Profound morphological and functional changes of rodent Purkinje cells between the first and the second postnatal weeks: a metamorphosis?

Between the first and the second postnatal week, the development of rodent Purkinje cells is characterized by several profound transitions. Purkinje cells acquire their typical dendritic “espalier” tree morphology and form distal spines. During the first postnatal week, they are multi-innervated by climbing fibers and numerous collateral branches sprout from their axons, whereas from the second postnatal week, the regression of climbing fiber multi-innervation begins, and Purkinje cells become innervated by parallel fibers and inhibitory molecular layer interneurons. Furthermore, their periods of developmental cell death and ability to regenerate their axon stop and their axons become myelinated. Thus a Purkinje cell during the first postnatal week looks and functions differently from a Purkinje cell during the second postnatal week. These fundamental changes occur in parallel with a peak of circulating thyroid hormone in the mouse. All these features suggest to some extent an interesting analogy with amphibian metamorphosis

Improving patient involvement in the lifecycle of medicines : insights from the EUPATI BE survey

EUPATI Belgium (EUPATI.be) is an informal gathering of local partners who are interested in improving patient involvement in healthcare innovation and medicines research and development. EUPATI.be brings together various stakeholders from different areas related to healthcare including patients, academia and industry. In doing so, we create an innovative collaborative approach where actors from different backgrounds work toward improving patient involvement in medical research, and putting the patient at the center of the Belgian healthcare system. Previously, we performed in-depth interviews with a small group of stakeholders on patient involvement. Here, we elaborate on our previous findings by using a nation-wide survey to inquire into Belgian stakeholders' perception on patient involvement. To this end, an electronic survey was available in French, Dutch and English, and accessible for 11 months. Twelve questions were asked, including 11 multiple choice questions and 1 open question. The latter was thematically analyzed according to the framework method. A total of 117 responses were registered and descriptive statistics were performed. The majority of respondents could be categorized into patient, academia and industry, whereas policy makers, payers, and healthcare professionals were underrepresented. We identified several barriers that hamper patient involvement, which were sometimes more reported by specific stakeholder groups. Next, we found that various stakeholders still consider patient involvement as a passive role, i.e., medical subject in a clinical trial. Respondents also reported that the role of the various stakeholders needed more clarification; this was also confirmed by the level of trust amongst the various stakeholders. Existing and the wish for more collaboration with the various stakeholders was reported by almost all respondents. Based on this survey, we can define the potential of involving patients in the medical research and development in the Belgian landscape. Our results will help to understand and tackle the various barriers that currently hamper patient involvement, whilst highlighting the need for a collaborative landscape from the multi-stakeholder perspective

Induction of early Purkinje cell dendritic differentiation by thyroid hormone requires RORα

<p>Abstract</p> <p>Background</p> <p>The active form (T₃) of thyroid hormone (TH) controls critical aspects of cerebellar development, such as migration of postmitotic neurons and terminal dendritic differentiation of Purkinje cells. The effects of T₃on early dendritic differentiation are poorly understood.</p> <p>Results</p> <p>In this study, we have analyzed the influence of T₃on the progression of the early steps of Purkinje cell dendritic differentiation in postnatal day 0 organotypic cerebellar cultures. These steps include, successively, regression of immature neuritic processes, a stellate cell stage, and the extension of several long and mature perisomatic protrusions before the growth of the ultimate dendritic tree. We also studied the involvement of RORα, a nuclear receptor controlling early Purkinje cell dendritic differentiation. We show that T₃treatment leads to an accelerated progression of the early steps of dendritic differentiation in culture, together with an increased expression of RORα (mRNA and protein) in both Purkinje cells and interneurons. Finally, we show that T₃failed to promote early dendritic differentiation in <it>staggerer </it>RORα-deficient Purkinje cells.</p> <p>Conclusions</p> <p>Our results demonstrate that T₃action on the early Purkinje cell dendritic differentiation process is mediated by RORα.</p

Gene expression signature of cerebellar hypoplasia in a mouse model of Down syndrome during postnatal development

Background Down syndrome is a chromosomal disorder caused by the presence of three copies of chromosome 21. The mechanisms by which this aneuploidy produces the complex and variable phenotype observed in people with Down syndrome are still under discussion. Recent studies have demonstrated an increased transcript level of the three-copy genes with some dosage compensation or amplification for a subset of them. The impact of this gene dosage effect on the whole transcriptome is still debated and longitudinal studies assessing the variability among samples, tissues and developmental stages are needed. Results We thus designed a large scale gene expression study in mice (the Ts1Cje Down syndrome mouse model) in which we could measure the effects of trisomy 21 on a large number of samples (74 in total) in a tissue that is affected in Down syndrome (the cerebellum) and where we could quantify the defect during postnatal development in order to correlate gene expression changes to the phenotype observed. Statistical analysis of microarray data revealed a major gene dosage effect: for the three-copy genes as well as for a 2 Mb segment from mouse chromosome 12 that we show for the first time as being deleted in the Ts1Cje mice. This gene dosage effect impacts moderately on the expression of euploid genes (2.4 to 7.5% differentially expressed). Only 13 genes were significantly dysregulated in Ts1Cje mice at all four postnatal development stages studied from birth to 10 days after birth, and among them are 6 three-copy genes. The decrease in granule cell proliferation demonstrated in newborn Ts1Cje cerebellum was correlated with a major gene dosage effect on the transcriptome in dissected cerebellar external granule cell layer. Conclusion High throughput gene expression analysis in the cerebellum of a large number of samples of Ts1Cje and euploid mice has revealed a prevailing gene dosage effect on triplicated genes. Moreover using an enriched cell population that is thought responsible for the cerebellar hypoplasia in Down syndrome, a global destabilization of gene expression was not detected. Altogether these results strongly suggest that the three-copy genes are directly responsible for the phenotype present in cerebellum. We provide here a short list of candidate genes

Expression of X-chromosome linked inhibitor of apoptosis protein in mature purkinje cells and in retinal bipolar cells in transgenic mice induces neurodegeneration

Transgenic mice with overexpression of the caspase-inhibitor, X-chromosome-linked inhibitor of apoptosis protein (XIAP) in Purkinje cell (PC) and in retinal bipolar cells (RBCs) were produced to study the regulation of cell death. Unexpectedly, an increased neurodegeneration was observed in the PCs in these L7-XIAP mice after the third postnatal week with the mice exhibiting severe ataxia. The loss of PCs was independent of Bax as shown by crossing the L7-XIAP mice with Bax gene–deleted mice. Electron microscopy revealed intact organelles in PCs but with the stacking of ER cisterns indicative of cell stress. Immunostaining for cell death proteins showed an increased phosphorylation of c-Jun in the PCs, suggesting an involvement in cell degeneration. Apart from PCs, the number of RBCs was decreased in adult retina in line with the expression pattern for the L7 promoter. The data show that overexpression of the anti-apoptotic protein XIAP in vulnerable neurons leads to enhanced cell death. The mechanisms underlying this neurodegeneration can be related to the effects of XIAP on cell stress and altered cell signaling.Supported by Sigrid Juselius Foundation, Academy of Finland, EU Biotech Grant, Liv och Hälsa, Maud Kuistila, Ylppö Foundation, Uppsala University and Minerva Foundation. We thank Dr. Urmas Arumäe for discussions, and Dr. Patrik Ernfors for the Bax KO mice, and Eeva Lehto for technical assistance. L7AUG was a kind gift from Dr. J. Oberdick, Ohio State University, USA.Peer reviewe

Intrinsic versus extrinsic determinants during the development of Purkinje cell dendrites

The peculiar shape and disposition of Purkinje cell (PC) dendrites, planar and highly branched, offers an optimal model to analyze cellular and molecular regulators for the acquisition of neuronal dendritic trees. During the first 2 weeks after the end of the proliferation period, PCs undergo a 2-phase remodeling process of their dendrites. The first phase consists in the complete retraction of the primitive but extensive dendritic tree, together with the formation of multiple filopodia-like processes arising from the cell body. In the second phase, there is a progressive disappearance of the somatic processes along with rapid growth and branching of the mature dendrite. Mature Purkinje cell dendrites bear two types of spiny protrusions, named spine and thorn. The spines are numerous, elongated, located at the distal dendritic compartment and form synapses with parallel fibers, whereas the thorns are shorter, rounded, emerge from the proximal compartment and synapse with climbing fibers. Different culture models and mutant mice analyses suggest the identification of intrinsic versus extrinsic determinants of the Purkinje cell dendritic development. The early phase of dendritic remodeling might be cell autonomous and regulated by specific transcription factors such as retinoid-related orphan receptor alpha (RORalpha). Afferent fibers, trophic factors and hormones regulate the orientation and growth of the mature dendritic tree contributing, with still unknown intrinsic factors, to sculpt its general architecture. The formation of spines appears as an intrinsic phenomenon independent of their presynaptic partner, the parallel fibers, and confined to the distal compartment by inhibitory influences of the climbing fibers along the proximal compartment.C.S. was supported by the Spanish Ministry of Education and Science, grant BFU2008-00588/BFI. I.D. was supported by CNRS, UPMC and ANR-07-NEURO-043-01.Peer reviewe

Identification des facteurs de transcription dont l'expression est régulée au cours de la maturation des cellules de Purkinje (rôle de Klf9 dans la survie cellulaire et le développement dendritique)

Au cours des 10 premiers jours de vie postnatale (P0-P10), les cellules de Purkinje de souris passent par une période de mort développpementale et subissent une régression puis une croissance dendritique. Afin de sélectionner des candidats susceptibles de contrôler l arrêt de la mort développementale ou la maturation dendritique, nous avons cherché les facteurs de transcription dont l expression varie entre P0 et P10. L analyse de transcriptomes de cortex cérébelleux à différents a ges, puis la validation de l expression des gènes candidats par différentes techniques, nous a permis de sélectionner 1 facteur de transcription dont l expression augmente : Klf9 (Krüppel like facteur). En culture organotypique de cervelet, l expression précoce de Klf9 par transduction lentivirale augmente la survie des cellules de Purkinje transduites, tandis que son inhibition par expression lentivirale de shARN la diminue. La diminution de cette survie peut être supprimée par ajout d IGF1, un facteur trophique des cellules de Purkinje. Le nombre de cellules de Purkinje diminue également dans le cervelet de souris Klf9-/- mis en culture organotypique. Ainsi, l expression de Klf9 est nécessaire et suffisante à la survie des cellules de Purkinje en culture organotypique, suggérant un rôle de ce facteur dans l arrêt de la mort développementale de ces neurones. Notre étude a permis également de montrer l induction de la rétraction des dendrites primaires et de la formation des épines des cellules de Purkinje suite à l expression précoce de Klf9. Ainsi, ce facteur intervient également dans le développement dendritique et la formation des épines des cellules de PurkinjePARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Interactions neurone-glie dans la mise en place de la cicatrice gliale après lésion traumatique du système nerveux central

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Régénération axonale et développement des oligodendrocytes dans le cervelet

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF