[Show abstract][Hide abstract] ABSTRACT: Ldb1, a ubiquitously expressed LIM domain binding protein, is essential in a number of tissues during development. It interacts with Gata1, Tal1, E2A and Lmo2 to form a transcription factor complex regulating late erythroid genes. We identify a number of novel Ldb1 interacting proteins in erythroleukaemic cells, in particular the repressor protein Eto-2 (and its family member Mtgr1), the cyclin-dependent kinase Cdk9, and the bridging factor Lmo4. MO-mediated knockdowns in zebrafish show these factors to be essential for definitive haematopoiesis. In accordance with the zebrafish results these factors are coexpressed in prehaematopoietic cells of the early mouse embryo, although we originally identified the complex in late erythroid cells. Based on the change in subcellullar localisation of Eto-2 we postulate that it plays a central role in the transition from the migration and expansion phase of the prehaematopoietic cells to the establishment of definitive haematopoietic stem cells.
[Show abstract][Hide abstract] ABSTRACT: We have described the application of a simple biotinylation tagging approach for the direct purification of tagged transcription factor complexes, based on the use of artificial short peptide tags that are specifically and efficiently biotinylated by the bacterial BirA biotin ligase, which is co-expressed in cells with the tagged factor. We used this approach to initially characterize complexes formed by the hematopoietic transcription factor GATA-1 in erythroid cells. GATA-1 is essential for the erythroid differentiation, its functions encompassing upregulation of erythroid genes, repression of alternative transcription programs, and suppression of cell proliferation. However, it was not clear how all of these GATA-1 functions are mediated. Our work describes, for the first time, distinct GATA-1 interactions with the essential hematopoietic factor Gfi-1b, the repressive MeCP1 complex, and the chromatin remodeling ACF/WCRF complex, in addition to the known GATA-1/FOG-1 and GATA-1/TAL-1 complexes. We also provide evidence that distinct GATA-1 complexes are associated with specific GATA-1 functions in erythroid differentiation, for example, GATA-1/Gfi-1b with the suppression of cell proliferation and GATA-1/FOG-1/MeCP1 with the repression of other hematopoietic transcription programs. We next applied the biotinylation tag to Ldb-1, a known partner of GATA-1, and characterized a number of novel interaction partners that are essential in erythroid development, in particular, Eto-2, Lmo4, and CdK9. Last, we are in the process of applying the same technology to characterize the factors that are bound to the suppressed gamma-globin promoter in vivo.
Full-text · Article · Feb 2005 · Annals of the New York Academy of Sciences