Stem cell leukemia protein directs hematopoietic stem cell fate

Abstract

Stem cell leukemia (SCL) protein has been shown to be an essential transcription factor during hematopoietic development in the embryo. In adult hematopoiesis, however, the role for SCL has remained largely unknown, whereas it is expressed in bone marrow hematopoietic stem cells (HSCs). In this study, we performed HSC transplantation and an in vitro HSC differentiation assay using retrovirally transduced HSCs with wild-type (WT) and dominant- IntroductionHematopoietic stem cells (HSCs) that can give rise to all lineages of blood cells are enriched in surface marker-defined populations, such as those that are lineage marker (Lin)-negative, c-Kitpositive, Sca-1-positive, and CD34-low/negative (Lin Ϫ c-Kit ϩ Sca-1 ϩ CD34 low/Ϫ [34 Ϫ KSL] 1 ) in adult mouse bone marrow. Recently, common myeloid progenitors (CMPs) 2 and common lymphoid progenitors (CLPs) 3 were identified by surface marker profiles as clonogenic cells that can generate all lineages of myeloid and lymphoid cells, respectively, without any potential to differentiate into one another. Therefore, the first step in blood production from an HSC must be initiated by commitment to a CMP 2 and a CLP. 3 This process, like other differentiation processes, is governed by an expression profile of transcription factors. Although a number of transcription factors are known to be involved in commitment and differentiation processes during hematopoiesis, 4 none have been identified that play roles in the progression from an HSC to a CLP and a CMP. It was reported that CLPs and CMPs differ in the expression pattern of transcription factors: stem cell leukemia (SCL), a basic helix-loop-helix (bHLH) motif-containing transcription factor, 5 and GATA2, a zinc finger motif-containing transcription factor, are expressed in HSCs and CMPs but not in CLPs. 2 SCL appears to play roles in hematopoietic cell differentiation into myeloid, erythroid, megakaryocyte, and mast cell lineages because it is preferentially expressed during early cell stages in these lineages. [6][7][8][9][10][11][12] Studies in knockout mice have revealed that SCL is indispensable in the early stages of primitive embryonic hematopoiesis, when it functions in the specification of ventral mesoderm to blood cells and in the formation or maintenance of immature blood progenitors. 13,14 Studies using embryonic stem cells in vitro have demonstrated that SCL is necessary for the development of bipotent progenitors of blood and endothelial cells in vertebrates. 15,16 Furthermore, ectopic expression of SCL promotes the proliferation and inhibits the apoptosis of 32D, a late myeloid progenitor cell line; these effects are dependent on the bHLH domain. 17 Essential roles for SCL in megakaryopoiesis and erythropoiesis in the adult mouse bone marrow were recently demonstrated by conditional targeting of the SCL gene. 18,19 To clarify the roles of SCL in the commitment process of an HSC to a CLP and a CMP, we performed HSC transplantation and an in vitro HSC differentiation assay using retrovirally transduced HSCs wit...

SCL/TAL1 expression level regulates human hematopoietic stem cell self-renewal and engraftment

“…Moreover, another study indicated that enforced TAL1 expression changes the differentiation but not the repopulation capability of mouse HSCs. 36 However, in this study, no secondary transplantation was performed to assay the effect of long-time exposure of mouse HSCs to enforced TAL1 expression; thus, no real conclusion can be drawn on the effect of TAL1 on mouse HSC self-renewal.…”

“…Moreover, another study indicated that enforced TAL1 expression changes the differentiation but not the repopulation capability of mouse HSCs. 36 However, in this study, no secondary transplantation was performed to assay the effect of long-time exposure of mouse HSCs to enforced TAL1 expression; thus, no real conclusion can be drawn on the effect of TAL1 on mouse HSC self-renewal.As a consequence of the enhancement of LT-SRC activity, we show an amplification of SRC-derived myeloid/erythroid progenitors (LTC-ICs and CFCs), finally resulting into an increase of mature myeloid and erythroid cells. This latter phenomenon is however quantitatively less important than the amplification of their direct progenitors and maybe reminiscent of HSC amplification by HOXB4 whereby hematopoietic homeostasis limits the expansion of differentiated cells 3 or because of the reduced crossreactivity of mouse cytokines implicated in late steps of human differentiation.…”

“…32,33 Moreover, the proportion of B-lymphoid cells and myeloid cells was inverted in TAL1 ϩ cells (B/myeloid ratio ϭ 0.1) as compared with GFP ϩ cells (B/myeloid ratio ϭ 5.7) ( Figure 2F-G Figure 2F) similarly to the results described recently in the mouse. 36 Because TAL1 is involved in human T-cell acute lymphoblastic leukemia (T-ALL), T-cell potential of transduced SRC-derived cells was also investigated in vivo in NOD-SCID thymuses. Indeed, the treatment of NOD-SCID mice with an anti-CD122 monoclonal antibody allows human T-cell development following long-term engraftment.…”

Notch mediates Wnt and BMP signals in the early separation of smooth muscle progenitors and blood/endothelial common progenitors

“…Fertilized quail eggs were purchased from Tokaiyuki (Toyohashi, Japan). dENotch1 (a gift from R. Kopan, Washington University, MS, USA) (Schroeter et al, 1998) with a 12ϫMyc-tag, DnSu(H) (a gift from Dr C. Kintner, Salk Institute, CA, USA) (Wettstein et al, 1997) with a 6ϫMyc-tag, dHAND (a gift from M. Howard, Medical University of Ohio, OH, USA) (Howard et al, 1999) with a 6ϫMyc-tag, and Scl (a gift from A. Chiba, University of Tokyo Hospital, Japan) (Kunisato et al, 2004) with a 6ϫMyc-tag were sub-cloned into the pCAGGS vector (a gift from H. Niwa, RIKEN, Japan) (Niwa et al, 1991), and a 3-4 μg/μl DNA concentration was used for electroporation. The CA-ALK6 expression construct was a gift from Dr H. Kondoh (Osaka University, Osaka, Japan) and Dr K. Miyazono (University of Tokyo, Tokyo, Japan).…”

Ubiquitination and Degradation of Tal1/SCL Are Induced by Notch Signaling and Depend on Skp2 and CHIP

“…Deletion of the gene specifically in hematopoietic lineages reveals that Tal1 is necessary for short term hematopoietic stem cell function but dispensable for long term stem cell activity (21,22). This protein is also thought to play an important role in erythroid differentiation, and its overexpression directs multipotent progenitors to develop along the myeloid lineage (23,24). Interestingly, Notch signaling is also thought to be involved in hematopoietic stem cell maintenance (25).…”