Anastasia S. Chvileva

The Notch signaling pathway is a critical regulator of embryonic brain development. Among its four mammalian receptors, Notch1 and Notch2 are particularly significant in the developing cortex, yet their roles in human neurodevelopment are not well understood. In murine cortex development, Notch1 primarily regulates early progenitor identity and neurogenesis, while Notch2 is required for maintaining radial glial cells at later stages. However, it is unclear whether these functions are conserved in the human developing brain. In this study, we used cerebral organoids as an in vitro model of early human corticogenesis and conducted lentiviral shRNA-mediated knockdowns of NOTCH1 and NOTCH2. Our findings indicate that NOTCH1 is essential for organoid growth, lumen morphogenesis, radial glial identity, and progenitor proliferation. In contrast, depleting NOTCH2 did not significantly affect these early developmental processes. These results demonstrate that NOTCH1 and NOTCH2 have potentially non-redundant and temporally distinct roles in early human corticogenesis, reflecting receptor-specific specialization within the Notch signaling pathway.

Many structural features of the human brain emerged during evolution as a result of large-scale changes in the molecular genetic mechanisms that control the development of this organ. One of the key genetic alterations involves mutations in regulatory regions of the human genome, which can change the spatiotemporal expression patterns of early developmental genes. This suggestion is supported by the recent discovery of DNA sequences that evolved rapidly in humans, known as human accelerated regions (HARs). These regions are predominantly noncoding and are located near genes involved in human embryonic development and genes expressed in the central nervous system. Most HARs are involved in the regulation of gene expression associated with human brain development, and mutations in them may be linked to the development of such diseases as schizophrenia, autism spectrum disorder, and Simpson-Golabi-Behmel syndrome. One such gene is CNTN6, in which HAR sequences within introns have been identified and found to be deleted due to structural rearrangements in many patients with neuropsychiatric developmental disorders. To study the role of HARs of the CNTN6 gene in the development of the human nervous system, we generated two human induced pluripotent stem cell (iPSC) lines with a homozygous deletion of one of the HARs in the CNTN6 gene (HARsv2_1748) using CRISPR/Cas9 genome-editing technology. The HARsv2_1748 deletion was confirmed by PCR genotyping and Sanger sequencing. Human iPSC lines have normal karyotype, express markers of pluripotency, and are able to spontaneously differentiate into derivatives of three germ layers.

Cohen syndrome is an autosomal recessive disorder caused by VPS13B (COH1) gene mutations. This syndrome is significantly underdiagnosed and is characterized by intellectual disability, microcephaly, autistic symptoms, hypotension, myopia, retinal dystrophy, neutropenia, and obesity. VPS13B regulates intracellular membrane transport and supports the Golgi apparatus structure, which is critical for neuron formation. We generated induced pluripotent stem cells from two patients with pronounced manifestations of Cohen syndrome and differentiated them into neural stem cells and neurons. Using transmission electron microscopy, we documented multiple new ultrastructural changes associated with Cohen syndrome in the neuronal cells. We discovered considerable disturbances in the structure of some organelles: Golgi apparatus fragmentation and swelling, endoplasmic reticulum structural reorganization, mitochondrial defects, and the accumulation of large autophagosomes with undigested contents. These abnormalities underline the ultrastructural similarity of Cohen syndrome to many neurodegenerative diseases. The cell models that we developed based on patient-specific induced pluripotent stem cells can serve to uncover not only neurodegenerative processes, but the causes of intellectual disability in general.