Anders Bäckström

Expression of neurotrophins and trk receptors in the avian retina.

Using the RNase protection assay, we have found that nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), and neurotrophin‐3 (NT‐3) are expressed in the avian retina during development. The expression peaks around embryonic days 12–15, with decreasing levels at later stages of development. Abundant levels of NGF and BDNF but low levels of NT‐3 mRNA were found in the adult retina. We also found that light/darkness regulated the levels of NGF and BDNF mRNAs but not the levels of NT‐3 mRNA in the 5‐day‐old chicken retina. It was demonstrated that NGF and BDNF mRNA levels were up‐regulated by light exposure. The cellular localization of mRNA expression for the neurotrophins and neurotrophin receptors TrkA, TrkB, and TrkC in the retina was studied using in situ hybridization. The patterns of NGF and trkA mRNA expression were very similar and were localized to the external part of the inner nuclear layer on the border with the outer plexiform layer and corresponded to the localization of horizontal cells. NT‐3 labeling was also found over the external part of the inner nuclear layer, whereas trkC mRNA was found over all layers in the retina. BDNF labeling was found over all layers in the retina, whereas TrkB labeling was intense over cells in the ganglion cell layer, which is in agreement with the response of ganglion cells to BDNF stimulation. Functional neurotrophin receptors were suggested by the response of retinal explants to neurotrophin stimulation. These data indicate that the neurotrophins play local roles in the retina that involve interactions between specific neuronal populations, which were identified by the localization of the Trk receptor expression. The data also suggest that NGF and BDNF expression is regulated by normal neuron usage in the retina.

Molecular cloning and cellular localization of trk C in the chicken embryo

Abstract Degenerate primers directed against conserved regions of the trk and trk B amino acid sequences were used in the polymerase chain reaction to isolate a 455 by fragment from embryonic day 3 chicken cDNA encoding the trk C. This fragment was subsequently used to synthesize an anti-sense trk C cRNA probe which was used in a RNase protection assay of total RNA from chicken embryos. trk C mRNA was found in the E2 embryo with increasing levels later in development. In the E9 embryo highest levels were found in brain and spinal cord with intermediate levels in eye, heart, gut and muscle. Low levels were found in kidney, liver, skin and yolk sac. Using the 455 bp trk C fragment as a probe in RNA blot analyses of poly A + RNA, a major transcript of 6.3 kb and two minor transcripts of 3 kb and 10 kb were found. In situ hybridization was performed on embryos taken at three stages of development (embryonic day 3, 9 and 19), using a 48-mer antisense oligonucleotide probe for chicken trk C. Within the sensory nervous system trk C mRNA expression at all ages was confined to the ventrolateral neurons of the spinal sensory and trigeminal ganglia as well as distal ganglia associated with the VIIth, IXth and Xth cranial nerves. Labelling for trk C mRNA was also observed within the developing CNS at E3 and the ganglion of Remak at E19. A barely detectable level of expression was observed in the sympathetic chain and no labelling was evident in the proximal ganglia of the cranial nerves. These results suggest that neurons have a very early capacity to respond to neurotrophin-3 which continues throughout embryonic development. The early expression of trk C mRNA was also support the growing evidence suggesting a role for neurotrophins in neuronal differentiation.

Retinoic Acid-Mediated Increase in TrkA Expression Is Sufficient to Elicit NGF-Dependent Survival of Sympathetic Neurons

Sympathetic neurons depend on the classical neurotrophin NGF for survival by the time they innervate their targets, but the mechanisms controlling the onset of NGF responsiveness in developing neuroblasts have not been defined. Immature chick sympathetic neurons are unresponsive to NGF, but express low mRNA levels of the high-affinity NGF receptor trkA. Treatment with retinoic acid (RA) leads to increased levels of both trkA mRNA and protein, a response mediated through retinoic acid receptor alpha (RAR alpha). Ectopic expression of trkA in these cells results in the ability to survive with NGF, suggesting that RA-induced trkA expression is sufficient to elicit NGF-dependent survival. Our data establish a mechanism controlling NGF responsiveness and implicate a function for RA at defined late stages of neuron development.

Developmentally Regulated Expression of mRNA for Neurotrophin High-Affinity (trk) Receptors within Chick Trigeminal Sensory Neurons

To investigate the distribution of neurons within the developing trigeminal sensory system which express mRNA for each of the three known high‐affinity neurotrophin receptors (trk, trkB and trkC), we have performed in situ hybridization histochemistry on serial sections through the trigeminal ganglion and trigeminal mesencephalic nucleus at various ages of development using specific antisense oligonucleotide probes. We show that trkC mRNA is first expressed in the chicken embryo at stage 13, in presumptive neurons prior to the formation of the ganglion, that trkB mRNA labelling is initially observed within peripheral neurons slightly later, at stage 19, and that trk mRNA expression is not detectable until around embryonic day 3.5 (stage 21/22). The neurons which exhibit mRNA labelling for each of the high‐affinity receptors occupy discrete regions within the ganglion, indicating that the ganglion comprises distinct neuronal subpopulations, each of which has a different capacity to respond to the different neurotrophins. Neurons which express trk mRNA are confined to the proximal region of the ganglion, whereas those which express trkB mRNA and trkC mRNA are located in two distinct regions within the distal aspect and also within the trigeminal mesencephalic nucleus. From the estimation of the number of neurons which exhibit labelling between embryonic days 9 and 18, we determined that the expression of mRNA for the high‐affinity receptors changes during embryonic development of the ganglion. This is consistent with the observed differences in the response to neurotrophins in vitro.

Molecular cloning of the chicken trkA and its expression in early peripheral ganglia

The neurotrophin tyrosine kinase receptors trkA, trkB, and trkC have been isolated and sequenced from several mammalian species. Their cognate ligands nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin‐4 (NT‐4), and neurotrophin‐3 (NT‐3) act as survival and trophic factors for neurons in the peripheral nervous system (PNS). In this study we have focused on the isolation and expression of the chicken trkA homologue. In addition to a near full‐length cDNA sequence described, including an extracellular six amino‐acid motif earlier found in neuronal TrkA in human and rat, a novel insert of 150 base pairs (bp) between subdomains IX and X in the otherwise well‐conserved intracellular kinase domain is reported. Phylogenetic analysis showed the relationship between chicken trkA and the mammalian trkA receptors. Comparisons of the extracellular domains showed some amino‐acid motifs of putative NGF binding function to be well conserved in chicken TrkA. The early expression of trkA mRNA, including the alternatively spliced insert form, was localized by in situ hybridization. As early as embryonal day 3 (E3), trkA mRNA is expressed in the condensing dorsal root ganglia, and at E4 distinct trkA mRNA expression appears in the primary sympathetic chain ganglia. Finally, using a reverse transcriptase‐polymerase chain reaction (RT‐PCR) approach, we found that among several tested growth factors only fibroblast growth factor‐2 (FGF‐2) upregulated trkA mRNA expression in E9 sympathetic ganglion explants. This upregulation of trkA was corroborated by subsequent NGF‐stimulated fiber outgrowth.

Molecular cloning and characterisation of a mouse gene encoding an isoform of the neuronal cyclin-dependent kinase 5 (CDK5) activator

We have isolated and characterised the mouse gene for the p39 activator, designated p39is, which encodes a protein of 369 amino acids. The mouse p39 protein exhibits 95% amino acid identity to a previously characterised human p39 cDNA and the novel gene sequence corresponds to a single genomic locus in mouse. The p39is mRNA is highly expressed in the mouse central nervous system.

Cloning of a new chicken TRKC extracellular isoform and its mRNA expression in E9 sensory and autonomic ganglia

Neuronal development and maintenance are regulated by trophic interactions with the target tissues and the innervating nerve. The neurotrophin family of polypeptide growth factors, consisting of nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3) and neurotrophin‐4/5 (NT‐4/5), are produced in limited amounts in target areas. They bind to tyrosine receptor kinases of the trk family, including trkA, trkB and trkC, which mediate intracellular signalling in the responding neurons. There are reports of different isoforms of trkA, trkB and trkC having different signalling capacities. This study reports a novel deletion of the first cysteine‐rich domain in the extracellular part of chicken trkC. We describe the mRNA expression of this isoform compared to non‐deleted forms in E9 peripheral ganglia studied by reversetranscriptase‐polymerase chain reaction (RT‐PCR) and in situ hybridization. We also compare the mRNA expression pattern of two existing signal peptide sequences and the distribution of trkC mRNA detected by the use of a kinase specific probe. The results show that the novel isoform is expressed in peripheral sensory and autonomic ganglia. Moreover both signal peptide forms are detected in these ganglia by RT‐PCR. In addition, in situ hybridization results showed a weak mRNA expression of the novel isoform in the E9 dorsal root ganglion (DRG) but not in Remaks ganglion. The two existing signal peptides are equally expressed in the DRG and Remaks ganglion, at labelling densities comparable to those for the full‐length catalytic form of trkC.

Religion on the Political Agenda

This chapter asks whether the growing religious diversity has implied a shift in the role of religion in Nordic political opinions and debates. The analysis shows continued links between individual religiosity and political party preferences, although people in Denmark, Norway, and Sweden have become more tolerant toward religious minorities. In political party platforms, Christianity and the majority churches are still used as references to national identity. There is a growing invocation of religion in parliamentary debates. Especially issues that are related to Islam and human rights have increased. Religion has become more diversified and contested in Nordic politics since the 1980s. The findings suggest a politicization of religion in a process of renegotiating social and cultural identities and values.

Embryonic Expression of Neurotrophin Trk Receptor mRNAs Within Sensory Neurons: Chicken Development as a Model

Publisher Summary The neurons of the chick sensory ganglia are derived from cells originating from two distinct regions of the ectoderm, the neural crest and the epidermal placodes. Cell labeling and chimeric embryo studies have determined that the neural crest gives rise to cells that differentiate to form neurons of the dorsal root, dorsomedial trigeminal, and jugular/superior ganglia. On the other hand, the neurons of the ventrolateral trigeminal, geniculate, vestibuloacoustic, petrosal, and nodose are derived from cells originating from the various placodes. Many studies have been undertaken to investigate the specificity of dependence of sensory neuronal populations on the different neurotrophic factors. The first reported study of the effects of nerve growth factor (NGF) on the neural crest-derived spinal sensory ganglion indicated that not all neurons were responsive to NGF. However, subsequent conflicting evidence led to the belief that NGF dependence within sensory neurons could be correlated with developmental origin in that the neurons derived from the neural crest responded to NGF and the ones that were placode derived were NGF independent. This chapter discusses NGF dependence within sensory neurons, the response of the trigeminal ganglion explanted at different ages of embryonic development and cultured in vitro in the presence of NGF, brain-derived neurotrophic factor and NT-3, the receptor mRNA expression and possible early effects, and the neurotrophin dependence and embryonic origin.

To change by education. On stability and development in theological university studies

Gives an overview of the results from the major study on stability and change of students attitudes in higer theological education in Sweden.