Tbx6-dependent Sox2 regulation determines neural or mesodermal fate in axial stem cells

The classical view of neural plate development held that it arises from the ectoderm, after its separation from the mesodermal and endodermal lineages. However, recent cell-lineage-tracing experiments indicate that the caudal neural plate and paraxial mesoderm are generated from common bipotential axial stem cells originating from the caudal lateral epiblast. Tbx6 null mutant mouse embryos which produce ectopic neural tubes at the expense of paraxial mesoderm must provide a clue to the regulatory mechanism underlying this neural versus mesodermal fate choice. Here we demonstrate that Tbx6-dependent regulation of Sox2 determines the fate of axial stem cells. In wild-type embryos, enhancer N1 of the neural primordial gene Sox2 is activated in the caudal lateral epiblast, and the cells staying in the superficial layer sustain N1 activity and activate Sox2 expression in the neural plate. In contrast, the cells destined to become mesoderm activate Tbx6 and turn off enhancer N1 before migrating into the paraxial mesoderm compartment. In Tbx6 mutant embryos, however, enhancer N1 activity persists in the paraxial mesoderm compartment, eliciting ectopic Sox2 activation and transforming the paraxial mesoderm into neural tubes. An enhancer-N1-specific deletion mutation introduced into Tbx6 mutant embryos prevented this Sox2 activation in the mesodermal compartment and subsequent development of ectopic neural tubes, indicating that Tbx6 regulates Sox2 via enhancer N1. Tbx6-dependent repression of Wnt3a in the paraxial mesodermal compartment is implicated in this regulatory process. Paraxial mesoderm-specific misexpression of a Sox2 transgene in wild-type embryos resulted in ectopic neural tube development. Thus, Tbx6 represses Sox2 by inactivating enhancer N1 to inhibit neural development, and this is an essential step for the specification of paraxial mesoderm from the axial stem cells.     

Diversity of immunoglobulin expression in leukaemic cells resembling B-lymphocyte precursors

Approximately 20% of patients with acute lymphocytic leukaemia (ALL) have leukaemic blasts with features of pre-B cells which are the recently characterized precursors of B lymphocytes in normal development (for a review, see ref. 2). Pre-B cells isolated from normal bone marrow or fetal liver, and malignant cells from patients with pre-B cell leukaemia, are rapidly dividing lymphoid cells that contain cytoplasmic immunoglobulin mu heavy chains, but have no detectable surface immunoglobulin. The resemblance of immunoglobulin-containing ALL cells to normal precursors of B lymphocytes and their availability in relatively pure preparations allowed us to explore them as models of early stages in the differentiation of the B-lymphocyte line. We report here observations on the occurrence of intermediate pre-B/B-cell phenotypes, immunoglobulin isotype switching and the asynchrony of immunoglobulin heavy and light chain expression in 30 cases of ALL and 3 cases of chronic myelogenous leukaemia in lymphoblastic crisis (CML-BC).     

Bmi-1蛋白在食管鳞状细胞癌中表达及临床意义

目的:观察Bmi-1蛋白在食管鳞状细胞癌组织中的表达,探讨Bmi-1与食管鳞状细胞癌的相关性.方法:应用免疫组织化学法检测南京医科大学附属淮安第一医院2005年1月至2006年2月间168例食管鳞状细胞癌组织和30例正常食管黏膜组织Bmi-1蛋白的表达.结果:食管鳞状细胞癌组织和正常食管黏膜组织中Bmi-1蛋白的阳性表达率分别为66.1%(111/168)、23.3%(7/30),Bmi-1蛋白阳性表达率在食管鳞状细胞癌组织和正常食管黏膜组织中差异具有统计学意义(P<0.001),Bmi-1蛋白表达与食管鳞状细胞癌组织学分级、TNM分期和淋巴结转移具有相关性(P=0.016,P=0.004,P<0.001),Bmi-1阴性组的5年生存率显著优于Bmi-1阳性组(P<0.001).结论:Bmi-1表达异常在食管鳞状细胞癌发生发展中具有重要作用,检测Bmi-1的表达对判断食管鳞状细胞癌的预后具有重要意义.