The Role of Protocadherin 19 in Human Cortical Development

About This Grant

PROJECT SUMMARY The genes associated with epilepsy, a major neurological disorder, are critical to the development of both neural progenitor cells (NPCs) and the early stages of human brains. However, the molecular mechanism of how NPCs shape the developing cortex and contribute to epilepsy and other neurodevelopmental disorders remains unclear. In particular, it is crucial to determine how the epilepsy associated gene variants disrupt NPC functions and alter both the complexity and expansion of human brains. Protocadherin-19 (PCDH19) Clustering Epilepsy (PCE) is one of the most common monogenic epilepsies, caused by loss-of-function mutations in the X-linked gene PCDH19. Unique among the epilepsy associated genes, PCE affects only heterozygous females and mosaic males. This is presumedly due to random X-inactivation (RXI), which generates mosaic PCDH19 expression. The prevailing theory hypothesize that this mosaicism causes abnormal cell–cell interactions, or “cellular interference,” between PCDH19 wild-type (WT) and mutant cells. Yet, how this cellular interference arises during cortical development and leads to epilepsy remains unknown. Here, we have developed a novel human pluripotent stem cell (hPSC)-derived cortical organoid (hCO) model that faithfully recapitulates mosaic PCDH19 expression during human neurodevelopment. Using this model, we discovered abnormal cell segregation in the ventricular/subventricular zone (VZ/SVZ), where WT and mutant cells form distinct stripes, accompanied by altered expression of PCDH19 and N-cadherin (NCAD) and abnormal radial glial (RG) cell morphology. PCDH19 expression labels dividing RG cells at the apical junction, implicating its role in progenitor polarity and neurogenesis. These observations let us to propose that PCDH19 regulates RG cell polarity and lineage progression through the NCAD-mediated adherent junction complex. Based on this hypothesis, mosaic PCDH19 loss disrupts early human cortical development, leading to epilepsy-associated neurodevelopmental abnormalities. Our proposed study will uncover novel mechanisms of PCDH19 function in human cortical development, providing critical insights into the pathogenesis of PCE. This project establishes the first human brain organoid research platform for undergraduate education at The University of Toledo, offering the students hands-on training in cutting-edge neuroscience techniques, including human stem cell culture, CRISPR/Cas9 genome editing, confocal imaging, and bioinformatics analysis. Through this research, the students will gain interdisciplinary research experience that will prepare them for advanced graduate and professional programs, directly supported by the educational mission of the NIH R15 AREA mechanism.