Serum response factor is an essential transcription factor in megakaryocytic maturation.
Serum response factor (Srf) is a MADS-box transcription factor that is critical for muscle differentiation. Its function in hematopoiesis has not yet been revealed. Mkl1, a cofactor of Srf, is part of the t(1;22) translocation in acute megakaryoblastic leukemia, and plays a critical role in megakaryopoiesis. To test the role of Srf in megakaryocyte development, we crossed Pf4-Cre mice, which express Cre recombinase in cells committed to the megakaryocytic lineage, to Srf(F/F) mice in which functional Srf is no longer expressed after Cre-mediated excision. Pf4-Cre/Srf(F/F) knockout (KO) mice are born with normal Mendelian frequency, but have significant macrothrombocytopenia with approximately 50% reduction in platelet count. In contrast, the BM has increased number and percentage of CD41(+) megakaryocytes (WT: 0.41% ± 0.06%; KO: 1.92% ± 0.12%) with significantly reduced ploidy. KO mice show significantly increased megakaryocyte progenitors in the BM by FACS analysis and CFU-Mk. Megakaryocytes lacking Srf have abnormal stress fiber and demarcation membrane formation, and platelets lacking Srf have abnormal actin distribution. In vitro and in vivo assays reveal platelet function defects in KO mice. Critical actin cytoskeletal genes are down-regulated in KO megakaryocytes. Thus, Srf is required for normal megakaryocyte maturation and platelet production partly because of regulation of cytoskeletal genes.
Department of Internal Medicine and Yale Cancer Center, Section of Hematology, 333 Cedar Street, New Haven, CT 06520, USA. stephanie.halene@yale.edu
Stephanie
S
Halene
Yuan
Y
Gao
Katherine
K
Hahn
Stephanie
S
Massaro
Joseph E
JE
Italiano
Vincent
V
Schulz
Sharon
S
Lin
Gary M
GM
Kupfer
Diane S
DS
Krause
D000818:Animals; D001760:Bleeding Time; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation; D019070:Cell Lineage; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D010976:Platelet Count; D010978:Platelet Factor 4 / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism*; D013921:Thrombocytopenia / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D008164:Luminescent Proteins; D026362:Serum Response Factor; D014157:Transcription Factors; D010978:Platelet Factor 4