Genes and Isoforms (Isoform Complexity)
Within mammals four genes are responsible for generating more than 40 different tropomyosin isoforms. Structurally the genes are very similar, suggesting that they arose through gene duplication of an ancestral gene. In humans these genes are no longer linked and are widely dispersed. In humans, the α-, β-, γ-, and δ-genes are formally known as TPM1, TPM2, TPM3 and TPM4 and are located at 15q22, 9p13, 1q22 and 19p13, respectively.
Isoforms are defined as highly related gene products that essentially perform similar biological functions, with variations existing between the isoforms in terms of biological activity, regulatory properties, temporal and spatial expression and/or the intercellular location. Isoforms are produced by two distinct mechanisms, gene duplication and alternative splicing. The former mechanism is a process by which multiple copies of a gene are generated through unequal crossing over, tandem duplication or by translocation. Alternative splicing is a mechanism where exons are either retained in the mRNA or targeted for removal in different combinations to create a diverse array of mRNAs from a single pre-mRNA
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