Neurodevelopmental Genetics Group - Research Focus

 

Background

To understand the relationship between genetically defined precursor groups and the neurons in the adult brain that arise from these precursors we are focusing on the generation of midbrain dopaminergic neurons. Midbrain dopaminergic neurons regulate movement and emotion and are selectively lost in neurodegenerative disorders such as Parkinson’s disease. Midbrain dopaminergic neurons are organized into specific clusters, including the ventral tegmental area (VTA) and substantia nigra (SN). In the adult, these neurons innervate diverse forebrain targets and have distinct molecular identities. We are interested in understanding the molecular mechanisms that direct dopaminergic neuron subset specification during development, how these neurons then segregate into discrete nuclei and ultimately how target innervation is specified.

 

The role of Sonic Hedgehog signaling in specification of midbrain dopaminergic neurons in vivo

The secreted morphogen Sonic Hedgehog (Shh) is required for dopaminergic neuron induction. In the absence of Shh signaling, midbrain dopaminergic neurons are not generated during embryonic development. It is unclear, however, whether Shh signaling also plays a role in the initial specification of midbrain dopaminergic neuron subsets. We are using a novel mosaic gene inactivation and fate mapping approach that allows us to inactivate Shh signaling in only a small subset of cells at a chosen time point. Using this system, we can then follow the fate of these cells throughout their life time. This will provide a detailed temporal and cellular insight into the role of Shh in the initial specification of dopaminergic neuron subclass identity.

 

The molecular code that directs substantia nigra (SN) or ventral tegmental area (VTA) identity during embryonic development

Our aim is to determine the molecular identity (gene expression profile) of SN or VTA dopaminergic neuron precursors. This information will allow us to understand the pathways and molecules that are required for the formation of the SN and VTA clusters and how specific SN or VTA projections to the forebrain are specified. Genetic inducible fate mapping (in vivo lineage tracing) in the mouse allows us to label the distinct precursor subsets before they are spatially segregated. This gives us the possibility to isolate SN and VTA subsets during embryonic development and to identify their gene expression profiles using microarrays. These will likely yield transcription factors that distinguish SN versus VTA neurons as well as cell surface receptors that regulate segregation (e.g. through cell adhesion) and axonal pathfinding of the two subpopulations. Moreover, identification of specific molecular identities of these subpopulation could provide insight into the selective vulnerability of SN dopaminergic neurons in Parkinson’s diseases.

 

Determine the influence of target innervation on SN and VTA formation

Dopaminergic neuron projections reach their forebrain targets shortly after they begin to differentiate and likely before they are fully segregated into distinct nuclei. This raises the possibility that target innervation feeds back to influence nucleus assembly. We are analyzing mice in which the target areas of SN and/or VTA neurons are altered but in which the specification of dopaminergic neurons remains intact. We will determine how changes in target innervation affect dopaminergic neuron segregation in these mutant mice and investigate the underlying molecular mechanisms.

A better understanding of the mechanisms underlying diversification of dopaminergic neurons will provide important insight into how the VTA and SN are formed and will add to our understanding of why dopaminergic neurons of the SN are selectively susceptible to cell death in Parkinson’s disease. In addition, elucidating the molecular code that determines dopaminergic neuron differentiation in vivo is a prerequisite for the successful differentiation of embryonic or neural stem cells into midbrain dopaminergic neurons for cell replacement strategies in Parkinson’s disease.

 

Methods and Techniques of the Neurodevelopmental Genetics group:

Mouse Models: Transgenes, conditional gene inactivation, mosaic gene inactivation, genetic inducible fate mapping.

Histology: Paraffin- and Cryosectioning, RNA in situ hybridization, Immunohistochemistry.

Molecular biology: PCR, RNA and DNA analysis, protein analysis, gene cloning and sequencing.

Cell culture: Brain explant cultures.

Biophotonics: Fluorescence microscopy, stereology, fluorescence live imaging.