STAT3 signalling drives tissue expansion during postimplantation mouse development [scRNA-seq]

STAT3 has been studied extensively in the context of self-renewal of naïve pluripotent mouse embryonic stem cells (mESCs). Although STAT3 is required to maintain ICM lineages when maternally eliminated, the role of STAT3 during gastrulation is unclear as the conventional knockout of Stat3 develops until E6.5. In this study, we observed that zygotic loss of Stat3 on CD1 genetic background leads to consistent developmental retardation from implantation to mid-gestation, beginning with a significant reduction in the number of epiblast cells by the time of implantation. Remarkably, mutants appear to scale normally and resemble non-affected embryos from the previous day at all postimplantation stages examined. Bulk RNA-seq analysis using isolated epiblast cells revealeed that E6.5 null epiblasts were intermediate between WT E5.5 and E6.5; E7.5 null epiblasts grouped more closely with WT E6.5 than E7.5 epiblasts. Gene ontology analysis revealed lipid metabolism was compromised in Stat3 null embryos as early as E6.5. Interestingly, Socs3, downstream target of STAT3, was not induced in WT rpiblast cells until E7.5. We found Y705 phospholylated STAT3 was not exist postimplantation epiblast, but S727 phoshorylated STAT3 was abundant over the time, suggesting postimplantation specific roles of S727 phosphorylated STAT3 in growth and differentiation. Our study revealed that while Stat3 null epiblast cells progress along a near normal differentiation trajectory, Stat3 deletion compromises lipid metabolism as early as E6.5.