EURON and THEME joint PhD meeting

51
EURON and THEME joint meeting 2011
The role of primary cilia in the development of
dopaminergic neurons in the murine ventral midbrain
Mary Gazea 1 , Christian Gojak 2 , Julia Franzen 2 , Kerry L. Tucker 2 and Sandra
Blaess 1
1 Neurodevelopmental Genetics, Institute of Reconstructive Neurobiology, Life and Brain Center, University
of Bonn, Sigmund-Freud-Str. 25, 53127 Bonn; 2 Interdisciplinary Center for Neurosciences and Department
of Anatomy, University of Heidelberg, 69120 Heidelberg, Germany.
Midbrain dopaminergic (DA) neurons develop from the ventral midbrain floor
plate. Sonic Hedgehog (Shh) signaling, which is mediated by the Gli zinc finger
transcription factors Gli2 and Gli3, is essential for DA progenitor induction.
Studies in spinal cord and forebrain have demonstrated that Shh signaling occurs
in primary cilia and that Gli2 and Gli3 are not functional in absence of primary
cilia. To assess whether primary cilia are important for Shh signaling in ventral
midbrain development, we analyzed DA neuron development in cobblestone (cbs)
mutants. Cbs mutants have reduced levels of the intraflagellar transport protein
88 (Ift88) resulting in defects in ciliary function and in Shh signaling. Analysis of
the developing ventral midbrain showed that the number of DA neurons and
progenitors was severely reduced compared to wild-type. Interestingly, this
phenotype was less severe than in mutants with inactivated Shh signaling. To
investigate whether the mild phenotype in cbs mutants is due to residual Ift88
function, we generated conditional knock-out (cko) mice in which the Ift88
allele was inactivated in the midbrain after E8.5 (about a day after the onset of
Shh signaling) and compared them with mutants with a conditional deletion of
Gli2 and Gli3 (Gli2/Gli3 cko). In Ift88 cko midbrain, primary cilia were reduced
innumber and deformed and Shh signaling appeared to be abolished. Ift88 cko
had a smaller DA progenitor domain and the number of DA neurons was reduced
by more than 50%. DA neurons and progenitors were also reduced in Gli2/3
cko embryos, but the reduction was more severe than in Ift88 cko mutants. In
summary, our data show that Ift88 plays an important role in the induction of
ventral midbrain DA neurons, likely by maintaining functional primary cilia and
consequently normal levels of Shh signaling.