WNT-mediating TCF/LEF transcription factor gene expression in early human pluripotency and cell lineages differs from the rodent paradigm.

Embryonic stem (ES) cell research has uncovered different requirements for WNT/β-catenin signalling in human naïve pluripotent cells compared to the mouse paradigm. It is therefore important to study WNT/β-catenin signalling directly in models that recapitulate early human development. Since TCF/LEF transcription factors mediate regulation of target genes downstream of WNT/β-catenin signalling, we examined the regulation, expression and protein localisation of the four TCF/LEF genes by analysing in vitro 'snapshots' of human development, leveraging naïve and primed pluripotent cells, blastoids and preimplantation blastocysts. Strikingly, we comprehensively confirm clear differences between mouse and human pluripotent stem cells, suggesting their differential requirements for WNT signalling reflects a pluripotent state-dependent manner. Human naïve ES cells express considerably lower levels of TCF7L1, unlike their mouse counterparts. TCF7L2 is robustly expressed in the trophectoderm derived from naïve ES cells, in blastoids and human preimplantation blastocysts. In primed pluripotent stem cells, active WNT/β-catenin signalling induces the expression of both TCF7 and LEF1, concomitant with hallmark gastrulation markers. The expression of human TCF/LEF genes indicates a differential requirement for WNT/β-catenin signalling throughout early human embryo development that warrants further investigation.