Transcription Elongation Factor S-II Is Required for Definitive Hematopoiesis

Abstract

Transcription elongation factor S-II/TFIIS promotes readthrough of transcriptional blocks by stimulating nascent RNA cleavage activity of RNA polymerase II in vitro. The biologic significance of S-II function in higher eukaryotes, however, remains unclear. To determine its role in mammalian development, we generated S-II-deficient mice through targeted gene disruption. Homozygous null mutants died at midgestation with marked pallor, suggesting severe anemia. S-II^−/− embryos had a decreased number of definitive erythrocytes in the peripheral blood and disturbed erythroblast differentiation in fetal liver. There was a dramatic increase in apoptotic cells in S-II ^−/− fetal liver, which was consistent with a reduction in Bcl-x_L gene expression. The presence of phenotypically defined hematopoietic stem cells and in vitro colony-forming hematopoietic progenitors in S-II ^−/− fetal liver indicates that S-II is dispensable for the generation and differentiation of hematopoietic stem cells. S-II-deficient fetal liver cells, however, exhibited a loss of long-term repopulating potential when transplanted into lethally irradiated adult mice, indicating that S-II deficiency causes an intrinsic defect in the self-renewal of hematopoietic stem cells. Thus, S-II has critical and nonredundant roles in definitive hematopoiesis.

We thank Toshiyuki Nakanishi for the gift of the anti-S-II antibody and critical review of the manuscript, Makoto M. Taketo for the pNeoDTA, Toshio Kitamura for the STAT5 expression vectors, Norio Komatsu for the Bcl-x_L reporter plasmids, and Kirin Brewery Co., Ltd., for the recombinant human erythropoietin.

This work was supported by grants from the Ministry of Education, Science, Sports, and Culture and the Japan Society for the Promotion of Science (JSPS).