Cell interactions and endoderm differentiation in cultured mouse embryos

Evidence for the existence of an early common biochemical pathway in the differentiation of F9 cells into visceral or parietal endoderm: Modulation by cyclic AMP

The technique of injecting genetically labelled cells into blastocysts was used in an attempt to determine whether the parietal and visceral endoderm originate from the same or different cell populations in the early embryo. When the developmental potential of 5th day primitive ectoderm and primitive endoderm cells was compared thus, only the latter were found to colonize the extraembryonic endoderm. Furthermore, single primitive endoderm cells yielded unequivocal colonization of both the parietal and the visceral endoderm in a proportion of chimaeras. However, in the majority of primitive endodermal chimaeras, donor cells were detected in the parietal endoderm only, cases of exclusively visceral colonization being rare. Visceral endoderm cells from 6th and 7th day post-implantation embryos also exhibited a striking tendency to contribute exclusively to the parietal endoderm following blastocyst injection. The above findings lend no support to a recent proposal that parietal and visceral endoderm are derived from different populations of inner cell mass cells. Rather, they suggest that the two extraembryonic endoderm layers originate from a common pool of primitive endoderm cells whose direction of differentiation depends on their interactions with non-endodermal cells.

Genetic and biochemical evidence that gastrulation defects in Pofut2 mutants result from defects in ADAMTS9 secretion

The visceral endoderm of mouse egg cylinders on the 7th and 8th days of gestation is divided into the visceral embryonic (VE) endoderm cell population which synthesizes alphafetoprotein (AFP), and the visceral extra-embryonic (VEX) endoderm population which does not synthesize AFP. Embryonic (E) and extra-embryonic (EX) ectoderm and visceral endoderm tissues were enzymically separated, reassociated in different combinations, and cultured in vitro for 48 h. The immunoperoxidase reaction on sections of cultured tissues showed that both VE and VEX endoderm cells synthesize high levels of AFP when cultured in isolation or in association with E ectoderm, but do not synthesize AFP when in close association with EX ectoderm. Both 7th and 8th day VEX endoderm cells synthesize detectable levels of AFP 12 h after isolation, and contain high levels by 24 h. It is concluded that both VE and VEX endoderm cells have the ability to synthesize AFP, but modulation of expression occurs through an inhibitory influence of the EX ectoderm.

Cell lineage analysis of the primitive and visceral endoderm of mouse embryos cultured in vitro

Miscarriages cause a greater loss-of-life than cardiovascular diseases, but knowledge about environmentally induced miscarriages is limited. Cultured naïve pluripotent embryonic stem cells (ESC) differentiate into extra-embryonic endoderm/extraembryonic endoderm (XEN) or formative pluripotent ESC, during the period emulating maximal miscarriage of peri-implantation development. In previous reports using small marker sets, hyperosmotic sorbitol, or retinoic acid (RA) decreased naïve pluripotency and increased XEN by FACS quantitation. Bulk and single cell (sc)RNAseq analyses of two cultured ESC lines was done, corroborated by qPCR. Transcriptomic responses were analyzed of cultured ESC stressed by Sorbitol, with Leukemia inhibitory factor (LIF + ; stemness growth factor), RA without LIF to control for XEN induction, and compared with normal differentiation (LIF - , ND). Sorbitol and RA increase subpopulations of 2-cell embryo-like (2CEL) and XEN sub-lineages; primitive, parietal, and visceral endoderm (VE) cells and suppress formative pluripotency, imbalancing alternate lineage choices of initial naïve pluripotent cultured ESC compared with ND. Although bulk RNAseq and gene ontology (GO) group analyses suggest that stress induces anterior VE-head organizer and placental markers, scRNAseq reveals relatively few cells. But VE and placental markers/cells were in adjacent stressed cell clusters in the UMAP, like recent, normal UMAP of conceptuses. UMAPs show that dose-dependent stress overrides stemness to force premature lineage imbalance. Hyperosmotic stress, and other toxicological stresses, like drugs with active ingredient RA, may cause premature, lineage imbalance, resulting in miscarriages or birth defects.

Stage-specific embryonic antigen 3 as a marker of visceral extraembryonic endoderm

Mechanical perspectives on the anterior-posterior axis polarization of mouse implanted embryos.

The anterior visceral endoderm (AVE), a signalling centre within the simple epithelium of the visceral endoderm (VE), is required for anterior-posterior axis specification in the mouse embryo. AVE cells migrate directionally within the VE, thereby properly positioning the future anterior of the embryo and orientating the primary body axis. AVE cells consistently come to an abrupt stop at the border between the anterior epiblast and extra-embryonic ectoderm, which represents an end-point to their proximal migration. Little is known about the underlying basis for this barrier and how surrounding cells in the VE respond to or influence AVE migration. We use high-resolution 3D reconstructions of protein localisation patterns and time-lapse microscopy to show that AVE cells move by exchanging neighbours within an intact epithelium. Cell movement and mixing is restricted to the VE overlying the epiblast, characterised by the enrichment of Dishevelled-2 (Dvl2) to the lateral plasma membrane, a hallmark of Planar Cell Polarity (PCP) signalling. AVE cells halt upon reaching the adjoining region of VE overlying the extra-embryonic ectoderm, which displays reduced neighbour exchange and in which Dvl2 is excluded specifically from the plasma membrane. Though a single continuous sheet, these two regions of VE show distinct patterns of F-actin localisation, in cortical rings and an apical shroud, respectively. We genetically perturb PCP signalling and show that this disrupts the localisation pattern of Dvl2 and F-actin and the normal migration of AVE cells. In Nodal null embryos, membrane localisation of Dvl2 is reduced, while in mutants for the Nodal inhibitor Lefty1, Dvl2 is ectopically membrane localised, establishing a role for Nodal in modulating PCP signalling. These results show that the limits of AVE migration are determined by regional differences in cell behaviour and protein localisation within an otherwise apparently uniform VE. In addition to coordinating global cell movements across epithelia (such as during convergence extension), PCP signalling in interplay with TGFβ signalling can demarcate regions of differing behaviour within epithelia, thereby modulating the movement of cells within them.

Embryoid bodies formed from teratocarcinoma stem cells differentiate an outer layer consisting of parietal and visceral endoderm or of visceral endoderm exclusively. We have previously shown that when these embryoid bodies are plated on collagen-coated substrates a parietal endoderm- like cell migrates onto the substrate, whereas all of the visceral endoderm remains associated with the stem cell mass, suggesting a role for substrate contact in parietal endoderm differentiation. We now identify fibronectin as the migration-promoting component in these cultures, and note that laminin and collagen type IV are 10-fold less effective at promoting both attachment and endoderm outgrowth. The RGDS tetrapeptide (arg-gly-asp-ser) from the cell attachment domain of fibronectin can specifically block attachment and outgrowth on both fibronectin- and laminin-coated substrates. In addition, the involvement of the 140-kD fibronectin receptor is demonstrated using an antibody directed against this molecule.

Retinoic acid induces discrete Wnt-signaling-dependent differentiation in F9 cells

Using H253 mouse stock harboring X-linked HMG-lacZ transgene, we examined X chromosome inactivation patterns in sectioned early female embryos. X-gal staining patterns were generally consistent with the paternal X inactivation in the trophectoderm and the primitive endoderm cell lineages and random inactivation in the epiblast lineages. The occurrence of embryonic visceral endoderm cells apparently at variance with the paternal X chromosome inactivation in 7.5 dpc embryos was explained by the replacement of visceral endoderm cells with cells of epiblast origin. The frequency of cells negative for X-gal staining in 4.5-5.5 dpc XmXp* embryos fluctuated considerably especially in the extraembryonic ectoderm and the primitive endoderm, whereas it was less variable in the embryonic ectoderm. We could not, however, determine whether it is a normal phenomenon revealed for the first time by the use of HMG-lacZ transgene or an abnormality caused by the multicopy transgene.

The first cell migration event in the mouse embryo is the movement of parietal endoderm cells from the surface of the inner cell mass facing the blastocoel cavity to line the inner surface of the trophectoderm. F9 embryoid bodies provide an in vitro model for this event. They have an inner core of undifferentiated stem cells surrounded by an outer visceral endoderm layer. When plated on a laminin coated substrate, visceral endoderm transitions to parietal endoderm and migrates onto the dish, away from the attached embryoid body. We now show that this outgrowth contains abundant focal complexes and focal adhesions, as well as lamellipodia and filopodia. Treatment with the ROCK inhibitor Y-27632 promotes a 2-fold increase in outgrowth, and a transition from focal adhesions and associated stress fibers, to focal complexes and a decrease in stress fibers. ROCK inhibition also leads to an increase in lamellipodia. Inhibition of RhoA by transfection of a vector encoding C3 transferase, direct administration of the C3 enzyme, or transfection of a vector encoding p190 Rho GTPase Activating Protein also promotes outgrowth and an apparent transition from focal adhesions to focal complexes. Parietal endoderm outgrowth generated using vinculin-deficient F9 stem cells migrates 2-fold further than wild type cultures, but this outgrowth retains the morphology of wild type parietal endoderm, including focal adhesions and stress fibers. Addition of Y-27632 to vinculin-null outgrowth cultures further stimulates migration an additional 2-fold, supporting the conclusion that Rho/ROCK and vinculin regulate parietal endoderm outgrowth by distinct pathways.

The nature and origin of the proliferating cells were studied in displaced visceral yolk sac in vivo and in organ culture in vitro. By ultrastructural examination and reactivity with antibodies against intermediate filaments it was shown that the poorly differentiated cells which appear in this membrane have features in common with visceral endodermal cells. Using plant lectins reacting with the rat visceral endoderm (DBA, PNA, SJA and BSA-1) it was demonstrated that the proliferating endodermal cells retrodifferentiate to earlier stages of endodermal development.

Expression of a glucose-regulated cell surface protein in early mouse embryos