3042 – GROUP F SOX GENES DIRECT HUMAN EMBRYONIC VASCULAR AND HAEMATOPOIETIC DEVELOPMENT

We explored the generation of endothelial (mCHERRY-SOX17) and haematopoietic (RUNX1C) development using in vitro differentiation of human pluripotent stem cells. Deletion of SOX17 or all GROUP F SOX genes (SOX7, SOX17, SOX18) did not influence extra-embryonic yolk sac-like haematopoiesis, but expression of the GROUP SOX F genes was required for the generation of a mCHERRY+DLL4+CXCR4+ arterial population. Intra-embryonic differentiation of SOX17-KO and GROUP F-KO cultures exhibited severely perturbed development of AGM-like vessels, reduced haemogenic capacity and resulted in a shift from arterial to venous patterning. Haematopoietic capacity was similarly disrupted, with an early wave of blood cell progenitors observed in GROUP F-KO cultures, leading to decreased colony forming ability, rapid CD90+CD45+CD34+ progenitor pool exhaustion and altered T-cell specification. This phenotype was mediated by dysregulated NOTCH signaling and recapitulated by inhibiting g-secretase. Transcriptional analysis of d7 CD34+ endothelial cells preempted reduced NOTCH signaling and arterial patterning, increased venous gene expression and early expression profile of haematopoietic genes observed in both SOX17-KO and GROUP F-KO cells. Together, these data illustrate the key role of GROUP F-KO genes in orchestrating human vascular and haematopoietic development.