The Zinc Finger Protein Nolz1 is Required for Striatal Development and Axon Guidance of Forebrain Tracts

The transcriptional regulator Nolz1 is expressed in the developing mouse brain within the striatum, diencephalon and midbrain. This thesis reports the characterisation of Nolz1 expressing cells within these regions during the development of both the mouse and human embryo. Parallel to this, mouse ESCs were differentiated into midbrain dopamine neurons and Nolz1 over-expression was induced in order to identify potential genes under the transcriptional control of Nolz1. The expression patterns lead to hypotheses on the function of Nolz1 in the development of these areas. Hypothesis 1: Nolz1 controls the specification of VTA subtypes. Hypothesis 2: Nolz1 controls the expression of axon guidance molecules in the ventral hypothalamus. Hypothesis 3: Nolz1 represses the expression of striatopallidal genes which allows the expression of striatonigral genes. Through the analysis of a constitutive Nolz1-/- mouse, hypothesis 1 and 2 are both found to be untrue, whilst hypothesis 3 is found to be correct and further to this, Nolz1’s role in the axon guidance of both the medial forebrain bundle (particularly midbrain dopaminergic neurons) and the thalamocortical tract is explained. Finally, in order to further evidence hypothesis 3, different conditional Cre lines were produced to remove Nolz1 expression from each of the three regions of interest: Foxg1-Cre from the striatum, FoxD1-Cre from the diencephalon, and Engrailed-Cre from the midbrain. Only the ablation of Nolz1 from the striatum produces the same phenotype as the constitutive knock-out. Parallel to this, a Nolz1-/- mouse ESC line was produced using CRISPR-Cas9. When these cells were differentiated into striatal neurons the same gene changes found in the Nolz1-/- embryos were found. These results are intriguing as they show how signals from the striatum itself can be responsible for guiding the dopamine neurons of the medial forebrain bundle towards the telencephalon and not signals from the midline as much of the literature would suggest.