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Blastocyst-derived stem cell lines were shown to self-organize into embryo-like structures in 3D cell culture environments. Here, we provide evidence that embryo-like structures can be generated solely based on transcription factor-mediated reprogramming of embryonic stem cells in a simple 3D co-culture system. Embryonic stem cells in these cultures self-organize into elongated, compartmentalized embryo-like structures reflecting aspects of the inner regions of the early post-implantation embryo. Single-cell RNA-sequencing reveals transcriptional profiles resembling epiblast, primitive-/visceral endoderm, and extraembryonic ectoderm of early murine embryos around E4.5–E5.5. In this stem cell-based embryo model, progression from rosette formation to lumenogenesis accompanied by progression from naïve- to primed pluripotency was observed within Epi-like cells. Additionally, lineage specification of primordial germ cells and distal/anterior visceral endoderm-like cells was observed in epiblast- or visceral endoderm-like compartments, respectively. The system presented in this study allows for fast and reproducible generation of embryo-like structures, providing an additional tool to study aspects of early embryogenesis., Synthetic embryo models have arisen as an approach to probe early development in vitro, facilitating the study of difficult to access stages. Here the authors present a simple system for generating embryo-like structures that resemble peri-implantation mouse embryos.

Summary Neurons differentiated from induced pluripotent stem cells (iPSCs) typically show regular spiking and synaptic activity but lack more complex network activity critical for brain development, such as periodic depolarizations including simultaneous involvement of glutamatergic and GABAergic neurotransmission. We generated human iPSC-derived neurons exhibiting spontaneous oscillatory activity after cultivation of up to 6 months, which resembles early oscillations observed in rodent neurons. This behavior was found in neurons generated using a more “native” embryoid body protocol, in contrast to a “fast” protocol based on NGN2 overexpression. A comparison with published data indicates that EB-derived neurons reach the maturity of neurons of the third trimester and NGN2-derived neurons of the second trimester of human gestation. Co-culturing NGN2-derived neurons with astrocytes only led to a partial compensation and did not reliably induce complex network activity. Our data will help selection of the appropriate iPSC differentiation assay to address specific questions related to neurodevelopmental disorders., Graphical Abstract, Highlights • Spontaneous oscillatory activity in iPSC-derived neurons after 4–6 months in culture • The activity resembled early oscillations seen in rodent neurons during development • Cell growth affects developmental changes of neuronal excitability • Biological age of neurons is determined based on electrophysiological activity, Rosa and colleagues have used two neural differentiation protocols to obtain induced pluripotent stem cell-derived neuronal cultures and address their relevance for the modeling of neurogenetic disorders. In neurons generated using one of the approaches, they report spontaneously occurring oscillations with properties corresponding to the neuronal activity seen during rodent and human brain development.

Human skin fibroblasts were isolated from a 40-year-old hereditary spastic paraplegia patient carrying an intronic splice site mutation (c.1687 + 2 T > A) in SPAST , leading to hereditary spastic paraplegia type 4 (SPG4). Fibroblasts were reprogrammed using episomal plasmids carrying hOCT4 , hSOX2 , hKLF4 , hL-MYC and hLIN28 . The generated transgene-free line iPS-SPG4-splice retained the specific mutation with no additional genomic aberrations, expressed pluripotency markers and was able to differentiate into cells of all germ layers in vitro . The generated iPS-SPG4-splice line might be a useful platform to study the pathomechanism of SPG4.