Extended Data Fig. 1: Blastocyst size is controlled by an embryo-autonomous mechanism.
From: Hydraulic control of mammalian embryo size and cell fate
a, Schematic representing mouse blastocyst development. The blastocyst, surrounded by a glycoprotein coat of the zona pellucida, is partitioned into the epithelial trophectoderm, the ICM and the cavity. The outer trophectoderm is further classified into the mural trophectoderm (which surrounds the blastocyst cavity) and the polar trophectoderm, which is in contact with the ICM. Apicobasal polarity is marked by the outer apical domains (red) and trophectoderm cell–cell contacts with the apically localized tight junctions and adherens junctions. Na+/K+ -ATPase pumps, enriched at the basolateral membrane of the trophectoderm cells, help to establish an osmotic gradient across the trophectoderm to drive fluid influx (green arrows). Together with the maturation of tight junctions that helps to seal the blastocyst against fluid outflow via paracellular junctions, blastocyst expansion then proceeds. b, Images of embryos without zona pellucida undergoing blastocyst development (representative data from three independent experiments). The corresponding cavity diameter as a function of time (bottom) shows cycles of blastocyst collapse and re-expansion similar to those of embryos with intact zona-pellucida. Scale bar, 20 μm. Dotted line denotes the cavity. Time is shown as h:min after E3.5. c, Top, images of E3.5 blastocyst expressing mTmG (left) and after segmentation (right). Bottom, box plot showing trophectoderm basal area normalized to cell volume in embryos of various sizes at the E3.5 (black, n = 11, 20 and 20 embryos for 1/4, 1/2 and whole embryos, respectively) and E4.5 stages (red, n = 16, 21 and 22 embryos for 1/4, 1/2 and whole embryos, respectively). Scale bar, 20 μm. Box plots show median, 25th and 75th percentiles, and whiskers extending to maximum and minimum data points.
