Intra-organ communication guides morphogenetic processes that are essential for an organ to carry out complex physiological functions. In the heart, the growth of the myocardium is tightly coupled to ...that of the endocardium, a specialized endothelial tissue that lines its interior. Several molecular pathways have been implicated in the communication between these tissues including secreted factors, components of the extracellular matrix, or proteins involved in cell-cell communication. Yet, it is unknown how the growth of the endocardium is coordinated with that of the myocardium. Here, we show that an increased expansion of the myocardial atrial chamber volume generates higher junctional forces within endocardial cells. This leads to biomechanical signaling involving VE-cadherin, triggering nuclear localization of the Hippo pathway transcriptional regulator Yap1 and endocardial proliferation. Our work suggests that the growth of the endocardium results from myocardial chamber volume expansion and ends when the tension on the tissue is relaxed.
Epithelial cells exhibit apical membrane protrusions, which confer specific functions to epithelial tissues. Microridges are short actin protrusions that are laterally long and form a maze-like ...pattern in the apical domain. They are widely found on vertebrate squamous epithelia including epidermis and have functions in mucous retention, membrane storage and abrasion resistance. It is largely unknown how the formation of these laterally long actin projections is regulated. Here, we show that antagonistic interactions between aPKC and Lgl-regulators of apical and basolateral domain identity, respectively,-control the length of microridges in the zebrafish periderm, the outermost layer of the epidermis. aPKC regulates the levels of Lgl and the active form of non-muscle myosinII at the apical cortex to prevent actin polymerization-dependent precocious fusion and elongation of microridges. Our data unravels the functional significance of exclusion of Lgl from the apical domain in epithelial cells.
Metabolic networks are well placed to orchestrate the coordination of multiple cellular processes associated with embryonic development such as cell growth, proliferation, differentiation and cell ...movement. Here, we discuss the advantages that gastruloids, aggregates of mammalian embryonic stem cells that self-assemble a rudimentary body plan, have for uncovering the instructive role of metabolic pathways play in directing developmental processes. We emphasise the importance of using such reductionist systems to link specific pathways to defined events of early mammalian development and their utility for obtaining enough material for metabolomic studies. Finally, we review the ways in which the basic gastruloid protocol can be adapted to obtain specific models of embryonic cell types, tissues and regions. Together, we propose that gastruloids are an ideal system to rapidly uncover new mechanistic links between developmental signalling pathways and metabolic networks, which can then inform precise in vivo studies to confirm their function in the embryo.
A fundamental question in developmental biology is how the early embryo establishes the spatial coordinate system that is later important for the organization of the embryonic body plan. Although we ...know a lot about the signaling and gene-regulatory networks required for this process, much less is understood about how these can operate to pattern tissues in the context of the extensive cell movements that drive gastrulation. In zebrafish, germ layer specification depends on the inheritance of maternal mRNAs 1–3, cortical rotation to generate a dorsal pole of β-catenin activity 4–8, and the release of Nodal signals from the yolk syncytial layer (YSL) 9–12. To determine whether germ layer specification is robust to altered cell-to-cell positioning, we separated embryonic cells from the yolk and allowed them to develop as spherical aggregates. These aggregates break symmetry autonomously to form elongated structures with an anterior-posterior pattern. Both forced reaggregation and endogenous cell mixing reveals how robust early axis specification is to spatial disruption of maternal pre-patterning. During these movements, a pole of Nodal signaling emerges that is required for explant elongation via the planar cell polarity (PCP) pathway. Blocking of PCP-dependent elongation disrupts the shaping of opposing poles of BMP and Wnt/TCF activity and the anterior-posterior patterning of neural tissue. These results lead us to suggest that embryo elongation plays a causal role in timing the exposure of cells to changes in BMP and Wnt signal activity during zebrafish gastrulation.
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•Whole-zebrafish 256-cell stage embryo explants elongate•Patterned germ layers are established•Mesoderm formation is robust to extensive cell mixing•Inhibition of morphogenesis blocks formation of signaling gradients
Fulton et al. demonstrate that, through explanting zebrafish blastomeres, termed pescoids, at the 256-cell stage, embryonic cells have the potential to form mesoderm, even in the absence of yolk-derived pre-pattern information caused by extensive cell mixing. Blocking explant morphogenesis results in failure to correctly pattern the neural tissue.
Patterning and growth are fundamental features of embryonic development that must be tightly coordinated. To understand how metabolism impacts early mesoderm development, we used mouse embryonic ...stem-cell-derived gastruloids, that co-expressed glucose transporters with the mesodermal marker T/Bra. We found that the glucose mimic, 2-deoxy-D-glucose (2-DG), blocked T/Bra expression and abolished axial elongation in gastruloids. However, glucose removal did not phenocopy 2-DG treatment despite a decline in glycolytic intermediates. As 2-DG can also act as a competitive inhibitor of mannose in protein glycosylation, we added mannose together with 2-DG and found that it could rescue the mesoderm specification both in vivo and in vitro. We further showed that blocking production and intracellular recycling of mannose abrogated mesoderm specification. Proteomics analysis demonstrated that mannose reversed glycosylation of the Wnt pathway regulator, secreted frizzled receptor Frzb. Our study showed how mannose controls mesoderm specification in mouse gastruloids.
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•2-Deoxy-D-Glucose affects mesoderm specification through mannose inhibition•De novo and salvage mannose synthesis pathways control mesoderm specification•Mannose controls mesoderm specification in gastruloids and gastrulating embryos•Mannose-dependent protein glycosylation is required for mesoderm specification
Dingare et al. identified a critical role for mannose-dependent glycosylation during early mesoderm specification both in mouse embryonic stem-cell-derived gastruloids and in gastrulating mouse embryos. Blocking intracellular mannose production and its usage in glycosylation inhibited mesoderm specification and symmetry breaking in gastruloids.
In some animal species, fertilization occurs through a funnel-like canal called the "micropyle." In teleost fishes, the micropyle is formed by a very specialized follicle cell, called the micropylar ...cell (MC). Very little is known about the mechanisms underlying the specification and differentiation of the MC, a unique cell among hundreds that compose the follicle cell layer. The Hippo pathway effector Taz is essential for this process and is the first reported MC marker. Here, we describe a method to identify and mark the micropylar cell following the immunostaining procedure on cryosections or combining it with the RNA in situ hybridization on whole-mount follicles.
Hippo signaling is a critical pathway that integrates extrinsic and intrinsic mechanical cues to regulate organ size. Despite its essential role in organogenesis, little is known about its role in ...cell fate specification and differentiation. Here, we unravel a novel and unexpected role of the Hippo pathway effector Taz (
) in controlling the size, shape and fate of a unique cell in the zebrafish ovary. We show that
mutant females are infertile. In teleosts, fertilization occurs through the micropyle, a funnel-like opening in the chorion, formed by a unique enlarged follicle cell, the micropylar cell (MC). We describe here, for the first time, the mechanism that underlies the differentiation of the MC. Our genetic analyses show that Taz is essential for MC fate acquisition and subsequent micropyle formation in zebrafish. We identify Taz as the first bona fide MC marker and show that Taz is specifically and strongly enriched in the MC precursor. Altogether, we performed the first genetic and molecular characterization of the MC and propose that Taz is a key regulator of MC fate.This article has an associated 'The people behind the papers' interview.
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