Gastruloids: Embryonic Organoids from Mouse Embryonic Stem Cells to Study Patterning and Development in Early Mammalian Embryos

Gastruloids are embryonic organoids made from small, defined numbers of mouse embryonic stem cells (mESCs) aggregated in suspension culture, which over time form 3D structures that mimic many of the features of early mammalian development. Unlike embryoid bodies that are usually disorganized when grown over several days, gastruloids display distinct, well-organized gene expression domains demarcating the emergence of the three body axes, anteroposterior axial elongation, and implementation of collinear Hox transcriptional patterns over 5–7 days of culture. As such gastruloids represent a useful experimental system that is complementary to in vivo approaches in studying early developmental patterning mechanisms regulating the acquisition of cell fates. In this protocol, we describe the most recent method for generating gastruloids with high reproducibility, and provide a comprehensive list of possible challenges as well as steps for protocol optimization

Dynamics of axial polarization in embyonic stem cells aggregates and the evolution of body axis establishment

Across metazoans, minimal in vitro systems from embryonic stem cells (ESCs) recapitulate the establishment of a body plan, particularly the anteroposterior (AP) axis. In contrast to actual embryos that generally require extraembryonic or maternally deposited signals, ESC aggregates undergo initial patterning in the absence of localized, external cues. We propose that such observations may reflect a basal capacity of ESCs that we summarize as a conserved developmental mode. To dissect the framework of AP axis establishment in a minimal system, we leverage gastruloids from mouse ESCs. We hence discover that alternate germ layer differentiation trajectories between in vivo and in vitro may converge onto similar cell fates. Furthermore, we delineate the robustness of this developmental mode of gastruloids by modifying the state of the initial ESC population and comparatively assessing AP polarization dynamics. Altogether, our findings may serve to inform inherent modes of patterning that underlie embryonic development.En metazous, l’agregació de poques cèl·lules mare embrionàries (CME) in vitro recapitula l'establiment d'un pla corporal bàsic, en particular l'eix anteroposterior (AP). A diferència dels embrions reals els quals requereixen de senyals externes, els agregats de CME són capaços d’adquirir patrons d’expressió gènica fins i tot en l’absència de morfògens externs. Proposem que aquest fenomen és fruit d’una capacitat inherent de les CME la qual reflecteix un mode de desenvolupament conservat. Per a estudiar la generació de l’eix AP in vitro, hem escollit gastruloids derivats de CME de ratolí. Mostrem que trajectòries de diferenciació cel·lular alternatives in vivo i in vitro convergeixen a destins cel·lulars similars. Addicionalment, explorem la variabilitat i robustesa dels modes de desenvolupament dels gastruloids modificant el grau de pluripotencia de la població inicial de CME, estudiant comparativament la dinàmica de polarització. Finalment, els nostres resultats poden servir per a entendre modes inherents de generació de patrons

Faunistic Studies on the Genus Medon Stephens, 1833 (Coleoptera: Staphylinidae: Paederinae) in Turkey

In this study, 702 specimens belonging to the genus Medon Sephens were examined. The material was obtained from various field trips between 2010-2019 by using aspirator, sifter, pitfall trap, berlese funnel and MSS trap methods. As a result of the study, 15 of the 22 known species from Turkey were identified. Medon brunneus (Erichson, 1839), M. ferrugineus (Erichson, 1840), M. lanugo Assing, 2004 and M. subfusculus Fagel, 1969 from the Aegean Region, M. semiobscurus (Fauvel, 1875), M. abantensis Bordoni, 1980 and M. lamellatus Assing, 2004 from the Central Anatolian Region are reported for the first time. Besides, M. rufiventris (Nordmann, 1837) is recorded for the first time from both the Aegean and Central Anatolian Regions. In addition, many new locality records of the recorded species were presented. The distributions of all Medon species in Turkey were mapped.Scientific and Technological Research Council of Turkey, TUBITAK [112T907, 215Z080]This study is partly prepared from a Doctorate Thesis approved by the Institute of Natural Sciences of Ege University on October 2019. This study was supported by the Scientific and Technological Research Council of Turkey, TUBITAK (Project no: 112T907 and 215Z080). We are grateful to Dr. Ersen Aydin Yagmur (Manisa), Serkan Yaman (Manisa) and Doruk Koksal (Aydin) for their help in our field trips, In addition to, Kadir Bogac Kunt (Bursa) and Mehmet Emin Bulut (Balikesir) for their gift to staphylinid specimens collected during their field trips

Axis Specification in Zebrafish Is Robust to Cell Mixing and Reveals a Regulation of Pattern Formation by Morphogenesis.

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. VIDEO ABSTRACT

An in vitro model of early anteroposterior organization during human development

The body plan of the mammalian embryo is shaped through the process of gastrulation, an early developmental event that transforms an isotropic group of cells into an ensemble of tissues that is ordered with reference to three orthogonal axes1. Although model organisms have provided much insight into this process, we know very little about gastrulation in humans, owing to the difficulty of obtaining embryos at such early stages of development and the ethical and technical restrictions that limit the feasibility of observing gastrulation ex vivo2. Here we show that human embryonic stem cells can be used to generate gastruloids-three-dimensional multicellular aggregates that differentiate to form derivatives of the three germ layers organized spatiotemporally, without additional extra-embryonic tissues. Human gastruloids undergo elongation along an anteroposterior axis, and we use spatial transcriptomics to show that they exhibit patterned gene expression. This includes a signature of somitogenesis that suggests that 72-h human gastruloids show some features of Carnegie-stage-9 embryos3. Our study represents an experimentally tractable model system to reveal and examine human-specific regulatory processes that occur during axial organization in early development