Interleukin-6 promotes primitive endoderm development in bovine blastocysts

Lydia K. Wooldridge,Alan D. Ealy

doi:10.1186/s12861-020-00235-z

Abstract

BackgroundInterleukin-6 (IL6) was recently identified as an embryotrophic factor in bovine embryos, where it acts primarily to mediate inner cell mass (ICM) size. This work explored whether IL6 affects epiblast (EPI) and primitive endoderm (PE) development, the two embryonic lineages generated from the ICM after its formation. Nuclear markers for EPI (NANOG) and PE (GATA6) were used to differentiate the two cell types.ResultsIncreases (P < 0.05) in total ICM cell numbers and PE cell numbers were detected in bovine blastocysts at day 8 and 9 post-fertilization after exposure to 100 ng/ml recombinant bovine IL6. Also, IL6 increased (P < 0.05) the number of undifferentiated ICM cells (cells containing both PE and EPI markers). The effects of IL6 on EPI cell numbers were inconsistent. Studies were also completed to explore the importance of Janus kinase 2 (JAK2)-dependent signaling in bovine PE cells. Definitive activation of STAT3, a downstream target for JAK2, was observed in PE cells. Also, pharmacological inhibition of JAK2 decreased (P < 0.05) PE cell numbers.ConclusionsTo conclude, IL6 manipulates ICM development after EPI/PE cell fates are established. The PE cells are the target for IL6, where a JAK-dependent signal is used to regulate PE numbers.

Highlights

Interleukin-6 (IL6) was recently identified as an embryotrophic factor in bovine embryos, where it acts primarily to mediate inner cell mass (ICM) size
Supplementation with IL6 influences ICM cell numbers The initial study was completed to describe whether IL6 supplementation increases embryo cell numbers when provided after blastocyst formation (Fig. 1)
After 24 h, blastocysts were processed to Blastocysts were cultured in SOF-BE1 until day 8, 9 or 10 post-fertilization, differential cell staining was completed to discriminate ICM cells (CDX2− / DAPI+) from TE cells (CDX2+ / DAPI+)

Summary

Introduction

Interleukin-6 (IL6) was recently identified as an embryotrophic factor in bovine embryos, where it acts primarily to mediate inner cell mass (ICM) size. Bovine blastocysts express the IL6-specific receptor subunit (IL6R) and the common IL6 family receptor subunit (IL6ST, known as GP130), and IL6R is the most abundantly expressed ligand-specific receptor subunit within this cytokine family in bovine blastocysts [3] Recent work from this group described that IL6 can influence in vitro-produced (IVP) bovine embryo development [3, 5]. Problems with ICM development likely contribute to the high rate of failed pregnancies in transferred IVP bovine embryos [6] These problems include reductions in ICM cell numbers, increases in the incidence of apoptosis within the ICM, and retarded post-transfer development of the embryonic disk, which develops from the ICM and produces all embryonic tissues and the yolk sac and allantoic membranes [7,8,9,10,11]

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