Showing papers by "Urban Lendahl published in 1997"

An evolutionarily conserved region in the second intron of the human nestin gene directs gene expression to CNS progenitor cells and to early neural crest cells

Abstract: Central nervous system (CNS) progenitor cells transiently proliferate in the embryonic neural tube and give rise to neurons and glial cells. A characteristic feature of the CNS progenitor cells is expression of the intermediate filament nestin and it was previously shown that the rat nestin second intron functions as an enhancer, directing gene expression to CNS progenitor cells. In this report we characterize the nestin enhancer in further detail. Cloning and sequence analysis of the rat and human nestin second introns revealed local domains of high sequence similarity in the 3' portion of the introns. Transgenic mice were generated with the most conserved 714 bp in the 3' portion of the intron, or with the complete, 1852 bp, human second intron, coupled to the reporter gene lacZ. The two constructs gave a very similar nestin-like expression pattern, indicating that the important control elements reside in the 714 bp element. Expression was observed starting in embryonic day (E)7.5 neural plate, and at E10.5 CNS progenitor cells throughout the neural tube expressed lacZ. At E12.5, lacZ expression was more restricted and confined to proliferating regions in the neural tube. An interesting difference, compared to the rat nestin second intron, was that the human intron at E10.5 mediated lacZ expression also in early migrating neural crest cells, which is a site of endogenous nestin expression. In conclusion, these data show that a relatively short, evolutionarily conserved region is sufficient to control gene expression in CNS progenitor cells, but that the same region differs between rodents and primates in its capacity to control expression in neural crest cells.

Adult Nestin‐expressing Subependymal Cells Differentiate to Astrocytes in Response to Brain Injury

Abstract: The adult brain contains a small population of central nervous system (CNS) cells in the subependyma which, like embryonic CNS progenitor cells, express the intermediate filament nestin. In this report, the differentiation capacity in vivo of these cells was analysed following a standardized trauma. Before the trauma, the subependymal cells expressed nestin but not the astrocytic and neuronal differentiation markers glial fibrillary acidic protein (GFAP) and neurofilament respectively. In response to injury, the majority of the subependymal cells coexpressed nestin and GFAP, but never nestin and neurofilament. Furthermore, cells coexpressing nestin and GFAP were found progressively further away from the subependyma and closer to the lesion at later time points after the injury, indicating that these cells migrate towards the lesion. Nestin was in addition re-expressed in reactive astrocytes near the lesion and in non-reactive astrocytes very far from the lesion throughout the ipsilateral cortex. In conclusion, our data indicate that the nestin-positive subependymal cells are an in vivo source for the generation of new astrocytes but not neurons after injury, and that nestin re-expression in astrocytes following traumatic stimuli can be used as a sensitive marker for astroglial activation.

Mouse Serrate-1 (Jagged-1): expression in the developing tooth is regulated by epithelial-mesenchymal interactions and fibroblast growth factor-4.

Abstract: Serrate-like genes encode transmembrane ligands to Notch receptors and control cell fate decisions during development. In this report, we analyse the regulation of the mouse Serrate-1 gene during embryogenesis. The Serrate-1 gene is expressed from embryonic day 7.5 (E7.5) and expression is often observed at sites of epithelial-mesenchymal interactions, including the developing tooth, where Serrate-1 is first (E11.5) expressed in all cells of the dental epithelium, but not in mesenchyme. A transient upregulation in dental mesenchyme (E12.5-15.5) is correlated with down-regulation of Serrate-1 expression in epithelial cells contacting the mesenchyme, i.e. in the cells destined to become ameloblasts. This expression pattern is reproduced in explants of dental epithelium and mesenchyme in vitro: epithelium induces Serrate-1 expression in mesenchyme, while epithelium in close proximity to this mesenchyme does not express detectable levels of Serrate-1 mRNA, suggesting that down-regulation of Serrate-1 expression in preameloblasts is caused by mesenchyme-derived signals. Finally, regulation of Serrate-1 expression differs from that of Notch genes. The Serrate-1 gene is induced in dental mesenchyme by fibroblast growth factor-4, but not by bone morphogenetic proteins, while the converse is true for Notch genes. This indicates that, at least during tooth development, the expression patterns observed for receptors and ligands in the Notch signaling pathway are generated by different induction mechanisms.

Transgenic analysis of central nervous system development and regeneration.

Abstract: The transgenic technique allows specific genetic alterations to be made in all cells of an animal and this has greatly improved our understanding of how the embryonic and adult central nervous system (CNS) develop. The CNS originates from the neuroectoderm in the neural plate on the dorsal side of the embryo and after closure of the neural tube the cells of the neuroepithelium, i.e. the CNS stem cells, transiently proliferate to generate neurons and glial cells. Here we review our attempts to gain insights into the control of CNS development. We have identified a gene, nestin, which is predominantly expressed in embryonic and adult CNS stem cells. In addition to its normal expression in the CNS stem cells, nestin is reexpressed in CNS tumors and in the adult spinal cord and brain after CNS injury. By using the lacZ reporter gene assay in transgenic mice, we have identified regulatory regions (enhancer) in the nestin gene required for expression in embryonic CNS stem cells and in the adult spinal cord after injury. In a second project, we have cloned and characterized the Notch gene family (the Notch 1, 2 and 3 genes) in mouse and man. These genes encode transmembrane receptors, which appear to be key regulatory molecules for proliferation and differentaition both in the developing CNS and in other tissues. Expression of an activated form of the Notch 3 receptor from the nestin promoter in transgenic mice leads to a lethal, exencephaly-like phenotype in the embryo, probably as a result of excess proliferation of the CNS stem cells. The recent finding that the Notch 3 gene is the genetic cause for familial stroke is discussed in the context of current models for Notch function.

Limb proprioceptive deficits without neuronal loss in transgenic mice overexpressing neurotrophin-3 in the developing nervous system

Abstract: The role of neurotrophin-3 (NT3) during sensory neuron development was investigated in transgenic mice overexpressing NT3 under the control of the promoter and enhancer regions of the nestin gene, an intermediate filament gene widely expressed in the developing nervous system. Most of these mice died during the first postnatal day, and all showed severe limb ataxia suggestive of limb proprioceptive dysfunction. Tracing and histological analyses revealed a complete loss of spindles in limb muscles, absence of peripheral and central Ia projections, and lack of cells immunoreactive to parvalbumin in the dorsal root ganglion (DRG). Despite these deficits, there was no neuronal loss in the DRG of these mice. At birth, transgenic DRG showed increased neuron numbers, and displayed a normal proportion of neurons expressing substance P, calcitonin gene-related peptide and the NT3 receptor trkC. Transgenic dorsal roots exhibited an increased number of axons at birth, indicating that all sensory neurons in transgenic mice projected to the dorsal spinal cord. Despite the absence of central Ia afferents reaching motorneurons, several sensory fibers were seen projecting towards ectopic high levels of NT3 in the midline of transgenic spinal cords. These findings suggest novel roles for NT3 in differentiation of proprioceptive neurons, target invasion and formation of Ia projections which are independent from its effects on neuronal survival.

Gene regulation in the formation of the central nervous system

Abstract: In this review recent advances in our understanding of the genetic control of central nervous system development will be discussed. Stem and/or progenitor cells in the neuroepithelium of the neural tube differentiate into neurons and glial cells in the brain and spinal cord. There is an emerging picture of how key regulatory genes act to control various steps in this differentiation pathway, including organization along the anterio-posterior and dorso-ventral body axes. Examples from our own research on nestin and Notch genes will also be presented. It is our hope that information about the biology of these genes may shed light on the nature of the central nervous system stem cell and its developmental decisions.