ABSTRACT
The blueprint of the mammalian body plan is laid out during gastrulation, when a trilaminar embryo is formed. This process entails a burst of proliferation, the ingression of embryonic epiblast cells at the primitive streak, and their priming toward primitive streak fates. How these different events are coordinated remains unknown. Here, we developed and characterized a 3D culture of self-renewing mouse embryonic cells that captures the main transcriptional and architectural features of the early gastrulating mouse epiblast. Using this system in combination with microfabrication and in vivo experiments, we found that proliferation-induced crowding triggers delamination of cells that express high levels of the apical polarity protein aPKC. Upon delamination, cells become more sensitive to Wnt signaling and upregulate the expression of primitive streak markers such as Brachyury. This mechanistic coupling between ingression and differentiation ensures that the right cell types become specified at the right place during embryonic development.
Subject(s)
Cell Differentiation , Gastrulation , Germ Layers , Animals , Mice , Germ Layers/cytology , Germ Layers/metabolism , T-Box Domain Proteins/metabolism , T-Box Domain Proteins/genetics , Pluripotent Stem Cells/cytology , Pluripotent Stem Cells/metabolism , Primitive Streak/cytology , Primitive Streak/metabolism , Fetal Proteins/metabolism , Fetal Proteins/genetics , Wnt Signaling Pathway , Cell Proliferation , Gene Expression Regulation, Developmental , Embryo, Mammalian/cytology , Embryo, Mammalian/metabolismABSTRACT
Studying human embryo development is technically and ethically challenging. An improved protocol to generate human embryo-like structures (blastoids) from human pluripotent stem cells (PSCs) (Kagawa et al., 2021) offers innovative opportunities to dissect the mechanisms of human embryogenesis.
Subject(s)
Pluripotent Stem Cells , Embryo, Mammalian , Embryonic Development , HumansABSTRACT
Appropriate remodeling of the female lower reproductive tract and pelvic floor is essential during normal mammalian pregnancy, labor, and postpartum recovery. During mouse pregnancy, in addition to reproductive tract modifications, the pubic symphysis (PS) is remodeled into a soft interpubic ligament (IpL) to provide safe delivery of the offspring and fast postpartum recovery. Although temporal changes in the phenotypes of myeloid cells, such as mononuclear phagocytes, are crucial to remodeling the lower reproductive tract organs in preparation for a safe delivery, little is known about the involvement of recruited monocytes or macrophages in mouse PS remodeling. We used combined light microscopy, electron microscopy, and qPCR analysis to investigate the profile of recruited monocytes and macrophage polarization markers in C57Bl6 mouse interpubic tissues during pregnancy (D12, D18, and D19) and early days postpartum (1 dpp and 3 dpp) to better identify their presence in proper remodeling of the mouse PS. Our morphological data show that the number of recruited monocytes is increased in interpubic tissues and that recruited monocytes differentiate into proinflammatory or anti-inflammatory macrophage phenotypes from D18 to 3 dpp, which may contribute to dynamic changes in the gene expression of specific inflammatory mediators involved in interpubic tissue remodeling at these time points. Therefore, our morphological and quantitative gene expression data suggest that both differentiated macrophages from recruited monocytes and polarized macrophages may collaborate for IpL relaxation at labor and the appropriate repair of the PS after the first pregnancy.
