The Birth of the 3D Genome during Early Embryonic Development Clemens B. Hug, Juan M. Vaquerizas  Trends in Genetics  Volume 34, Issue 12, Pages 903-914 (December 2018) DOI: 10.1016/j.tig.2018.09.002 Copyright © 2018 The Authors Terms and Conditions

Figure 1 Schematic Illustrating the Hierarchical Nature of 3D Chromatin Organization. The nucleus is divided into territories occupied by single chromosomes, which do not overlap and intermingle significantly, except for compartment associations at their interfaces. There are two compartments active A-compartments and inactive B-compartments. They comprise many interaction clusters distributed throughout the nucleus, where chromatin of the same compartment type associates. Locally, chromatin assembles into topologically associating domains (TADS). Two different TAD models are depicted for mouse (top) and Drosophila (bottom). The orange arrows indicate movement of cohesin during loop extrusion. Abbreviations: CTCF, CCCTC-binding factor; RNA Pol II, RNA polymerase II. Trends in Genetics 2018 34, 903-914DOI: (10.1016/j.tig.2018.09.002) Copyright © 2018 The Authors Terms and Conditions

Figure 2 Dynamics of the 3D Genome in the Germline and during Early Embryonic Development. (A) Schematic Hi-C contact maps depicting typical 3D chromatin architecture during M-phase, pre-zygotic genome activation (pre-ZGA; around nuclear cycle 12 in Drosophila or the early two-cell stage in mouse) and post-ZGA. (B) Dynamics of structural features during germ line development and maternal-to-zygotic transition (MZT) in mice. The timing of transcription activation during ZGA is indicated at the top. Each row represents the strength of a structural feature on a scale from ‘–’, representing no or very weak, to ‘ + + + +’, representing very strong representation of the feature at the indicated stage. The features are, in order, topologically associating domains (TADs), compartments, and focal loops. (C) Dynamics of TAD structure during Drosophila MZT. Abbreviations: GV, germinal vesicle; hpf, hours post fertilization; MII, meiosis II; na, not analyzed; nc, nuclear cycle. Trends in Genetics 2018 34, 903-914DOI: (10.1016/j.tig.2018.09.002) Copyright © 2018 The Authors Terms and Conditions