Suppressor of fused controls cerebellar neuronal differentiation in a manner modulated by GLI3 repressor and Fgf15.

BACKGROUND: Deficiency of Suppressor of Fused (SuFu), an intracellular mediator of Hedgehog signaling, in the murine mid-hindbrain disrupts cerebellar morphogenesis and cell differentiation in a manner that is rescued by constitutive expression of GLI3 transcriptional repressor (GLI3R). Here, we determined SuFu functions in cerebellar radial precursors following the stage of mid-hindbrain specification using a Blbp-Cre transgene. RESULTS: SuFu-deficient cerebella were severely dysplastic, and characterized by laminar disorganization, and delayed differentiation of ventricular zone-derived precursors. In vitro analysis of cerebellar precursors isolated from control and mutant mice demonstrated an increased proportion of radial glial precursors vs. Tuj1-positive neurons in mutant cultures. Abnormal cell differentiation in SuFu-deficient precursors was rescued by a constitutively expressed GLI3R knock-in allele, albeit with variable penetrance. Using RNA expression analysis in control and SuFu-deficient cerebellar anlage, we identified up-regulation of Fgf15 in mutant tissue. Strikingly, exogenous hFGF19, a mFGF15 ortholog, inhibited neuronal differentiation in cultures of wild-type cerebellar precursors. Moreover, siRNA-mediated knockdown of Fgf15 in SuFu-deficient cerebellar precursors rescued their delayed differentiation to neurons. CONCLUSIONS: Together, our results show that SuFu promotes cerebellar radial precursor differentiation to neurons. SuFu function is mediated in part by GLI3R and down-regulation of Fgf15 expression. Developmental Dynamics 247:156-169, 2018. © 2017 Wiley Periodicals, Inc.