Summary To acquire the capacity for multi-lineage differentiation, pluripotent stem cells must undergo a transition from naïve pluripotency to lineage competency. This transition requires epithelialization and changes in nuclear architecture. We sought to determine whether the cell and tissue mechanics intrinsic to epithelialization drive pluripotency progression and subsequent lineage commitment to neuroectodermal fate. We demonstrate that naïve mouse embryonic stem cells (mESCs) undergoing early differentiation in vitro recapitulate features of epithelialization in the peri-implantation epiblast, specifically apical constriction. We further demonstrate that cell contractility during apical constriction induces a distinct nuclear mechanoresponse, notably enrichment of emerin at the outer nuclear membrane, nuclear envelope localization of SUN2, and the global loss of H3K9me3 heterochromatin which is compensated by H3K27me3. Importantly, these nuclear phenotypes and subsequent neuroectodermal lineage priming require myosin II-mediated contractility, an intact LINC complex, and emerin. We demonstrate that LINC-dependent mechanotransduction through emerin regulates H3K27me3 occupancy on the key early neuroectodermal transcription factor gene, Sox1 , implicating a mechanical switch in chromatin mediation of neuroectodermal lineage competence. These results indicate that epithelialization-induced nuclear mechanotransduction poises a critical lineage gene for subsequent expression. Highlights Adherent naïve mESCs in vitro recapitulate in utero apical constriction morphogenesis. Contractility, the LINC complex and emerin are required for neuroectodermal lineage competence. Contractility and the LINC complex are required for widespread loss of H3K9me3 and gain of H3K27me3 on Sox1 promoter.