MKL1 and MKL2 play redundant and crucial roles in megakaryocyte maturation and platelet formation.
Serum response factor and its transcriptional cofactor MKL1 are critical for megakaryocyte maturation and platelet formation. We show that MKL2, a homologue of MKL1, is expressed in megakaryocytes and plays a role in megakaryocyte maturation. Using a megakaryocyte-specific Mkl2 knockout (KO) mouse on the conventional Mkl1 KO background to produce double KO (DKO) megakaryocytes and platelets, a critical role for MKL2 is revealed. The decrease in megakaryocyte ploidy and platelet counts of DKO mice is more severe than in Mkl1 KO mice. Platelet dysfunction in DKO mice is revealed by prolonged bleeding times and ineffective platelet activation in vitro in response to adenosine 5'-diphosphate. Electron microscopy and immunofluorescence of DKO megakaryocytes and platelets indicate abnormal cytoskeletal and membrane organization with decreased granule complexity. Surprisingly, the DKO mice have a more extreme thrombocytopenia than mice lacking serum response factor (SRF) expression in the megakaryocyte compartment. Comparison of gene expression reveals approximately 4400 genes whose expression is differentially affected in DKO compared with megakaryocytes deficient in SRF, strongly suggesting that MKL1 and MKL2 have both SRF-dependent and SRF-independent activity in megakaryocytopoiesis.
Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
Elenoe C
EC
Smith
Jonathan N
JN
Thon
Matthew T
MT
Devine
Sharon
S
Lin
Vincent P
VP
Schulz
Yanwen
Y
Guo
Stephanie A
SA
Massaro
Stephanie
S
Halene
Patrick
P
Gallagher
Joseph E
JE
Italiano
Diane S
DS
Krause
D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001760:Bleeding Time; D001792:Blood Platelets / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D003433:Crosses, Genetic; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D020869:Gene Expression Profiling; D006410:Hematopoiesis; D008533:Megakaryocytes / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D015539:Platelet Activation; D013921:Thrombocytopenia / Q000209:etiology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
C478036:MRTFB protein, human; C511173:Mrtfa protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D000244:Adenosine Diphosphate