Funktionelle Analyse des Transkriptionsfaktors Uncx4.1 im murinen Mittelhirn

Abstract

The development of the brain is a complex process, which involves a lot of finely regulated processes. The best known disease which is associated with the midbrain is morbus parkinson. In the last years a lot of effort was done to identify new transcription factors involved in midbrain development. Uncx4.1 is a transcription factor, which is known to be expressed in the somites, the kidney and the central nervous system (CNS) of the mouse embryo. Although its expression starts early on at embryonic day 9.5 (E 9.5) in the mouse mesencephalon, so far a functional study in this brain area is missing. Its function was until now only analyzed in the somites, parts of the forebrain and in the olfactory bulb. The present study shows the first functional study of Uncx4.1 in the mouse midbrain. The results demonstrate, that in the midbrain Uncx4.1 is nearly exclusively expressed in postmitotic neurons and that its expression is not restricted to a specific neuronal fate. It was detected in dopaminergic, GABAergic and glutamatergic neurons of the midbrain. Its expression in the transition zone of mitotic and postmitotic neurons point out the possibility, that Uncx4.1 is important during neuronal differentiation. Furthermore this work identified Uncx4.1 as a new factor in the regulatory network of midbrain dopaminergic neuron generation. This work show, that the number of midbrain dopaminergic neurons (mDA) is partially reduced in the substantia nigra (SN) and the ventral tegmental area (VTA) of Uncx4.1-knockout embryos. The co-localization of Uncx4.1 with Tyrosine Hydroxylase (TH) at E 11.5 suggests a role of Uncx4.1 during mDA neuronal differentiation, potentially by regulating the expression of Ngn2 . Beside this, the populations of GABAergic and glutamatergic neurons in Uncx4.1-knockout midbrain were analyzed. While the loss of Uncx4.1 has no effect on the population of midbrain GABAergic neurons, Uncx4.1 seems to act during differentiation of midbrain glutamatergic neuron subgroups. Uncx4.1-deficient midbrain display an increased number of Pax6-positive glutamatergic neurons at E 13.5. Besides the function of Uncx4.1 during midbrain neurogenesis it could be demonstrated in this thesis that Uncx4.1 plays a role during axonal development in the superior colliculus. The axons of the superior colliculus in Uncx4.1-deficient embryos are shorter than in wildtype animals. Moreover a marker analysis revealed different expression patterns in mutant and wildtype embryos. It is possible that the observed defects are due to the loss of Ngn2-mRNA in this region. To summarize, this work identified Uncx4.1 as a new player in mDA neuron differentiation. In general the present study support the idea that Uncx4.1 plays a general role during neuronal differentiation. To know in which molecular pathway Uncx4.1 acts could be an interesting topic for further studies.