Current Research

Generation of cell diversity in the sympathoadrenal cell lineage of the neural crest

The neural crest (NC) gives rise to different types of neurons, glial, endocrine, and mesenchymal cells and, hence, is an excellent model for exploring mechanisms underlying the generation of cell diversity. We focus on neuroendocrine (chromaffin) derivatives of the NC (see Fig. 1). We have shown that, contrary to a classic hypothesis, glucocorticoid hormones and adrenal cortical cells are not required for most aspects of chromaffin cell differentiation [1, 2]. Currently, we study the role of BMP-4 and its receptors in the induction of chromaffin cell fate and differentiation. BMP-4 is an essential factor for inducing a catecholaminergic phenotype in NC cells. It is secreted by cells in the wall of the dorsal aorta and surrounding mesenchyme, rapidly downregulated in sympathetic ganglionic anlagen, but persistent in adrenal cortical cells [7]. This raised the question whether BMP-4 might be important in the induction and differentiation of the chromaffin phenotype. In a series of loss- and gain-of-function experiments in chick embryos we found that BMP-4 did not switch neuronal to chromaffin cell fate, but significantly promoted further differentiation  of chromaffin cells.By GFP electroporation into neural tube and NC cells we try to analyze the temporal sequence of delamination of distinct progenitor subpopulations. Preliminary results suggest that the vast majority of single NC cells can give rise to both, sympathetic neurons and neuroendocrine chromaffin cells.

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Fig. 1. In situ hybridisation showing TH mRNA (red) in adrenal chromaffin cells and BMP4 mRNA (blue) in adrenal cortical cells of an E9 chick embryo

Development of a CNS-peripheral nervous system circuitry

Neurons located in the lateral spinal cord and in the brainstem link the central and peripheral portions of the autonomic nervous system. These neurons innervate peripheral autonomic ganglia and chromaffin cells. Their trophic regulation is not well understood. We have recently discovered that cardiotrophin-1 and the LIFRß are crucial for the postnatal maintenance of this neuron population [3]. By comparing neurons of the pre-and paravertebral sympathetic ganglia we found marked differences, as e.g. in NGF dependence. It is possible that prevertebral in contrast to paravertebral ganglia receive a second neurotrophic signal from their innervation targets (enteric nervous system and gut). If so, neurons in the prevertebral ganglia should, in addition to trkA, express a further neurotrophic factor receptor. To test this, we currently started an in situ hybridization analysis using different probes for trophic factor receptors (e.g. neurotrophin receptors and GFR-α receptors).

Neuron survival and the roles of ERK

A classic perception of the molecular bases of neuron death implies ERK as an important regulator of neuron survival. We have now found that ERK has also a key role in promoting neuronal death of cerebellar granule cells induced by K+ withdrawal [4, 5]. Specifically, neuronal death mediated by plasma membrane damage is accompanied by a late and sustained activation of ERK. Inhibition of ERK activation results in a dramatic reduction of neuron death. Classic growth factors, as e.g. IGF-1, induce an early and transient ERK activation (15 min to 2h), and also abrogate the appearance of late and sustained ERK (6 to 24h) suggesting that IGF-1 can positively and negatively regulate the ERK pathway [4].

Functions of a novel TGF-ß in neuronal development and maintenance

GDF-15 is a novel distant member of the TGF-ßs, originally identified as a potent trophic factor for midbrain dopaminergic neurons. We have generated a GDF-15 knockout mouse, which exhibits motoneuron and neural stem cell phenotypes. There is a progressive postnatal loss of hindbrain and spinal cord motoneurons from 3 to 6 months of age resulting in an approx. 20% deficit. In addition, mutant mice have revealed hypermyelination of axons and increased expression of myelin proteins. This would be consistent with Schwann cells as a source and a role of GDF-15 in regulating myelination. However, mechanisms underlying motoneuron death still remain to be explored. Neural stem cells (NSC) express high levels of GDF-15 mRNA, and GDF-15 KO mice have less EGFR expressing NSC that wt mice. Details of GDF-15 functions in NSC proliferation and differentiation are currently under investigation.

TrkB and trkC neurotrophin receptors: spine morphology and dopamine neurons

Current analyses of adult and aged heterozygous trkB and trkC mice as well as of young adult conditional CamKIItrkB knockout mice have revealed the importance of these receptors for the maintenance of dendritic spine numbers and dendritic spine morphology in the hippocampal field CA1 [6]. These analyses of adult and aged heterozygous trkB and trkC mice also showed that these receptors are crucially important for the maintenance of the dopaminergic nigrostriatal system in aged mice. The aged heterozygous knockout mice showed a reduction in the number of dopaminergic neurons in the substantia nigra (SN). This was accompanied by a massive accumulation of alpha-synuclein in the remaining neurons of the SN (Fig. 2), underscoring the significance of trk mediated signaling for preventing degeneration and death of this neuron population.

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Fig 2 . Alpha-synuclein accumulating neurons in the SNpc of an aged trkB/C(+/-)/(+/-) mouse (cell nuclei are stained in blue by DAPI; alpha-synuclein immunoreactivity is shown in red).


[1] Finotto, S., et al. (1999) Development 126, 2935 – 2944
[2] Gut, P., et al. (2005) Development 132, 4611 – 4619
[3] Oberle, S., et al (2006) J. Neurosci. 26, 1823 - 1832
[4] Subramaniam, S., et al. (2004) J. Cell Biol. 165, 357 – 369
[5] Subramaniam, S., et al. (2005) J. Neurosci. 25, 2838 – 2852
[6] von Bohlen und Halbach, O., et al. (2006) Biol. Psychiatry. 59, 793-800
[7] Huber, K., et al. (2008) Neural Dev 3, 28

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Latest Revision: 2012-09-11
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