Gene Splicing

A single gene can be processed to create numerous gene products, or proteins and this process is referred to as alternative splicing. In this case, a different combination of exons remain in the processed RNA. Alternate gene splicing at various intron-exon sites within a gene can be used to create several proteins from the same pre-RNA molecule. Proteins are made up of multiple domains. Different exons can code for different domains. Selective splicing can remove unwanted exons as well as introns. The combination of proteins that can be produced from alternate splicing are related in structure or function but are not identical. By using a single gene to create multiple proteins, the cells DNA can be utilized more efficiently.

Alternate splicing can be tissue specific such that different proteins are made from the same original gene by two or more different cell types. Or one cell type may make multiple configurations using the same gene. For instance, a type of immune cell called a B-cell manufactures antibodies to numerous antigens. Antigens are foreign substances which trigger immune responses and antibodies bind and antigens so that they can be broken down and removed. Although an infinite number of antibodies can be produced, all antibodies fall into one of five basic subtypes. Alternate splicing is used to create these five antibody-types from the same gene.

Antibodies are made up of multiple immunoglobulin (Ig) molecules. These molecules in turn have multiple domains. A particular domain called the heavy chain constant region distinguishes the five antibody subtypes, called IgM, IgD, IgG, IgE, and IgA. The different types of antibodies serve various functions in the body and act in distinct body tissues. For example, IgAs are secreted into the gastrointestinal mucosa, and IgGs passes through the placenta. The gene encoding these heavy chain regions contains exons that direct the production of individual subtypes, and the gene is alternately spliced to yield a final mRNA transcript, which can make any one of them.

Most genes yield only one transcript; however, genes that yield multiple transcripts have numerous cellular and developmental roles. Alternate splicing controls sex determination in Drosophila melanogaster flies. And a number of proteins are differentially expressed from the same gene in various cells. Different muscle cells use alternate splicing to create cell-specific myosin proteins. And embryonic cells in varying developmental stages produce multiple forms of the protein, retinoic acid. Some transcripts differ from related transcripts in the 5' end and others can vary at the 3' end.