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Isoform-specific cDNAs for human embryonic, neonatal, and slow skeletal myosin heavy chains
H H Stedman1, A M Kelly, N A Rubinstein
1Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Abstract:
A series of cDNA fragments encoding immunodetectable portions of the human slow/beta, neonatal, and embryonic isoforms of myosin heavy chain (MHC) were isolated from a human fetal muscle cDNA expression library. A 6 kb fragment isolated on a secondary screen represents the first cloned cDNA encoding a full-length vertebrate MHC (the human embryonic isoform). In the 3'-untranslated regions, 70-80% nucleotide sequence homology exists among orthologous human and rat cDNAs, whereas the homology is less than 65% among the paralogous cDNAs. Furthermore, approximately the same level of untranslated sequence conservation is observed at the 5'-terminus of the embryonic transcript. These results suggest that for both the 3'- and the 5'-untranslated domains, the rate of evolutionary sequence divergence is limited by functional constraints.
Insights
Researchers cloned the first full-length human embryonic myosin heavy chain (MHC) cDNA. Conserved sequences in untranslated regions suggest functional constraints limit evolutionary divergence in MHC genes.
Area of Science:
- Molecular Biology
- Genetics
- Evolutionary Biology
Background:
- Myosin heavy chain (MHC) is crucial for muscle function, with various isoforms expressed during development.
- Understanding MHC gene evolution provides insights into muscle development and function.
Purpose of the Study:
- To clone and characterize cDNA fragments encoding human myosin heavy chain (MHC) isoforms.
- To identify the first full-length cDNA for a vertebrate MHC, specifically the human embryonic isoform.
- To analyze sequence homology in untranslated regions of MHC genes to understand evolutionary constraints.
Main Methods:
- Screening a human fetal muscle cDNA expression library.
- Isolating cDNA fragments encoding immunodetectable MHC portions.
- Secondary screening to identify a full-length 6 kb embryonic MHC cDNA.
- Nucleotide sequence analysis of 3' and 5' untranslated regions.
Main Results:
- Successfully isolated cDNA fragments for human slow/beta, neonatal, and embryonic MHC isoforms.
- Cloned the first full-length vertebrate MHC cDNA (human embryonic isoform).
- High nucleotide sequence homology (70-80%) in 3'-untranslated regions between human and rat orthologous MHC cDNAs.
- Significant sequence conservation (<65% homology) among paralogous MHC cDNAs.
- Similar conservation levels observed in the 5'-untranslated regions of the embryonic transcript.
Conclusions:
- The cloning of the full-length human embryonic MHC provides a valuable resource for studying muscle development.
- Conserved sequences in both 5' and 3' untranslated regions of MHC transcripts indicate strong functional constraints.
- These constraints limit the rate of evolutionary sequence divergence in these critical gene domains.