Behavioral and molecular effects of Ubtf knockout and knockdown in mice

Abstract

The UBTF E210K neuroregression syndrome is caused by de novo dominant mutations in UBTF (NM_014233.3:c.628G > A, p.Glu210Lys). In humans, onset is typically at 2.5 to 3 years and characterized by slow progression of global motor, cognitive and behavioral dysfunction. Other potentially pathogenic UBTF variants have been reported in humans with severe neurological disease and it remains undetermined if the UBTF E210K mutation operates via gain- and/or loss-of-function. Here we examine the behavioral, cognitive, motor, and molecular effects of Ubtf knockout and knockdown in mice as a means of gauging the role of loss-of-function in humans. Ubtf^+/- mice show progression of behavioral (dominance tube), cognitive (cross maze), and mild motor abnormalities from 3 to 18 months. At 18 months, Ubtf^+/- mice had more slips on a raised 9-mm round beam task, shorter latencies to fall on the accelerated rotarod, reduced open field vertical and jump counts, and significant deficits in spatial learning and memory. Via crosses to Nestin-Cre (Nes^Cre) mice we found that homozygous Ubtf deletion limited to the central nervous system was embryonic lethal. Tamoxifen-induced homozygous knockdown of Ubtf in adult mice with the Cre-ERT2 system was associated with precipitous deterioration in neurological functioning. At the molecular level, 18-month-old Ubtf^+/- mice showed mild increases in cerebellar 53BP1 immunoreactivity. These findings show that UBTF is essential for embryogenesis and survival in adults, and the deleterious effects of UBTF haploinsufficiency progress with age. Loss-of-function mechanisms may contribute, in part, to the human UBTF E210K neuroregression syndrome.

Keywords: Mouse; Neuroregression; Nucleolus; UBTF; rRNA.

Fig. 1.

Repeated measures analysis of vertical rope climbing in 74 mice (A), weight normalized vertical rope climbing in 74 mice (B), 12 mm raised round beam task in 72 mice (C), 9 mm raised round beam task in 72 mice (D), weight normalized grip strength in 74 mice (E), accelerating rotarod in 68 mice (F), cross maze analysis in 71 mice (G), and tube dominance in 78 mice (H). *, adjusted P < 0.05 Šídák’s multiple comparisons test

Fig. 2.

Cerebellar 53BP1 immunoreactivity (green) in cerebellar cortex from Ubtf^+/+ (N = 3) and Ubtf^+/− (N = 3) mice. Calbindin immunoreactivity (red) is used to label Purkinje cells and define the layers of cerebellar cortex. Nuclei are labeled with DAPI. Graph shows percentages of 53BP1-positive (+ve) cells. Scale bar, 100 μm.