Of apoptosis and inhibitory neurons in cortical organoids generated from human induced pluripotent stem cells

Modeling human brain diseases in a laboratory setting is critical to understanding the underlying pathology and developing new treatments for patients. Organoids are 3D tissue cultures that provide a promising way to model human brain development in vitro and have been used previously to gain novel insights into diseases unique to humans. We are examining a method for generating cortical organoids with a single internal lumen from induced pluripotent stem cells. It is still unclear how well these organoids represent the many cell types present in the brain. To establish cortical organoids as a model for the developing human cortex, my study focused on the characterization of inhibitory neuron subtypes in cortical organoids and the origins of the ventricle-like lumen. The primary aims were to determine the role cell death and apoptosis played in creating the organoid structure, and to determine the nature of inhibitory neurons present within that structure. I analyzed confocal microscopy images of immunostainings to determine cell identities and distributions. First, in examination of apoptotic cells, we showed cell death was occurring in a low proportion of cells (1.10±0.54%) and that apoptotic cells were distributed away from the center of the organoid. Second, by examining stains unique to specific subtypes of inhibitory neurons, we showed the presence of parvalbumin (PV) (4.41±2.65% of inhibitory neurons), somatostatin (SST) (6.15±2.81%), calretinin (CR) (3.85±0.19%), and calbindin (CB) (4.65±2.91%) expressing subtypes. Together, these results indicate that the organoids’ internal lumen is not an area of excessive cell death and that the organoids contain of a diverse population of inhibitory neurons. This broadens current understanding of the connections between in vivo and in vitro growth and the capabilities organoids can provide for understanding neurodevelopmental disorders. TABLE OF CONTENTS ABSTRACT