Zebrafish Development in 3D: Vertebrate development has classically been characterized qualitatively, but—by combining expertise in physics, mathematics, and biology— Olivier et al. (p. 967 ) used label-free conformal nonlinear time-lapse microscopy and image analysis to calculate the spatiotemporal cell lineage of zebrafish embryos throughout their first 10 division cycles. The work reconstructs complete lineage trees, annotated with cell-shape measurements, and allows for visualization with interactive tools.

The recent description of virus-induced fish IFNs has raised questions about the evolution of this complex antiviral system. Identification of the receptor of the zebrafish virus-induced IFN (zIFN) was sought to help resolve these questions. We set up an experimental system to study the zIFN system in the course of a viral infection of zebrafish embryos. In this setting, zIFN was induced by viral infection, and we identified zIFN-dependent induced transcripts. Embryos quickly died from the infection, but zIFN overexpression increased their survival. We took advantage of this experimental system to perform in vivo loss and gain of function analysis of candidate receptors of the class II helical receptor family and identified zCRFB1 and zCRFB5 as the two subunits of the zebrafish IFN receptor. Based on the organization of the zIFN gene and the protein structure of the identified receptor components, the virus-induced fish IFNs appear as orthologs of mammalian IFN-λ, specifying type III IFN as the ancestral antiviral system of vertebrates.

A monoclonal antibody has allowed the characterization of various forms of uvomorulin, a glycoprotein involved in the process of compaction of mouse morula. In addition to various degradation products, uvomorulin exists as a 120-kilodalton exocellular molecule stable at the cell surface. A short-lived 135-kilodalton precursor of uvomorulin has been detected after 10-min pulse labeling. Uvomorulin-like molecules are found on various tissues at various stages of development of the mouse.

The study of multicellular development is grounded in two complementary domains: cell biomechanics, which examines how physical forces shape the embryo, and genetic regulation and molecular signalling, which concern how cells determine their states and behaviours. Integrating both sides into a unified framework is crucial to fully understand the self-organized dynamics of morphogenesis. Here we introduce MecaGen, an integrative modelling platform enabling the hypothesis-driven simulation of these dual processes via the coupling between mechanical and chemical variables. Our approach relies upon a minimal ‘cell behaviour ontology’ comprising mesenchymal and epithelial cells and their associated behaviours. MecaGen enables the specification and control of complex collective movements in 3D space through a biologically relevant gene regulatory network and parameter space exploration. Three case studies investigating pattern formation, epithelial differentiation and tissue tectonics in zebrafish early embryogenesis, the latter with quantitative comparison to live imaging data, demonstrate the validity and usefulness of our framework.

Fluorescent polymer nanoparticles for long‐term labeling and tracking of living cells with any desired color code are developed. They are built from biodegradable poly(lactic‐co‐glycolic acid) polymer loaded with cyanine dyes (DiO, DiI, and DiD) with the help of bulky fluorinated counterions, which minimize aggregation‐caused quenching. At the single particle level, these particles are ≈20‐fold brighter than quantum dots of similar color. Due to their identical 40 nm size and surface properties, these nanoparticles are endocytosed equally well by living cells. Mixing nanoparticles of three colors in different proportions generates a homogeneous RGB (red, green, and blue) barcode in cells, which is transmitted through many cell generations. Cell barcoding is validated on 7 cell lines (HeLa, KB, embryonic kidney (293T), Chinese hamster ovary, rat basophilic leucemia, U97, and D2A1), 13 color codes, and it enables simultaneous tracking of co‐cultured barcoded cell populations for >2 weeks. It is also applied to studying competition among drug‐treated cell populations. This technology enabled six‐color imaging in vivo for (1) tracking xenografted cancer cells and (2) monitoring morphogenesis after microinjection in zebrafish embryos. In addition to a robust method of multicolor cell labeling and tracking, this work suggests that multiple functions can be co‐localized inside cells by combining structurally close nanoparticles carrying different functions.