Delineating the Functions of Cohesin Stag1 during Terminal Erythroid Differentiation

Erythroid terminal differentiation is defined by a series of precise, orchestrated and dynamic changes in the genomic architecture that is consistent with the transcriptional programing towards producing mature blood cells. In recent times, these architectural shifts are under scrutiny, not only because they shed light into the mechanisms underlying erythroid differentiation, but also because corruption of the organization principle can result in compromised hematopoietic function and tumor formation. Functionally, genome organization relies upon the concerted action of proteins such as the cohesion complex and CTCF. In this study, we identify Stag1, a cohesin protein, as a factor that contributes to the erythroid transcriptional machinery during terminal differentiation. Stag1 levels increase during terminal differentiation and depletion of Stag1 either using short hairpin RNA or using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR-Cas) in Hudep2 or CD34+ cells, results in a drastic reduction of both adult globins, α- and β-globin. This is not the case when Stag1's paralogue, Stag2, is knocked-down. Further, we observe faster proliferation in erythroid cells after Stag1 depletion and these cells also demonstrate an undercondensed nucleus and a larger cell-size. This could reflect the delayed differentiation, as the cells proceeded to undergo slower differentiation as compared to their WT counterparts. Metaphase spreads of the Stag1 depleted cells suggests an altered cohesion phenotype and further provides clues into a possible epigenetic defect underlying the observed phenotypes in erythroid cells, which is being further investigated.