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The mesoderm is the middle layer of cells in very early vertebrate and insect embryos. It is one of the three primary germ cell layers and gives rise to tissues and organs such as muscle, bone, blood and the heart.
Gene expression is regulated at several levels, including through the modulation of protein translation. Here the authors find that translation control diversifies gene expression between developing tissues and regulates major signalling pathways through a complex landscape of upstream open reading frames (uORFs).
Differentiation of human pluripotent stem cells (hPSC) mimics aspects of embryonic development in vitro but is poorly understood. Here, the authors identify bulk cell density as a key parameter directing transition from pluripotency to primitive streak-like priming in hPSCs via secreted LEFTY/CERBERUS.
It is unclear how the dorsal-ventral (DV) and anterior-posterior (AP) axes established in the gastrula affect tissues. Here, the authors show that in zebrafish kidney development, with regard to non-axial mesoderm, the classic DV axis corresponds to the AP axis, and is regulated by BMP and retinoic acid.
An ex vivo primary culture assay is developed that recapitulates mouse embryonic mesodermal patterning and segment formation; using this approach, it is shown that oscillating gene activity is central to maintain stable proportions during development.
Haematopoietic stem/progenitor cells (HSPCs) transform from aortic endothelium into migratory cells that move through stroma and enter circulation to colonize haematopoietic tissues. Here the authors show that HSPCs' passage is facilitated by primitive macrophages that secrete extracellular matrix-degrading enzymes.
The endoderm layer destined to be primitive gut is a mosaic of earlier visceral endoderm and definitive endoderm that arises later, during gastrulation. Live imaging now reveals that in mouse embryos, definitive endoderm cells egress from underlying mesoderm and intercalate into the overlying cell layer. This process requires SOX17-mediated control of basement membrane organization.