ZFP423, a transcription factor implicated in Joubert Syndrome and Cerebellar Vermis Hypoplasia, orchestrates the pace and mode of cerebellar neurogenesis

Abstract

Neurogenesis is a tightly regulated process, both in the embryonic and in the adult brain. Its success depends on the ability of a germinative epithelium to establish the appropriate balance between maintaining an undifferentiated progenitor pool and giving birth to sequential generations of neurons and glia. The Zfp423 gene encodes a 30 Zn-finger transcription factor (TF) which interacts with the SMAD1- SMAD4 complex (BMP signaling), Notch intracellular domain, retinoic acid receptors and Collier/Olf-1/EBF TFs. This gene has been previosly implicated in cerebellar development. Mutations in the human ortholog ZNF423 have been identified in patients carrying cerebellar vermis hypoplasia (CVH) or Joubert Syndrome (JS), and/ or exhibiting other signs of ciliopathy outside the central nervous system. We have been analyzing two mouse mutant lines carrying allelic in-frame deletions of Zfp423. One of them lacks Zn-finger domains 9-20 (Δ9-20), implicated in BMP and Notch signal transduction, while the other lacks a C-terminal domain (Δ28-30). Both mutants exhibit cerebellar malformations and severe ataxia. However, our results indicate that the two protein domains play sharply distinct roles in the context of cerebellar neurogenesis. In Zfp423Δ9-20/Δ9-20 mutants, GABAergic Purkinje cell (PC) neurogenesis is impaired and the PC progenitor pool in the ventricular zone is precociously depleted. Conversely, Zfp423Δ28-30/Δ28-30 mutants display a selective impairment in the development of glutamatergic cerebellar neurons.