Funktionelle Analyse des Transkriptionsfaktors Pitx3 während der Entwicklung dopaminerger Neuronen im murinen Mittelhirn

Abstract

The transcription factor PITX3 is expressed only in postmitotic mDA neurons of the midbrain and shows a complete co-expression of TH in the VTA and the SN. At a loss to PITX3 expression (aphakia mouse) the mDA neurons of the VTA show almost no change, while not develop the neurons of the SN. The reasons for this are unclear. The aim of the present study was to analyze the role PITX3 plays during the neurogenesis of mDA, and for that, PITX3 was specifically overexpressed in the murine midbrain. These are the first results of an in vivo PITX3 overexpression studie in mice and the results can be compiled almost as follows: • Expression of TH, DAT and Nurr1-positive cells in the medial region of the dopaminergic area, from which the VTA arises, was significantly increased in all mutants (Shh-Cre + / Pitx3OE, Foxa2-Cre + / Pitx, Wnt1-Cre + / Pitx3OE and En1-Cre + / Pitx3OE). This phenotype was evident the most in the Wnt1-Cre + / Pitx3OE mutants. • At E12.5, the expression of Lmx1a and Lmx1b is significantly increased in all mutants in the VZ. • In the Wnt1-Cre + / Pitx3OE mutants, at E12.5 there was a strong ectopic Wnt1 expression in the areas of the VZ and SVZ. Furthermore, the proliferation rate (BrdU, Ki67) was increased at the same time where a reduction of neurogenesis (Ngn2) was observed. In the areas of ectopic Wnt1 expression an inhibition of Shh expression was detected at E12.5. • At E12.5 an ectopic Wnt1 expression was observed at the Wnt1-Cre+/Lmx1aOE and the Wnt1-Cre+/Lmx1bOE mutants in the areas in which Lmx1a/b was conditionally overexpressed. The results revealed a strong reduction of TH and PITX3 expression that could be probably caused by a malfunction of the IsO. In general it can be concluded that PITX3 is not only involved in the differentiation, but also in processes of coordination of proliferation and specification in the sense of maintaining the area and the delineation of alternative mDA neuronal cell fates. Here PITX3 probably indirectly affects the canonical Wnt signaling pathway by forming a feedback loop with Lmx1a and / or Lmx1b, or an intermediate factor.