Production of Neuroepithelial Organoids from Human-Induced Pluripotent Stem Cells for Mimicking Early Neural Tube Development

Organoids have emerged as robust tools for unravelling the mechanisms that underly tissue development. They also serve as important in vitro systems for studying fundamentals of stem cell behavior and for building advanced disease models. During early development, a crucial step in the formation of the central nervous system is patterning of the neural tube dorsal-ventral (DV) axis. Here we describe a simple and rapid culture protocol to produce human neuroepithelial (NE) cysts and DV-patterned organoids from single human-induced pluripotent stem cells (hiPSCs). Rather than being embedded within a matrix, hiPSCs undergo a 5-day differentiation process in medium containing soluble extracellular matrix and are allowed to self-organize into 3D cysts with defined central lumen structures that express early neuroepithelial markers. Moreover, upon stimulation with sonic hedgehog proteins and all-trans retinoic acid, NE cysts further develop into NE organoids with DV patterning. This rapid generation of patterned NE organoids using simple culture conditions enables mimicking, monitoring, and longitudinal manipulation of NE cell behavior. This straightforward culture system makes NE organoids a tractable model for studying neural stem cell self-organization and early neural tube developmental events.

ZIC2 in Holoprosencephaly

The ZIC2 transcription factor is one of the most commonly mutated genes in Holoprosencephaly (HPE) probands. HPE is a severe congenital defect of forebrain development which occurs when the cerebral hemispheres fail to separate during the early stages of organogenesis and is typically associated with mispatterning of the embryonic midline. Recent study of genotype-phenotype correlations in HPE cases has defined distinctive features of ZIC2-associated HPE presentation and genetics, revealing that ZIC2 mutation does not produce the craniofacial abnormalities generally thought to characterise HPE but leads to a range of non-forebrain phenotypes. Furthermore, the studies confirm the extent of ZIC2 allelic heterogeneity and that pathogenic variants of ZIC2 are associated with both classic and middle interhemispheric variant (MIHV) HPE which arise from defective ventral and dorsal forebrain patterning, respectively. An allelic series of mouse mutants has helped to delineate the cellular and molecular mechanisms by which one gene leads to defects in these related but distinct embryological processes.