Human brain organoids on a chip reveal the physics of folding

Abstract

Human brain wrinkling has been implicated in neurodevelopmental disorders and yet its origins remain unknown. Polymer gel models suggest that wrinkling emerges spontaneously due to compression forces arising during differential swelling, but these ideas have not been tested in a living system. Here, we report the appearance of surface wrinkles during the in vitro development and self-organization of human brain organoids in a micro-fabricated compartment that supports in situ imaging over a timescale of weeks. We observe the emergence of convolutions at a critical cell density and maximal nuclear strain, which are indicative of a mechanical instability. We identify two opposing forces contributing to differential growth: cytoskeletal contraction at the organoid core and cell-cycle-dependent nuclear expansion at the organoid perimeter. The wrinkling wavelength exhibits linear scaling with tissue thickness, consistent with balanced bending and stretching energies. Lissencephalic (smooth brain) organoids display reduced convolutions, modified scaling and a reduced elastic modulus. Although the mechanism here does not include the neuronal migration seen in in vivo, it models the physics of the folding brain remarkably well. Our on-chip approach offers a means for studying the emergent properties of organoid development, with implications for the embryonic human brain.

An On‐Chip Method for Long‐Term Growth and Real‐Time Imaging of Brain Organoids

“…The thin culture chamber also allows for efficient diffusion throughout the organoid; nutrient exchange is independent of organoid diameter. We have used RNA sequencing to verify that the organoid acquires forebrain identity during development (Karzbrun et al., ) and expresses markers previously observed in 3D human brain organoids. Other cortical hallmarks have been observed such as the interkinetic nuclear motion of radial glia cells and the laminar organization of neuronal and progenitor layers.…”

“…Here we describe an on‐chip organoid culture technique recently used in a study on the emergence of wrinkles in brain organoids (Karzbrun et al., ). At the heart of the technique is a micro‐fabricated chamber in which the organoids are cultured.…”

Stem Cells, Genome Editing, and the Path to Translational Medicine

“…Exploiting the self-organizing capacity of neuroectodermal precursor cells, cerebral organoids recapitulate many features of human brain development and morphology, including ventricle and neural tube-like structures with apical-basal polarity, progenitor zone organization with outer radial glial stem cells, cortical plate development and electrophysiological mature neurons that participate in neuronal network activity (Kadoshima et al, 2013; Karzbrun et al, 2018; Lancaster et al, 2013; 2017; Li et al, 2017b; Paşca et al, 2015; Quadrato et al, 2017). Cerebral organoids have already provided novel insights into human-specific processes, which could not be studied in conventional 2D culture systems, such as brain gyrification (Karzbrun et al, 2018; Li et al, 2017b), cell migration and outer radial glial mitosis defects in Miller-Dieker syndrome (Bershteyn et al, 2017).…”

“…Cerebral organoids have already provided novel insights into human-specific processes, which could not be studied in conventional 2D culture systems, such as brain gyrification (Karzbrun et al, 2018; Li et al, 2017b), cell migration and outer radial glial mitosis defects in Miller-Dieker syndrome (Bershteyn et al, 2017). …”

“…Organoid models are now a common tool to study neurodevelopmental disorders, including microcephaly (Lancaster et al, 2013; Li et al, 2017a), autism spectrum disease associated with macrocephaly (Mariani et al, 2017; Wang et al, 2017), lissencephally (Bershteyn et al, 2017; Karzbrun et al, 2018), Rett Syndrom (Mellios et al, 2017), Thymothy syndrome (Birey et al, 2017), lysosomal storage diseases such as Sandhoff disease (Allende et al, 2018), schizophrenia (Srikanth et al, 2018; Stachowiak et al, 2017) and Zika infection on neonatal brain development (reviewed in (Qian et al, 2017). Despite the early success with this approach for disease-modelling, challenges remain.…”