page_title: Alternative splicing
section_title: Exon skipping: Drosophila dsx
hierarchical_section_title: Alternative splicing / Mechanisms / Examples / Exon skipping: Drosophila dsx
caption_attribution_description: English: Alternative splicing of Drosophila dsx gene. Pre-mRNAs from the D. melanogaster gene dsx contain 6 exons. In males, exons 1,2,3,5,and 6 are joined to form the mRNA, which encodes a transcriptional regulatory protein required for male development. In females, exons 1,2,3, and 4 are joined, and a polyadenylation signal in exon 4 causes cleavage of the mRNA at that point. The resulting mRNA is a transcriptional regulatory protein required for female development[1]. This is an example of exon skipping alternative splicing. The intron upstream from exon 4 has a weak-consensus polypyrimidine tract, to which U2AF proteins bind poorly without assistance from splicing activators. This 3' splice acceptor site is therefore not used in males. Females, however, produce the splicing activator Transformer (Tra). The SR protein Tra2 is produced in both sexes and binds to an ESE in exon 4; if Tra is present, it binds to Tra2 and, along with another SR protein, forms a complex that assists U2AF proteins in binding to the weak polypyrimidine tract. U2 is recruited to the associated branch point, and this leads to inclusion of exon 4 in the mRNA[1][2]. Notes ↑ a b Lynch KW, Maniatis T (August 1996). "Assembly of specific SR protein complexes on distinct regulatory elements of the Drosophila doublesex splicing enhancer". Genes Dev. 10 (16): 2089–101. PMID 8769651. ↑ Graveley BR, Hertel KJ, Maniatis T (June 2001). "The role of U2AF35 and U2AF65 in enhancer-dependent splicing". RNA 7 (6): 806–18. PMID 11421359. PMC: 1370132.
context_page_description: Alternative splicing, or alternative RNA splicing, or differential splicing, is a regulated process during gene expression that results in a single gene coding for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed messenger RNA produced from that gene. Consequently, the proteins translated from alternatively spliced mRNAs will contain differences in their amino acid sequence and, often, in their biological functions. Notably, alternative splicing allows the human genome to direct the synthesis of many more proteins than would be expected from its 20,000 protein-coding genes.
  Alternative splicing occurs as a normal phenomenon in eukaryotes, where it greatly increases the biodiversity of proteins that can be encoded by the genome; in humans, ~95% of multi-exonic genes are alternatively spliced. There are numerous modes of alternative splicing observed, of which the most common is exon skipping. In this mode, a particular exon may be included in mRNAs under some conditions or in particular tissues, and omitted from the mRNA in others.
context_section_description: Pre-mRNAs from the D. melanogaster gene dsx contain 6 exons. In males, exons 1,2,3,5,and 6 are joined to form the mRNA, which encodes a transcriptional regulatory protein required for male development. In females, exons 1,2,3, and 4 are joined, and a polyadenylation signal in exon 4 causes cleavage of the mRNA at that point. The resulting mRNA is a transcriptional regulatory protein required for female development.
  This is an example of exon skipping. The intron upstream from exon 4 has a polypyrimidine tract that doesn't match the consensus sequence well, so that U2AF proteins bind poorly to it without assistance from splicing activators. This 3' splice acceptor site is therefore not used in males. Females, however, produce the splicing activator Transformer (Tra) (see below). The SR protein Tra2 is produced in both sexes and binds to an ESE in exon 4; if Tra is present, it binds to Tra2 and, along with another SR protein, forms a complex that assists U2AF proteins in binding to the weak polypyrimidine tract. U2 is recruited to the associated branchpoint, and this leads to inclusion of exon 4 in the mRNA.
caption: Alternative splicing of dsx pre-mRNA
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