The Aryl Hydrocarbon Receptor Directs the Differentiation of Progenitor Blastomeres

Key regulatory decisions during cleavage divisions in mammalian embryogenesis determine the fate of preimplantation embryonic cells. Single-cell RNA-sequencing of early stage—2-cell, 4-cell, and 8-cell—blastomeres show that the aryl hydrocarbon receptor (AHR), traditionally considered as an environmental sensor, directs the segregation of 4-cell blastomeres. Disruption of endogenous AHR functions in Ahr knockout embryos or in embryos from dams exposed to dioxin, the prototypic xenobiotic AHR agonist, significantly impairs blastocyst formation by causing repression of OCT4 expression, decline of CDX2 expression, loss of OCT4 and CDX2 transcriptional heterogeneity, and incidence of nonspecific pluripotency downregulation. Trajectory and gene variability analyses further confirm that deregulation of OCT4 functions and changes of transcriptional heterogeneity resulting from disruption of AHR functions restrict the emergence of differentiating blastomeres within these embryos. It appears that AHR governs the differentiation of progenitor blastomeres and that interference with AHR functions significantly perturbs embryogenesis.