The Aryl Hydrocarbon Receptor Promotes Differentiation During Mouse Preimplantational Embryo Development

Abstract

Mammalian embryogenesis is a complex process controlled by transcription factors that dynamically regulate the balance between pluripotency and differentiation. Transcription factor AhR is known to regulate Oct4/Pou5f1 and Nanog, both essential genes in pluripotency, stemness and early embryo development. Yet, the molecular mechanisms controlling Oct4/Pou5f1 and Nanog during embryo development remain largely unidentified. Here, we show that AhR is required for proper embryo differentiation by regulating pluripotency factors and by maintaining adequate metabolic activity. AhR lacking embryos (AhR-/-) showed a more pluripotent phenotype characterized by a delayed expression of differentiation markers of the first and second cell divisions. Accordingly, central pluripotency factors OCT4/POU5F1, NANOG, and SOX2 were overexpressed in AhR-/- embryos at initial developmental stages. An altered intracellular localization of these factors was observed in absence of AhR and, importantly, OCT4 had an opposite expression pattern with respect to AhR from the 2-cell stage to blastocyst, suggesting a negative regulatory mechanism of OCT4/POU5F by AhR. Hippo signalling, rather than being repressed, was upregulated in very early AhR-/- embryos, possibly contributing to their undifferentiation at later stages. Consistently, AhR-null blastocysts overexpressed the early marker of inner cell mass (ICM) differentiation Sox17 whereas downregulated extraembryonic differentiation-driving genes Cdx2 and Gata3. Moreover, the persistent pluripotent phenotype of AhR-/- embryos was supported by an enhanced glycolytic metabolism and a reduction in mitochondrial activity. We propose that AhR is a regulator of pluripotency and differentiation in early mouse embryogenesis and that its deficiency may underline the reduced viability and increased resorptions of AhR-null mice.

Liver regeneration after partial hepatectomy is improved in the absence of aryl hydrocarbon receptor

“…We have shown that Ahr is required to adjust liver regeneration after acute toxic injury 22 and we and others have reported that Ahr serves to reduce hepatocarcinogenesis burden caused by postnatal exposure to diethylnetrosamine in mice 22,41 . Moreover, previous work also suggest that the higher regenerative potential and increased susceptibility to carcinogenesis of Ahr-null mice could be due to their more undifferentiated and pluripotent phenotype in different organs including liver 21,22,30,[42][43][44][45] . In this study, we have investigated potential mechanisms through which Ahr adjusts liver regeneration in response to a massive tissue removal resembling that used in humans.…”

“…Reverse transcription was done using random priming and the iScript Reverse Transcription Super Mix (Bio-Rad). Real-time PCR (qPCR) was performed using SYBR ® Select Master Mix (Life Technologies) in a Step One Thermal Cycler (Applied Biosystems) as indicated 42,43 . Gapdh was used to normalize target gene expression (ΔCt) and 2 −ΔΔCt to calculate changes in mRNA levels with respect to untreated control conditions.…”