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Sundby LJ, Southern WM, Sun J, Patrinostro X, Zhang W, Yong J, Ervasti JM. Deletion of exons 2 and 3 from Actb and cell immortalization lead to widespread, β-actin independent alterations in gene expression associated with cell cycle control. Eur J Cell Biol 2024; 103:151397. [PMID: 38387258 DOI: 10.1016/j.ejcb.2024.151397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Revised: 02/11/2024] [Accepted: 02/12/2024] [Indexed: 02/24/2024] Open
Abstract
The cytoplasmic actin proteins, β- and γ-actin, are 99% identical but thought to perform non-redundant functions. The nucleotide coding regions of cytoplasmic actin genes, Actb and Actg1, are 89% identical. Knockout (KO) of Actb by Cre-mediated deletion of first coding exons 2 and 3 in mice is embryonic lethal and fibroblasts derived from KO embryos (MEFs) fail to proliferate. In contrast, Actg1 KO MEFs display with a much milder defect in cell proliferation and Actg1 KO mice are viable, but present with increased perinatal lethality. Recent studies have identified important protein-independent functions for both Actb and Actg1 and demonstrate that deletions within the Actb nucleotide sequence, and not loss of the β-actin protein, cause the most severe phenotypes in KO mice and cells. Here, we use a multi-omics approach to better understand what drives the phenotypes of Actb KO MEFs. RNA-sequencing and mass spectrometry reveal largescale changes to the transcriptome, proteome, and phosphoproteome in cells lacking Actb but not those only lacking β-actin protein. Pathway analysis of genes and proteins differentially expressed upon Actb KO suggest widespread dysregulation of genes involved in the cell cycle that may explain the severe defect in proliferation.
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Affiliation(s)
- Lauren J Sundby
- Program in Molecular, Cellular, Developmental Biology, and Genetics, University of Minnesota, Minneapolis, MN 55455, USA
| | - William M Southern
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - Jiao Sun
- Department of Computer Science, University of Central Florida, Orlando, FL 32816, USA
| | - Xiaobai Patrinostro
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - Wei Zhang
- Department of Computer Science, University of Central Florida, Orlando, FL 32816, USA
| | - Jeongsik Yong
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - James M Ervasti
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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Sundby LJ, Southern WM, Hawbaker KM, Trujillo JM, Perrin BJ, Ervasti JM. Nucleotide- and Protein-Dependent Functions of Actg1. Mol Biol Cell 2022; 33:ar77. [PMID: 35594181 PMCID: PMC9582642 DOI: 10.1091/mbc.e22-02-0054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 05/10/2022] [Accepted: 05/11/2022] [Indexed: 11/11/2022] Open
Abstract
Cytoplasmic β- and γ-actin proteins are 99% identical but support unique organismal functions. The cytoplasmic actin nucleotide sequences Actb and Actg1, respectively, are more divergent but still 89% similar. Actb-/- mice are embryonic lethal and Actb-/- cells fail to proliferate, but editing the Actb gene to express γ-actin (Actbc-g) resulted in none of the overt phenotypes of the knockout revealing protein-independent functions for Actb. To determine if Actg1 has a protein-independent function, we crossed Actbc-g and Actg1-/- mice to generate the bG/0 line, where the only cytoplasmic actin expressed is γ-actin from Actbc-g. The bG/0 mice were viable but showed a survival defect despite expressing γ-actin protein at levels no different from bG/gG with normal survival. A unique myopathy phenotype was also observed in bG/0 mice. We conclude that impaired survival and myopathy in bG/0 mice are due to loss of Actg1 nucleotide-dependent function(s). On the other hand, the bG/0 genotype rescued functions impaired by Actg1-/-, including cell proliferation and auditory function, suggesting a role for γ-actin protein in both fibroblasts and hearing. Together, these results identify nucleotide-dependent functions for Actg1 while implicating γ-actin protein in more cell-/tissue-specific functions.
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Affiliation(s)
- Lauren J. Sundby
- Program in Molecular, Cellular, Developmental Biology, and Genetics, and
| | - William M. Southern
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Katelin M. Hawbaker
- Department of Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46022
| | - Jesús M. Trujillo
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Benjamin J. Perrin
- Department of Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46022
| | - James M. Ervasti
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
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Zhang Z, Zhang W, Blakes R, Sundby LJ, Shi Z, Rockey DC, Ervasti JM, Nam YJ. Fibroblast fate determination during cardiac reprogramming by remodeling of actin filaments. Stem Cell Reports 2022; 17:1604-1619. [PMID: 35688153 PMCID: PMC9287671 DOI: 10.1016/j.stemcr.2022.05.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 05/12/2022] [Accepted: 05/13/2022] [Indexed: 11/23/2022] Open
Abstract
Fibroblasts can be reprogrammed into induced cardiomyocyte-like cells (iCMs) by forced expression of cardiogenic transcription factors. However, it remains unknown how fibroblasts adopt a cardiomyocyte (CM) fate during their spontaneous ongoing transdifferentiation toward myofibroblasts (MFs). By tracing fibroblast lineages following cardiac reprogramming in vitro, we found that most mature iCMs are derived directly from fibroblasts without transition through the MF state. This direct conversion is attributable to mutually exclusive induction of cardiac sarcomeres and MF cytoskeletal structures in the cytoplasm of fibroblasts during reprogramming. For direct fate switch from fibroblasts to iCMs, significant remodeling of actin isoforms occurs in fibroblasts, including induction of α-cardiac actin and decrease of the actin isoforms predominant in MFs. Accordingly, genetic or pharmacological ablation of MF-enriched actin isoforms significantly enhances cardiac reprogramming. Our results demonstrate that remodeling of actin isoforms is required for fibroblast to CM fate conversion by cardiac reprogramming. Mature iCMs are not derived from myofibroblasts Sarcomeres of iCMs and stress fibers are mutually exclusive Repressing fibroblast actin organization facilitates cardiac reprogramming Remodeling of actin isoforms is required for cardiac reprogramming
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Affiliation(s)
- Zhentao Zhang
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA; Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, USA
| | - Wenhui Zhang
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA; Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, USA
| | - Robert Blakes
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA; Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, USA
| | - Lauren J Sundby
- Program in Molecular, Cellular, Developmental Biology, and Genetics, University of Minnesota, Minneapolis, MN, USA
| | - Zengdun Shi
- Department of Internal Medicine, Medical University of South Carolina, Charleston, SC, USA
| | - Don C Rockey
- Department of Internal Medicine, Medical University of South Carolina, Charleston, SC, USA
| | - James M Ervasti
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, USA; Program in Molecular, Cellular, Developmental Biology, and Genetics, University of Minnesota, Minneapolis, MN, USA
| | - Young-Jae Nam
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA; Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, USA.
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