NUBP2 deficiency disrupts the centrosome-check point in the brain and causes primary microcephaly

Microcephaly affects 1 in 2,500 babies per year. Primary microcephaly results from aberrant neurogenesis leading to a small brain at birth. This is due to altered patterns of proliferation and/or early differentiation of neurons. Premature differentiation of neurons is associated with defects in the centrosome and/or primary cilia. In this study, we report on the first patients identified with NUBP2 -deficiency and utilize a conditional mouse model to ascertain the molecular mechanisms associated with NUBP2 -deficient primary microcephaly. We identified homozygous NUBP2 variants in these patients who displayed profound primary microcephaly in addition to intrauterine growth restriction, cervical kyphosis, severe contractures of joints, and facial dysmorphia. We then generated a mouse model using Emx1-Cre to ablate Nubp2 from the forebrain. The mice presented with severe microcephaly starting at E18.5. Neurospheres generated from the forebrain of Emx1-Cre; Nubp2 ^flox/flox conditional deletion mice were used to support the pathogenicity of the patient variants. We show that loss of Nubp2 increases both canonical and non-canonical cell death, but that loss of p53 fails to rescue microcephaly in the mouse model. Examination of neurogenesis in Emx1-Cre; Nubp2 ^flox/flox mice revealed distinct alterations in proliferation and cellular migration accompanied by supernumerary centrosomes and cilia. We therefore propose that NUBP2 is a novel primary microcephaly-related gene and that the role of Nubp2 in centrosome and cilia regulation is crucial for proper neurogenesis.