转录因子GATA-1在造血系统中的作用(综述)

转录因子GATA-1为正常红细胞发育和分化成熟所必需。GATA-1的表达严格限制于造血细胞系,主要调控红系的增殖和分化,对巨核系、肥大细胞系及嗜酸性粒细胞系也起一定的作用。GATA-1参与自身启动子的正调节,而且GATA-1和PU.1可以通过交互作用抑制各自的功能;GATA-1与红系Kr櫣ppel样因子(EKLF)、FKLF-2、SCL、生长因子骨形态生成蛋白(BMP-4)及其他GATA转录因子之间存在相互调控作用。GATA-1可在急性非淋巴细胞性白血病等多种类型白血病中表达,它的表达还可影响急性髓性白血病的预后。GATA-1还与遗传性球形红细胞增多症、伴有严重贫血的多发性骨髓瘤的发病机制有关。     

Developmental regulation of a cloned adult beta-globin gene in transgenic mice

At different stages of mammalian development, distinct embryonic, fetal and adult haemoglobins are synthesized in erythroid cells, a process termed haemoglobin switching. The cellular and molecular mechanisms controlling haemoglobin switching have been intensively studied, but remain poorly understood. To study the developmental regulation of globin gene expression, we have produced transgenic mice in which cloned globin genes are present in erythroid cells throughout development. Recently, we reported that adult mice in several transgenic lines carrying a hybrid mouse/human adult beta-globin gene, expressed the gene in a correct tissue-specific manner. This finding raised the question of whether an exogenous globin gene could also be subject to appropriate stage-specific regulation. We report here that the hybrid beta-globin gene, like the endogenous adult beta-globin genes, is inactive in yolk sac-derived embryonic erythroid cells and is expressed for the first time in fetal liver erythroid cells. Our results indicate that a stage-specific pattern of expression can be conferred by cis-acting regulatory elements closely linked to an adult beta-globin gene. They also suggest that the embryonic and adult beta-globin genes in the mouse are activated (or repressed) by distinct trans-acting regulatory factors present in embryonic, fetal and adult erythroid cells.     

An embryonic pattern of expression of a human fetal globin gene in transgenic mice

During the evolution of the beta-globin family gene in vertebrates, different globin genes acquired different developmental patterns of expression. In mammals, specific 'embryonic' beta-like globins are synthesized in the earliest erythroid cells, which differentiate in the yolk sac of the embryo. In most mammals the embryonic globin chains are replaced by 'adult' beta-globins in fetal and adult erythrocytes, which arise in the liver and bone marrow, respectively. However, in simian primates (including humans), a distinct 'fetal' type of beta-like globin chain predominates in fetal erythroid cells. Based on the pattern of DNA sequence homologies between different mammalian species, these fetal globin genes, G gamma and A gamma, are thought to have descended from an ancestral gene, 'proto-gamma', which was embryonic in its pattern of expression. In the mouse, as well as in most other mammalian species, the descendants of the proto-gamma gene continue to function as embryonic genes. To investigate the evolutionary changes that led to the 'fetal recruitment' of the gamma-globin genes in primates, we have introduced the cloned human G gamma-globin gene into the mouse germ line. We report here that the human G gamma gene reverts to an embryonic pattern of expression in the developing mouse. This observation suggests that during evolution a shift occurred in the timing of expression of a trans-acting signal controlling the proto-gamma gene.     

cdx4 mutants fail to specify blood progenitors and can be rescued by multiple hox genes

Organogenesis is dependent on the formation of distinct cell types within the embryo. Important to this process are the hox genes, which are believed to confer positional identities to cells along the anteroposterior axis. Here, we have identified the caudal-related gene cdx4 as the locus mutated in kugelig (kgg), a zebrafish mutant with an early defect in haematopoiesis that is associated with abnormal anteroposterior patterning and aberrant hox gene expression. The blood deficiency in kgg embryos can be rescued by overexpressing hoxb7a or hoxa9a but not hoxb8a, indicating that the haematopoietic defect results from perturbations in specific hox genes. Furthermore, the haematopoietic defect in kgg mutants is not rescued by scl overexpression, suggesting that cdx4 and hox genes act to make the posterior mesoderm competent for blood development. Overexpression of cdx4 during zebrafish development or in mouse embryonic stem cells induces blood formation and alters hox gene expression. Taken together, these findings demonstrate that cdx4 regulates hox genes and is necessary for the specification of haematopoietic cell fate during vertebrate embryogenesis.     

Consecutive inactivation of both alleles of the pim-1 proto-oncogene by homologous recombination in embryonic stem cells

Specific genes can be inactivated or mutated in the mouse germ line. The phenotypic consequences of the mutation can provide pivotal information on the function of the gene in development and maintenance of the mammalian organism. The procedure entails homologous recombination in embryonic stem cells, which, on fusion to recipient blastocysts, give rise to chimaeric mice that can transmit the mutant gene to their offspring. Inbreeding can then yield mice carrying the mutation in both alleles allowing the phenotypic analysis of recessive mutations. In addition to mice lacking a particular gene function, cell lines carrying null alleles of normally expressed genes can be instrumental in assessing the function of the gene. These cell lines can either be obtained from homozygous animals or, should the mutation be lethal early in embryonic development, be generated by consecutive inactivation of both alleles by homologous recombination in cultured cells. Here we illustrate the feasibility of this latter approach by the efficient consecutive inactivation of both alleles of the pim-1 proto-oncogene in embryonic stem cells.     

Changing potency by spontaneous fusion

Recent reports have suggested that mammalian stem cells residing in one tissue may have the capacity to produce differentiated cell types for other tissues and organs 1-9. Here we define a mechanism by which progenitor cells of the central nervous system can give rise to non-neural derivatives. Cells taken from mouse brain were co-cultured with pluripotent embryonic stem cells. Following selection for a transgenic marker carried only by the brain cells, undifferentiated stem cells are recovered in which the brain cell genome has undergone epigenetic reprogramming. However, these cells also carry a transgenic marker and chromosomes derived from the embryonic stem cells. Therefore the altered phenotype does not arise by direct conversion of brain to embryonic stem cell but rather through spontaneous generation of hybrid cells. The tetraploid hybrids exhibit full pluripotent character, including multilineage contribution to chimaeras. We propose that transdetermination consequent to cell fusion 10 could underlie many observations otherwise attributed to an intrinsic plasticity of tissue stem cells 9.     

A cell autonomous function of Brachyury in T/T embryonic stem cell chimaeras

Developmental genetics has shown that the Brachyury (T) gene has a key role in mesoderm formation during gastrulation in the mouse. Homozygous embryos have a defective allantois, degenerate or absent notochord and disrupted primitive streak and node. The neural tube is kinked and somite formation interrupted. The T gene has been cloned and is expressed during the early stages of gastrulation, being restricted to the primitive streak region, nascent mesoderm and notochord. Neither the sequence of the gene nor its expression pattern define its developmental function. To study the cell autonomy of the T mutation we have isolated and genetically characterized embryonic stem cell lines and studied their behaviour in chimaeras. T/+ embryonic stem cells form normal chimaeras, whereas T/T in equilibrium with +/+ chimaeras mimic the T/T mutant phenotype. The results indicate that the T gene acts cell autonomously in the primitive streak and notochord but may activate a signalling pathway involved in the specification of other mesodermal tissues.     

Monoclonal mice generated by nuclear transfer from mature B and T donor cells

Cloning from somatic cells is inefficient, with most clones dying during gestation. Cloning from embryonic stem (ES) cells is much more effective, suggesting that the nucleus of an embryonic cell is easier to reprogram. It is thus possible that most surviving clones are, in fact, derived from the nuclei of rare somatic stem cells present in adult tissues, rather than from the nuclei of differentiated cells, as has been assumed. Here we report the generation of monoclonal mice by nuclear transfer from mature lymphocytes. In a modified two-step cloning procedure, we established ES cells from cloned blastocysts and injected them into tetraploid blastocysts to generate mice. In this approach, the embryo is derived from the ES cells and the extra-embryonic tissues from the tetraploid host. Animals cloned from a B-cell nucleus were viable and carried fully rearranged immunoglobulin alleles in all tissues. Similarly, a mouse cloned from a T-cell nucleus carried rearranged T-cell-receptor genes in all tissues. This is an unequivocal demonstration that a terminally differentiated cell can be reprogrammed to produce an adult cloned animal.