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4 April 2018 Sox17 is essential for proper formation of the marginal zone of extraembryonic endoderm adjacent to a developing mouse placental disk
Hitomi Igarashi, Mami Uemura, Ryuji Hiramatsu, Ryuto Hiramatsu, Saki Segami, Montri Pattarapanawan, Yoshikazu Hirate, Yuki Yoshimura, Haruo Hashimoto, Hiroki Higashiyama, Hiroyuki Sumitomo, Masamichi Kurohmaru, Yukio Saijoh, Hiroshi Suemizu, Masami Kanai-Azuma, Yoshiakira Kanai
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Abstract

In mouse conceptus, two yolk-sac membranes, the parietal endoderm (PE) and visceral endoderm (VE), are involved in protecting and nourishing early-somite-stage embryos prior to the establishment of placental circulation. Both PE and VE membranes are tightly anchored to the marginal edge of the developing placental disk, in which the extraembryonic endoderm (marginal zone endoderm: ME) shows the typical flat epithelial morphology intermediate between those of PE and VE in vivo. However, the molecular characteristics and functions of the ME in mouse placentation remain unclear. Here, we show that SOX17, not SOX7, is continuously expressed in the ME cells, whereas both SOX17 and SOX7 are coexpressed in PE cells, by at least 10.5 days postconception. The Sox17-null conceptus, but not the Sox7-null one, showed the ectopic appearance of squamous VE-like epithelial cells in the presumptive ME region, together with reduced cell density and aberrant morphology of PE cells. Such aberrant ME formation in the Sox17-null extraembryonic endoderm was not rescued by the chimeric embryo replaced with the wild-type gut endoderm by the injection of wild-type ES cells into the Sox17-null blastocyst, suggesting the cell autonomous defects in the extraembryonic endoderm of Sox17-null concepti. These findings provide direct evidence of the crucial roles of SOX17 in proper formation and maintenance of the ME region, highlighting a novel entry point to understand the in vivo VE-to-PE transition in the marginal edge of developing placenta.

Summary Sentence

The marginal extraembryonic endoderm adjacent to a developing placental disk continuously expresses SOX17 during mouse placentation; its aberrant formation was observed in Sox17-null but not Sox7-null concepti in the pregnant uterus.

© The Author(s) 2018. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com
Hitomi Igarashi, Mami Uemura, Ryuji Hiramatsu, Ryuto Hiramatsu, Saki Segami, Montri Pattarapanawan, Yoshikazu Hirate, Yuki Yoshimura, Haruo Hashimoto, Hiroki Higashiyama, Hiroyuki Sumitomo, Masamichi Kurohmaru, Yukio Saijoh, Hiroshi Suemizu, Masami Kanai-Azuma, and Yoshiakira Kanai "Sox17 is essential for proper formation of the marginal zone of extraembryonic endoderm adjacent to a developing mouse placental disk," Biology of Reproduction 99(3), 578-589, (4 April 2018). https://doi.org/10.1093/biolre/ioy079
Received: 24 January 2018; Accepted: 3 April 2018; Published: 4 April 2018
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