EH004: Lmx1a encodes a rostral set of mesodiencephalic dopaminergic neurons marked by the Wnt/b-catenin signaling activator Rspo2

Recent developments in molecular programming of mesodiencephalic dopaminergic (mdDA) neurons have led to the identification of many transcription factors playing a role in mdDA specification. LIM homeodomain transcription factor Lmx1a is essential for chick mdDA development, and for the efficient differentiation of ES-cells towards a dopaminergic phenotype. In this study, we aimed towards a more detailed understanding of the subtle phenotype in Lmx1a-dr/dr mice. Therefore, microarray analysis was performed, to elucidate the exact molecular programming underlying the neuronal deficits after loss of Lmx1a. Subsequent expression analysis confirmed that Nurr1 is regulated by Lmx1a, and additional downstream targets were identified, like Pou4f1, Pbx1, Pitx2, C130021l20Rik, Calb2 and Rspo2. In line with a specific, rostral-lateral loss of expression of most of these genes during development, Nurr1 and C130021l20Rik were affected in the SNc of the mature mdDA system. Interestingly, this deficit was marked by the complete loss of the Wnt/b-catenin signaling activator Rspo2 in this domain. Expression analysis in Rspo2-/- embryos revealed affected mdDA neurons, partially phenocopying the Lmx1a mutant. Together, in this study we reveal that Lmx1a is essential for a rostral-lateral subset of the mdDA neuronal field, where it might serve a critical function in modulating proliferation and differentiation of mdDA progenitors through the activation of the Wnt activator Rspo2. Microarray expression study comparing 4 samples of homozygous LMX1A dr/dr mice, midbrain E12.5 with a pooled sample of their wt/wt littermates. Two samples were analyzed in opposite dye orientation.