Novel lissencephaly-associated NDEL1 variant reveals distinct roles of NDE1 and NDEL1 in nucleokinesis and human cortical malformations.

The development of the cerebral cortex involves a series of dynamic events, including cell proliferation and migration, which rely on the motor protein dynein and its regulators NDE1 and NDEL1. While the loss of function in NDE1 leads to microcephaly-related malformations of cortical development (MCDs), NDEL1 variants have not been detected in MCD patients. Here, we identified two patients with pachygyria, with or without subcortical band heterotopia (SBH), carrying the same de novo somatic mosaic NDEL1 variant, p.Arg105Pro (p.R105P). Through single-cell RNA sequencing and spatial transcriptomic analysis, we observed complementary expression of Nde1/NDE1 and Ndel1/NDEL1 in neural progenitors and post-mitotic neurons, respectively. Ndel1 knockdown by in utero electroporation resulted in impaired neuronal migration, a phenotype that could not be rescued by p.R105P. Remarkably, p.R105P expression alone strongly disrupted neuronal migration, increased the length of the leading process, and impaired nucleus-centrosome coupling, suggesting a failure in nucleokinesis. Mechanistically, p.R105P disrupted NDEL1 binding to the dynein regulator LIS1. This study identifies the first lissencephaly-associated NDEL1 variant and sheds light on the distinct roles of NDE1 and NDEL1 in nucleokinesis and MCD pathogenesis.

A lissencephaly-associated BAIAP2 variant causes defects in neuronal migration during brain development.

Lissencephaly is a neurodevelopmental disorder characterized by a loss of brain surface convolutions caused by genetic variants that disrupt neuronal migration. However, the genetic origins of the disorder remain unidentified in nearly one-fifth of people with lissencephaly. Using whole-exome sequencing, we identified a de novo BAIAP2 variant, p.Arg29Trp, in an individual with lissencephaly with a posterior more severe than anterior (P>A) gradient, implicating BAIAP2 as a potential lissencephaly gene. Spatial transcriptome analysis in the developing mouse cortex revealed that Baiap2 is expressed in the cortical plate and intermediate zone in an anterior low to posterior high gradient. We next used in utero electroporation to explore the effects of the Baiap2 variant in the developing mouse cortex. We found that Baiap2 knockdown caused abnormalities in neuronal migration, morphogenesis and differentiation. Expression of the p.Arg29Trp variant failed to rescue the migration defect, suggesting a loss-of-function effect. Mechanistically, the variant interfered with the ability of BAIAP2 to localize to the cell membrane. These results suggest that the functions of BAIAP2 in the cytoskeleton, cell morphogenesis and migration are important for cortical development and for the pathogenesis of lissencephaly in humans.