Cellular differentiation is associated with dynamic chromatin remodeling in establishing a cell-type-specific epigenomic landscape. Here, we find that mouse testis-specific and replication-dependent histone H3 variant H3t is essential for very early stages of spermatogenesis. H3t gene deficiency leads to azoospermia because of the loss of haploid germ cells. When differentiating spermatogonia emerge in normal spermatogenesis, H3t appears and replaces the canonical H3 proteins. Structural and biochemical analyses reveal that H3t-containing nucleosomes are more flexible than the canonical nucleosomes. Thus, by incorporating H3t into the genome during spermatogonial differentiation, male germ cells are able to enter meiosis and beyond.

The Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathway is an important signaling pathway of interferons and cytokines. We examined the activation of STAT proteins induced by interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or erythropoietin (EPO) using the human leukemia cell line, UT-7, which requires these cytokines for growth. IL-3, GM-CSF, and EPO induced DNA-binding activity to the oligonucleotides corresponding to the sis-inducible elements (SIE) of c-fos, in addition to the ␤-casein promoter (␤-CAP), SIE-and ␤-CAP-binding proteins were identical to Stat1␣ and Stat3 complex and to Stat5 protein, respectively. This indicates that IL-3, GM-CSF, and EPO commonly activated Stat1␣, Stat3, and Stat5 proteins in UT-7. However, EPO hardly activated Stat1␣ and Stat3 in UT-7/GM, which is a subline of UT-7 that grows slightly in response to EPO. Transfection studies revealed that UT-7/GM cells constitutively expressing Stat1␣, but not Stat3, can grow as well in response to EPO as GM-CSF, suggesting that Stat1␣ is involved in the EPO-induced proliferation of UT-7. Thus, although Stat1␣, Stat3, and Stat5 proteins are activated by GM-CSF, IL-3, and EPO, our data suggest that each STAT protein has a distinctive role in the actions of cytokines.

UT-7 is a human megakaryoblastic leukemia cell line with absolute dependence on interleukin-3, granulocyte-macrophage colony-stimulating factor, or erythropoietin (EPO) for growth and survival. We investigated the effect of thrombopoietin (TPO), the ligand for the receptor encoded by c-mpl proto-oncogene, on the proliferation and differentiation of UT-7 and its sublines. We found that UT-7/GM, which is a subline of UT-7, but neither UT-7 nor UT-7/EPO, can proliferate in response to TPO. The subline, UT-7/TPO, was established from UT-7/GM by culture at lower concentrations of TPO. UT-7/TPO cells had morphologically mature megakaryocytic characteristics such as developed demarcation membrane in the cytoplasm and multinucleated appearance. This was also confirmed by the high expression of platelet factor-4 and glycoprotein IIb at the mRNA levels and by the high level of DNA content. UT-7/TPO can be maintained by TPO alone, with a doubling time of 24 hours in log growth phase. In the absence of TPO, the majority of the cells died within a few days. Thus, UT-7/TPO has an absolute dependence on TPO for growth and survival and has mature megakaryocytic features. The mRNA for c-mpl was detected in UT-7/TPO and, to a lesser degree, in UT-7/GM. The mRNA level of NF- E2 p45, reported to be an erythroid-specific transcription factor, was upregulated in UT-7/TPO, whereas it was down-regulated in the erythroid subline, UT-7/EPO. There were no significant differences in GATA-1 and GATA-2 mRNA levels among UT-7 and its sublines. Not only EPO but also TPO induced the tyrosine phosphorylation of JAK2 tyrosine kinase and STAT5-related protein. These findings indicate that UT-7/TPO would be a useful model with which to analyze the gene regulation of megakaryocytic maturation- associated proteins and to study the specific actions of TPO.

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Acquired hemophilia A is a rare and potentially fatal condition of coagulopathy caused by autoantibodies against clotting factor VIII (factor VIII inhibitor). We report a case of a 63-year-old woman, who presented with a sudden onset of severe hemorrhagic tendency with exclusively prolonged activated partial thromboplastin time (APTT). She was diagnosed with acquired hemophilia A due to a decrease in factor VIII activity and a high titer of factor VIII inhibitor. Hemorrhage was well controlled by recombinant activated factor VII. Although the level of factor VIII inhibitor did not decline with prednisolone and cyclophosphamide, it became undetectable with rituximab. In parallel with controlling hemorrhage, malignancy, which may cause acquired hemophilia A, was searched for and sigmoid colon cancer was found. After the eradication of factor VIII inhibitor, surgical resection was performed uneventfully. Thereafter, acquired hemophilia A has been in complete remission without any additional therapy. The present case suggests the efficacy of rituximab for refractory acquired hemophilia A and the importance of the identification of underlying diseases that can cause acquired hemophilia A.