The role of Septin6 Group in Murine and Human Hematopoiesis

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(PLEASE KEEP IN WORD, DO NOT PDF) Title: The role of Septin6 Group in Murine and Human Hematopoiesis 1 R01 DK137172-01 Septins are highly conserved GTPase proteins which regulate a variety of cellular functions including cytokinesis, polarity, cell cycle, vesicle trafficking, exocytosis, and creation of diffusion barriers. We have recently identified a non-syndromic newborn with severe neutropenia (Renella, AJH 2022) with a novel X-linked germline mutation in the C-terminus of SEPTIN6 gene (SEPTIN6 c.1282T>C p.428Glnext*9) associated with dysmyelopoiesis. Editing the germline mutation into normal male CD34+ hematopoietic stem and progenitor cells (HSC/P) phenocopied key pathologic features of the clinical syndrome, including large, multinucleated nuclei and reduced myeloid progenitor growth in vitro (preliminary data). The C-terminus has been proposed to play a key role in filament stabilization, bundling and bending as well as interactions with other septins and in silico modeling suggest the addition of 9 amino acids (aa) associated with the SEPTIN6 c.1282T>C p.428Glnext*9 mutation would alter function by interfering with SEPTIN6 protein interactions. Based on our initial publication, a second patient with severe neutropenia has since been identified in Seattle with a distinct mutation in the same codon (SEPTIN6 c.1282T>A) (Mohamad, Allensbach, Williams, accepted for presentation, ASH 2022). While the aa substitution is different, modeling predicts that SEPTIN6 variants adopt the same structure. Both identified patients had a high degree of myeloid tetraploidy in the marrow and were refractory to G-CSF.