Alternative splicing from a single gene or transcription from distinct genes are the two most important genetic mechanisms used to generate protein isoforms. This study concerns the ascidian Ciona intestinalis and the genetic mechanism used in this primitive chordate organism to produce differentially expressed isoforms of the muscle protein troponin I (TnI). / Through cDNA cloning and reverse-transcription PCR approaches, the mRNA sequences encoding two distinct Ciona ThI isoforms were determined. These mRNAs were found to be tissue-specifically expressed; one in the heart and the other in body-wall muscle. They encode long (229-residue) and short (182-residue) TnI protein isoforms homologous to vertebrate heart and skeletal muscle TnI isoforms, respectively. By sequence comparison, allelic polymorphism analysis, and gene structure determination, the two mRNAs were shown to be produced from a single gene by inclusion/exclusion of two serial internal exons. This tissue-specific alternative splicing mechanism contrasts with the vertebrate strategy of TnI isoform. production by differential transcription of a multigene family. This is the first reported case in which homologous tissue-specific protein isoforms are produced by non-homologous molecular mechanisms in related organismal lineages, implying that the molecular mechanism of isoform generation was entirely reworked in one of these lineages. An evolutionary scenario is presented that can account for such a reworking through a series of reasonable steps.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.20272 |
| Date | January 1997 |
| Creators | MacLean, Darren. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001608803, proquestno: MQ44214, Theses scanned by UMI/ProQuest. |
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