we applied mouse retrotransposon
capture sequencing (mRC-seq) and whole-genome sequencing (WGS)
to pedigrees of C57BL/6J animals, and uncovered an L1
insertion rate of $geq$1 event per eight births. We traced
heritable L1 insertions to pluripotent embryonic cells and,
strikingly, to early primordial germ cells (PGCs). New L1
insertions bore structural hallmarks of target-site primed
reverse transcription (TPRT) and mobilized efficiently in a
cultured cell retrotransposition assay. Together, our results
highlight the rate and evolutionary impact of heritable L1
retrotransposition and reveal retrotransposition-mediated
genomic diversification as a fundamental property of
pluripotent embryonic cells in vivo.
Kempen, Marie-Jeanne H C; Bodea, Gabriela O; Faulkner, Geoffrey J
In: Human Retrotransposons in Health and Disease, pp. 107–125, Springer, Cham, 2017.
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The neuronal genome has long been considered as a stably
persisting entity interpreted as the foundation of neurobiology.
Over the past decade, it has become increasingly clear that
mobile genetic elements, such as the retrotransposon LINE-1
(L1), are actively transcribed and transpose in the healthy
brain. L1 activity therefore provides a route to somatic genome
diversity and dynamism in neuronal populations. Here, we discuss
the discovery of L1 retrotransposition during neurogenesis, and
consider how neuronal cells regulate retrotransposition in
response to endogenous and environmental stimuli. We also bring
forward hypotheses relating to how L1 impacts normal brain
development and function, as well as how abnormal L1
mobilisation could contribute to neurological disease
susceptibility and pathophysiology.
Upton, Kyle R; Gerhardt, Daniel J; Jesuadian, Samuel J; Richardson, Sandra R; Sánchez-Luque, Francisco J; Bodea, Gabriela O; Ewing, Adam D; Salvador-Palomeque, Carmen; van der Knaap, Marjo S; Brennan, Paul M; Vanderver, Adeline; Faulkner, Geoffrey J
Ubiquitous L1 mosaicism in hippocampal neurons (Journal Article)
In: Cell, 161 (2), pp. 228–239, 2015.
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Somatic LINE-1 (L1) retrotransposition during neurogenesis is
a potential source of genotypic variation among neurons. As a
neurogenic niche, the hippocampus supports pronounced L1
activity. However, the basal parameters and biological impact
of L1-driven mosaicism remain unclear. Here, we performed
single-cell retrotransposon capture sequencing (RC-seq) on
individual human hippocampal neurons and glia, as well as
cortical neurons. An estimated 13.7 somatic L1 insertions
occurred per hippocampal neuron and carried the sequence
hallmarks of target-primed reverse transcription. Notably,
hippocampal neuron L1 insertions were specifically enriched in
transcribed neuronal stem cell enhancers and hippocampus
genes, increasing their probability of functional relevance.
In addition, bias against intronic L1 insertions sense
oriented relative to their host gene was observed, perhaps
indicating moderate selection against this configuration in
vivo. These experiments demonstrate pervasive L1 mosaicism at
genomic loci expressed in hippocampal neurons.
Bodea, Gabriela O; Blaess, Sandra
Establishing diversity in the dopaminergic system (Journal Article)
In: FEBS letters, 589 (24 Pt A), pp. 3773–3785, 2015, ISSN: 1873-3468.
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Midbrain dopaminergic neurons (MbDNs) modulate cognitive processes, regulate voluntary movement, and encode reward prediction errors and aversive stimuli. While the degeneration of MbDNs underlies the motor defects in Parkinson's disease, imbalances in dopamine levels are associated with neuropsychiatric disorders such as depression, schizophrenia and substance abuse. In recent years, progress has been made in understanding how MbDNs, which constitute a relatively small neuronal population in the brain, can contribute to such diverse functions and dysfunctions. In particular, important insights have been gained regarding the distinct molecular, neurochemical and network properties of MbDNs. How this diversity of MbDNs is established during brain development is only starting to be unraveled. In this review, we summarize the current knowledge on the diversity in MbDN progenitors and differentiated MbDNs in the developing rodent brain. We discuss the signaling pathways, transcription factors and transmembrane receptors that contribute to setting up these diverse MbDN subpopulations. A better insight into the processes that establish diversity in MbDNs will ultimately improve the understanding of the architecture and function of the dopaminergic system in the adult brain.
Bodea, Gabriela Oana; Spille, Jan-Hendrik; Abe, Philipp; Andersson, Aycan Senturk; Acker-Palmer, Amparo; Stumm, Ralf; Kubitscheck, Ulrich; Blaess, Sandra
In: Development (Cambridge, England), 141 (3), pp. 661–673, 2014, ISSN: 1477-9129.
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The proper functioning of the dopaminergic system requires the coordinated formation of projections extending from dopaminergic neurons in the substantia nigra (SN), ventral tegmental area (VTA) and retrorubral field to a wide array of forebrain targets including the striatum, nucleus accumbens and prefrontal cortex. The mechanisms controlling the assembly of these distinct dopaminergic cell clusters are not well understood. Here, we have investigated in detail the migratory behavior of dopaminergic neurons giving rise to either the SN or the medial VTA using genetic inducible fate mapping, ultramicroscopy, time-lapse imaging, slice culture and analysis of mouse mutants. We demonstrate that neurons destined for the SN migrate first radially and then tangentially, whereas neurons destined for the medial VTA undergo primarily radial migration. We show that tangentially migrating dopaminergic neurons express the components of the reelin signaling pathway, whereas dopaminergic neurons in their initial, radial migration phase express CXC chemokine receptor 4 (CXCR4), the receptor for the chemokine CXC motif ligand 12 (CXCL12). Perturbation of reelin signaling interferes with the speed and orientation of tangentially, but not radially, migrating dopaminergic neurons and results in severe defects in the formation of the SN. By contrast, CXCR4/CXCL12 signaling modulates the initial migration of dopaminergic neurons. With this study, we provide the first molecular and functional characterization of the distinct migratory pathways taken by dopaminergic neurons destined for SN and VTA, and uncover mechanisms that regulate different migratory behaviors of dopaminergic neurons.
Barry, David; Roque, Hélio; Dumoux, Maud; Kriston-Vizi, Janos; Bodea, Gabriela O; Harper, Callista
Meeting report - imaging in cell biology: where next? (Journal Article)
In: Journal of Cell Science, 126 (Pt 1), pp. 43–44, 2013, ISSN: 1477-9137.
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Bodea, Gabriela Oana; Blaess, Sandra
In: Journal of Visualized Experiments: JoVE, (59), pp. e3350, 2012, ISSN: 1940-087X.
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The mouse is an excellent model organism to study mammalian brain development due to the abundance of molecular and genetic data. However, the developing mouse brain is not suitable for easy manipulation and imaging in vivo since the mouse embryo is inaccessible and opaque. Organotypic slice cultures of embryonic brains are therefore widely used to study murine brain development in vitro. Ex-vivo manipulation or the use of transgenic mice allows the modification of gene expression so that subpopulations of neuronal or glial cells can be labeled with fluorescent proteins. The behavior of labeled cells can then be observed using time-lapse imaging. Time-lapse imaging has been particularly successful for studying cell behaviors that underlie the development of the cerebral cortex at late embryonic stages (1-2). Embryonic organotypic slice culture systems in brain regions outside of the forebrain are less well established. Therefore, the wealth of time-lapse imaging data describing neuronal cell migration is restricted to the forebrain (3,4). It is still not known, whether the principles discovered for the dorsal brain hold true for ventral brain areas. In the ventral brain, neurons are organized in neuronal clusters rather than layers and they often have to undergo complicated migratory trajectories to reach their final position. The ventral midbrain is not only a good model system for ventral brain development, but also contains neuronal populations such as dopaminergic neurons that are relevant in disease processes. While the function and degeneration of dopaminergic neurons has been investigated in great detail in the adult and ageing brain, little is known about the behavior of these neurons during their differentiation and migration phase (5). We describe here the generation of slice cultures from the embryonic day (E) 12.5 mouse ventral midbrain. These slice cultures are potentially suitable for monitoring dopaminergic neuron development over several days in vitro. We highlight the critical steps in generating brain slices at these early stages of embryonic development and discuss the conditions necessary for maintaining normal development of dopaminergic neurons in vitro. We also present results from time lapse imaging experiments. In these experiments, ventral midbrain precursors (including dopaminergic precursors) and their descendants were labeled in a mosaic manner using a Cre/loxP based inducible fate mapping system (6).
Dinu, Diana; Bodea, Gabriela Oana; Ceapa, Corina Diana; Munteanu, Maria Cristina; Roming, Florentina Israel; Serban, Andreea Iren; Hermenean, Anca; Costache, Marieta; Zarnescu, Otilia; Dinischiotu, Anca
In: Toxicon: Official Journal of the International Society on Toxinology, 57 (7-8), pp. 1023–1032, 2011, ISSN: 1879-3150.
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The mycotoxin deoxynivalenol (DON), a contaminant of certain foods and feeds, is cytotoxic and genotoxic to mammalians cells. Exposure of human embryonic kidney (Hek-293) cells to DON led to a dose- and time-dependent decrease in cell viability, with an IC(50) about 7.6 μM. The DON effects on Hek-293 morphology, reactive oxygen species, lipid peroxidation and antioxidative system and caspase 3 and bcl-2 expression were studied. Cells became round and in some are progressive loss of cell attachment appeared. These biochemical parameters were assessed after 6, 12 and 24 h of treatment with 2.5 and 5 μM DON. An increase in superoxide dismutase activity within the interval 6-12 h and almost complete recovery by the end of experiment for both concentrations was observed, whereas the profile of catalase activity was the same with the superoxide dismutase one for 2.5 μM and decreased in a time-dependent manner for 5 μM. A temporary activation of glutathione peroxidase and glutathione reductase was recorded at 12 h post-exposure, while the glutathione-S-transferase activity was unchanged for both concentrations. The NADP(+)-dependent isocitrate dehydrogenase activity showed a transient increase at the 12 h post-exposure. The caspase 3 expression remained unchanged and the bcl-2 one decreased after 24 h of exposure for the two concentrations. Our results showed the dose- and time specific changes in the antioxidants system of Hek-293 cells, which could not counteract efficiently the effects DON exposure. The different types of cell death which could be activated by this DON induced changes are mentioned.
Blaess, Sandra; Bodea, Gabriela O; Kabanova, Anna; Chanet, Soline; Mugniery, Emilie; Derouiche, Amin; Stephen, Daniel; Joyner, Alexandra L
In: Neural Development, 6 , pp. 29, 2011, ISSN: 1749-8104.
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BACKGROUND: The ventral midbrain contains a diverse array of neurons, including dopaminergic neurons of the ventral tegmental area (VTA) and substantia nigra (SN) and neurons of the red nucleus (RN). Dopaminergic and RN neurons have been shown to arise from ventral mesencephalic precursors that express Sonic Hedgehog (Shh). However, Shh expression, which is initially confined to the mesencephalic ventral midline, expands laterally and is then downregulated in the ventral midline. In contrast, expression of the Hedgehog target gene Gli1 initiates in the ventral midline prior to Shh expression, but after the onset of Shh expression it is expressed in precursors lateral to Shh-positive cells. Given these dynamic gene expression patterns, Shh and Gli1 expression could delineate different progenitor populations at distinct embryonic time points.
RESULTS: We employed genetic inducible fate mapping (GIFM) to investigate whether precursors that express Shh (Shh-GIFM) or transduce Shh signaling (Gli1-GIFM) at different time points give rise to different ventral midbrain cell types. We find that precursors restricted to the ventral midline are labeled at embryonic day (E)7.5 with Gli1-GIFM, and with Shh-GIFM at E8.5. These precursors give rise to all subtypes of midbrain dopaminergic neurons and the anterior RN. A broader domain of progenitors that includes the ventral midline is marked with Gli1-GIFM at E8.5 and with Shh-GIFM at E9.5; these fate-mapped cells also contribute to all midbrain dopaminergic subtypes and to the entire RN. In contrast, a lateral progenitor domain that is labeled with Gli1-GIFM at E9.5 and with Shh-GIFM at E11.5 has a markedly reduced potential to give rise to the RN and to SN dopaminergic neurons, and preferentially gives rise to the ventral-medial VTA. In addition, cells derived from Shh- and Gli1-expressing progenitors located outside of the ventral midline give rise to astrocytes.
CONCLUSIONS: We define a ventral midbrain precursor map based on the timing of Gli1 and Shh expression, and suggest that the diversity of midbrain dopaminergic neurons is at least partially determined during their precursor stage when their medial-lateral position, differential gene expression and the time when they leave the ventricular zone influence their fate decisions.
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