Human neural tube organoid morphogenesis after ZIC2 knockdown. Image credit: Huang et al. (CC BY-4.0)
Proper organ morphology is a critical outcome of embryonic development. However, the genetic basis of human developmental disorders affecting tissue morphogenesis, such as neural tube closure (a process essential for the formation of the brain and spinal cord), has proven difficult to study because of ethical limitations on human embryo research.
Three-dimensional stem cell-derived models of human embryogenesis and organogenesis provide a promising alternative for investigating the genetics of morphogenesis. Nevertheless, high-throughput genetic screens in organoid systems typically rely on ‘pooled perturbation approaches’, in which only a small fraction of cells within each organoid carries a given genetic perturbation. While these methods have advanced our understanding of gene function at the single-cell level, they are not ideal for studying how individual genes regulate multicellular processes such as morphogenesis.
Huang et al. sought to identify genes required for neural tube closure in the developing human forebrain using a stem cell-derived organoid model. The researchers first aimed to establish a more reproducible three-dimensional model of human neural tube closure. They then sought to develop a high-throughput method for targeting individual genes across micropatterned organoids, enabling parallel assessment of gene-specific contributions to neural tube closure.
Huang et al. developed an approach for uniform gene knockdown across entire human pluripotent stem cell (hPSC)-derived organoids. They used this method to identify three transcriptional regulators of neural tube closure in the developing human forebrain. They found that arranging organoids in a hexagonal pattern promoted highly symmetrical breaking of ectodermal tissues, resulting in a reproducible three-dimensional model of human neural tube closure.
They next developed a high-throughput method for targeting single genes broadly and uniformly across each organoid, by generating and applying a high density of lentiviruses carrying gene-editing tools (CRISPRi dual-guide RNAs). This allowed them to examine the roles of individual genes in the tissue-wide process of morphogenesis. Guided by neural gene expression analyses, 77 transcription factor candidates were screened, and three genes (ZIC2, SOX11, and ZNF521) were identified as essential for proper neural tube closure.
The platform developed by Huang et al. is broadly applicable to genetic investigations of morphogenesis in human stem cell-derived models, enabling high-throughput analyses of genes that regulate developmental processes. Future studies could evaluate the roles of ZIC2, SOX11 and ZNF521 in human neural tube defects by assessing their sequence and expression in patients affected by such conditions. In addition, the relationship between these genes and other known genetic contributors to neural tube defects remains an important area for future investigation.
