Transcriptional cyclin-dependent kinases Cdk8 and Cdk19 are required for normal macrophage differentiation

Cyclin-dependent kinases CDK8 and CDK19 together with their activating partner, cyclin C, regulate gene expression as a part of the Mediator complex and by phosphorylating DNA sequence-specific transcription factors. Here, we investigated the <i>in vivo</i> requirement for Cdk8 and Cdk19 in hematopoiesis by generating double knockout (DKO) mice lacking Cdk8 and Cdk19 expression in hematopoietic cells. DKO mice displayed relatively normal hematopoiesis and largely unperturbed gene expression in the bone marrow, indicating that the Mediator kinases are not essential for the regulation of gene expression during hematopoiesis. However, DKO mice showed an expansion of splenic macrophages. Bone marrow-derived DKO macrophages displayed an increased expression levels of both M1-like and M2-like markers, altered cytokine secretion, deregulated gene expression, precocious cell cycle exit and impaired Fc-mediated phagocytosis. Our findings reveal a highly cell type-specific role of Cdk8/19 in gene transcription during hematopoiesis.