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Abstract Droplet microfluidic methods have massively increased the throughput of single-cell sequencing campaigns. The benefit of scale-up is, however, accompanied by increased background noise when processing challenging samples and the overall RNA capture efficiency is lower. These drawbacks stem from the lack of strategies to enrich for high-quality material or specific cell types at the moment of cell encapsulation and the absence of implementable multi-step enzymatic processes that increase capture. Here we alleviate both bottlenecks using fluorescence-activated droplet sorting to enrich for droplets that contain single viable cells, intact nuclei, fixed cells or target cell types and use reagent addition to droplets by picoinjection to perform multi-step lysis and reverse transcription. Our methodology increases gene detection rates fivefold, while reducing background noise by up to half. We harness these properties to deliver a high-quality molecular atlas of mouse brain development, despite starting with highly damaged input material, and provide an atlas of nascent RNA transcription during mouse organogenesis. Our method is broadly applicable to other droplet-based workflows to deliver sensitive and accurate single-cell profiling at a reduced cost.

How pluripotency transcription factors regulate the cellular architecture and energetics has remained largely unknown. Here the authors identify Lima1 as a key effector that mediates the pluripotency control of membrane dynamics and cellular metabolism.

Abstract Polarization of the mammalian embryo at the right developmental time is critical for its development to term and would be valuable in assessing the potential of human embryos. However, tracking polarization requires invasive fluorescence staining, impermissible in the in vitro fertilization clinic. Here, we report the use of artificial intelligence to detect polarization from unstained time-lapse movies of mouse embryos. We assembled a dataset of bright-field movie frames from 8-cell-stage embryos, side-by-side with corresponding images of fluorescent markers of cell polarization. We then used an ensemble learning model to detect whether any bright-field frame showed an embryo before or after onset of polarization. Our resulting model has an accuracy of 85% for detecting polarization, significantly outperforming human volunteers trained on the same data (61% accuracy). We discovered that our self-learning model focuses upon the angle between cells as one known cue for compaction, which precedes polarization, but it outperforms the use of this cue alone. By compressing three-dimensional time-lapsed image data into two-dimensions, we are able to reduce data to an easily manageable size for deep learning processing. In conclusion, we describe a method for detecting a key developmental feature of embryo development that avoids clinically impermissible fluorescence staining.

Human early development remains largely inaccessible, owing to technical and ethical limitations of working with natural embryos. Here the authors assess the extent to which human expanded pluripotent stem cells can specify distinct cell lineages and capture aspects of early human embryogenesis.

Single cell analysis of early human embryos identifies key changes in pluripotency, the requirement of FGF signalling for embryo survival, and defines a putative anterior-like region of hypoblast cells, providing insights into how early human development is regulated.

Aneuploidy, abnormal chromosome number, is a major cause of early pregnancy loss. Here the authors determine the extent of post-implantation development of human embryos with common aneuploidies in culture, finding developmental arrest of monosomy 21 embryos, and trophoblast hypo-proliferation in trisomy 16 embryos.

The mechanisms behind the plasticity of embryos and how they deal with aneuploid cells are unclear. Here, the authors show that aneuploid cells in a mouse embryo are preferentially eliminated during pre- and peri-implantation development in a p53-dependent process involving both autophagy and apoptosis.

How the shape of the pre-implantation murine embryo changes dramatically upon implantation is unclear. Here, the authors use live imaging with a cdx2-GFP reporter line in combination with loss of function experiments to demonstrate that FGF signalling mediated trophectoderm morphogenesis orchestrates this process.

What breaks symmetry in early mammalian embryonic development has been much questioned. Here, Magdalena Zernicka-Goetz and colleagues propose that compartmentalized intracellular reactions generate micro-scale inhomogeneity, which is amplified in the developing embryo, driving pattern formation.

In development, the switch from pluripotency to differentiation is important but it is often unclear how it is regulated. Here, the authors show that the tumour suppressor RASSF1A mediates this switch by promoting YAP-p73 transcription, which in turn enables differentiation.

The molecular trigger that establishes cell polarity in the mammalian embryo is unclear. Here, the authors show that de novo polarisation of the mouse embryo at the 8-cell stage is directed by Phospholipase C and Protein kinase C and occurs in two phases: polarisation of actomyosin followed by the Par complex.

The developmental potential of mosaic embryos of euploid and aneuploid cells is unknown. Here, the authors create a mouse model of chromosome mosaicism, showing that aneuploid cells in the fetus are eliminated by apoptosis and developmental potential is dependent on the presence of sufficient euploid cells.