A cis-regulatory mutation in troponin-I of Drosophila reveals the importance of proper stoichiometry of structural proteins during muscle assembly.
Rapid and high wing-beat frequencies achieved during insect flight are powered by the indirect flight muscles, the largest group of muscles present in the thorax. Any anomaly during the assembly and/or structural impairment of the indirect flight muscles gives rise to a flightless phenotype. Multiple mutagenesis screens in Drosophila melanogaster for defective flight behavior have led to the isolation and characterization of mutations that have been instrumental in the identification of many proteins and residues that are important for muscle assembly, function, and disease. In this article, we present a molecular-genetic characterization of a flightless mutation, flightless-H (fliH), originally designated as heldup-a (hdp-a). We show that fliH is a cis-regulatory mutation of the wings up A (wupA) gene, which codes for the troponin-I protein, one of the troponin complex proteins, involved in regulation of muscle contraction. The mutation leads to reduced levels of troponin-I transcript and protein. In addition to this, there is also coordinated reduction in transcript and protein levels of other structural protein isoforms that are part of the troponin complex. The altered transcript and protein stoichiometry ultimately culminates in unregulated acto-myosin interactions and a hypercontraction muscle phenotype. Our results shed new insights into the importance of maintaining the stoichiometry of structural proteins during muscle assembly for proper function with implications for the identification of mutations and disease phenotypes in other species, including humans.
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India Centre for Life Sciences, Central University of Jharkhand, Ranchi 835 205, India.
Hena
H
Firdaus
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India Department of Studies in Zoology, University of Mysore, Manasagangotri, Mysore 570 006, India.
Jayaram
J
Mohan
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India.
Sarwat
S
Naz
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India.
Prabhashankar
P
Arathi
Department of Studies in Zoology, University of Mysore, Manasagangotri, Mysore 570 006, India.
Saraf R
SR
Ramesh
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India upendra@mrdg.iisc.ernet.in.
Upendra
http://orcid.org/0000-0002-0616-5995
U
Nongthomba
D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism; D009119:Muscle Contraction; D009154:Mutation; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D012518:Sarcomeres / Q000378:metabolism* / Q000502:physiology; D019210:Troponin I / Q000235:genetics* / Q000378:metabolism
D029721:Drosophila Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D019210:Troponin I; C000604654:wupA protein, Drosophila
Drosophila; flight muscles; muscle hypercontraction; protein stoichiometry; troponin