Critical roles of miRNA-mediated regulation of TGFβ signalling during mouse cardiogenesis.
OBJECTIVE
MicroRNAs (miRNAs) play critical roles during the development of the cardiovascular system. Blocking miRNA biosynthesis in embryonic hearts through a conditional gene inactivation approach led to differential cardiac defects depending on the Cre drivers used in different studies. The goal of this study is to reveal the cardiogenic pathway that is regulated by the miRNA mechanism at midgestation, a stage that has not been evaluated in previous publications.


RESULTS
We specifically inactivated Dicer1, which is essential for generation of functional mature miRNAs, in the myocardium by crossing cTnt-Cre mice with Dicer1(loxP) mice. cTnt-Cre efficiently inactivates target genes in cardiomyocytes at midgestation. All mutants died between E14.5 and E16.5 with severe myocardial wall defects, including reduced cell proliferation, increased cell death, and spongy myocardial wall. Expression of TGFβ type I receptor (Tgfbr1), which encodes the Type I receptor of TGFβ ligands, was up-regulated in mutant hearts. As expected, TGFβ activity was increased in Dicer1-inactivated hearts. Our further molecular analysis suggested that Tgfbr1 is a direct target of three miRNAs. Reducing TGFβ activities using a pharmacological inhibitor on in vitro cultured hearts, or through an in vivo genetic approach, partially rescued the cardiac defects caused by Dicer1 inactivation.


CONCLUSIONS
We show for the first time that TGFβ signalling is directly regulated by the miRNA mechanism during myocardial wall morphogenesis. Increased TGFβ activity plays a major role in the cardiac defects caused by myocardial deletion of Dicer1. Thus, miRNA-mediated regulation of TGFβ signalling is indispensable for normal cardiogenesis.
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA.
Yin
Y
Peng
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA.
Lanying
L
Song
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA.
Mei
M
Zhao
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA.
Cristina
C
Harmelink
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA.
Paige
P
Debenedittis
Department of Biostatistics, The University of Alabama at Birmingham, Birmingham, USA.
Xiangqin
X
Cui
Department of Cell, Developmental and Integrative Biology, The University of Alabama at Birmingham, Birmingham, USA.
Qin
Q
Wang
Division of Research, Department of Genetics, The University of Alabama at Birmingham, 720 20th St. S., 768 Kaul Building, Birmingham AL 35294, USA kjiao@uab.edu.
Kai
K
Jiao
D000818:Animals; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D006321:Heart / Q000196:embryology*; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D035683:MicroRNAs / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism; D038081:Organogenesis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D043244:Ribonuclease III / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D035683:MicroRNAs; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625842:Tgfbr1 protein, mouse; C509781:Dicer1 protein, mouse; D043244:Ribonuclease III; D053487:DEAD-box RNA Helicases
Cardiogenesis; MicroRNAs; TGFβ