Nuclear distribution of SOX2 in embryonic stem cells

MC DIAZ, C OSES, M FRANCIA, P VERNERI, M STORTZ, MC DE ROSSI, A GUBERMAN, V LEVI

Congreso; REUNIÓN CONJUNTA SAIC SAB AAFE AACYTAL 2023; 2023

The transcription factors (TFs) OCT4, SOX2 and NANOG maintainthe fundamental properties of embryonic stem cells (ESCs): unlimitedcapability of self-renewal and pluripotency. In mouse ESCs theseTFs distribute heterogeneously forming condensates or foci. It wasproposed that OCT4 condensates are involved in the reorganizationof genome topologically associated domains required for cell reprogramming.This evidence suggests that TFs condensates could berelevant to cell fate decisions. However, it remains elusive whetherSOX2 or NANOG incorporate in these condensates in live cells andtheir impact in pluripotency. Here, we studied the nuclear distributionof SOX2 by using confocal microscopy in living mouse ESCsexpressing this TF fused to the fluorescent protein YPet. We analyzedthe biophysical behavior of the foci formed by SOX2-YPet toassess if they present properties compatible with those expected forliquid condensates and studied their response to osmolarity changes,to perturbations in the chromatin structure, and to the disruptionof the nucleus-cytoskeleton mechanical communication. Finally,we tested SOX2-OCT4 interactions at condensates and analyzedthe dynamics of TFs exchange by performing FCS (Fluorescencecorrelation spectroscopy) and FRAP (Fluorescence recovery afterphotobleaching) experiments. Our results suggest that SOX2 dynamicallypartitions in OCT4 condensates although this recruitmentdoes not require OCT4-SOX2 interactions. In addition, chemicalagents that perturb the epigenetic landscape of chromatin affectedSOX2 condensates suggesting that these structures depend on thechromatinic environment. These results could contribute to unveilingthe molecular mechanisms involved in the interplay between pluripotencyTFs, impacting in gene regulation programs that ultimatelydefine cell identity.