Novel binding partners of Ldb1 are required for haematopoietic development

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.

Functional Interactions between Erythroid Kruppel-like Factor (EKLF/KLF1) and Protein Phosphatase PPM1B/PP2Cβ

“…Regulation of ␤-Globin Induction by Ppm1b-Previous studies have demonstrated that depletion or inhibition of Cdk9 results in a specific defect in definitive hematopoiesis (35) and erythroid induction (36). This may be by virtue of the fact that Cdk9 associates in an erythroid-specific transcription complex with SCL, Ldb1, Runx1, and GATA1 (35,36).…”

“…This may be by virtue of the fact that Cdk9 associates in an erythroid-specific transcription complex with SCL, Ldb1, Runx1, and GATA1 (35,36). In addition, Cdk9 localization to the murine ␤-globin promoter and coding region increases when MEL cells are induced to terminally differentiate (37).…”

“…Ppm1b has been shown to dephosphorylate Cdk9 at Thr-186, acting either as a negative regulator of pTEF-b function (33) or as a positive effector that enables pTEF-b release from its inhibitory complex (34). As removal of Cdk9 (35) or inhibition of its activity (36) results in a defect in erythropoiesis, and because Cdk9 binds to the ␤-globin locus in vivo (37), we postulated that silencing of Ppm1b would alter erythropoietic gene expression. Table S2.…”

Transcriptional control of erythropoiesis: emerging mechanisms and principles

“…Single-stranded DNAbinding protein 2 increases steady-state levels of endogenous Ldb1 and LMO2, GATA-E-box DNA binding activity, and facilitates expression of a direct target of the GATA-E-box-binding complex Protein 4.2 (P4.2) in erythroid precursor cells (Xu et al, 2007). Proteomic studies identified Eto-2 and cyclin-dependent kinase Cdk9 as Ldb1-interacting proteins (Meier et al, 2006). Ldb1 forms multiple complexes during erythroid differentiation, and morpholino-dependent knockdown of these components in zebrafish revealed that they are essential for definitive hematopoiesis (Meier et al, 2006).…”

“…Proteomic studies identified Eto-2 and cyclin-dependent kinase Cdk9 as Ldb1-interacting proteins (Meier et al, 2006). Ldb1 forms multiple complexes during erythroid differentiation, and morpholino-dependent knockdown of these components in zebrafish revealed that they are essential for definitive hematopoiesis (Meier et al, 2006). SCL activity is regulated via standard mechanisms involving post-translational modifications and interactions with coregulators, although many questions remain unanswered regarding the precise mechanisms.…”