The splicing factor Sf3b1 regulates erythroid maturation and proliferation via TGFβ signaling in zebrafish.

The spliceosomal component Splicing Factor 3B, subunit 1 (SF3B1) is one of the most prevalently mutated factors in the bone marrow failure disorder myelodysplastic syndrome. There is a strong clinical correlation between SF3B1 mutations and erythroid defects, such as refractory anemia with ringed sideroblasts, but the role of SF3B1 in normal erythroid development is largely unknown. Loss-of-function zebrafish mutants for develop a macrocytic anemia. Here, we explore the underlying mechanism for anemia associated with deficiency in vivo. We found that mutant erythroid progenitors display a G0/G1 cell-cycle arrest with mutant erythrocytes showing signs of immaturity. RNA-sequencing analysis of mutant erythroid progenitors revealed normal expression of red blood cell regulators such as genes, and heme biosynthetic factors, but upregulation of genes in the transforming growth factor β (TGFβ) pathway. As TGFβ signaling is a known inducer of quiescence, the data suggest that activation of the pathway could trigger deficiency-induced anemia via cell-cycle arrest. Indeed, we found that inhibition of TGFβ signaling released the G0/G1 block in erythroid progenitors. Surprisingly, removal of this checkpoint enhanced rather than suppressed the anemia, indicating that the TGFβ-mediated cell-cycle arrest is protective for -mutant erythrocytes. Together, these data suggest that macrocytic anemia arising from Sf3b1 deficiency is likely due to pleiotropic and distinct effects on cell-cycle progression and maturation.