title: Conditional mutagenesis of the murine serum response factor gene blocks cardiogenesis and the transcription of downstream gene targets.
abstract: Serum response factor (SRF) homozygous-null embryos from our backcross of SRF(LacZ/)(+) "knock-in" mice failed to gastrulate and form mesoderm, similar to the findings of an earlier study (Arsenian, S., Weinhold, B., Oelgeschlager, M., Ruther, U., and Nordheim, A. (1998) EMBO J. 17, 6289-6299). Our use of embryonic stem cells provided a model system that could be used to investigate the specification of multiple embryonic lineages, including cardiac myocytes. We observed the absence of myogenic alpha-actins, SM22alpha, and myocardin expression and the failure to form beating cardiac myocytes in aggregated SRF null embryonic stem cells, whereas the appearance of transcription factors Nkx2-5 and GATA4 were unaffected. To study the role of SRF during heart organogenesis, we then performed cardiac-specific ablation of SRF by crossing the transgenic alpha-myosin heavy chain Cre recombinase line with SRF LoxP-engineered mice. Cardiac-specific ablation of SRF resulted in embryonic lethality due to cardiac insufficiency during chamber maturation. Conditional ablation of SRF also reduced cell survival concomitant with increased apoptosis and reduced cellularity. Significant reductions in SRF (> or =95%), atrial naturetic factor (> or =80%), and cardiac (> or =60%), skeletal (> or =90%), and smooth muscle (> or =75%) alpha-actin transcripts were also observed in the cardiac-conditional knock-out heart. This was consistent with the idea that SRF directs de novo cardiac and smooth muscle gene activities. Finally, quantitation of the knock-in LacZ reporter gene transcripts in the hearts of cardiac-conditional knock-out embryos revealed an approximately 30% reduction in gene activity, indicating SRF gene autoregulation during cardiogenesis.
authors.affiliation: Center for Cardiovascular Development, Division of Cardiovascular Sciences, Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, 77030, USA.
authors.forename: Zhiyv
authors.initials: Z
authors.lastname: Niu
authors.forename: Wei
authors.initials: W
authors.lastname: Yu
authors.forename: Shu Xing
authors.initials: SX
authors.lastname: Zhang
authors.forename: Matthew
authors.initials: M
authors.lastname: Barron
authors.forename: Narasimhaswamy S
authors.initials: NS
authors.lastname: Belaguli
authors.forename: Michael D
authors.initials: MD
authors.lastname: Schneider
authors.forename: Michael
authors.initials: M
authors.lastname: Parmacek
authors.forename: Alfred
authors.initials: A
authors.lastname: Nordheim
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schwartz
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D019070:Cell Lineage; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D004622:Embryo, Mammalian / Q000378:metabolism; D050991:GATA4 Transcription Factor; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D007763:Lac Operon; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D018482:Muscle, Skeletal / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D026362:Serum Response Factor / Q000235:genetics* / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D019076:Transgenes; D001616:beta-Galactosidase / Q000378:metabolism; D000099251:Myocardin
chemical_list: D000199:Actins; D004268:DNA-Binding Proteins; D050991:GATA4 Transcription Factor; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D026362:Serum Response Factor; D015534:Trans-Activators; D014157:Transcription Factors; D001616:beta-Galactosidase; D000099251:Myocardin; C484469:Nkx2-5 protein, mouse